NEWS FEATURE BY LEE BILLINGS Engineered structures with bizarre optical properties are set to migrate out of the laboratory and into the marketplace. om Driscoll would be happy if he commercialization are of more interest to Driscoll, a never heard the phrase ‘Harry Potter- physicist who oversees metamaterials commercializa- 3 REF. style invisibility cloak’ again. But he tion at Intellectual Ventures, a patent-aggregation firm knows he will. The media can’t seem in Bellevue, Washington. Applications such as cheaper to resist using it when they report satellite communications, thinner smartphones and the latest advances in metamaterials ultrafast optical data processing are “where metama- — arrays of minuscule ‘elements’ that bend, scat- terials are poised to make a huge impact”, he says. Tter, transmit or otherwise shape electromagnetic Researchers still face some daunting challenges, radiation in ways that no natural material can. It is he adds — notably, finding cheap ways to fabricate true that meta­materials could, in principle, route and manipulate metamaterial elements on a scale light around objects and render them invisible, not of nanometres. But the first metamaterial-based unlike the cloak of a certain fictional wizard. And products are expected to come onto the market in a many metamaterials researchers are trying to make year or so. And, not long after that, Driscoll expects cloaking a reality, not least because the military has that average consumers will start to enjoy the ben- eagerly funded the development of such capabilities. efits, such as faster, cheaper Internet connectivity on However, if such applications ever come to pass board planes and from mobile phones. Such appli- it will be decades from now. Technologies closer to cations, he says, will move from being the stuff of 138 | NATURE | VOL 500 | 8 AUGUST 2013 © 2013 Macmillan Publishers Limited. All rights reserved FEATURE NEWS peoples’ fantasies “to becoming things they signals if they are coming from the satellite. can’t contemplate living without”. This technology is more compact than Wave The first laboratory demonstration of a meta­ alternatives such as dish antennas, says Smith. material was announced in 2000 by physicist It offers “significant savings in terms of cost, engineering David Smith and his colleagues at the University weight and power draw”. Kymeta has already Metamaterial elements scatter incoming 1 radiation in very precise ways. They can be any of California, San Diego . Following up on theo- performed demonstrations of this technology shape; common examples include spheres, rings, retical work done in the 1990s by John Pendry for investors and potential development part- crosses and chevrons. Their electromagnetic of Imperial College London, these researchers ners. But Smith cautions that the company has properties can often be changed by software. showed that an array of tiny copper wires and yet to set a price for the antenna and that it rings had a negative refractive index for micro- must still work to bring production costs down The spacing waves — meaning that microwave radiation while maintaining the strict performance between the elements can vary, flowing into the material is deflected in a direc- standards that regulatory agencies demand but is always less tion opposite to that normally observed (see for any device communicating with satellites. than the wavelength ‘Wave engineering’). That triggered intense Kymeta has shared so few details of its of the radiation. interest in metamaterials, in part because the antenna that researchers say it is hard to offer ability to bend radiation in such a way had an evaluation. But Smith is highly regarded potential for creating invisibility cloaks. in the field. If Kymeta brings the product to Since then, Smith and others have explored market, it may first offer its antenna for use a host of variations on the metamaterial idea, on private jets and passenger planes. If buyers often looking to manipulate radiation in ways respond well, the company hopes to incorpo- that have nothing to do with a negative refrac- rate the technology into other product lines, tive index. They have also moved beyond static such as portable, energy-efficient satellite- arrays, devising techniques to change the way communication units for rescue workers or the elements are arranged, how they are shaped researchers in the field. and how they respond to radiation. The result- In January, Smith’s group turned heads when ing materials can do things such as turn from it announced its demonstration of another opaque to transparent or from red to blue — all metamaterial device: a camera that can create Collectively, the array of elements at the flick of a switch. compressed microwave images without a lens functions similarly 2 or any moving parts . One important applica- to a hologram, Market movers tion of the device might be to reduce the cost shaping the radiation in ways no In January, Smith, now at Duke University in and complexity of airport security scanners. natural material can. Durham, North Carolina, took on a concur- In their current form, these scanners have to rent role as director of metamaterials com- physically sweep a microwave sensor over and mercialization efforts at Intellectual Ventures. around the subject. This produces an unwieldy Example: Negative index “I felt that the time was right, and we didn’t amount of data that has to be stored before it of refraction need to do any more science for some of these is processed into an image. The Duke group’s Metamaterials can be things,” he says. device requires very little data storage. It takes engineered to bend radiation in a direction A test case may come as early as next year. numerous snapshots by sending beams of opposite to that observed Kymeta of Redmond, Washington, a spin-off microwaves of multiple wavelengths across the in ordinary materials. from Intellectual Ventures, hopes to market a target at about ten times per second. When the compact antenna that would be one of the first microwaves are reflected back by the subject, consumer-oriented products based on meta- they fall on a thin strip of square copper meta- Positive Negative materials. The relatively inexpensive device material elements, each of which can be tuned refraction refraction would carry broadband satellite communi- to block or let through reflected radiation. The cations to and from planes, trains, ships, cars resulting pattern of opaque and transparent ele- and any other platform required to function ments can be varied very rapidly, with each con- in remote locations far from mobile networks. figuration transmitting a simplified snapshot of Application: At the heart of the antenna — the details of a scanned object into a single sensor. The sensor Invisibility cloak Radiation A cloak made of a negative- source which are confidential — is a flat circuit board measures the total intensity of radiation from index metamaterial can containing thousands of electronic metamat­ each snapshot, then outputs a stream of num- bend radiation around an object inside it, making that erial elements, each of which can have its bers that can be digitally processed to recon- object seem invisible. properties changed in an instant by the device’s struct a highly compressed image of the subject. internal software. This allows the antenna to This is admittedly just a first step: demon- track a satellite across the sky without having strations carried out so far have been crude to maintain a specific orientation towards it, affairs restricted to two-dimensional images the way a standard dish antenna does. Instead, of simple metallic objects. Expanding it to the antenna remains still while the software three-dimensional images of complex objects constantly adjusts the electrical properties of remains a challenge. But if that challenge can each individual metamaterial element. When be overcome, says Driscoll, airports could retire this is done correctly, waves emitted from the bulky, expensive, slow booths that currently the elements will reinforce one another and constitute security checkpoints, and instead use propagate skywards only in the direction of the a larger number of thin, inexpensive metamate- satellite; waves emitted in any other direction rial cameras hooked up to computers. Such a will cancel one another out and go nowhere. shift, Driscoll says, could extend security scan- Metamaterial At the same time — and for much the same ning to rooms, hallways, and corridors through- cloak reason — the array will most readily pick up out airports and other sensitive facilities. 8 AUGUST 2013 | VOL 500 | NATURE | 139 © 2013 Macmillan Publishers Limited. All rights reserved NEWS FEATURE In the meantime, a key research goal for of gold metamaterial elements carved out of a The team has since been working to refine the Smith and his group is the development of 60-nanometre-thick silicon wafer using elec- superlens concept; in 2007 the researchers robust and marketable metamaterial devices tron-beam lithography techniques developed advanced the idea by developing ‘hyperlenses’ that are not restricted to radio, microwave for the microchip industry. The elements are from curved, nested layers of compounds such or infrared wavelengths. If the technologies fixed, so cannot be tuned after fabrication. But as silver, aluminium and quartz6. The lenses not could be made to work with visible light, they by selecting a specific size and spacing during only capture evanescent waves, but can also feed would become much more useful for applica- the manufacturing process, physicists can shape them into a conventional optical system. Ulti- tions such as fibre-optic communications or light of a chosen wavelength in exactly the right mately, this could allow sub-wavelength details consumer-oriented cameras and displays. way to make it come to a point. to be viewed through the eyepiece of a stand- “It won’t be easy,” cautions Stephane Capasso warns that commercial applications ard microscope.