Smartphone Foldable Phones Are Just the Beginning— Stretchable, Wearable Displays Are Already in the Laboratory P

GALLIUM NITRIDE VACUUM TUBES GREENHOUSE-GAS HOW LOW CAN GETS READY FOR 6G OF THE COLD WAR SENSING SATELLITES LATENCY GO? Jump in efficiency Nine wild devices Microsatellites spot Wireless researchers astounds experts you’ve never heard of methane—for a profit push the limits P. 07 P. 30 P. 38 P. 44

FOR THE TECHNOLOGY INSIDER | 11.20

The Incredible BENDABLE Smartphone Foldable phones are just the beginning— stretchable, wearable displays are already in the laboratory P. 24 Keep pushing the limits!

Congratulations to Peter Grutter and his group at the Nanoscience & SPM Lab at McGill University on bridging the gap between high spatial and ultrafast temporal resolution to advance molecular and quantum electronics. Observing 100 fs non-linear

Megan Cowie, Nanoscience & SPM Group, optical interactions and quantized vibration-modified McGill University electron transfer in single molecules with AFM are impressive achievements that set new standards at the forefront of scientific research.

We are excited to continue our collaboration and look forward to finding new ways of using lock-in amplifiers and boxcar averagers to push the limits of SPM applications.

Zurich www.zhinst.com Instruments Your Application. Measured. CONTENTS_11.20

30 THE 9 GREATEST 38 MICRO- 44 BREAKING 06 NEWS DISPLAYS VACUUM TUBES SATELLITES SPOT THE MILLISECOND 16 HANDS ON YOU’VE NEVER MYSTERY METHANE BARRIER It will take 20 CROSSTALK HEARD OF These LEAKS Keeping a lot of tricks to push 52 PAST FORWARD THAT BEND tubes excel where carbon-capping network latencies solid-state devices schemes on track below 1 millisecond. fall short. needs tech that can go By Shivendra Panwar AND STRETCH By Carter M. anywhere. Armstrong By Jason McKeever, Here’s how engineers are making Dylan Jervis & displays that are amazingly flexible. Mathias Strupler by Huanyu Zhao & Tae-woo Lee Page 24

On the cover and this page Conceptual photograph for IEEE Spectrum by Dan Saelinger

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SPECTRUM.IEEE.ORG | NOV 2020 | 01 BACK STORY

LIFE OF A TUBE GUY Increased Performance for Connected Hardware f you’d told me I’d spend my career working on vacuum tubes, I’d have said, ‘No way. That’s crazy!’ ” So says Carter M. Armstrong, who has in fact spent the last Designed to perform in 40-some years working on vacuum devices. It started in graduate high vibration environments school, when his Ph.D. advisor at the University of Maryland turned him on to electron beams. And it continued through With surface mount solder tabs for stints at North Carolina State University, the Naval Research additional board retention strength, I Laboratory, Northrop Grumman, Litton, and most recently Archer Kontrol can withstand L3Harris, in Torrance, Calif., where he is director of advanced lateral and twisting forces in high development for the company’s Electron Devices division. vibration environments. Throughout, Armstrong says, the work has been intellectually stimulating and emotionally rewarding. “It’s good to work on hard Ensuring reliability in the problems,” he says. “The physics is hard, the engineering is hard, next generation of connected and it’s all interrelated. Not everybody can do this kind of work, but devices. it gets in your blood, it really does.” n Temperature range of In the photo above, Armstrong, an IEEE Fellow, holds two of -55°C to +125°C the devices he helped develop: a millimeter-wave mini traveling- n Assists with blind mating wave tube and a microwave power module, both of which he describes in “The 9 Greatest Vacuum Tubes You’ve Never Heard n Tested to perform up to Of” [p. 30]. Beyond the ubiquitous magnetrons in microwave ovens 500 operations and the traveling-wave tubes in communications satellites, he says, n Up to 3 Gbit/s data rate vacuum devices still find their way into a surprisingly broad array of applications where “you need high efficiency, high power, and wide amplification bandwidth.” Those applications include cancer harwin.com/archer-kontrol therapy, fusion reactors, industrial heating, particle accelerators, radar, missile defense, and electronic warfare. Almost all of the tubes in Armstrong’s article are ones he helped design or came across during his career, but he included one based on the recommendation of his son Derek, a musician. That’s the Telefunken VF14M, a specialized audio tube used in the much- Connect with confidence revered Neumann U47 and U48 microphones. Over the decades, many recording artists have favored those mics, including Ella Fitzgerald, Frank Sinatra, and the Beatles.

11.20 “I’m a huge Beatles fan, so I was more than happy to include that

one,” Armstrong says. ■ MARTIN MICHAEL

02 | NOV 2020 | SPECTRUM.IEEE.ORG Harwin Archer Kontrol IEEE Spectrum Sept 20.indd 1 03/08/2020 09:45 CONTRIBUTORSCONTRIBUTORS_

EDITOR IN CHIEF Susan Hassler, [email protected] ADVERTISING PRODUCTION +1 732 562 6334 EXECUTIVE EDITOR Glenn Zorpette, [email protected] ADVERTISING PRODUCTION MANAGER EDITORIAL DIRECTOR, DIGITAL Felicia Spagnoli, [email protected] Daniel P. Dern SENIOR ADVERTISING PRODUCTION COORDINATOR Harry Goldstein, [email protected] Dern is a veteran technology and business writer MANAGING EDITOR Elizabeth A. Bretz, [email protected] Nicole Evans Gyimah, [email protected] based in Boston. He also pens science fiction SENIOR ART DIRECTOR EDITORIAL ADVISORY BOARD, IEEE SPECTRUM and is an amateur magician. For this issue, Dern Mark Montgomery, [email protected] Susan Hassler, Chair; David C. Brock, Ronald F. DeMara, interviewed Merryl Gross about designing user SENIOR EDITORS Shahin Farshchi, Lawrence O. Hall, Jason K. Hui, experiences (UX) [p. 19]. Although he and Gross Stephen Cass, [email protected] Leah Jamieson, Mary Lou Jepsen, Deepa Kundur, have known each other for decades and attend the Erico Guizzo (Digital), [email protected] Gianluca Lazzi, Allison Marsh, Carmen Menoni, Sofia Olhede, Jean Kumagai, [email protected] Maurizio Vecchione, Edward Zyszkowski same sci-fi conferences, he says, “I hadn’t had the Samuel K. Moore, [email protected] chance to learn what she does as an information EDITORIAL ADVISORY BOARD, THE INSTITUTE Tekla S. Perry, [email protected] architect, and what UX is all about. I love talking Kathy Pretz, Chair; Qusi Alqarqaz, Philip Chen, Roberto Graglia, Philip E. Ross, [email protected] with people about how they got into their fields.” Shashank Gaur, Susan Hassler, Cecilia Metra, San Murugesan, David Schneider, [email protected] Mirela Sechi Annoni Notare, Tapan K. Sarkar, Joel Trussell, Eliza Strickland, [email protected] Hon K. 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IEEE BOARD OF DIRECTORS PUBLICATIONS Steven Heffner PRESIDENT & CEO Toshio Fukuda, [email protected] +1 212 705 8958, [email protected] Mark Pesce +1 732 562 3928 FAX: +1 732 981 9515 CHIEF MARKETING OFFICER Karen L. Hawkins +1 732 562 3964, [email protected] Pesce writes IEEE Spectrum’s Macro & Micro PRESIDENT-ELECT Susan K. “Kathy” Land CORPORATE ACTIVITIES Donna Hourican column. An Honorary Associate in Digital Cultures TREASURER Joseph V. Lillie SECRETARY Kathleen A. Kramer +1 732 562 6330, [email protected] at the University of Sydney, he is a columnist PAST PRESIDENT José M.F. Moura MEMBER & GEOGRAPHIC ACTIVITIES Cecelia Jankowski for The Register, has written seven books, and VICE PRESIDENTS +1 732 562 5504, [email protected] produces two podcasts: “The Next Billion Seconds” Stephen M. Phillips, Educational Activities; Tapan K. Sarkar, STANDARDS ACTIVITIES Konstantinos Karachalios and, with Jason Calacanis, “This Week in Startups Publication Services & Products; Kukjin Chun, Member & +1 732 562 3820, [email protected] Australia.” In this issue, Pesce considers the blurry Geographic Activities; Kazuhiro Kosuge, Technical Activities; EDUCATIONAL ACTIVITIES Jamie Moesch Robert S. Fish, President, Standards Association; James M. +1 732 562 5514, [email protected] line between simulation software and gaming Conrad, President, IEEE-USA GENERAL COUNSEL & CHIEF COMPLIANCE OFFICER [p. 23]. “That line has been fading for decades,” DIVISION DIRECTORS Sophia A. Muirhead +1 212 705 8950, [email protected] he says. “Will we know when it disappears?” Alfred E. “Al” Dunlop (I); David B. Durocher (II); Sergio CHIEF FINANCIAL OFFICER Thomas R. Siegert Benedetto (III); John P. Verboncoeur (IV); Thomas M. Conte (V); +1 732 562 6843, [email protected] Manuel Castro (VI); Miriam P. Sanders (VII); Elizabeth L. “Liz” TECHNICAL ACTIVITIES Mary Ward-Callan Burd (VIII); Rabab Kreidieh Ward (IX); Ljiljana Trajkovic (X) +1 732 562 3850, [email protected] Huanyu Zhou REGION DIRECTORS MANAGING DIRECTOR, IEEE-USA Chris Brantley Eduardo F. Palacio (1); Wolfram Bettermann (2); +1 202 530 8349, [email protected] Zhou is studying for a doctorate at Seoul National Jill I. Gostin (3); David Alan Koehler (4); James R. University under the direction of Tae-Woo Lee, a IEEE PUBLICATION SERVICES & PRODUCTS BOARD Look (5); Keith A. Moore (6); Jason Jianjun Gu (7); professor of materials science and engineering. Tapan K. Sarkar, Chair; Sergio Benedetto, Edhem Custovic, Magdalena Salazar-Palma (8); Alberto Sanchez (9); Stefano Galli, Lorena Garcia, Ron B. Goldfarb, In this issue, Zhou and Lee write about flexible Akinori Nishihara (10) Lawrence O. Hall, W. Clem Karl, Hulya Kirkici, Paolo Montuschi, displays for consumer electronics [p. 24]. DIRECTOR EMERITUS Theodore W. Hissey Sorel Reisman, Gaurav Sharma, Maria Elena Valcher, Although foldable phones are already on the John P. Verboncoeur, John Vig, Bin Zhao IEEE STAFF market, the technology is immature, and the EXECUTIVE DIRECTOR & COO Stephen Welby IEEE OPERATIONS CENTER price is still very high, Zhou says. “None of my +1 732 562 5400, [email protected] 445 Hoes Lane, Box 1331 friends or family own one. I’ve only seen them CHIEF INFORMATION OFFICER Cherif Amirat Piscataway, NJ 08854-1331 U.S.A. in the Samsung store.” +1 732 562 6017, [email protected] Tel: +1 732 981 0060 Fax: +1 732 981 1721

SPECTRUM.IEEE.ORG | NOV 2020 | 03 SPECTRAL LINES

Another respondent at Face- book wrote, “It makes sense. Your pay is always defined by the job market. When you move from Austin to the Bay Area do you tell your company to keep [the] same pay? No. You ask for a hike for the Bay Area market.” A respondent at VMware wrote, “I’ll gladly do this. It’s only a reduction on base, and base makes up half of my [total compensation]. So a net 6.5 percent decrease in my total to move to a place where houses are 20 percent of the Take a Pay Cut and Work price and taxes alone make up the difference? Sign me up.” Wherever You Want Those who would not take But should the value of your work depend such a cut argue that regional on where it gets done? salary differences are inher- ently unfair. Wrote a respondent at Hulu: arlier this year, as the tech workforce moved into the virtual “You guys aren’t getting it. It doesn’t matter that ‘pay world, Facebook announced that at least some employees could is always based on location.’ That old way of thinking work from home permanently—and choose to relocate. There is needs to die because it exploits labor. The employee’s a catch to that: Salaries, the company said, would be adjusted labor provides the same value regardless of working to reflect local costs of living. Over the summer, job search firm location. Ask the company tough questions. ‘Is my Hired released a study that reported that only 32 percent of tech value to the company less if I live in North Carolina professionals around the world would be willing to take such or Colorado?’ If they won’t budge, quit.” E a cut. • Now, in the final months of 2020, as remote workers A respondent at Splunk would go even further: settle into their commute-less work life, the numbers of those willing to “Honestly, the companies should give work-from- accept a pay cut seems to have grown. Blind, a company that operates home employees pay raises, not cuts. Why? Because private social networks for tech employees, surveyed 5,591 tech profes- they aren’t having to pay for a physical location to sionals and found that 44 percent would be willing to take a pay cut linked employ you anymore. If the company downsizes to a lower cost of living and 8 percent were indifferent; 48 percent would their offices, this saves the company a boatload. be opposed to such a cut. • The numbers vary by employer, with tech Also, the pay should be based on the job, not the professionals working at Square, Lyft, Facebook, VMware, and Dropbox location where you choose to live. If you thought I the most willing to sacrifice salary for the ability to relocate, and Expedia, was worth 400k when living in San Francisco, how PayPal, Microsoft, and Oracle the least. • Comments from those will- did my skills suddenly decrease when I live some- ing to take a cut generally fell into the what’s-the-big-deal category. One where else?” —Tekla S. Perry Facebook employee wrote: “I don’t understand all the fuss, are people demanding everyone around the world be paid the same? Let’s be real, A version of this article appears in our your pay range is based on your location. People who feel they moved View from the Valley blog. to a place that had 30–50 percent lower range [and] shouldn’t be paid

like the local employees crack me up.” ↗ POST YOUR COMMENTS at https://spectrum.ieee.org/salaries-nov2020 ISTOCKPHOTO

04 | NOV 2020 | SPECTRUM.IEEE.ORG Invented in the 1800s. Optimized for today.

Visualization of the von Mises stress distribution in the housing of an induction motor by accounting for electromechanical effects.

In the 19th century, two scientists separately invented the AC induction motor. Today, it’s a common component in robotics. How did we get here and how can modern-day engineers continue to improve the design? The COMSOL Multiphysics® software is used for simulating designs, devices, and processes in all fields of engineering, manufacturing, and scientific research. See how you can apply it to robotics design.

comsol.blog/induction-motor News Who knew you could get change for an electron? Researchers have designed a nanoelectronic circuit that can tease into existence a strange new kind of quantum “particle.” Its existence confirms decades of speculation about the behavior of electronic circuits in very low temperatures and high magnetic fields—and opens the door for possible applications in next-generation quantum computers. However, this quasiparticle, or “anyon,” carries only a fraction of an electron’s charge. It is, to be clear, not substantively an actual single particle but rather more likely an ensemble of electrons acting collectively in certain extreme quantum environments. In other, significant ways, an anyon does behave like a particle. Much like an electron hole in conventional semiconductors, an anyon acts as its own discrete entity with its own characteristic mass, charge, and spin. And, unlike the +1 charge of an electron hole, these newly studied anyons (whose name Nobel laureate Frank Wilczek jokingly coined after their seemingly “anything goes” nature) carry just one-third of an electron’s charge. FRACTIONAL James Nakamura, postdoctoral researcher in the lab of Michael Manfra at Purdue University, in Lafayette, “PARTICLES” Ind., says the quantum trajectories of the anyon are also curious. Its paths through the test circuit interact with COULD MEAN NEW other anyons—and indeed even with other quantum incarnations of itself ELECTRONICS moving through other elements of the PARTLY PARTICLES: Purdue researchers have induced the appearance of exotic Quasiparticles might lead to new kinds of quasiparticles inside an interferometer at

quantum computers cryogenic temperatures. UNIVERSITY PURDUE

06 | NOV 2020 | SPECTRUM.IEEE.ORG circuit—and form interference interference measurements. . . patterns. . . Electrons, since they’re quan- JOURNAL WATCH These interference patterns tum mechanical, have a phase. are analogous, Nakamura says, Also, these quasiparticles have to the wavy patterns of ripples a phase. And that’s what we’re New Form of Gallium in a conventional laser interfer- studying.” Nitride Sets Up 6G ometer. But instead of the pat- Nakamura says the group’s terns of light and darkness that experiment and these fraction- With 5G just rolling out and destined to take years a laser interferometer produces ally charged anyons may not to mature, it might seem odd to worry about 6G. on a screen, this interferometer have immediate applications But some engineers say that this is the perfect tracks anomalous shifts in con- for any quantum technologies time to worry about it. One group, based at the ductance, as parameters like yet devised. However, he says, University of California, Santa Barbara, has been gate voltage and magnetic-field slightly weaker magnetic fields developing a device that could be critical to strength slowly vary. with slightly different condi- efficiently pushing 6G’s near-terahertz-frequency The circuit—cooled to tions are also expected to pro- signals out of the antennas of future smartphones 10,000th of a degree above duce an anyon with one-fourth and other connected devices. They reported absolute zero (10 millikelvins) of an electron’s charge. This key aspects of the device—including an N-polar and immersed in a powerful quasiparticle has already been gallium nitride high-electron-mobility transistor magnetic field of 9 teslas—exhib- discussed as a possible fault- (HEMT)—in two papers that recently appeared in its discrete jumps in its conduc- tolerant qubit for an advanced IEEE Electron Device Letters. tance. Manfra, Nakamura, and “topological” quantum com- Testing so far has focused on 94-gigahertz their coauthors infer from these puter, which codes its quan- frequencies. “We have just broken through records observations the presence of the tum information in an anyon’s of millimeter-wave operation by factors which long-hypothesized anyon. changing state as it interacts are just stunning,” says Umesh K. Mishra, an IEEE The finding recalls Robert A. with itself and other anyons Fellow who heads the UC Santa Barbara group Millikan’s 1909 oil-drop experi- moving through a circuit. that published the papers. “If you’re in the device ments, which measured an elec- But all of that would depend field, if you improve things by 20 percent people tron’s fundamental charge. Here, on future experiments that are happy. Here, we have improved things by 200 the Manfra group discovered a begin by first doing what Manfra, to 300 percent.” quantum of charge that’s only Nakamura, and their coauthors A HEMT is formed around a junction between 33 percent of the charge con- did for the one-third-charged two materials having different bandgaps, in this tained by the seemingly indi- anyon: observing the quasi case gallium nitride (GaN) and aluminum gallium visible electron. The group, particle and proving that you can nitride (AlGaN). At this heterojunction, gallium which published its findings in a track it through the circuits of a nitride’s natural polarity causes a sheet of excess recent issue of the journal Nature nanosize interferometer. Then charge—a two-dimensional electron gas—to Physics, not only adduce the exis- it would be possible to discover collect. The presence of this charge gives the tence of these one-third-charged what a universe composed of device the ability to operate at high frequencies anyons but also track how the fractional charges could cook up. because the electrons are free to move quickly anyons evolve as they move —MARK ANDERSON through it without obstruction. through the interferometer. Gallium nitride HEMTs are already contenders “Quantum-mechanical phase is A version of this article appears in for 5G power amplifiers. But to efficiently amplify a very subtle thing,” Nakamura our Tech Talk blog. near-terahertz frequencies, the typical GaN HEMT said. “But there is a way you can needs to scale down in a particular way. Just as POST YOUR COMMENTS AT see phases, and that’s through spectrum.ieee.org/quasiparticle-nov2020 for a silicon transistor with a logic gate, bringing a HEMT’s gate closer to the channel through which current flows—the electron gas in this case—lets it NEWS control the flow of current, thus using less energy

SPECTRUM.IEEE.ORG | NOV 2020 | 07 and making the device more efficient. More specifically, explains Mishra, you want to maximize the ratio of the length of the gate versus the distance from the gate to the electron gas. That’s usually done by reducing the amount of barrier material between the gate’s metal and the rest of the device. But you can go only so far with that strategy. Eventually the material will be too thin to prevent current from leaking through, thereby harming efficiency. But Mishra says his group has come up with a better way: They stood the gallium nitride on its head. Ordinary gallium nitride is what’s called gallium polar. That is, if you look 30-KILOMETER BLUETOOTH down at the surface, the top layer of the crystal will always be gallium. But the Asset and inventory tracking demand that UC Santa Barbara team discovered a transmissions go to great lengths way to make nitrogen-polar crystals so that the top layer is always nitrogen. It might seem like a small difference, but When you think about Blue- where its backhoes are on a large con- it means that the structure that makes tooth, you probably think struction site. Inventory tracking refers the sheet of charge, the heterojunction, about things like wireless more to things like a retail store keeping is now upside down. headphones, computer mice, and other correct product counts on the shelves, This delivers a bunch of advantages. personal devices that utilize the short- or a hospital noting how quickly it’s First, the source and drain electrodes range, low-power technology. That’s going through its store of gloves. now make contact with the electron where Bluetooth has made its mark, Asset and inventory tracking typi- gas via a lower bandgap material (a after all—as an alternative to Wi-Fi, cally use labor-intensive techniques nanometers-thin layer of GaN) rather using unlicensed spectrum to make like bar-code or passive RFID scan- than a higher-bandgap one (AlGaN), quick connections between devices. ning, which are limited both by dis- thus lowering resistance. Second, But it turns out that Bluetooth can tance (a couple of meters at most, in the gas itself is better confined as go much farther than the couple of both cases) and the fact that a person the device approaches its lowest meters for which most people rely on has to be directly involved in scan- current state, because the AlGaN it. Apptricity, a company that provides ning. Alternatively, companies can layer beneath acts as a barrier against asset- and inventory-tracking tech- use satellite or LTE tags to keep track scattered charge. nologies, has developed a Bluetooth of stuff. While such tags don’t require Devices made to take advantage of beacon that can transmit signals over a person to actively track items, they these two characteristics have already 32 kilometers (20 miles). The company are far more expensive, requiring a yielded record-breaking results. At believes its beacon is a cheaper, more costly subscription to either a satel- 94 GHz, one device produced 8.8 watts secure alternative to established asset- lite or LTE network. per millimeter at 27 percent efficiency, and inventory-tracking technologies. So, the burning question: How do you says Mishra. A similar gallium-polar A quick primer, if you’re not entirely send a Bluetooth signal over 30-plus device produced only about 2 W/mm at clear on asset tracking versus inventory km? Typically, Bluetooth’s distance that efficiency. tracking: There’s some gray areas in the is limited because large distances The UC Santa Barbara team plans to middle, but by and large, asset tracking would require a prohibitive amount eventually test the new devices at even refers to an IT department registering of power, and its use of unlicensed higher frequencies—140 and 230 GHz. which employee has which laptop, or a spectrum means that the greater the

—SAMUEL K. MOORE construction company keeping tabs on distance, the more likely it will inter- IMAGES ARTHUS-BERTRAND/GETTY YANN

A version of this article appears on our website in the Journal Watch section. NEWS

08 | NOV 2020 | SPECTRUM.IEEE.ORG WHEREVER YOU GO: Bluetooth-tracking beacons that send and receive signals for kilometers can help keep tabs on valuable ESTONIA’S PANDEMIC assets, such as construction equipment.

fere with other wireless signals. EDGE COMES FROM IT The key new wrinkle, according to Apptricity’s CEO, Tim Garcia, is Avoiding legacy IT has kept the country’s precise tuning within the Bluetooth online systems up and running spectrum. Garcia says it’s the same principle as a tightly focused laser beam. A laser beam will travel farther The COVID-19 pandemic has perately poor. The Russians “took without its signal weakening beyond spotlighted the problems that everything,” Eaves notes, but the recovery if the photons making up legacy IT systems pose for compa- country was “lucky” in that it was the beam are all as close to a specific nies, and how they especially affect left with essentially a clean slate in frequency as possible. Apptricity’s governments. A story that discusses terms of its IT and telecommunica- Bluetooth beacons use firmware how government legacy IT systems tions environment. developed by the company to achieve in Japan are holding back that coun- And Estonia was “good,” Eaves such precise tuning, but with Blue- try’s economic recovery further illus- says, because its political leadership tooth signals instead of photons. Thus, trates the magnitude of the problem. was savvy enough to recognize how the beacons can send and receive Japanese economist Yukio important modern technology was, data without interfering with other Noguchi, quoted in a recent Japan not only to its future economy but wireless signals and without requir- Today story, warned that the coun- also its political stability and inde- ing unwieldy amounts of power. try is “behind the world by at least pendence. Eaves says being poor Garcia says RFID tags and bar-code 20 years” in administrative technol- meant that the country’s leader- scanning don’t actively provide infor- ogy. This helps explain why, despite ship could not “afford to make bad mation about assets or inventory. By being the world’s third-largest econ- decisions,” like richer countries. contrast, not only can Bluetooth pin- omy, Japan is now ranked only 34th Estonia began by modernizing its point where something is, it can also out of 63 countries when it comes to telecommunications infrastruc- send updates about a piece of equip- digital competitiveness as measured ture—mobile first because it was ment that needs maintenance or just by the IMD World Competitiveness easiest and cheapest, followed by a routine checkup. Center, a Swiss business school. a fiber-optic backbone, and then, By its own estimation, Apptricity’s By contrast, Estonia’s IT systems beginning in 2001, setting up pub- Bluetooth beacons are 90 percent have weathered the pandemic lic Wi-Fi areas across the country. cheaper than LTE or satellite tags, well. According to an article from What’s more, Estonia embarked specifically because Bluetooth the World Economic Forum, dur- on a program to digitize government devices don’t require paying for a sub- ing the country’s pandemic lock- operations and allow its citizens to scription to an established network. down Estonia’s online government communicate and interact with the The company’s current transmis- services continued to be readily government via the Internet. Eaves sion distance record for its Bluetooth available. Further, its schools expe- states that Estonia’s political lead- beacons is 38 km (23.6 miles). rienced little difficulty supporting ership also understood that to do The company has also demon- digital learning, remote working so successfully required legal steps strated noncommercial versions seems to have been a nonissue, and such as ensuring the protection of of the beacons for the U.S. Depart- its health-information systems were individual privacy, safeguarding per- ment of Defense with broadcast quickly reconfigured to provide sonal information, and providing ranges between 80 and 120 km. information about newly diagnosed total transparency regarding how —Michael Koziol COVID-19 cases in near real time. personal data would be used. David Eaves, from the Harvard On top of that, Estonia set out A version of this article appears in our Kennedy School of Government, to avoid being encumbered with Tech Talk blog. says Estonia is a prime example old technologies that would bury of being both “lucky” and “good.” it in IT system maintenance costs. POST YOUR COMMENTS AT spectrum.ieee.org/bluetooth-nov2020 After the Baltic country won back With that in mind, the government its independence from Russia in decreed that “IT solutions of mate- August 1991 and the last Russian rial importance must never be older troops left in 1994, the country of than 13 years.” While the 13-year 1.3 million people found itself des- period seems arbitrary, it serves the

SPECTRUM.IEEE.ORG | NOV 2020 | 09 HowHow toto selectselect thethe rightright adhesiveadhesive forfor AEROSPACEAEROSPACE APPLICATIONSAPPLICATIONS

RECORDED WEBINAR purpose of a forcing function to IT SUPREMACY: Estonia’s emphasis on ensure existing systems don’t fall having updated IT infrastructure served it well when COVID-19 forced the world to into the prevailing twilight world work, shop, and learn remotely. Watch this webinar for a of technology maintenance. practical discussion on: Estonia proudly proclaims on ically underfunded for several its “e-governance” website that 99 years. A September 2019 Organi- Factors affecting percent of its public services are zation for Economic Cooperation adhesive selection: online 24/7: “E-services are only and Development report indicates impossible for marriages, divorces, that Estonia must spend approxi- • Type of application and real-estate transactions—you mately 1.5 percent of the state bud- • Service conditions still have to get out of the house for get on its digitalization efforts, but • Performance properties those.” Everything else, including is currently spending only around • Processing constraints voting and filing taxes, can eas- 1.1 percent to 1.3 percent. ily be done securely and quickly Meanwhile, despite its seeming online. And since the 2007 adop- e-governance prowess, Estonia is Adhesive chemistries tion of the nation’s “once only” surprisingly ranked only 28th by information policy, the Estonian the IMD in global competitiveness. Cure mechanisms government cannot ask citizens to To improve that rank, the govern- enter the same information twice. ment will have to fund even more IT and fillers Scaling up Estonia’s ecosystem initiatives. But making up the short- of e-governance in larger coun- fall will be challenging, given the 6 case studies tries might not be easy. However, pandemic’s global economic impact. there is still much to be learned So Estonia has reached an inflec- about what an e-government tion point. It will be interesting to approach can achieve, and which see whether the country will be Scan IT legacy modernization strategies able to find the funding for both to watch might be quickly implemented, new IT initiatives and IT modern- webinar Eaves argues. izations, or if it will choose to fund Yet, even in Estonia, there are a the former over the latter—and few dark clouds forming in the dis- end up stumbling into the legacy tance that could rain on its IT sys- IT system trap that so many other tems’ parade. The government’s countries have. chief information officer, Siim —ROBERT N. CHARETTE Sikkut, has repeatedly warned that while there has been fund- A version of this article appears in ing available to build new online our Risk Factor blog. capabilities, the country’s existing POST YOUR COMMENTS AT IT infrastructure has been chron- spectrum.ieee.org/estonia-nov2020 154 Hobart St., Hackensack, NJ 07601 USA +1.201.343.8983 • mainmasterbond.com NEWS www.masterbond.com KRISTI SITS/BRAND ESTONIA SITS/BRAND KRISTI

10 | NOV 2020 | SPECTRUM.IEEE.ORG AI DIAGNOSES AUTISM EARLY New tool likely to eliminate years of delay in treating small children

In September, Cognoa, a company based in Palo Alto, Calif., announced it will seek approval from the U.S. Food and Drug Administration (FDA) to market a first- of-its-kind autism spectrum disorder (ASD) diagnostic tool. Cognoa’s technology uses artificial intelligence to make an ASD diagnosis within weeks of parents expressing concern—far faster than the current standard of care can achieve. If cleared by the FDA, the company says, it would be the first tool ILLUMINATE ENGAGE enabling primary care pediatricians the possibilities a wider audience in to diagnose autism. of technology by appreciating the value The approach is “innovative,” says using it to address and importance of Robin Goin-Kochel, a clinical autism global challenges engineering and technology researcher at Baylor College of Medi- cine and associate director for research EDUCATE ENERGIZE at Texas Children’s Hospital’s Autism the next generation innovation Center. Goin-Kochel, who is not affil- of innovators by celebrating iated with Cognoa, says that the field and engineers technological excellence absolutely needs a way to “minimize the time between first concerns about development or behavior and eventual ASD diagnosis.” The world’s most daunting challenges require The application of AI could enable innovations in engineering, and IEEE is committed more doctors to diagnose autism, to finding the solutions. thereby opening a critical bottleneck The IEEE Foundation is leading a special campaign in children’s health care. While most par- to raise awareness, create partnerships, and generate ents of children with autism notice devel- financial resources needed to combat these opmental changes early on (within the global challenges. first three years of life), the median age at which children in the United States Our goal is to raise $30 million by 2020. are diagnosed is 4.3 years old. That’s because families often wait months, even years, to see a specialist and get DONATE NOW a diagnosis. The time lost during that period is critical: Numerous studies ieeefoundation.org show that early intervention, before the syndrome is fully manifest, can reduce the severity of ASD and improve a child’s brain and behavioral development.

SPECTRUM.IEEE.ORG | NOV 2020 | 11 Cognoa’s technology comes out of the lab of company founder Dennis Wall, an associate professor of pediatrics at the Stanford University School of Medicine. “I went into this,” w Best Ne Journal in says Wall, “with the hope of objectively asking the question: 15 STM 20 Can we reduce the complexity of the autism diagnostic process without loss of accuracy?” By feeding electronic health-record data into a set of algorithms, Wall’s team was able to identify key characteristics Become a that are central to an ASD diagnosis. These include social and emotional behaviors, such as whether a child smiles in published author response to another person’s smile or whether he or she can share attention toward an object, and the extent of traits such in 4 to 6 weeks. as creativity and imagination. The team’s ASD diagnostic tool seeks to capture those features with three modules: a parent Published online only, IEEE Access is ideal survey, home videos, and a clinician questionnaire. for authors who want to quickly announce David Happel, CEO of Cognoa, explains how the tool works: When a parent expresses concern at a pediatrician appoint- recent developments, methods, or new ment, or a child fails an ASD screening questionnaire, the products to a global audience. pediatrician gives the parent a code to access Cognoa’s smartphone app. Once in the app, the parent answers a 15-minute IEEE Access is a multidisciplinary questionnaire about the child’s behavioral patterns, and then journal that allows you to: uploads two 1- or 2-minute home videos capturing the child’s • Reach millions of global users through the behavior in a natural environment. The videos are sent to a IEEE Xplore® digital library with free access to all trained Cognoa professional who reviews them and answers pertinent questions. Those answers are fed into Cognoa’s AI • Submit multidisciplinary articles that do not fit along with the parent’s answers and a short questionnaire neatly in traditional journals filled out by the pediatrician. Then the algorithm sends a result • Expect a rapid yet rigorous peer review— to the pediatrician, and the pediatrician renders a diagnosis. a key factor why IEEE Access is included in The tool’s algorithms are trained on data from hundreds Web of Science (and has an Impact Factor) of real cases across genders, races, and ethnic backgrounds, • Establish yourself as an industry pioneer by says Happel. “[The tool] has proven not only to accelerate the contributing to trending, interdisciplinary topics time of diagnosis but also to remove a lot of the biases that are in one of the Special Sections inherent in the current system,” he says. Today’s standard • Integrate multimedia and track usage and ASD diagnostic tools, Happel notes, were constructed with citation data for each published article health data from young Caucasian boys, so girls and children • Connect with readers through commenting of nonwhite backgrounds are not well recognized by these • Publish without a page limit for tools, contributing to delays in diagnosis for those groups. only $1,750 per article A Cognoa study published in March reported that an earlier version of its ASD diagnostic tool outperformed standard tools, including questionnaires answered by a parent, teacher, or clinician that flag some at-risk children. Since then, the company has completed a pivotal, double- IEEE Access... a multidisciplinary blind clinical trial at 14 sites around the United States. The open access trial involved 425 participants, aged between 18 months and journal that’s 72 months, whose parents or doctors had expressed concern worthy of about their development but had not previously been eval- the IEEE. uated for ASD, according to a press release. Each child was assessed twice—once using Cognoa’s tool, and once by a specialist clinician based on criteria from the Diagnostic and Sta- tistical Manual of Mental Disorders, Fifth Edition (DSM-5); that diagnosis was then validated by a second specialist clinician. The results of the trial have yet to be published, so there is Learn more at: no specific data to report, but the company says the trial “sur- ieeeaccess.ieee.org passed its targeted benchmarks.” Moreover, says Cognoa, the 17-PUB-013 3/17 tool proved to be accurate regardless of gender or ethnicity.

12 | NOV 2020 | SPECTRUM.IEEE.ORG SOONER THE BETTER: A new tool uses artificial intelligence to diagnose autism spectrum disorder within weeks of parents spotting signs of concern.

important to understand the plan for how new tools and technologies will be implemented in primary pediatric care,” says Goin-Kochel. Doctors are often slow to adopt new models, especially for making diagnoses they may not feel comfortable making, she notes. New technologies raise practical questions, such as when they should be applied and whether insurance companies will pay. “I’m very hopeful there is a near-term future where this product is available,” says Cognoa’s Dennis Wall, “covered Because the study ran from July 2019 publication in coming months (and to by insurance, and made available to through May 2020, some of the children the FDA as well), says Cognoa hopes to everybody as immediately as possible.” were evaluated this spring during the receive crucial regulatory approval in —Megan Scudellari pandemic via telemedicine. The tool the second half of 2021. The company’s performed just as well when adminis- timetable calls for it to be ready to launch A version of this article appears in our tered remotely as when it was used for the product into the hands of pediatri- Human OS blog. in-office analysis, says Happel. cians two months after that. Happel, who confirms that the com- If and when Cognoa’s technology or POST YOUR COMMENTS AT pany plans to submit the full study for others become available, “it will be really spectrum.ieee.org/autism-nov2020

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SPECTRUM.IEEE.ORG | NOV 2020 | 13 PHOTON FLIGHT

IF YOU’RE GOING TO JUMP out of a perfectly good airplane for sport, you could choose any old aircraft. But eco-adventurer Raphaël Domjan chose the SolarStratos, a solar-powered aircraft that’s expected to become the first crewed solar plane to fly in the stratosphere. In August, Domjan jumped from the sleek two-seater as it cruised over Payerne, in western Switzerland, to publicize his SolarStratos project: Rather than exiting early and landing via parachute, he plans to pilot the plane during the entire record-breaking flight.

THE BIG PICTURE NEWS GUTTER CREDIT GOES HERE GOES CREDIT GUTTER

14 | NOV 2020 | SPECTRUM.IEEE.ORG PHOTOGRAPH BY Laurent Gillieron/AFP/Getty Images GUTTER CREDIT GOES HERE GOES CREDIT GUTTER

SPECTRUM.IEEE.ORG | NOV 2020 | 15 HANDS ON BY DAVID SCHNEIDER

16 | NOV 2020 | SPECTRUM.IEEE.ORG ILLUSTRATIONS BY James Provost Hands On

PEDALING OUT OF THE DARK BUILD A DOUBLE-BACKUP HOME POWER SUPPLY

AS THIS ARTICLE GOES TO want to do that for a few reasons. In particular, I re- press, Hurricane Delta is making land- called stories about what went on after Hurricane fall not far from where Hurricanes Sally Sandy in 2012, when many people using such and Laura came ashore earlier in the season. I live backup generators had trouble finding fuel, in- on the East Coast of the United States, and fairly cluding the IEEE Operations Center, in New Jersey. far inland, so such storms are not as frequent or in- My first thought was to use photovoltaics, so I tense as they are in states bordering on the Gulf of purchased two 100-watt panels on Amazon for Mexico. But they are still a concern, if only because less than US $1/W. I had a 35-ampere DC-to- they can topple trees and cause widespread power DC converter from an earlier project to use as a outages. And ice storms during the winter here are charge controller, so my next step was to spec out also apt to bring down power lines. a deep-cycle lead-acid battery to keep things go- I don’t mind the resulting darkness so much. ing at night. What I really don’t relish, though, is losing Internet Some experiments with a watt meter led me to access—especially now that it is my main connec- conclude that a battery of at least 300 watt-hours tion to the world due to the pandemic. And the capacity could keep four laptops, a cable modem, pandemic is reducing the number of field crews and a wireless router running for about 4 hours, available to fix power lines, making outages last while also charging the family’s phones and flash- that much longer. So this year, I figured I’d get pre- lights. That should get us through dark evenings. pared for a blackout in the most self-sufficient It would also suffice at a reduced load if the sun way possible. were hidden behind clouds all day. So I purchased I could, of course, just purchase a conventional a 12‑volt, 35-ampere-hour battery (which nomi- small gasoline-powered generator. But I didn’t nally can store 420 Wh).

HANDS ON BY DAVID SCHNEIDER DEPARTMENTS

SPECTRUM.IEEE.ORG | NOV 2020 | 17 HANDS ON BY DAVID SCHNEIDER

ploys magnets and eddy cur- rents to create drag forces on a shaft that presses against the back wheel to increase exercise intensity. I ripped out all that drag- inducing stuff and attached a brushless motor to the shaft using a flexible coupler and a wooden spacer. Then I connected the three leads of the motor— originally intended to motorize a skateboard and now acting as a generator—to a three-phase bridge rectifier. The output of the rectifier in turn is connected to my battery through a Drok meter. This meter allows me to monitor the voltage, current, wattage, and total energy produced. Testing my power-producing bicycle stand quickly revealed a flaw in my logic. Pedaling at a comfortable pace, meaning one that I could keep up for a PARALLEL POWER: My system primarily relies on photovoltaic panels to charge a deep-cycle lead-acid battery via a long time, produced only about DC-DC converter. When there’s not enough sunlight to use the panels, I switch over to a generator driven by the back wheel of a conventional bike mounted in a stand. This requires a rectifier and a meter mounted on the handlebars to monitor the 60 W, not 80. In retrospect, I power produced and fed into the battery. decided that I had failed to con- sider the inefficiencies of power conversion, which surely are significant because my motor/ But what if skies remained gray for many lations (I’m small and typically cycle around generator gets pretty hot after a while. But days in a row? Rather than trying to purchase 22 kilometers per hour). That 80 Wh is only even 60 Wh would do in a pinch. And there’s enough battery storage to cover all reason- a fraction of what my solar panels can pro- no rule that says I couldn’t cycle for longer able eventualities, I decided that my backup vide in a day, but it would be enough to keep than an hour. Even better, I can get my kids source of electricity needed a backup itself, my laptop connected to the Internet for a few to contribute a little sweat to support their one that I could use to charge that battery hours, charge phones, and so forth. And ped- phone and computer use during the gray during times when my photovoltaic panels aling my own power seemed like a healthy, days of a winter power outage. won’t function. When necessary, I’d simply stress reducing, activity to pass the time dur- Actually, generating power with their detach the battery from the panels and at- ing a power outage. muscles provides a valuable lesson for kids, tach it to my backup source to be recharged. I discovered from one blogger that it whether or not the power goes out. Every I briefly considered whether a wind turbine wouldn’t be hard to modify a stationary time they switch on a lightbulb or a tele might serve that role, but then opted for bike stand to generate electrical power. vision, they will think more about what this something I figured would be more depend- Although I had a bike stand already, mine energy consumption means, given the con- able: my two legs. provides frictional drag using a fluid-filled siderable effort it takes to produce those I cycle regularly for about an hour a day, chamber, which I was reluctant to crack watts yourself. —DAVID SCHNEIDER during which I probably put out an aver- open. Instead, I purchased one similar to POST YOUR COMMENTS AT age of 80 W, based on some rough calcu- the one that the blogger used, which em- spectrum.ieee.org/pedal-nov2020

18 | NOV 2020 | SPECTRUM.IEEE.ORG Careers

MERRYL GROSS, INFORMATION ARCHITECT FROM COCKPITS TO CLINICS, USER EXPERIENCES CAN MEAN LIFE OR DEATH

For kidney patients who do their and GE Healthcare, which, as software archi- own dialysis at home, nurses must tectures evolved, brought her to working on review information data gathered during software as a service (SaaS) and Web apps. a treatment session. “These nurses need For people interested in a UX design role, to know quickly when there is a problem Gross says, “You can start with a subspecialty like peritonitis, which can kill a patient in a like usability testing, then add, like, informa- day—but not be overwhelmed with alerts tion architecture or interaction design to and messages,” says Merryl Gross, an infor- broaden your focus.” Someone with coding mation architect and senior UX Designer for experience “may be able to start as a UI de- Fresenius Medical Care North America. The signer.” Or, Gross says, “You could go the company’s Web-based software for clinics graphic artist route, if a company needs con- and nurses who are responsible for dialy- trols designed as part of the work. If you do sis and other services needs to be carefully technical writing, there are UI writers who do crafted. It has to display information in a way the text parts of user interfaces.” that draws nurses’ attention to both immedi- where one power plant had replaced the She also suggests some skills that it’s ate and long-term problems, without being numbered levers for the control rods with good to have in your portfolio: “Wireframing, confusing or overwhelming. levers from beer taps,” recalls Gross. “It ideation, conducting iterative design re- “Basically [it’s] applying human psychology meant that if there was an emergency reviews, usability testing, and creating func- to the design of made objects,” says Gross. quiring quick action, instead of yelling ‘Drop tional specifications.” For specific software “Different fields have their own names for this,” lever No. Six!,’ which could take a new— tools, Gross recommends getting experi- Gross notes. “When it’s a control panel in an or stressed—employee several seconds ence with “Adobe XD, Sketch, Balsamiq, or airplane cockpit, we call it human-factors to identify, they could yell ‘Drop the Coors other wireframing tools; outlining and flow engineering. When it’s software, we call it lever!,’ which even a new employee could lo- tools like Overflow or [Microsoft] Visio; and usability and user experience (UX).” cate instantly.” collaboration tools like InVision or Miro.” Gross started on her path by taking an After graduating from MIT, “I did human- In addition to traditional job listings, Gross elective course in human factors as an MIT factors engineering at Telephonics, design- suggests looking at specialty recruiters like undergraduate in the early 1980s. Field ing control panels for radios for military and Clear/Point Staffing Consultants for those trips included visits to the control tower aviation use.... But after a year, I decided that interested in UX. But she warns, “Beware at Boston’s Logan Airport and the control to do more of the human-factors parts I need- of any listing that asks for someone to room in New Hampshire’s Seabrook Nuclear ed a master’s degree, so I went to Tufts and wireframe, design, and code the entire Power Plant—places where rapid, correct re- got my master’s in engineering psychology.” front end—that’s a place that doesn’t know sponses by staff are critical. From there, Gross went on to work on the what they need.” —DANIEL P. DERN The high stakes force clear, if sometimes UX aspect of software design at companies surprising, interface decisions. “We saw including IBM, SilverPlatter, IDX Systems, POST YOUR COMMENTS AT spectrum.ieee.org/ux-nov2020

DEPARTMENTS

ILLUSTRATION BY Gluekit SPECTRUM.IEEE.ORG | NOV 2020 | 19 CrossTalkNUMBERS DON’T LIE_BY VACLAV SMIL OPINION

HOW VERY DIVERTING

Egypt drinks from the River Nile, and the country stands to lose should anything cut the flow from its tributaries, which originate deep within Africa. Just such a threat now looms EGYPT following the inauguration of the Grand Ethiopian Renaissance Dam.

Grand Ethiopian Renaissance Dam

ERITREA

Grand Ethiopian Renaissance Dam Reservoir: 74 km3

ETHIOPIA

flooded Sudd swamps of South Sudan, CLAIMING THE NILE this allocation left all the other states along the Nile tributaries with no claims to the water at all. Egypt still upholds this allocation, THE COMPLETION OF THE Grand which adds 26 km3/year. The Atbara but in 2009 Ethiopia began a de facto Ethiopian Renaissance Dam on the Blue adds 11.1 km3. These rivers, coming out dismantling of the arrangement with Nile has made Egypt fear for its very exis- of Ethiopia, together provide about the completion of a dam on the Tekezé tence. To understand why requires the 70 percent of the Nile’s flow into Egypt. River, a tributary to the Atbara. At appreciation of basic water-flow and The Anglo-Egyptian treaty of 1929 188 meters high, it is the tallest African water-use numbers in the region. secured for Egypt the rights to 48 km3 arch dam (shaped to resist water pres- The Blue Nile flows from Ethiopia’s of water; the 1959 treaty update raised sure), although it has an installed hydro- Lake Tana, carrying 48.3 cubic kilo the amount to 55.5 km3, with Sudan get- power capacity of just 300 megawatts meters of water a year. In Khartoum, ting 18.5 km3. After accounting for the and a relatively small reservoir, hold- 3

Sudan, it merges with the White Nile, intervening water losses in the annually ing 9 km . The next Ethiopian action,

NUMBERS DON’T LIE BY VACLAV SMIL ↗ POST YOUR COMMENTS at https://spectrum.ieee.org/ xxx1019

20 | NOV 2020 | SPECTRUM.IEEE.ORG ILLUSTRATION BY Francesco Muzi/StoryTK the Tana Beles hydro project (460 MW), The dam, completed in June 2020, has lessly impoverished to support a better- began to generate electricity in 2010 and an installed hydropower capacity of off country? has no storage. Instead, it gets its water 6.45 gigawatts and a reservoir designed Partial solutions are possible, but straight from Lake Tana and discharges to hold 74 km3. The rainy season of 2020 none is easy or easily affordable. Egypt’s it into the Beles River, a tributary of the has already put in 5 km3 of water. own Aswan High Dam (2.1 GW), com- Blue Nile. By themselves, these two proj- Filling the rest of the reservoir in five pleted in 1970, impounds 132 km3 but, ects would cause little worry to Egypt, years would cut the annual flow out of situated in one of the world’s hottest were its dependence on the Nile’s water Ethiopia by 30 percent and thus the regions, it loses annually up to 15 km3 to not becoming precarious. flow into Egypt by just over 20 percent evaporation. Storing this water in a less In 1959 Egypt’s population was about (that is, 30 percent of 70 percent). This extreme environment (the best location 26 million, by 2020 it had nearly qua- would deprive Egypt of one-fifth of its would be in South Sudan) would reduce drupled to just over 100 million, and it is water, and even after the reservoir has the loss but deprive Egypt of 2.1 GW of now increasing by a little under 2 million been filled, retention of flows during installed capacity and of water control a year. This growth has reduced the dry years would continue to limit the for its deltaic irrigation. Channeling country’s per capita annual supply of downstream supply. the White Nile through South Sudan, fresh water to only 550 cubic meters, What Egypt sees as a mortal chal- around the Sudd swamps, would cut less than half the U.S. rate. Should the lenge, Ethiopia considers to be its the region’s huge evaporation losses, population reach its projected size of inalienable right: That country num- but ever since gaining its independence 160 million in 2050, this rate might fall bers 115 million people, growing by in 2011, that nation has experienced below 400 cubic meters. 2.6 million a year, and it has a per cap- endless civil war, tribal fighting, and The challenge is greatly increased by ita gross domestic product less than chronic political instability. n the new Renaissance dam on the Blue 20 percent of the Egyptian average. POST YOUR COMMENTS AT spectrum.ieee.org/ Nile, near Ethiopia’s border with Sudan. Should Ethiopia forever remain hope- nile-nov2020

32,174 Great Pyramids of Giza: 74 km3

Great Pyramid of Giza: 0.0023 km3

CROSSTALK ↗ POST YOUR COMMENTS at https://spectrum.ieee.org/ xxx1019

SPECTRUM.IEEE.ORG | NOV 2020 | 21 INTERNET OF EVERYTHING BY STACEY HIGGINBOTHAM CROSSTALK

is short for “long-range.”) But Giezeman sees that as the necessary element for later providing the sensors and software that deliver the real IoT applications customers want to buy. Trying to sell both the network and the devices is like running a restaurant that makes diners buy and set up the stove before it cooks their meals. The Things Network sets up the “stove” and includes the cost of operating it in the “meal.” But, because Giezeman is a big believer in the value of open source software and creating a sense of abundance around last-mile connectivity, he’s also asking customers to opt in to turning their networks into public networks. Senet does something similar, letting customers share their networks. Helium is using cryptocurrencies to entice people to set up LoRaWAN hotspots on their networks and rewarding them with tokens for keeping the networks operational. When NETWORK INCLUDED someone uses data from an individual’s Helium node, that individual also gets tokens that might be worth something one day. I actually run a Helium hotspot ALONG WITH everything area network (WAN) that provides signifi- in my home, although I’m more interested else going on, we may look cant coverage and supports a plethora of in the LoRa coverage than the potential back at 2020 as the year devices that are enticing to use. for wealth. that companies finally hit It certainly didn’t help such network And there’s Amazon, which plans to upon a better business model for Inter- companies as Ingenu, MachineQ, Senet, embed its own version of a low-power net of Things (IoT) networks. Established and SigFox that they’re all marketing half a WAN into its Echo and its Ring security network companies such as the Things dozen similar proprietary networks. Even devices. Whenever someone buys one Network and Helium, and new players the cellular carriers, which are promot- of these devices they’ll have the option such as Amazon, have seemingly given ing both LTE-M for machine-to-machine of adding it as a node on the Amazon up on the idea of making money from networks and NB-IoT for low-data-rate Sidewalk network. Amazon’s plan is to selling network connectivity. Instead, networks, have historically struggled to build out a decentralized network for IoT they’re focused on getting the network justify their investments in IoT network devices, starting with a deal to let man- out there for developers to use, assum- infrastructure. After COVID-19 started ufacturer Tile use the network for its ing in the process that they’ll benefit spreading in Japan, NTT DoCoMo called Bluetooth tracking devices. from the effort in the long run. it quits on its NB-IoT network, citing a After almost a decade of following vari- IoT networks have a chicken-and-egg lack of demand. ous low-power IoT networks, I’m excited problem. Until device makers see widely “Personally, I don’t believe in business to see them abandon the idea that the net- available networks, they don’t want to models for [low-power WANs],” says work is the big value, and instead recog- build products that run on the network. Wienke Giezeman, the CEO and cofounder nize that it’s the things on the network that And customers don’t want to pay for a net- of the Things Network. His company does entice people. Let’s hope this year marks work, and thus, fund its development, if deploy long-range low-power WAN gate- a turning point for low-power WANs. n there aren’t devices available to use. So it’s ways for customers that use the LoRa Alli- ↗ POST YOUR COMMENTS hard to raise capital to build a new wide- ance’s LoRaWAN specifications. (“LoRa” spectrum.ieee.org/iotnetworks-nov2020

22 | NOV 2020 | SPECTRUM.IEEE.ORG ILLUSTRATION BY Greg Mably MACRO & MICRO BY MARK PESCE CROSSTALK

Hurricane Laura, I wonder whether an upgrade to the game will one day allow players to pilot real drones into a future storm’s eye wall. If that prospect seems far-fetched, con- sider what’s going on hundreds of kilometers higher up. That’s the realm of Saber Astronautics, whose software can be used to visualize—and manage—the immense number of objects orbiting Earth. Before Saber, space-mission control- lers squinted at numbers on a display screen to judge whether there was a dan- ger from space debris. Now they can work with a visualization that blends observa- tional data with computational simulations, just as Flight Simulator 2020 does. That makes it far easier to track threats and gently nudge the orbits of satellites before they run into a piece of space flot- sam, which could turn the kind of cas- cading collisions of orbital space junk WHEN GAMES GET REAL depicted in the filmGravity into a real- life catastrophe. We’ve now got the data, the networks, and the software to create a unified MY NEPHEW RECENTLY ping the controls so tightly that it hurts. simulation of Earth, from its surface all sent me an email about our All that realism begins with the cockpit the way into space. That could be valu- latest shared obsession: instruments and controls, but it extends able for entertainment, sure—but also Microsoft’s Flight Simulator well beyond. Players fly over terrain and for much more. Weaving together data 2020. “Flying a Cessna 152 in this game buildings streamed from Microsoft’s Bing from weather sensors, telescopes, air- feels exactly like flying one in real life,” Maps data set, and the inclusion of real- craft traffic control, and satellite track- he wrote. And he should know. Grow- time air traffic control information means ing could transform the iconic “Whole ing up next to a small regional airport, players need to avoid the flight paths of Earth” image photographed by a NASA he saw private aircraft flying over his actual aircraft. For a final touch of real- satellite in 1967 into a dynamic model, home every day, and he learned to fly ism, the game also integrates real-time one that could be used for entertaining as soon as his feet were long enough to meteorological data, generating simu- simulations or to depict goings-on in reach the rudder pedals. lated weather conditions that mirror the real world. It would provide enor- While he relaxes with the game, my those of the real world. mous opportunities to explore, to play, experiences with it have been more Flight Simulator 2020 purposely mixes and to learn. stressful. Covered with sweat as I care- a simulation of something imaginary It’s often said that what can’t be mea- fully adjust ailerons, trim, and throttle, with a visualization of actual conditions. sured can’t be managed. We need to I worked my way through the how-to-fly Does that still qualify as a game? I’d argue manage everything from the ground to lessons, emerging exhausted. “It’s just it’s something new, which is possible outer space, for our well-being and for a simulation,” I keep telling myself. “It only now because of the confluence of the planet’s. At last, we now have a class doesn’t matter how often I crash.” But fast networks, big data, and cheap but of tools—ones that look a lot like toys— the game is so realistic that crashing incredibly powerful hardware. Seeing to help us do that. n scares the daylights out of me. So while YouTube videos of Flight Simulator 2020 ↗ POST YOUR COMMENTS playing I remain hypervigilant, grip- users flying their simulated aircraft into spectrum.ieee.org/simulator-nov2020

ILLUSTRATION BY Edmon de Haro SPECTRUM.IEEE.ORG | NOV 2020 | 23 That Bend And

SOME Conceptual photograph by SMARTPHONES Dan Saelinger CAN NOW FOLD LIKE A WALLET. IN A FEW YEARS, YOU MAY WEAR ONE ON YOUR SKIN By Huanyu Zhou & Tae-Woo Lee

24 | NOV 2020 | SPECTRUM.IEEE.ORG GUTTER CREDIT GOES HERE GOES CREDIT GUTTER

PHOTOGRAPH BY Firstname Lastname SPECTRUM.IEEE.ORG | NOV 2020 | 25 DISPLAYS THAT BEND AND STRETCH

MOTOROLA DEMONSTRATED THE VERY quite tight bends at that, with a radius of curvature of just 3 millimeters. But the first handheld mobile phone almost a half FlexPai phone was more of a prototype century ago. It was the size of a brick and than a mature product. A review pub- weighed half as much. That prototype lished in The Verge, for example, called spawned the first commercial mobile phone it “charmingly awful.” Soon afterward, Samsung and Huawei, a decade later. It, too, was ungainly, but the world’s two largest smartphone it allowed a person to walk around while makers, began offering their own fold- sending and receiving phone calls, which able models. Samsung Mobile officially at that point was a great novelty. Since announced its Galaxy Fold in February • 2019. It features dual foldable displays then, mobile phones have acquired many that can be bent with a radius of cur- other functions. They now have the ability to vature as small as 1 mm, allowing the handle text messages, browse the Web, play phone to fold up with the display on the music, take and display photos and videos, inside. Huawei announced its first foldable smartphone, the Mate X, later that locate the owner on a map, and serve count- month. The Mate X is about 11 mm thick less other uses—applications well beyond when folded, and its display (like that of what anybody could have imagined when the FlexPai) is on the outside, meaning mobile phones were first introduced. that the bending radius of the display is roughly 5 mm. And in February of this year, each company introduced a second foldable model: Samsung’s Galaxy Z Flip and Huawei’s Mate Xs/5G. But smartphones, nimble as they are, to you here so that you’re ready when a The most challenging part of engineer- have struggled to overcome one seem- phone with a large, bright, flexible dis- ing these phones was, of course, devel- ingly fundamental drawback: Their display comes to a pocket near you—not to oping the display itself. The key was to plays are small. Sure, some phones have mention even more radical electronic reduce the thickness of the flexible dis- been made larger than normal to provide devices that will be possible when their play panel so as to minimize the bend- more real estate for the display. But make screens can stretch as well as bend. ing stresses it has to endure when folded. the phone too big and it outgrows the The smartphone industry has just figured owner’s pocket, which is a nonstarter out how to do that, and panel suppliers for many people. RESEARCHERS HAVE BEEN SERIOUSLY such as Samsung Display and Beijing- The obvious solution is to have the dis- investigating how to make flexible dis- based BOE Technology Group Co. are play fold up like a wallet. For years, devel- plays for about two decades. But for years, now mass-producing foldable displays. oping suitable technology for that has they remained just that—research proj- Like those found in conventional been one of our goals as researchers at ects. In 2012, though, Bill Liu and some smartphones, these are all active-matrix Seoul National University. It’s also been other Stanford engineering graduates set organic light-emitting-diode (AMOLED) a goal for smartphone manufacturers, out to commercialize flexible displays by displays. But instead of fabricating these who just in the past year or two have been founding the Royole Corp. (which now AMOLEDs on a rigid glass substrate, as able to bring this technology to market. has headquarters in both Fremont, Calif., is normally done, these companies use Soon, phones with foldable screens and Shenzhen, China). a thin, flexible polymer. On top of that will no doubt proliferate. You or some- In late 2018, Royole introduced the flexible substrate is the backplane—the one in your family will probably have FlexPai, whose flexible display allows layer containing the many thin-film tran- one, at which point you’ll surely wonder: the device to unfold into something that sistors needed to control individual pix- How in the world is it possible for the dis- resembles a tablet. The company dem- els. Those transistors incorporate a buffer play to bend like that? We figured we’d onstrated that this foldable display could layer that can prevent cracks from form- explain what’s behind that technology withstand 200,000 bending cycles—and ing when the display is flexed.

26 | NOV 2020 | SPECTRUM.IEEE.ORG A CLOSED BOOK: In late 2018, Royole Corp. developed the first commercial smartphone with a bendable display, the FlexPai. It folds closed with the screen still visible on the outside.

of indium tin oxide (ITO) fills this role. But ITO is quite brittle under tension, making it a bad choice for flexible displays. To make matters worse, ITO tends to adhere poorly to flexible polymer substrates, causing it to buckle and delami- nate when compressed. Researchers battling this problem a decade ago found a few strategies for improving the adhesion between ITO and a flexible substrate. One is to treat the substrate with oxygen plasma before depositing the ITO electrode on top. Another is to insert a thin layer of metal (such as silver) between the electrode and the substrate. It also helps to place the top of the substrate in the exact middle of the layer cake that makes up the display. This arrangement puts the fragile inter- Although flexible displays constructed bringing the outside surface of a flexed face with the ITO layer on the display’s along these lines are fast becoming more display closer to the inside surface, which mechanical neutral plane, which experi- common for phones and other consumer is to say to make the device very thin. ences neither compression nor tension products, the standards that apply to To make the display as thin as possible, when flexed. Currently, the leading elec- these displays, as well as language for designers omit the protective film and tronics companies that make foldable describing their ability to bend, are still, polarizer that normally go on top, along displays are using this strategy. you might say, taking shape. These dis- with the adhesive applied between these Even simpler, you can get rid of the ITO plays can be at least broadly characterized layers. While removing those elements electrodes altogether. While that hasn’t according to the radius of curvature they is not ideal, both the protective film and been done yet in commercial devices, can withstand when flexed: “Conform- antireflection polarizer are optional com- this strategy is attractive for reasons hav- able” refers to displays that don’t bend ponents for AMOLED displays, which ing nothing to do with the desire for flex- all that tightly, “rollable” refers to ones generate light internally rather than ibility. You see, indium is both toxic and with intermediate levels of flexibility, and modifying the amount of light transmit- expensive, so you really don’t want to use “foldable” describes those that can accom- ted from an LED backlight, as in liquid- it if you don’t have to. Fortunately, over modate a very small radius of curvature. crystal displays. the years researchers, including the two Because any material, be it a smart- of us, have come up with several other phone display or a steel plate, is in ten- materials that could function as trans- sion on the outside surface of a bend and NOTHER DIFFERENCE parent electrodes for flexible displays. in compression on the inside, the elec- between flexible and conven- A flexible film that contains silver tronic components that make up a dis- tional displays has to do with nanowires is probably the most prom- play must resist those stresses and the the transparent conductive ising candidate. These vanishingly tiny corresponding deformations they induce. A electrodes that sandwich the wires form a mesh that conducts electric- And the easiest way to do that is by mini- light-emitting organic materials that ity while remaining largely transparent. mizing those shape-changing forces by make the pixels shine. Normally, a layer Such a layer can be prepared at low cost ROBYN BECK/GETTY IMAGES BECK/GETTY ROBYN

SPECTRUM.IEEE.ORG | NOV 2020 | 27 DISPLAYS THAT BEND AND STRETCH

by applying a solution containing silver nanowires to the substrate in a manner similar to that of printing ink on newsprint. Most of the research on silver nano wires has been focused on finding ways to reduce the resistance of the junctions between individual wires. You can do that by adding certain other materials to the nanowire mesh, for example. Or you can physically treat the nanowire layer by heating it in an oven or by send ing enough electricity through it to fuse the nanowire junctions through Joule heating. Or you can also treat it by hot- pressing it, subjecting it to a plasma, or irradiating it with a very bright flash to fuse the junctions. Which of these treat ments is the best to use will depend in large part on the nature of the substrate onto which the nanowires are applied. A polymer substrate, such as polyethylene terephthalate (PET, the same material that many clear plastic food containers are made of ), is prone to problematic polystyrene sulfonate—a mouthful that ited. Think of it as a high-tech stenciling amounts of deformation when heated. normally goes by the shorter name operation. Those metal masks with their Polyimide is less sensitive to heat, but it PEDOT:PSS. Such polymers can be dis very fine patterns are hard to fabricate, has a yellowish color that can compro solved in water, which allows thin, trans though, and much of the applied mate mise the transparency of an electrode parent electrodes to be easily fabricated rial is wasted, contributing to the high created in this way. by printing or spin coating (an industrial cost of large display panels. But metal nanowires aren’t the only process akin to making spin art). The An interesting alternative, however, has possible substitute for ITO when creat right chemical additives can significantly emerged for fabricating such displays: ing transparent conductive electrodes. improve the ability of a film of this con inkjet printing. For that, the organic Another one is graphene, a form of car ductive polymer to bend or even stretch. material you want to apply is dissolved bon in which the atoms are arranged Careful selection of additives can also in a solvent and then jetted onto the sub in a two-dimensional honeycomb pat boost the amount of light that displays strate where it is needed to form the tern. Graphene doesn’t quite match emit for a given amount of current, mak many pixels, followed by a subsequent ITO’s superb conductivity and optical ing them brighter than displays fabri heating step to drive off any solvent that transparency, but it is better able to with cated using ITO electrodes. remains. DuPont, Merck, Nissan Chemi stand bending than any other electrode cal Corp., and Sumitomo are pursuing material now being considered for flex this tactic, even though the efficiency ible displays. And graphene’s somewhat UP TO NOW, THE ORGANIC LED DIS- and reliability of the resulting devices lackluster electrical conductivity can be plays used in mobile phones, computer still remain far lower than needed. But improved by combining it with a conduct monitors, and televisions have mainly if one day these companies succeed, the ing polymer or by doping it with small been fabricated by putting the substrate cost of display fabrication should dimin amounts of nitric acid or gold chloride. under vacuum, evaporating whatever ish considerably. Yet another possibility is to use a con organic material you want to add to For makers of small displays for smart ductive polymer. The prime example it, and then using metal masks to con phones, an even higher priority than is poly(3,4-ethylenedioxythiophene) trol where those substances are depos keeping costs down is reducing power TOLGA AKMEN/GETTY IMAGES AKMEN/GETTY TOLGA

28 | NOV 2020 | SPECTRUM.IEEE.ORG by conductive pathways that can withstand the deformation that accompa- nies stretching. More recently, though, there’s been progress in developing intrinsically stretchable displays—ones in which the conductors and semiconductors as well as the substrate can all be stretched. Such displays require some novel materials, to be sure, but perhaps the greatest hur- dle has been figuring out how to devise stretchable materials to encapsulate these devices and protect them from the damaging effects of moisture and oxygen. Our research team has recently made good progress in that regard, successfully developing air-stable, intrinsically stretchable light-emitting devices that do not require stretchable protective coatings. These devices can be stretched to almost twice their normal length without failing. Today, only very crude prototypes of stretchable displays have been fab- consumption. Organic LEDs (OLEDs) BENT ON COMPETING: In 2019, Huawei and ricated, ones that provide just a coarse are becoming less power hungry, but Samsung introduced their own lines of phones grid of luminous elements. But industry’s with flexible displays. Shown are Huawei’s the more mature the OLED industry Mate Xs [left] and Samsung’s Galaxy Fold [right]. interest in stretchable displays is huge. becomes, the more difficult it will be to This past June, South Korea’s Ministry further trim power consumption from of Trade, Industry and Energy assigned its current value of around 6 milliwatts LG Display to lead a consortium of indus- per square centimeter (about 40 mw likely use these devices initially to visu- trial and academic researchers to develop per square inch). And the diminishing alize various kinds of biometric data, but stretchable displays. returns here are especially problematic other applications will no doubt emerge. With just a little imagination, you can for foldable phones, which boast dis- And perhaps such wearable displays will envision what’s coming down the road: plays that are much larger than normal. one day be used just to make a high-tech athletes festooned with biometric dis- So it’s probably a safe bet that your fold- fashion statement. plays attached to their arms or legs, able phone, compact as it is, will have to The materials used to produce such smartphones we wear on the palms of contain an especially hefty battery, at a display should, of course, be soft our hands, displays that drape conform- least in the near term. enough not to be bothersome when ably over various curved surfaces. The attached to the skin. What’s more, they people who are working hard now to would have to be stretchable. Fabricat- develop such future displays will surely HAT’S NEXT FOR flexible ing intrinsically stretchable conductors benefit from the many years of research displays after they allow our and semiconductors is an enormous that have already been done to create smartphones to fold? Given challenge, though. So for several years today’s foldable displays for smart- how much people seem researchers have been exploring the phones. Without doubt, the era for not W glued to their phones now, next-best thing: geometrically stretch- just bendable but also stretchable elec- we anticipate that in the not-so-distant able displays. These contain rigid but tronics will soon be here. n future, people will start wearing displays tiny electronic components attached to POST YOUR COMMENTS AT spectrum.ieee.org/ that attach directly to the skin. They’ll a stretchable substrate and connected bendabledisplays-nov2020 JUNG YEON-JE/AFP/GETTY IMAGES YEON-JE/AFP/GETTY JUNG

SPECTRUM.IEEE.ORG | NOV 2020 | 29 THE 9 GREATEST VACUUM TUBES You’ve Never Heard Of

IN AN AGE PROPPED UP BY quintillions of solid-state These vacuum devices, should you even care about vacuum tubes? You defi- devices stood nitely should! For richness, drama, and sheer brilliance, few technological timelines can match the 116-year (and counting) guard during history of the vacuum tube. To prove it, I’ve assembled a list the Cold War, of vacuum devices that over the past 60 or 70 years inargu- ably changed the world. • And just for good measure, you’ll advanced also find here a few tubes that are too unique, cool, or weird particle physics, to languish in obscurity. • Of course, anytime anyone offers up a list of anything—the comfiest trail-running shoes, the most treated cancer authentic Italian restaurants in Cleveland, movies that are bet- patients, and ter than the book they’re based on—someone else is bound to weigh in and either object or amplify. So, to state the obvious: made the Beatles This is my list of vacuum tubes. But I’d love to read yours. Feel sound better free to add it in the comments section of the online version of this article (where you will find two more tubes not included in print). • My list isn’t meant to be comprehensive. Here you’ll find no gas-filled glassware like Nixie tubes or thyratrons, no By CARTER M. “uber high” pulsed-power microwave devices, no cathode-ray ARMSTRONG display tubes. I intentionally left out well-known tubes, such as satellite traveling-wave tubes and microwave-oven magnetrons. And I’ve pretty much stuck with radio-frequency tubes, so I’m ignoring the vast panoply of audio-frequency tubes—with one notable exception. • But even within the parameters I’ve chosen, there are so many amazing devices that it was rather hard to pick just nine of them. So here’s my take, in no particular order, on some tubes that made a difference. TELEDYNE E2V TELEDYNE

30 | NOV 2020 | SPECTRUM.IEEE.ORG Medical Magnetron

WHEN IT COMES to efficiently generating coherent radio-frequency power in a compact package, you can’t beat the magnetron. The magnetron first rose to glory in World War II, to power British radar. While the magnetron’s use in radar began to wane in the 1970s, the tube found new life in industrial, scientific, and medical applications, which continues today. It is for this last use that the medical magnetron shines. In a linear accelerator, it creates a high-energy electron beam. When electrons in the beam are deflected by the nuclei in a target—consisting of a material having a high atomic number, such as tungsten— copious X-rays are produced, which can then be directed to kill cancer cells in tumors. The first clinical accelerator for radiotherapy was installed at London’s Hammersmith Hospital in 1952. A 2-megawatt magnetron powered the 3-meter-long accelerator. High-power magnetrons continue to be developed to meet the demands of radiation oncology. The medical magnetron shown here, manufactured by e2v Technologies (now Teledyne e2v), generates a peak power of 2.6 MW, with an average power of 3 kilowatts and an efficiency of more than 50 percent. Just 37 centimeters long and weighing about 8 kilograms, it’s small and light enough to fit the rotating arm of a radiotherapy machine.

SPECTRUM.IEEE.ORG | NOV 2020 | 31 Mini Traveling- Wave Tube

AS ITS NAME SUGGESTS, a traveling- much gain. Enter the mini TWT, shown wave tube (TWT) amplifies signals through here in an example from L3Harris Electron the interaction between an electric field of Devices. With a gain of around 1,000 a traveling, or propagating, electromagnetic (or 30 decibels), a mini TWT is meant for wave in a circuit and a streaming electron applications where you need output power beam. [For a more detailed description of in the 40- to 200-watt range, and where how a TWT works, see “The Quest for the small size and lower voltage are desirable. Ultimate Vacuum Tube,” IEEE Spectrum, A 40-W mini TWT operating at 14 gigahertz, December 2015.] for example, fits in the palm of your hand Most TWTs of the 20th century were and weighs less than half a kilogram. designed for extremely high power gain, As it turns out, military services have with amplification ratios of 100,000 or a great need for mini TWTs. Soon after more. But you don’t always need that their introduction in the 1980s, mini TWTs

Gyrotron

CONCEIVED IN THE 1960s in the Soviet Union, the gyrotron is a high-power vacuum device used primarily for heating plasmas in nuclear-fusion experiments, such as ITER, now under construction in southern France. These experimental reactors can require temperatures of up to 150 million °C. So how does a megawatt-class gyrotron work? The name provides a clue: It uses beams of energetic electrons rotating or gyrating in a strong magnetic field inside a cavity. (We tube folks love our -trons and -trodes.) The interaction between the gyrating electrons and the cavity’s electromagnetic field generates high- frequency radio waves, which are directed into the plasma. The high-frequency waves accelerate the electrons within the plasma, heating the plasma in the process. A tube that produces 1 MW of average power is not going to be small. Fusion gyrotrons typically stand around 2 to 2.5 meters tall and weigh around a metric ton, including a 6- or 7-tesla superconducting magnet. In addition to heating fusion plasmas, gyrotrons are used in material processing and nuclear magnetic resonance spectroscopy. They have also been explored for nonlethal crowd control, in the U.S. military’s Active Denial System. This system projects a relatively wide millimeter-wave beam, perhaps a meter and a half in diameter. The beam is designed to heat the surface of a person’s skin, creating a burning sensation but without penetrating into or damaging the tissue below.

32 | NOV 2020 | SPECTRUM.IEEE.ORG were adopted in electronic warfare systems on planes and ships for protection against radar-guided missiles. In the early 1990s, device designers began integrating mini TWTs with a compact high-voltage power supply to energize the device and a solid-state amplifier to drive it. The combination created what is known as a microwave power module, or MPM.

Due to their small size, low weight, and high efficiency, MPM CLOCKWISE FROM LEFT: NUCLEAR amplifiers found immediate use in radar and communications FUSION/IAEA; L3HARRIS ELECTRON DEVICES; ARCHIVES AND HISTORY transmitters aboard military drones, such as the Predator and OFFICE/SLAC NATIONAL ACCELERATOR Global Hawk, as well as in electronic countermeasures. LABORATORY

Accelerator Klystron

THE KLYSTRON HELPED usher in the era of big science in high-energy physics. Klystrons convert the kinetic energy of an electron beam into radio-frequency energy. The device has much greater output power than does a traveling-wave tube or a magnetron. The brothers Russell and Sigurd Varian invented the klystron in the 1930s and, with others, founded Varian Associates to market it. These days, Varian’s tube business lives on at Communications and Power Industries. Inside a klystron, electrons emitted by a cathode accelerate toward an anode to form an electron beam. A magnetic field keeps the beam from expanding as it travels through an aperture in the anode to a beam collector. In between the anode and collector are hollow structures called cavity resonators. A high-frequency signal is applied to the resonator nearest the cathode, setting up an electromagnetic field inside the cavity. That field modulates the electron beam as it passes through the resonator, causing the speed of the electrons to vary and the electrons to bunch as they move toward the other cavity resonators downstream. Most of the electrons decelerate as they traverse the final resonator, which oscillates at high power. The result is an output signal that is much greater than the input signal. In the 1960s, engineers developed a klystron to serve as the RF source for a new 3.2-kilometer linear particle accelerator being built at Stanford University. Operating at 2.856 gigahertz and using a 250-kilovolt electron beam, the SLAC klystron produced a peak power of 24 MW. More than 240 of them were needed to attain particle energies of up to 50 billion electron volts. The SLAC klystrons paved the way for the widespread use of vacuum tubes as RF sources for advanced particle physics and X-ray light-source facilities. A 65-MW version of the SLAC klystron is still in production. Klystrons are also used for cargo screening, food sterilization, and radiation oncology.

SPECTRUM.IEEE.ORG | NOV 2020 | 33 Ring-Bar Traveling- Wave Tube

ONE COLD WAR TUBE that is still going strong is the huge ring-bar traveling- wave tube. This high-power tube stands over 3 meters from cathode to collector, making it the world’s largest TWT. There are 128 ring-bar TWTs providing the radio-frequency oomph for an exceedingly powerful phased-array radar at the Cavalier Air Force Station in North Dakota. Called the Perimeter Acquisition Radar Attack Characterization System (PARCS), the 440-megahertz radar looks for ballistic missiles launched toward North America. It also monitors space launches and orbiting objects as part of the Space Surveillance Network. Built by GE in 1972, PARCS tracks more than half of all Earth-orbiting objects, and it’s said to be able to identify a basketball-size object at a range of 2,000 miles (3,218 km). An even higher-frequency version of the ring-bar tube is used in a phased-array radar on remote Shemya Island, about 1,900 km off the coast of Alaska. Known as Cobra Dane, the radar monitors non-U.S. ballistic missile launches. It also collects surveillance data on space launches and satellites in low Earth orbit. The circuit used in this behemoth is known as a ring bar, which consists of circular rings connected by alternating strips, or bars, repeated along its length. This setup provides a higher field intensity across the tube’s electron beam than does a garden-variety TWT, in which the radio- frequency waves propagate along a helix- shaped wire. The ring-bar tube’s higher field intensity results in higher power gain and good efficiency. The tube shown here was developed by Raytheon in the early 1970s; it is now manufactured by L3Harris Electron Devices.

34 | NOV 2020 | SPECTRUM.IEEE.ORG Ubitron

FIFTEEN YEARS BEFORE the term “free-electron laser” was coined, there was a vacuum tube that worked on the same basic principle—the ubitron, which sort of stands for “undulating beam interaction.” The 1957 invention of the ubitron came about by accident. Robert Phillips, an engineer at the General Electric Microwave Lab in Palo Alto, Calif., was trying to explain why one of the lab’s traveling- wave tubes oscillated and another didn’t. Comparing the two tubes, he noticed variations in their magnetic focusing, which caused the beam in one tube to wiggle. He figured that this undulation could result in a periodic interaction with an electromagnetic wave in a waveguide. That, in turn, could be useful for creating exceedingly high levels of peak radio-frequency power. Thus, the ubitron was born. From 1957 to 1964, Phillips and colleagues built and tested a variety of ubitrons. The 1963 photo below is of GE colleague Charles Enderby holding a ubitron without its wiggler magnet. Operating at 70,000 volts, this tube produced a peak power of 150 kW at 54 GHz, a record power level that stood for well over a decade. But the U.S. Army, which funded the ubitron work, halted R&D in 1964 because there were no antennas or waveguides that could handle power levels that high. Today’s free-electron lasers employ the same basic principle as the ubitron. In fact, in recognition of his pioneering work on the ubitron, Phillips received the Free-Electron Laser Prize in 1992. The FELs now installed in the large light and X-ray sources at particle accelerators produce powerful electromagnetic radiation, which is used to explore the dynamics of chemical bonds, to understand photosynthesis, to analyze how drugs bind with targets, and even to create warm, dense matter to study how gas planets form. Carcinotron

THE FRENCH TUBE called the carcinotron is another fascinating example born of the Cold War. Related to the magnetron, it was conceived by Bernard Epsztein in 1951 at Compagnie Générale de Télégraphie Sans Fil (CSF, now part of Thales). Like the ubitron, the carcinotron grew out of an attempt to resolve an oscillation problem on a conventional tube. In this case, the source of the oscillation was traced to a radio-frequency circuit’s power flowing backward, in the opposite direction of the tube’s electron beam. Epsztein discovered that the oscillation frequency could be varied with voltage, which led to a patent for a voltage-tunable “backward wave” tube. For about 20 years, electronic jammers in the United States and Europe employed carcinotrons as their source of RF power. The tube shown here was one of the first manufactured by CSF in 1952. It delivered 200 W of RF power in the S band, which extends from 2 to 4 GHz. Considering the level of power they can handle, carcinotrons are fairly compact. Including its permanent focusing magnet, a 500-W model weighs just 8 kg and measures 24 by 17 by 15 cm, a shade smaller than a shoebox. And the strange name? Philippe Thouvenin, a vacuum electronics scientist at Thales Electron Devices, told me that it comes from a Greek word, karkunos, which means crayfish. And crayfish, of

FROM LEFT: L3HARRIS ELECTRON DEVICES; ROBERT PHILLIPS; THALES PHILLIPS; ROBERT DEVICES; ELECTRON L3HARRIS LEFT: FROM course, swim backwards.

SPECTRUM.IEEE.ORG | NOV 2020 | 35 POST YOUR COMMENTS AT spectrum.ieee.org/ vacuumtubes-nov2020 Coaxitron

ALL THE TUBES I’ve described a unique permutation of the so far are what specialists call cylindrical design. The electrons beam-wave devices (or stream- flow radially from the cylindrical wave in the case of the magnetron). coaxial cathode to the anode. But But before those devices came rather than having a single electron along, tubes had grids, which emitter, the coaxitron’s cathode is are transparent screenlike metal segmented along its circumference, electrodes inserted between with numerous heated filaments the tube’s cathode and anode to serving as the electron source. control or modulate the flow of Each filament forms its own little electrons. Depending on how many beamlet of electrons. Because the grids the tube has, it is called a beamlet flows radially to the anode, diode (no grids), a triode (one grid), no magnetic field (or magnet) is a tetrode (two grids), and so on. required to confine the electrons. Low‑power tubes were referred The coaxitron is thus very compact, to as “receiving tubes,” because considering its remarkable power they were typically used in radio level of around a megawatt. receivers, or as switches. (Here A 1-MW, 425-MHz coaxitron I should note that what I’ve been weighed 130 pounds (59 kg) referring to as a “tube” is known to and stood 24 inches (61 cm) tall. the British as a “valve.”) While the gain was modest (10 to There were, of course, higher- 15 dB), it was still a tour de force power grid tubes. Transmitting as a compact ultrahigh-frequency tubes were used in—you guessed power booster. RCA envisioned the it—radio transmitters. Later on, coaxitron as a source for driving RF high-power grid tubes found their accelerators, but it ultimately found way into a wide array of interesting a home in high-power UHF radar. industrial, scientific, and military Although coaxitrons were recently applications. overtaken by solid-state devices, Triodes and higher-order grid some are still in service in legacy tubes all included a cathode, a radar systems. current-control grid, and an anode or collector (or plate). Most of these tubes were cylindrical, with a central cathode, usually a filament, surrounded by electrodes. The coaxitron, developed by RCA beginning in the 1960s, is

three grids. When that even simulates the tube’s used in a microphone, 55-V heater circuit. But can it however, it operates replicate that warm, lovely tube as a triode, with sound? On that one, audio snobs Telefunken Audio Tube two of its grids will never agree. n strapped together and connected to

the anode. This was THUMP/SOUNDGAS BOTTOM: RCA; TOP: done to exploit the AN IMPORTANT CONVENTIONAL Sinatra and by the Beatles’ producer supposedly superior sonic qualities tube with grids resides at the Sir George Martin. Fun fact: There’s of a triode. The VF14’s heater circuit, opposite end of the power/ a Neumann U47 microphone on which warms the cathode so that frequency spectrum from display at the Abbey Road Studio in it emits electrons, runs at 55 V. megawatt beasts like the klystron London. The “M” in the VF14M tube That voltage was chosen so that and the gyrotron. Revered by designation indicates it’s suitable two tubes could be wired in series audio engineers and recording for microphone use and was only across a 110-V main to reduce artists, the Telefunken VF14M was awarded to tubes that passed power-supply costs, which was employed as an amplifier in the screening at Neumann. important in postwar Germany. legendary Neumann U47 and U48 The VF14 is a pentode, meaning Nowadays, you can buy a solid- microphones favored by Frank it has five electrodes, including state replacement for the VF14M

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EYE IN THE SKY: The microsatellite Claire has spotted a number of methane plumes over the last four years, including at the following locations: 1) the Balkan Region of western Turkmenistan; 2) a gas facility in Yamalo-Nenets Autonomous Okrug, in northwestern Siberia; 3) the Permian Basin, in western Texas; 4) the Lom Pangar Dam, in eastern Cameroon; and 5) a coal mine in Shanxi, China. 6) Our newest satellite, Iris, launched in September and underwent electromagnetic testing earlier this year. GHGSAT (6) EYES IN THE SKY ENABLE ACTION ON CLIMATE CHANGE

5 MICROSATELLITES SPOT MYSTERY METHANE LEAKS

By JASON McKEEVER, DYLAN JERVIS & MATHIAS STRUPLER

SOMETHING NEW HAPPENED IN SPACE IN JANUARY 2019. For the first time, a previously unknown leak of natural gas was spotted from orbit by a microsatellite, and then, because of that detection, plugged. The microsatellite, Claire, had been flying since 2016. That day, Claire was monitoring the output of a mud volcano in Central Asia when it spied a plume of methane where none should be. Our team at GHGSat, in Montreal, instructed the spacecraft to pan over and zero in on the origin of the plume, which turned out to be a facility in an oil and gas field in Turkmenistan. The need to track down methane leaks has never been more important. In the slow-motion calamity that is climate change, methane emissions get less public attention than the carbon dioxide coming from smokestacks and tailpipes. But methane—which mostly comes from fossil-fuel production but also from livestock farming and other sources—has an outsize impact. Mol- ecule for molecule, methane traps 84 times as much heat in the atmosphere as carbon dioxide does, and it accounts for about a quarter of the rise in atmospheric temperatures. Worse, research from earlier this year shows that we might be enormously underestimating the amount released—by as much as 25 to 40 percent.

SPECTRUM.IEEE.ORG | NOV 2020 | 39 15-kilogram year. When we’re done, there will be nowhere for methane on Earth Those scientific behemothsdotheirjob admirably,Those scientific butthey view things THE CREATION OF CLAIRE when 40 neering andamoreneering focused goal, our company hasmanaged to build innovationneed and technological to make such observations practical nal instrument wasnal instrument better tunedfor reason methane.But thebusiness Overneeded less. time,governments could allotment shrink thetotal past September, andathird scheduledto go is upbefore theendof satellite, launcheditself. dubbedIris, Oursecondmethane-seeking this taxes or implemented carbon-trading mechanisms. Bytaxes mechanisms. 2019, orimplemented carbon-trading car these to begin toto reduce begin thedrivers ofclimate change. to emitmore could thenpurchase credits from emissions thosethat they could release into theatmosphere year. each Thosethat needed sites.Majortrial emitters would number beallotted oftons acertain of that they would implementamarket-based “cap andtrade” system. The the core technology—a miniaturized version known of an instrument leaks toleaks hide. VERY PROUD bon markets covered 22 percent gov and earned of global emissions bon dioxide from space for nearly years, 20 butittook aconfluenceof become the focus of our origi systems. One reason technological—our is team at the Space of Carbon Pricing 2020of Carbon . Flight Laboratory, a 15-kilogram microsatellite that andperform previ feats ofdetection - and accurate enough to do them for profit. Through someclever engi- as a wide-angle Fabry-Pérotas a wide-angle imaging spectrometer—and the spacecraft Satellites have beenable ernments $45 billion,according to theWorld Bank’sState andTrends which wasemissions, growing imposed steadily asmore jurisdictions of meters. Soapolluter (or anybody determine notjustwhat else)can resolveClaireon a kilometer can scale. down methane emissions to tens ously weren’t possible,even withaUS$100million,1,000-kg spacecraft. carbon—or itsequivalentcarbon—or in methane and othergreenhouse gases—that challenge. was andatechnology borninmid-2011, part Thebusiness case PARENTS: in Toronto,with microsatellite. methane-sensing a brandnew gas field is involvedgas field but which well inthat field. systems would emitted a attribute value by to ton each of carbon indus- Despite thosebillions,it’s dioxide, methane,notcarbon that has Even there in2011, was awider, multibillion-dollar market for carbon Since launching Claire, our firstmicrosatellite, we’ve improved onboth |NOV 2020 | SPECTRUM.IEEE.ORG Quebec (GHGSat’s homeprovince) andCalifornia announced each The to seegreenhouse gases and its siblings was driven by a business like methaneandcar - - - - The spectrometers break down theincoming The greater the concentration of those mole with a precision that’swith aprecision better than1 percent of (launched satellites These in 2009). measure Imaging Absorption spectroMeter for Atmo ultimately reduce them. mostly Existing, ual industrial facilities anywhere facilities industrial ual in the world. path will absorb a certain pattern ofwavepath willabsorbacertain instruments areinstruments huge. Thespectrometer por measure methaneconcentrations from orbit missions such asEurope’smissions Envisat (which oper is the simpler one: Methane thesimplerone: hasvalue whetheris tion of Envisat, called SCIAMACHYtion ofEnvisat, called (SCanning far from what we needed. For the onething, that collect sunlight scattering off the earth. off the sunlight scattering that collect operatorstrial would flockto asingle,less there’s trading system agreenhouse-gas ornot. light by wavelength. Molecules in the light’s lengths, leavinglengths, dark bandsinthespectrum. background levels. ated from 2002 to andJapan’s 2012) GOSat answered, to a degree, by space pioneering availability. Our company’s bet was that indus accuracy, asto andvaried theirgeographic of methane tracking, their technology was theirtechnology of methanetracking, thedarkercules, methodcan thebands.This chambers, operators sites to better- ofindustrial mea only question was:we Could doit? expensive, more solution precise that could ground-based methodsusingsystems like flux gas imagingwere fairly expensive, oflimited sure their emissions so they can controlsure and sothey can theiremissions surface-level usingspectrometers trace gases fromspot emissions greenhouse-gas individ While thosesatellites proved theconcept Markets for greenhouse motivate gases the One part of the question hadOne part already been Once we’d plan,the onour business decided eddy covariance towers , andoptical ------

GHGSAT SENSING METHANE FROM SPACE

The satellite measures the way a plume of gas Two infrared rays of different The etalon is made up of two partially mirrored surfaces [bottom] [pink] absorbs portions of the spectrum of wavelengths streaking up to held micrometers apart. A portion of the light passes through both reflected sunlight. The key instrument involved the satellite [top] from different surfaces; the rest reflects within the mirrored cavity before it passes is called a wide-angle Fabry-Pérot etalon. points on the ground enter the through. If the light is of the right wavelength and enters at a particular satellite at different angles. angle, it will constructively interfere with itself [left]. The result is an angle-dependent wavelength filter [right]. Sun

Microsatellite

1,640 nm 1,650 nm Focal- plane array

Imaging optics

Methane plume Fabry-Pérot Partially etalon reflective glass

θ 2 θ θ1 2 θ2 Well θ1

Ground Earth

spheric CHartographY), contained nearly THE MOST CRITICAL enabling technology to meet those constraints 200 kg of complex optics; the entire space- was our spectrometer—the wide-angle Fabry-Pérot etalon (WAF-P). (An craft carried eight other scientific instruments etalon is an interferometer made from two partially reflective plates.) To and weighed 8.2 metric tons. GOSat, which is help you understand what that is, we’ve first got to explain a more common dedicated to greenhouse-gas sensing, weighs type of spectrometer and how it works in a hyperspectral imaging system. 1.75 metric tons. Hyperspectral imaging detects a wide range of wavelengths, some of Furthermore, these systems were designed to which, of course, are beyond the visible. To achieve such detection, you measure gas concentrations across the whole need both a spectrometer and an imager. planet, quickly and repeatedly, in order to The spectrometers in SCIAMACHY are based on diffraction gratings. A inform global climate modeling. Their instru- diffraction grating disperses the incoming light as a function of its wave- ments scan huge swaths of land and then length—just as a prism spreads out the spectrum of white light into a rain- average greenhouse-gas levels over tens or bow. In space-based hyperspectral imaging systems, one dimension of hundreds of square kilometers. And that is the imager is used for spectral dispersion, and the other is used for spatial far too coarse to pinpoint an industrial site imaging. By imaging a narrow slit of a scene at the correct orientation, you responsible for rogue emissions. get a spectrum at each point along that thin strip of land. As the spacecraft To achieve our goals, we needed to design travels, sequential strips can be imaged to form a two-dimensional array something that was the first of its kind—an of points, each of which has a full spectrum associated with it. orbiting hyperspectral imager with spatial If the incoming light has passed through a gas—say, Earth’s atmosphere— resolution in the tens of meters. And to make in a region tainted with methane, certain bands in the infrared part of it affordable enough to launch, we had to fit it that spectrum should be dimmer than otherwise in a pattern character- in a 20-by-20-by-20-centimeter package. istic of that chemical.

ILLUSTRATION BY James Provost SPECTRUM.IEEE.ORG | NOV 2020 | 41 light’s radial position within the scene. Since we’re looking at light transmitted through the atmosphere, we end up with dark rings at specific radii corresponding to molecular absorption lines. The etalon can be miniaturized more easily than a diffraction-grating spectrometer, because the spectral discrimination arises from interference that happens within a very small gap of tens to hundreds of micrometers; no large path lengths or beam separation is required. Furthermore, since the etalon consists of substrates that are parallel to one another, it doesn’t add significantly to aberrations, so you can use relatively straightforward optical-design techniques to obtain sufficient spatial resolution. However, there are complications associated with the WAF-P imaging spectrometer. For example, the imager behind the etalon picks up both the image of the scene (where the gas well is) and the interference pattern PUTTING IT TOGETHER: To determine the complete spectrum of an entire scene, the satellite must take up to 200 images as it passes overhead [top]. That way (the methane spectrum). That is, the spectral each feature will be measured at all the relevant wavelengths [red rings, bottom]. rings are embedded in—and corrupted by—the The process, called a retrieval, reproduces an image of a methane plume. actual image of the patch of Earth the satellite is pointing at. So, from a single camera frame, Such a spectral-imaging system works well, but making it compact is you can’t distinguish variability in how much challenging for several reasons. One challenge is the need to minimize light reflects off the surface from changes in the optical aberrations to achieve a sharp image of ground features and emis- amount of greenhouse gases in the atmosphere. sion plumes. However, in remote sensing, the signal strength (and hence Separating spatial and spectral information, so signal-to-noise ratio) is driven by the aperture size, and the larger this is, that we can pinpoint the origin of a methane the more difficult it is to minimize aberrations. Adding a dispersive grat- plume, took some innovation. ing to the system leads to additional complexity in the optical system. A Fabry-Pérot etalon can be much more compact without the need for THE COMPUTATIONAL PROCESS used to a complex imaging system, despite certain surmountable drawbacks. extract gas concentrations from spectral mea- It is essentially two partially mirrored pieces of glass held very close surements is called a retrieval. The first step in together to form a reflective cavity. Imagine a beam of light of a certain getting this to work for the WAF-P was charac- wavelength entering the cavity at a slight angle through one of the mir- terizing the instrument properly before launch. rors. A fraction of that beam would zip across the cavity, squeak straight That produces a detailed model that can help through the other mirror, and continue on to a lens that focuses it onto predict precisely the spectral response of the a pixel on an imager placed a short distance away. The rest of that beam system for each pixel. of light would bounce back to the front mirror and then across to the But that’s just the beginning. Separating the back mirror. Again, a small fraction would pass through, the rest would etalon’s mixing of spectral and spatial infor- continue to bounce between the mirrors, and the process would repeat. mation took some algorithmic magic. We over- All that bouncing around adds distance to the light’s paths toward the came this issue by designing a protocol that pixel. If the light’s angle and its wavelength obey a particular relation- captures a sequence of 200 overlapping images ship to the distance between the mirrors, all that light will constructively as the satellite flies over a site. At our satellite’s interfere with itself. Where that relation holds, a set of bright concentric orbit, that means maximizing the time we have rings forms. Different wavelengths and different angles would produce to acquire images by continuously adjusting a different set of rings. the satellite’s orientation. In other words, we In an imaging system with a Fabry-Pérot etalon like the ones in our have the satellite stare at the site as it passes satellites, the radius of the ring on the imager is roughly proportional to by, like a rubbernecking driver on a highway the ray angle. What this means for our system is that the etalon acts as passing a car wreck. an angle-dependent filter. So rather than dispersing the light by wave- The next step in the retrieval procedure is

length, we filter the light to specific wavelengths, depending on the to align the images, basically tracking all the (3) GHGSAT

42 | NOV 2020 | SPECTRUM.IEEE.ORG ILLUSTRATION BY James Provost ground locations within the scene through WE’VE LEARNED A LOT in the four years since Claire started its obser- the sequence of images. This gives us a col- vations. And we’ve managed to put some of those lessons into practice lection of up to 200 readings where a feature, in our next generation of microsatellites, of which Iris is the first. The say, a leaking gas well, passes across the com- biggest lesson is to focus on methane and leave carbon dioxide for later. plete interference pattern. This effectively is If methane is all we want to measure, we can adjust the design of measuring the same spot on Earth at decreas- the etalon so that it better measures methane’s corner of the infrared

ing infrared wavelengths as that spot moves spectrum, instead of being broad enough to catch CO2’s as well. This, outward from the center of the image. If the coupled with better optics that keep out extraneous light, should result methane concentration is anomalously high, in a 10-fold increase in methane sensitivity. So Iris and the satellites to this leads to small but predictable changes in follow will be able to spot smaller leaks than Claire can. signal level at specific positions on the image. We also discovered that our next satellites would need better radiation Our retrievals software then compares these shielding. Radiation in orbit is a particular problem for the satellite’s changes to its internal model of the system’s imaging chip. Before launching Claire, we’d done careful calculations spectral response to extract methane levels in of how much shielding it needed, which were then balanced with the parts per million. increased cost of the shielding’s weight. Nevertheless, Claire’s imager At this point, the WAF-P’s drawbacks has been losing pixels more quickly than expected. (Our software par- become an advantage. Some other satel- tially compensates for the loss.) So Iris and the rest of the next genera- lites use separate instruments to visualize tion sport heavier radiation shields.

the ground and sense the methane or CO2 Another improvement involves data downloads. Claire has made about spectra. They then have to realign those 6,000 observations in its first four years. The data is sent to Earth by two. Our system acquires both at once, so radio as the satellite streaks past a single ground station in northern the gas plume automatically aligns with its Canada. We don’t want future satellites to run into limits in the number point of origin down to the level of tens of of observations they make just because they don’t have enough time meters. Then there’s the advantage of high to download the data before their next appointment with a methane spatial resolution. Other systems, such as leak. So Iris is packed with more memory than Claire has, and the new Tropomi (TROPOspheric Monitoring Instru- microsatellite carries an experimental laser downlink in addition to its ment, launched in 2017), must average meth- regular radio antenna. If all goes to plan, the laser should boost down- ane density across a 7-kilometer-wide pixel. load speeds 1,000-fold, to 1 gigabit per second. The peak concentration of a plume that Claire could spot would be so severely diluted by IN ITS POLAR ORBIT, 500 kilometers above Earth, Claire passes over Tropomi’s resolution that it would seem only every part of the planet once every two weeks. With Iris, the frequency 1/200th as strong. So high-spatial-resolution of coverage effectively doubles. And the addition in December of Hugo systems like Claire can detect weaker emit- and three more microsatellites due to launch in 2021 will give us the ters, not just pinpoint their location. ability to check in on any site on the planet almost daily—depending Just handing a customer an image of their on cloud cover, of course. methane plume on a particular day is useful, With our microsatellites’ resolution and frequency, we should be able but it’s not a complete picture. For weaker to spot the bigger methane leaks, which make up about 70 percent of emitters, measurement noise can make it dif- emissions. Closing off the other 30 percent will require a closer look. ficult to detect methane point sources from a For example, with densely grouped facilities in a shale gas region, it single observation. But temporal averaging of may not be possible to attribute a leak to a specific facility from space. multiple observations using our analytics tools And a sizable leak detectable by satellite might be an indicator of sev- reduces the noise: Even with a single satellite eral smaller leaks. So we have developed an aircraft-mounted version we can make 25 or more observations of a site of the WAF-P instrument that can scan a site with 1-meter resolution. per year, cloud cover permitting. The first such instrument took its test flights in late 2019 and is now in Using that average, we then produce an commercial use monitoring a shale oil and gas site in British Columbia. estimation of the methane emission rate. The Within the next year we expect to deploy a second airplane-mounted process takes snapshots of methane density instrument and expand that service to the rest of North America. measurements of the plume column and cal- By providing our customers with fine-grained methane surveys, we’re culates how much methane must be leak- allowing them to take the needed corrective action. Ultimately, these ing per hour to generate that kind of plume. leaks are repaired by crews on the ground, but our approach aims to Retrieving the emission rate requires knowl- greatly reduce the need for in-person visits to facilities. And every edge of local wind conditions, because the source of fugitive emissions that is spotted and stopped represents a excess methane density depends not only on meaningful step toward mitigating climate change. n the emission rate but also on how quickly the wind transports the emitted gas out of the area. POST YOUR COMMENTS AT spectrum.ieee.org/microsatellites-nov2020

SPECTRUM.IEEE.ORG | NOV 2020 | 43

BREAKING THE MILLISECOND BARRIER ROBOTS AND SELF-DRIVING CARS WILL NEED BY SHIVENDRA PANWAR COMPLETELY REENGINEERED NETWORKS ILLUSTRATION BY Greg Mably SPECTRUM.IEEE.ORG | NOV 2020 | 45 BREAKING THE MILLISECOND BARRIER

OR COMMUNICATIONS NETWORKS, latencies will look like. There’s no bandwidth has long been king. With every one‑size-fits-all technique that will enable these extremely low-latency net- generation of fiber optic, cellular, or Wi-Fi works. Only by combining solutions to technology has come a jump in throughput that all these sources of latency will it be has enriched our online lives. Twenty years ago possible to build networks where time we were merely exchanging texts on our phones, is never wasted. but we now think nothing of streaming videos UNTIL THE 1980s, latency-sensitive from YouTube and Netflix. No wonder, then, that video now technologies used dedicated end-to- Fconsumes up to 60 percent of Internet bandwidth. If this end circuits. Phone calls, for example, trend continues, we might yet see full-motion holography were carried on circuit-switched networks that created a dedicated link delivered to our mobiles—a techie dream since Princess between callers to guarantee minimal Leia’s plea for help in Star Wars. • Recently, though, high delays. Even today, phone calls need to bandwidth has begun to share the spotlight with a different have an end-to-end delay of less than 150 milliseconds, or it’s difficult to con- metric of merit: low latency. The amount of latency varies verse comfortably. drastically depending on how far in a network a signal travels, At the same time, the Internet was car- how many routers it passes through, whether it uses a wired rying delay-tolerant traffic, such as emails, or wireless connection, and so on. The typical latency in using technologies like packet switching. Packet switching is the Internet equivalent a 4G network, for example, is 50 milliseconds. Reducing of a postal service, where mail is routed latency to 10 milliseconds, as 5G and Wi-Fi are currently through post offices to reach the cor- doing, opens the door to a whole slew of applications that rect mailbox. Packets, or bundles of data between 40 and 1,500 bytes, are sent from high bandwidth alone cannot. With virtual-reality headsets, point A to point B, where they are reas- for example, a delay of more than about 10 milliseconds sembled in the correct order. Using the in rendering and displaying images in response to head technology available in the 1980s, delays movement is very perceptible, and it leads to a disorienting routinely exceeded 100 milliseconds, with the worst delays well over 1 second. experience that is for some akin to seasickness. • Multiplayer Eventually, Voice over Internet Pro- games, autonomous vehicles, and factory robots also tocol (VoIP) technology supplanted need extremely low latencies. Even as 5G and Wi-Fi make circuit-switched networks, and now the last circuit switches are being phased 10 milliseconds the new standard for latency, researchers, out by providers. Since VoIP’s triumph, like my group at New York University’s NYU Wireless there have been further reductions in research center, are already working hard on another latency to get us into the range of tens order-of-magnitude reduction, to about 1 millisecond of milliseconds. Latencies below 1 millisecond would or less. • Pushing latencies down to 1 millisecond will open up new categories of applications require reengineering every step of the communications that have long been sought. One of them is process. In the past, engineers have ignored sources of haptic communications, or communicat- ing a sense of touch. Imagine balancing a minuscule delay because they were inconsequential to the pencil on your fingertip. The reaction time overall latency. Now, researchers will have to develop new between when you see the pencil begin- methods for encoding, transmitting, and routing data to ning to tip over and then moving your shave off even the smallest sources of delay. And immutable finger to keep it balanced is measured in milliseconds. A human-controlled tele laws of physics—specifically the speed of light—will dictate operated robot with haptic feedback firm restrictions on what networks with 1-millisecond would need a similar latency level.

46 | NOV 2020 | SPECTRUM.IEEE.ORG ENDTOEND LATENCY (ms) diately and reschedules the transmission 150 if it collides with another device’s transmission in the link. The upside is that this method has shorter delays if there 120 is no congestion, but the delays build up quickly as more device transmissions compete for the same channel. The latest 90 version of Wi-Fi, Wi-Fi Certified 6 (based on the draft standard IEEE P802.11ax) addresses the congestion problem by 60 introducing scheduled transmissions, just as 4G and 5G networks do. When a data packet is traveling through 30 the series of network links connecting 10 its origin to its destination, it is also sub- 2.5 2.5 2 1 ject to congestion delays. Packets are VoIP VIDEO MULTIPLAYER VIRTUAL AUGMENTED HAPTICS AUTONOMOUS 6G often forced to queue up at links as both CHAT GAMING REALITY REALITY VEHICLES NETWORKS the amount of data traveling through a link and the amount of available bandwidth fluctuate naturally over time. In the DELAYS EXPECTED: No network offers zero latency, but evening, for example, more data-heavy some applications are more delay resistant than others. video streaming could cause congestion delays through a link. Sending data packets through a series of wireless links is like drinking through a straw that is con- Robots that aren’t human controlled I SHOULD MENTION here that my stantly changing in length and diameter. would also benefit from 1-millisecond research is focused on what’s called the As delays and bandwidth change, one latencies. Just like a person, a robot can transport layer in the multiple layers of second you may be sucking up dribbles avoid falling over or dropping something protocols that govern the exchange of of data, while the next you have more only if it reacts within a millisecond. But data on the Internet. That means I’m con- packets than you can handle. the powerful computers that process cerned with the portion of a communica- Congestion delays are unpredictable, real-time reactions and the batteries that tions network that controls transmission so they cannot be avoided entirely. The run them are heavy. Robots could be rates and checks to make sure packets responsibility for mitigating congestion lighter and operate longer if their “brains” reach their destination in the correct delays falls to the Transmission Control were kept elsewhere on a low-latency order and without errors. While there Protocol (TCP), one part of the collec- wireless network. are certainly small sources of delay on tion of Internet protocols that governs Before I get into all the ways engineers devices themselves, I’m going to focus how computers communicate with one might build ultralow-latency networks, on network delays. another. The most common implemen- it would help to understand how data The first issue is frame duration. A wire- tations of TCP, such as TCP Cubic, mea- travels from one device to another. Of less access link—the link that connects sure congestion by sensing when the course, the signals have to physically a device to the larger, wired network— buffers in network routers are at capac- travel along a transmission link between schedules transmissions within periodic ity. At that point, packets are being lost the devices. That journey isn’t limited by intervals called frames. For a 4G link, the because there is no room to store them. just the speed of light, because delays are typical frame duration is 1 millisecond, Think of it like a bucket with a hole in it, caused by switches and routers along so you could potentially lose that much placed underneath a faucet. If the fau- the way. And even before that, data time just waiting for your turn to trans- cet is putting more water into the bucket must be converted and prepped on the mit. But 5G has shrunk frame durations, than is draining through the hole, it fills device itself for the journey. All of these lessening their contribution to delay. up until eventually the bucket overflows. parts of the process will need to be rede- Wi-Fi functions differently. Rather than The bucket in this example is the router signed to consistently achieve submilli- using frames, Wi-Fi networks use random buffer, and if it “overflows,” packets are

SOURCES: ITU; TECHTARGET; BRITISH ESPORTS ASSOCIATION; GSMA; ARXIV:1803.03586V1; SAMSUNG ARXIV:1803.03586V1; GSMA; ASSOCIATION; ESPORTS BRITISH TECHTARGET; ITU; SOURCES: second latencies. access, where a device transmits imme- lost and need to be sent again, adding

SPECTRUM.IEEE.ORG | NOV 2020 | 47 BREAKING THE MILLISECOND BARRIER

to the delay. The sender then adjusts its routers to prioritize time-sensitive data transmission rate to try and avoid flood- like real-time video packets. But not all ing the buffer again. routers are capable of doing this, and L4S The problem is that even if the buffer is less useful in those situations. doesn’t overflow, data can still be stuck My group is figuring out how to take the there queuing for its turn through the most effective parts of these TCP versions bucket “hole.” What we want to do is and combine them into a more versatile allow packets to flow through the net- whole. Our most promising approach so work without queuing up in buffers. far has devices continually monitoring for YouTube uses a variation of TCP devel- data-packet delays and reducing trans- oped at Google called TCP BBR, short for mission rates when delays are building Bottleneck Bandwidth and Round-Trip up. With that information, each device on RIGHT ON TIME propagation time, with this exact goal. Frame durations a network can independently figure out It works by adjusting the transmission dictate how just how much data it can inject into the rate until it matches the rate at which frequently devices network. It’s somewhat like shoppers at and routers can data is passing through routers. Going transmit data. a busy grocery store observing the check- back to our bucket analogy, it constantly Reducing those out lines to see which ones are moving adjusts the flow of water out of the fau- durations means faster, or have shorter queues, and then more data can be sent cet to keep it the same as the flow out of more rapidly. choosing which lines to join so that no the hole in the bucket. one line becomes too long. For further reductions in congestion, For wireless networks specifically, reli- engineers have to deal with previously ably delivering latencies below 1 milli- ignorable tiny delays. One example of second is also hampered by connection such a delay is the minuscule variation handoffs. When a cellphone or other in the amount of time it takes each spe- device moves from the coverage area of cific packet to transmit during its turn to one base station (commonly referred to access the wireless link. Another is the as a cell tower) to the coverage of a neigh- slight differences in computation times boring base station, it has to switch its of different software protocols. These can connection. The network initiates the both interfere with TCP BBR’s ability to switch when it detects a drop in signal determine the exact rate to inject pack- strength from the first station and a cor- ets into the connection without leaving DROP IN THE responding rise in the second station’s capacity unused or causing a traffic jam. BUCKET signal strength. The handoff occurs dur- Like water dripping A focus of my research is how to rede- into a leaky bucket, ing a window of several seconds or more sign TCP to deliver low delays combined data packets can as the signal strengths change, so it rarely with sharing bandwidth fairly with other get held up at nodes interrupts a connection. if more are coming connections on the network. To do so, in than can be sent But 5G is now tapping into milli- my team is looking at existing TCP ver- out. Congestion meter waves—the frequencies above sions, including BBR and others like delays can be eased 20 gigahertz—which bring unprecedented by allowing devices the Internet Engineering Task Force’s to monitor their hurdles. These frequency bands have not L4S (short for Low Latency Low Loss transmission rates been used before because they typically Scalable throughput). We’ve found that and throttle them if don’t propagate as far as lower frequen- they’re too high. these existing versions tend to focus cies, a shortcoming that has only recently on particular applications or situa- been addressed with technologies like tions. BBR, for example, is optimized beamforming. Beamforming works by for YouTube videos, where video data using an array of antennas to point a nar- typically arrives faster than it is being row, focused transmission directly at the viewed. That means that BBR ignores intended receiver. Unfortunately, obsta- bandwidth variations because a buffer cles like pedestrians and vehicles can of excess data has already made it to the entirely block these beams, causing fre- end user. L4S, on the other hand, allows quent connection interruptions.

48 | NOV 2020 | SPECTRUM.IEEE.ORG ILLUSTRATIONS BY Greg Mably One option to avoid interruptions like Finally, considering that the robot would these is to have multiple millimeter- need round-trip communications below wave base stations with overlapping 1 millisecond, the maximum possible dis- coverage, so that if one base station is tance between the robot and its brain is blocked, another base station can take about 100 km. And that’s ignoring every over. However, unlike regular cell-tower other source of possible delay. handoffs, these handoffs are much more The only solution we see to this problem frequent and unpredictable because is to simply move away from traditional they are caused by the movement of cloud computing toward what is known people and traffic. as edge computing. Indeed, the push for My team at NYU is developing a solu- submillisecond latencies is driving the tion in which neighboring base stations development of edge computing. This FUMBLE THE are also connected by a fiber-optic ring HANDOFF method places the actual computation network. All of the traffic to this group 5G networks as close to the devices as possible, rather of base stations would be injected into, require frequent than in server farms hundreds of kilo signal handoffs, and then circulate around, the ring. Any meaning plenty meters away. However, finding the real base station connected to a cellphone or of opportunities estate for these servers near users will other wireless device can copy the data as to waste time on be a costly challenge to service providers. a dropped signal. it passes by on the ring. If one base station “Baggage carousels” There’s no doubt that as researchers becomes blocked, no problem: The next of base stations, and engineers work toward 1-millisecond one can try to transmit to the device. If it, linked with fiber delays, they will find more sources of optics, could work too, is blocked, the one after that can have together to keep a latency I haven’t mentioned. When every a try. Think of a baggage carousel at an air- connection intact. microsecond matters, they’ll have to port, with a traveler standing near it wait- get creative to whittle away the last few ing for her luggage. She may be “blocked” slivers on the way to 1 millisecond. Ulti- by others crowding around the carou- mately, the new techniques and tech- sel, so she might have to move to a less nologies that bring us to these ultralow crowded spot. Similarly, the fiber-ring sys- latencies will be driven by what people tem would allow reception as long as the want to use them for. mobile device is anywhere in the range of When the Internet was young, no one at least one unblocked base station. knew what the killer app might be. Uni- POINT OF versities were excited about remotely THERE’S ONE FINAL source of latency NO RETURN accessing computing power or facilitating The speed of light that can no longer be ignored, and it’s sets a hard limit on large file transfers. The U.S. Department immutable: the speed of light. Because how far a signal can of Defense saw value in the Internet’s light travels so quickly, it used to be pos- travel and still reach decentralized nature in the event of an its destination in a sible to ignore it in the presence of other, millisecond, which attack on communications infrastructure. larger sources of delay. It cannot be dis- means either building But what really drove usage turned out regarded any longer. servers and data to be email, which was more relevant centers closer to Take for example the robot we dis- devices or finding to the average person. Similarly, while cussed earlier, with its computational a way to break a factory robots and remote surgery will “brain” in a server in the cloud. Servers fundamental law of certainly benefit from submillisecond physics. and large data centers are often located latencies, it is entirely possible that nei- hundreds of kilometers away from end ther emerges as the killer app for these devices. But because light travels at a technologies. In fact, we probably can’t finite speed, the robot’s brain, in this confidently predict what will turn out to case, cannot be too far away. Moving be the driving force behind vanishingly at the speed of light, wireless commu- small delays. But my money is on multi- nications travel about 300 kilometers player gaming. n per millisecond. Signals in optical fiber POST YOUR COMMENTS AT spectrum.ieee.org/ are even slower, at about 200 km/ms. millisecondlatency-nov2020

SPECTRUM.IEEE.ORG | NOV 2020 | 49 The Department of Electrical and Computer Engineering in the Samuel Ginn College of Engineering at Auburn The Center for Advanced Power Systems at The Florida State University seeks to hire (3) full- University invites applications for tenure-track Assistant time research faculty with an academic MS degree from an accredited institution or equivalent Professor positions in the areas of machine learning, qualifications based on professional experience and otherwise qualified to perform assigned duties. cybersecurity, and magnetic resonance imaging. Please visit www.eng.auburn.edu/elec for details Position (1) is in the computer-related discipline. This position entails maintaining a state-of-the-art real- about these positions and application instructions.

time simulation testbed for electrical power systems as well as significant research and development to Auburn University is an EEO/Vet/Disability Employer. continuously improve those facilities. The potential candidate should have interest in device-level software Auburn University is understanding of and sensitive to the development and a good understanding of modern computer architectures. Proficiency in C++17 (or above), family needs of faculty, including dual career couples. Python, and VHDL programming languages is highly desirable. Must be able to work on projects restricted by US Export Control law. Ability to obtain a US security clearance preferred. IEEE.tv gets a Position (2) is in in the electrical or computer engineering discipline. Background in system engineering preferred. Basic understanding of electric power systems and proficiency in at least one major computer mobile makeover programming language is required. Interest in practical work in the lab as well as experience in computer Bring an award- simulations of electric power systems and in industrial controls is desired. Must be able to work on projects winning network restricted by US Export Control law. Ability to obtain a US security clearance preferred. of technology programs with you. Position (3) is in in the electrical technology discipline. Background in electrical or electronics engineering, or condensed matter physics, preferred. Basic understanding of dielectric phenomena, high voltage, Go mobile or get the app. diagnostics, signal processing, software for electric field simulation. Interest in practical www.ieee.tv laboratory and on-field testing work. Must be able to work on projects restricted by US Export Control law. Ability to obtain a US security clearance preferred.

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50 | NOV 2020 | SPECTRUM.IEEE.ORG Department of Electrical and Computer Engineering Graduate School of Engineering and Management Air Force Institute of Technology (AFIT) Dayton, Ohio Faculty Position Professor/ Associate Professor/ Assistant Professor School of Microelectronics Department of ElectricalThe Department and of Computer Electrical and Computer Engineering Engineering at the Air Force Southern University of Science and Technology (Shenzhen, China) Institute of Technology is seeking applications for a tenured or tenure- track faculty position. All academic ranks will be considered. Applicants Graduate School of Engineeringmust have an earned doctorate and in ElectricalManagement Engineering, Computer Post Specifications Engineering, Computer Science, or a closely affiliated discipline School of Microelectronics (SME) ，National Exemplary School of Microelec- Air Force Instituteby the timeof ofTechnology their appointment (anticipated (AFIT) 1 September 2021). tronics, Southern University of Science and Technology (SUSTech) invites highly qualified candidates to fill multiple tenure-track/tenured faculty positions We are particularly interested in applicants specializing in one or more of in the areas of (but not limited) Emerging Microelectronic Devices (Wide-band- Dayton,the following areas: Ohio autonomy, artificial intelligence / machine learning, gap, Nonvolatile memory, MEMS Sensor), and IC-Chip Designs (Next-genera- navigation with or without GPS, cyber security, and VLSI. Candidates in tion Computing/Communication/Biomedical SoC). other areas of specialization are also encouraged to apply. This position Faculty Position Junior applicants should have (i) a PhD degree in related fields; and (ii) out- requires teaching at the graduate level as well as establishing and standing potential in teaching and research. Candidates for senior post are sustaining a strong DoD relevant externally funded research program expected to have demonstrated exceptional academic leadership and strong The Department of Electrical andwith a sustainableComputer record Engineering of related peer-reviewed at the publications. Air Force commitment to be excellent in teaching, research, and services. Institute of Technology is seekingThe Air Force applications Institute of Technology for (AFIT)a tenured is the premier or Department tenure- of Applications track faculty position. All academicDefense (DoD) ranks institution will for be graduate considered. education in science, Applicants technology, Submit (in English, PDF version) a cover letter, a statement in research and engineering, and management, and has a Carnegie Classification as teaching, a CV plus copies of 3 most significant publications, and contacts of must have an earned doctoratea High Researchin Electrical Activity Doctoral Engineering, University. The Computer Department of three referees to: [email protected] entitled with “Apply for Faculty Posi- Engineering, Computer Science,Electrical or and a Computerclosely Engineering affiliated offers accrediteddiscipline M.S. andby Ph.D.the tion”. Applicants are required to specify the rank of the position in their letter degree programs in Electrical Engineering, Computer Engineering, and of application. The positions will be open until they are filled by appropriate time of their appointment (anticipatedComputer Science 1 September as well as an MS degree2020). program in Cyber Operations. candidates. We are particularly interested Applicantsin applicants must be U.S.specializing citizens. Full detailsin one on orthe moreposition, ofthe Salary and Fringe Benefits department, applicant qualifications, and application procedures can be Salary and startup funds are highly competitive, commensurate with experience the following areas: autonomy,found artificial at https://www.afit.edu/ENG/page.cfm?page=1232 intelligence / machine learning, and academic accomplishment. All regular faculty members will join the tenure- track system in accordance with international practice for progress evaluation navigation with or without GPS,Review cyber of applications security, will begin and on 4 VLSI.January 2021Candidates. The United States in and promotion. Applicants are encouraged to check out the details about the other areas of specialization areAir Force also is an encouraged equal opportunity, affirmativeto apply. action This employer. position university at: http://www.sustech.edu.cn. requires teaching at the graduate level as well as establishing and sustaining a strong DoD relevant externally funded research program with a sustainable record of related peer-reviewed publications. The Air Force Institute of TechnologyApplications are invited(AFIT) for:- is the premier Department of Department of Mechanical and Automation Engineering Defense (DoD) institution for graduateProfessors / Associate education Professors in / Assistant science, Professors technology, engineering, and management,(Ref. 200001GH)and has a Carnegie Classification as a The Chinese University of Hong Kong (CUHK) is ranked one of the top 50 universities worldwide ESE Tenured or Tenure-track High Research Activity Doctoralaccording University. to the QS World University The Rankings Department of 2020/21. It is also ofnamed Electrical the Most Innovativ e University in Hong Kong by Thomson Reuters in four consecutive years (2016-19). In the 2014 Research Faculty Openings, 2020 - 2021 and Computer Engineering offersAssessment Exercise,accredited the mechanical e ngineeringM.S. discipline and of CUHKPh.D. was ranked degree ﬁ rst among its programs in Electrical Engineering,counterparts Computerof all universities in Hong Engineering, Kong in terms of the ratio of wandorld leading Computer research (top category of 4*). Further information about the Department is available at http://www.mae.cuhk.edu.hk. The Department of Electrical and Systems Engineering is engaged in an Science as well as an MS degreeThe Department program of Mechanical in and Cyber Automation EngineeringOperations. (MAE) at CUHK is seeking excellent aggressive, multi-year hiring effort for multiple tenure-track positions at all levels. candidates in the following areas: Candidates must hold a Ph.D. in Electrical Engineering, Computer Engineering, Applicants must be U.S. citizens.• Robotics and automationFull ,details in particular with on expertise the of medical position, sensors, robot actuators, the and soft robotics with connection to the CUHK T Stone Robotics Institute, which focuses its primary Systems Engineering, or related area. Leadership in cross-disciplinary and multi- department, applicant qualifications,research on medical and and serviceapplication robotics through collaboration procedures among experts incan engineering, be disciplinary collaborations is of particular interest. We are interested in candidates medicine and social science; and in all areas that enhance our research strengths in: found at http://www.afit.edu/ENG/• Smart cities, .energy, Review green buildings of. applications will begin Nanodevices and nanosystems on January 6, 2020. The UnitedApplicants States should have Air (i) a PhD Force degree in Mechanicalis an Engineering equal or aopportunity, related discipline; and (ii) a • (nanoelectronics, MEMS/NEMS, power proven record of academic scholarship and high potential for excellence in teaching and research. electronics, nanophotonics, nanomagnetics, quantum devices, integrated affirmative action employer. The appointees will (a) teach undergraduate and postgraduate courses; (b) develop an externally devices and systems at nanoscale); https://apptrkr.com/2007345 funded high impact research programme; (c) supervise postgraduate students; and (d) provide service to the Department/Faculty/University, professional organizations and the community. • Circuits and computer engineering (analog, RF, mm-wave, digital Similar to tenure tracked positions at universities in USA, appointments will initially be made on circuits, emerging circuit design, computer engineering, IoT, beyond 5G, contract basis for up to three years initially commencing August 2021, which, subject to mutual https://apptrkr.com/2007396 agreement, may lead to longer-term appointment or substantiation later. Outstanding candidates with and cyber-physical systems); substantial experience for Professor rank may be considered for substantive appointment forthwith. The rank and exact start date will be negotiated with the successful applicants. • Information and decision systems (control, optimization, robotics, data [Those who have responded to the previous advertisement for the posts (Refs. 180001TU and science, machine learning, communications, networking, information theory, 160001CP) are under consideration and need not re-apply in this instance.] signal processing). https://apptrkr.com/2008071 For more information, please contact Ms. YL Kan at [email protected]. Application Procedure Diversity candidates are strongly encouraged to apply. Interested persons should Applicants please upload the full resume with a cover letter, copies of academic credentials, submit an online application by following the links above and include curriculum publication list with abstracts of selected published papers, details of courses taught and evaluation vitae, research, teaching, and diversity statements, and at least three references. results (if available), a research plan, a teaching statement, together with names, addresses and e-mail addresses of three to ﬁ ve referees for providing references. Review of applications will begin on January 4, 2021. The University only accepts and considers applications submitted online for the posts above. For University of Pennsylvania is an EEO/AA Employer. more information and to apply online, please visit http://career.cuhk.edu.hk.

SPECTRUM.IEEE.ORG | NOV 2020 | 51 PAST FORWARD BY ALLISON MARSH

IF THE X-RAY FITS One hundred and twenty-five years ago this month, Wilhelm Röntgen accidentally discovered a mysterious light that could pass through solid objects, leaving behind a ghostly image of the object’s interior. He called the light “X-rays,” the “X” standing for the unknown. The medical community immediately seized upon X-rays as a diagnostic tool. For a time, the retail world also found them useful. From the 1920s through the 1950s, shoe-fitting fluoroscopes were a mainstay in shoe stores across North America and Europe. Customers stood with their shoe-clad feet inserted in a slot in the device, and an X-ray tube would illuminate the feet from below. They could then view the result, showing the bones of the feet and the outline of the shoes. Eventually, the dangers of excess radiation caught up with the fad, bringing about the demise of a technology that was never really needed in the first place. ■

↗ For more on the history of X-rays and shoe fitting, see spectrum. ieee.org/pastforward-nov2020 OAK RIDGE ASSOCIATED UNIVERSITIES (2) UNIVERSITIES ASSOCIATED RIDGE OAK

52 | NOV 2020 | SPECTRUM.IEEE.ORG Date:10-5-2020 2:14 PM| Client:UCSD| Studio Artist: Austin Marshall / Austin Marshall| Printed At: None Job number: UCSD0239 | UCSD0239_Look_Deeper_FP_IEEE_v1.indd T: 7.875” x 10.5”, L: 7” x 10”, B:8.125” x 10.75”, Gutter: None, Bind: SS, Linescreen: None, MD: 300, Color: None Notes: SWOP3

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Unbreakable materials lead to unbreakable bonds. At UC San Diego’s CaliBaja Center, engineering professor and director Olivia Graeve has brought together some of the biggest brains in the U.S. and Mexico to tackle the smallest of engineering challenges: developing hyper-durable nanoparticles. But she doesn’t stop there. Here, at the No. 1 public university in the nation, she’s uniting students from both countries in a summer research program. Proof that artiﬁ cial borders can’t hold back the power of a common goal.

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