Energie uit de lucht gegrepen

Citation for published version (APA): Visser, H. J. (2014). Energie uit de lucht gegrepen. Technische Universiteit Eindhoven.

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Download date: 27. Sep. 2021 Intreerede prof.dr.ir. Huib Visser 19 december 2014

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Energie uit de lucht gegrepen

Where innovation starts Inaugural lecture prof.dr.ir. Huib Visser

Energy out of Thin Air Energie uit de lucht gegrepen

Presented on December 19, 2014 at Eindhoven University of Technology

3

Introduction

“Opportunity is missed by most people because it is dressed in overalls and looks like work” Thomas Alva Edison

I’d like to welcome you all for this inaugural lecture entitled “Energy out of thin air”. In this lecture I will – in 45 minutes – outline the contents and challenges that I hope to address in the of “ data and power transfer for miniature and environment-independent electronics”.

To do this, I will start with a brief history of , dealing with wireless data transfer, followed by a brief history of Wireless Power Transfer (WPT) that is closely related to the . From there I will continue to the state of the art, followed by the challenges encountered in further developing WPT. Finally I will focus very briefly on educational aspects. 4

A Brief History of Radio

“The farther backward you can look, the farther forward you are likely to see” Sir Winston Churchill

In this brief history of radio [1] I will guide you through the observations, discoveries and developed laws of during the last two centuries that have led to radio as we know it today. The term radio – from the Latin radius (spoke of a wheel, beam of light, radius) – is short for radio (in the UK wireless from wireless telegraphy) and was adapted in 1912 by the US Navy to distinguish radio from several other wireless communication technologies such as the (transmission of speech on a beam of light, Bell 1880).

This guide is similar to the path that I follow with students in class. The difference is that now it is condensed into a matter of minutes and will hardly be embellished by equations. By following the early observations concerning electricity, magnetics and electromagnetics, the resulting interrelationships found between the different observed phenomena and the new developments make it easier to understand the physics and grasp new developments.

I have separated the history into two eras: pre-Volta and post-Volta. In the pre- Volta era, i.e. before the invention of the electric battery, experiments in electricity were limited to what could be achieved with the discharge of a capacitor known then as the Leyden jar. With the introduction of the Voltaic pile or battery it became possible to conduct electrical experiments in a controlled and repeatable way.

The post-Volta era “Ampère was the Newton of electricity” James Clerk Maxwell

It was with a Voltaic pile that Johannes Ørsted observed in 1819 that a wire carrying an electric current changes the position of an adjacently positioned compass needle. This interaction of electricity and magnetism was termed electromagnetism by Ørsted. In that same year (1819) André-Marie Ampère Energy out of Thin Air 5

explained the theory of the experiment: the electric current induces a which also explains why parallel currents attract and anti-parallel currents repel.

While Ørsted observed how an electric current induced a magnetic field, in 1831 Michael Faraday observed that a changing electric current in a coil induced an electric current in another coil. The changing in the first coil induced a magnetic field and this changing magnetic field induced an electric field in the second coil. Faraday had discovered electromagnetic induction. Later, he showed that a moving magnet, i.e. a changing magnetic field, induces an electric field in a coil, see figure 1.

I

N

S

Figure 1 A changing magnetic field induces an electric current in a loop [1].

So, electricity was understood, magnetism was understood and one was aware of an interaction between the two, but a complete understanding had not yet developed.

Maxwell “The special theory of relativity owes its origins to Maxwell’s equations of the electromagnetic field” Albert Einstein

In the same year that Faraday discovered electromagnetic induction (1831), James Clerk Maxwell was born. In contrast to Faraday, Maxwell received an academic education and evolved not into an experimental scientist but a brilliant thinker and 6 prof.dr.ir. Huib Visser

mathematician. In 1873 he published “A Treatise on Electricity and Magnetism” [2] in which he formulated what we nowadays know as (in the notation introduced by ) the Maxwell equations, relating electricity and magnetism, see figure 2.

Gauss’s law

Gauss’s law for magnetism

Faraday’s law of induction

Ampère’s law with Maxwell’s addition Figure 2 The Maxwell equations.

The Maxwell equations consist of the Gauss law for electricity, relating a static electric field to charges, the Gauss law for magnetism, stating that magnetic charges do not exist, Faradays law of induction, describing how a varying magnetic field creates an electric field, and a modified version of Ampère’s law. Maxwell’s contribution is the modification that states that a magnetic field may be generated by an electric current (Ampère’s law), but also by a changing electric field. It is this latter aspect that makes the existence of electromagnetic possible.

It means that once you create the correct changing electric field (i.e. accelerate or decelerate charge), this field will create a changing magnetic field that, in turn, will create a changing electric field and so on, see figure 3. This expansion of the disturbance in space will continue, even when the source has ceased to exist. This is what we call propagation. Note that this wave propagation was predicted theoretically by Maxwell. It needed another 13 years before it was proven experimentally. Energy out of Thin Air 7

E Figure 3 H Two-dimensional schematic representation of wave propagation [1].

Hertz “I do not think that the wireless waves I have discovered will have any practical application” Heinrich Rudolf Hertz

In 1886 in Karlsruhe, Germany, Heinrich Rudolf Hertz successfully undertook the task to experimentally verify Maxwell’s theory. Starting out with two coaxially mounted so-called Knochenhauer spirals, he was able to induce a spark in one of the spirals if he discharged a Leyden jar in the other spiral. He then transformed this closed resonance system relying on magnetic induction into an open resonance system relying on unguided wave propagation. One of the spirals he

Adjustable capacitor sphere Switch Interrupter Battery Spark gap

Spark gap One-turn Pri Sec coil

Core

Induction coil

Figure 4 Transmitter Receiver Hertz’s open resonance system [1]. 8 prof.dr.ir. Huib Visser

replaced with a pair of straight wires, connected at the centre to a spark gap. The spark gap was connected to the secondary windings of an induction coil that was operated by a mechanical interrupter. The straight wires were equipped with electrically conducting spheres able to move over the wire segments. The transmitting resonance circuit consisted of the straight wire segments and the conducting spheres. The other spiral Hertz replaced with a single turn coil with a small gap. By adjusting the perimeter of this one-turn receiving coil, Hertz was able to demonstrate resonance. With the receiver placed several meters from the transmitter, small sparks could be seen (and heard) in the gap of the receiver when the transmitter discharged. The two wire segments at the transmitter we recognize as a half-wave dipole . The receiver is recognized as a loop antenna, see figure 4.

Marconi “Every day sees humanity more victorious in the struggle with space and time”

Guglielmo Marconi, a real engineer, saw the practical and commercial potential of Hertz’s invention and started repeating the Hertz experiments at his father’s estate in Italy. His father was strongly opposed to these experiments, but his mother – a heiress of the Irish whisky distilling family, the Jamesons – supported him strongly.

Figure 5 a b Marconi’s antennas in 1895. a. Diagram of the transmitter used by Marconi at Villa Griffone. b. Diagram of the receiver used by Marconi at Villa Griffone [1]. Energy out of Thin Air 9

Marconi undertook the task of increasing the transmit power and increasing the receiver sensitivity. Starting with the latter he succeeded in improving the coherer, an electromagnetic detection device invented by Eugène Branly in 1890 and improved by Oliver Lodge in 1894. The coherer replaced the receiving spark-gap and acted as a switch turning on a battery-operated Morse writer.

By finding the ‘right’ (monopole) antenna he succeeded in creating a radio system at sub-GHz and over distances that progressively increased up to and beyond 1.5 km, see figure 5. The term antenna was introduced by Marconi in a speech held for the Royal Netherlands Institute of Engineers in May 1909 [3] and replaced the term ‘elevated wire’ or ‘aerial’ that had been used up till that point.

Since the Italian government did not want to support his experiments financially, he went to Great Britain in 1896, cooperating with the British Post Office. In 1897 messages were exchanged over a distance of 14 km and in 1899 a regular radio- telegraph service between England and France was put into service. By then he had founded the Wireless Telegraph and Signal Co., which became Marconi’s Wireless Telegraph Co. in 1900. In 1901 Marconi succeeded in conducting the first transatlantic transmission, covering a distance of 3684 km. In 1907 a regular, reliable transatlantic telegraphy service was operating. In 1909 he received the Nobel Prize for physics, together with Karl Ferdinand Braun, “in recognition of their contributions to the development of wireless telegraphy” [4].

The success of Marconi started with the use of long and appropriate antennas. These antennas were found by experimental trial and error. Marconi was more of an inventor/engineer – and above all an entrepreneur – than an academic scientist. One of his strengths, however, was to employ scientists in the Marconi Company. In 1900 he approved Ambrose Fleming, professor at University College, London as scientific adviser. It was Fleming who in 1906 gave a mathematical explanation, based on image theory, of the operation. It is assumed that this was the first time that an antenna design had been accomplished both experimentally and theoretically. Up to the mid 1920s it was common practice to design antennas empirically and produce a theoretical explanation after the successful development of a working antenna. I will come back to this in discussing education.

Since then developments followed one another quickly. To mention a few: in 1900, was able to transmit intelligible speech over 1.6 km , using an electrolytic rectifier or barretter in the receiver; in 1905, John Ambrose Fleming 10 prof.dr.ir. Huib Visser

invented the thermionic valve or diode; in 1907, Lee de Forest invented the audion or triode, which made amplification of signals possible; radio was introduced into the Boer War in South Africa (1899-1902) and into the First World War; in between the two World Wars was introduced; and during the second World War radio was made more compact, operating at higher frequencies and with more power and radar was developed.

We will, however dwell a bit on the Hertz – Marconi period and look into the matter of Wireless Power Transfer (WPT). 11

Wireless Power Transfer

“For a successful technology, reality must take precedence over public relations, for nature cannot be fooled” Richard Phillips Feynman

When Heinrich Hertz made his first radio transmission, he was transferring not only data, visible in the received sparks, but also power, equally visible in those sparks. While Hertz did not see the practical potential of his invention and died too young to develop such a vision, Marconi did see the potential for transferring data in the form of Morse codes. The idea of transferring power wirelessly may be attributed to , the Serbian American inventor.

Tesla “For more than eighteen years I have been reading treatises, reports of scientific transactions, and articles on Hertz-wave telegraphy, to keep myself informed, but they have always impressed me like the works of fiction” Nikola Tesla

Although having played a role in the development of (wired) AC power transmission, most of the reports on his contributions to wireless transfer of data and power are factually challenged. Tesla is now, posthumously, creating a group of followers that – with a sometimes religious fanaticism – interpret his notebooks and attribute all kinds of inventions, including radio telegraphy, to him. Fact is that Tesla wanted to create wireless power transfer, but was convinced that Hertzian waves were longitudinal (like sound waves) and actually a loss mechanism [5]. According to Tesla the power and data transfer was accomplished through currents flowing through the and through a rarefied air layer acting as return ‘wire’. This return ‘wire’ would act similar to a fluorescent light tube and would, according to Tesla, illuminate the sky at night. In order to realize his system, Tesla created high voltage transformers that are shown in the (promotional, multi- exposure) photographs of his laboratories, see figure 6, but he was not able to demonstrate his power transfer system. The patents filed for his system [6, 7] show equipment that resembles the transmitter and receiver drawings of Marconi’s 1895 wireless telegraph at Villa Griffone as shown by Marconi in his 12 prof.dr.ir. Huib Visser

Nobel Prize lecture [8], see figure 5, which may account for (erroneously) attributing the invention of radio telegraphy to Tesla.

Figure 6 Multiple exposure of Tesla’s Colorado Springs Laboratory. Photograph taken in 1899 by Dickenson V. Alley for Century Magazines.

The widespread belief that the United States Supreme Court overturned all of Marconi’s patents in 1943 and proclaimed Tesla as the ‘true inventor’ of radio telegraphy is not true. The Supreme Court case was about governmental compensation for the use of patents primarily during the First World War. A former Marconi patent on tuning was invalidated in favor of the earlier work and patents of Oliver Lodge and [9]. Notwithstanding all of this, we may attribute the idea of wireless power transfer to Nikola Tesla, but for the realization of power transfer over longer distances we will resort to Hertzian waves.

Noble The first successful experiment in wireless power transfer (WPT) using radio waves was undertaken at the Westinghouse Laboratory by Harrell V. Noble. He used identical, 100 MHz, half- dipole antennas for transmitting and receiving, placed approximately 5 meters apart. This experiment was the basis for a wireless power transfer demonstration at the Westinghouse exhibit at the Chicago World Fair of 1933-1934, see figure 7. Energy out of Thin Air 13

Figure 7 Harrell Vaun Noble of Westinghouse demonstrating radiative WPT (press photograph 1931).

In this demonstration 15 kW of power was transmitted by an overhead dipole antenna. The receiving antenna was connected to a light bulb that was powered to distances of up to 12 m. Since human body temperature increases by 1 degree per minute within this range, the demonstrations are believed to have been, and if not should have been, very short.

After this demonstration interest in WPT diminished. The prime reason for this was the inability at that time to focus energy of sufficient power. Directive antennas of practicable dimensions could only be realized at frequencies and sufficient power could not be generated at these frequencies. That became possible after the Second World War when high-power microwave sources and high solid-state rectifiers became available.

Brown In 1964, William Brown demonstrated a practical application of WPT, in the form of a microwave-powered model helicopter [10, 11]. In this demonstration, part of the Raytheon Airborne Microwave Platform (RAMP) project, the transmitter was a 2.45 GHz, 5 kW magnetron connected to a 3 m diameter parabolic reflector antenna. The helicopter flew at a height of 9 m and collected 270 W peak dc power from a 1.5 m2 antenna containing 4480 diodes. 14 prof.dr.ir. Huib Visser

When the funding for the RAMP project was stopped in 1965, work continued, initially funded personally by Brown, later through the sponsorship of the Marshall Space Flight Center and from 1977 to 1980 in the joint Department of Energy (DoE) and National Aeronautic and Space Administration (NASA) “Satellite Power Systems Concept Development and Evaluation Program”. Within this program the Solar-Power Satellite (SPS) concept was being investigated. The SPS concept was introduced by Peter Glaser in 1968 [12] and comprises capturing the sun’s radiation by photovoltaic cells on a satellite that is in geosynchronous orbit, converting this captured power into RF microwave power and beaming this to Earth where it is converted into usable electrical power. The DoE/NASA SPS program ended in 1980 concluding that no ‘showstoppers’ had been found for development of a SPS system. The SPS concept is still being studied, especially by Japanese companies and government.

The renewed interest In the last decade interest in WPT has been reignited and since the latter half of this decade two distinct flavors of WPT have become apparent: non-radiative WPT for short distance and radiative WPT for long distance. For now, we will stick to the latter and we will discuss the former afterwards.

Figure 8 Artist impression of the employment of wirelessly powered sensors in a greenhouse. Energy out of Thin Air 15

The main reason for the renewed interest in longer distance, radiative WPT or energy out of thin air, is believed to be due to the success of radio frequency identification (RFID) and the recent advances in realizing (ultra) low power electronics. With wireless sensors demanding average dc power in the range of tens of microwatts instead of tens of milliwatts, it has become feasible to power these sensors from a central broadcasting station transmitting within the legal power limits. For the year 2020 the World Wireless Research Forum (WWRF) estimates that seven trillion wireless devices will serve seven billion people [13]. The vast majority of these devices will be sensors and monitoring devices that cannot all be grid or battery powered. Near future applications are envisaged in the field of smart factories and homes and in logistics, see figure 8.

Research is concentrated on the receiving side. The receiver in its most basic form consists of an antenna that is connected to a rectifier. This combination is commonly denoted rectenna. The receiving antenna intercepts a part of the RF signal broadcasted by the transmitter and this varying signal is converted to a dc signal using a (Schottky) diode or (Schottky) diode based circuit. The dc signal is used to power an application. The basic rectenna may be improved by adding impedance matching networks, power management circuits and energy storage devices (capacitors or rechargeable batteries), see figure 9.

source transmit far- antenna field

Z DC DC

receive impedance rectification boost energy load Figure 9 antenna matching conversion storage Radiative WPT system. 16 prof.dr.ir. Huib Visser

Non-radiative coupling Inductive, non-radiative, power transfer uses coils both for transmitting and for receiving. The coils are positioned coaxially. For a coil-to-coil distance that is less than the size of the smallest coil diameter, power efficiencies well above 90% may be achieved. This technology was introduced in the 1990s by Oral B for wirelessly charging electric toothbrushes. The mechanical design of the chargers is such that alignment of the transmitter and receiver coils and a near contact are ensured. To overcome the alignment and distance limits, non-radiative, resonant inductive coupling for power transfer was introduced by Karalis et al. in 2008 [14]. By making both the transmitter and receiver coil resonant, through the use of capacitors, the transmitter and receiver coils may be separated a few times the value of the coil diameter. Besides, more freedom in the lateral displacement is allowed without too much of a power conversion efficiency degradation being caused. The technology is used nowadays for charging the batteries of power- hungry mobile devices like smart phones and even cars. For the former, the Qi standard developed by the Wireless Power Consortium has been in use since 2009 [15]. 17

Future Research

“To invent, you need a good imagination and a pile of junk” Thomas Alva Edison

So we see that in time non-radiative WPT has come of age and that radiative WPT has become feasible for lower transmit power levels. We are at the brink of commercializing radiative WPT technology, but the technology is far from fully developed. A radiative WPT system is shown in figure 9. Elements for improvement can be found in the receive antenna, the rectifier, the combination of radiative and non-radiative WPT, the combination of data and power transfer and the transmitting antenna and propagation channel. All this can best be executed in national and international cooperation.

Antenna For powering wireless sensor nodes we want the rectifying antenna or rectenna to be small in size. The size is dictated by the frequencies used and for microwave frequencies will be dominated by the antenna. Thus we need to minimize the size of the antenna. Conjugated matching of the antenna to the rectifier – making use of the required low real part of the impedance – has enabled us to accomplish this for free standing antennas. Next, we must accomplish this for antennas that are environment-independent. We must be able to place the antenna on a carrier, whether plastic, human or metal, while keeping the dimensions small. Of course, these requirements will also apply to a broad range of communication antennas. Using metamaterial-based ground planes will be a line of research.

Rectifier So far we have analyzed the rectifier by using approximate models for the rectifier under special conditions, like being short-circuited at the load position. For realistic loads we have made use of a commercially available Harmonic Balance simulator as is common practice in literature. We are working now on extending our earlier developed approximate models to account for a realistic loading and cascading rectifier stages. The benefit of this model will be that it will contribute to a better understanding of the rectifier physics and will give us a means to 18 prof.dr.ir. Huib Visser

investigate the proper employment of higher harmonic currents generated by the non-linear devices.

Radiative and non-radiative power transfer A clear distinction exists between near-contact and remote WPT. For the former, inductive WPT is applied, for the latter radiative WPT is used. To bridge the gap between the two, hybrid solutions using resonant coupling, far-field radiative WPT and near-field focusing (NFF) WPT are needed as recently stipulated in an imec patent [16]. We will continue our research in the field of NFF-WPT, extend the basic knowledge we are developing in the field of resonant coupling and will research the combination of these. Through our international contacts we will make the learning curve concerning non-radiative WPT as steep as possible.

Power and data As already mentioned, all the actions taken for miniaturizing the rectenna and making it environment-independent also apply for a broad range of antennas. What applies for the transfer of power also applies for the transfer of data. Since we want to power wireless sensors with radio waves, it makes sense to use the same structure as a receive antenna for the rectenna and as a communication antenna for the wireless sensor, not necessarily but also not excluding operating at the same frequency. We may accomplish this by having multi-port antennas or combining RF and dc on a single port. Both strategies will be lines of research.

Transmit antenna and propagation channel When we employ WPT, we will bring our own transmitter into the system. This means that we will have access to the transmit antenna and, to some extent, to the propagation channel. In line with near-field focusing research, we will look at low-cost array antenna structures for creating adaptive, multiple-beam antennas. Thus it will be possible to maximize constructive interference at rectenna positions. The propagation channel may be influenced by adding Fresnel lens structures or modifications to allow for wave propagation.

RF Harvesting When we employ RF harvesting we do not have access to the transmitter, so we will make use of RF signals present in the ambient, the most likely being those produced for the Global System of Mobile communication (GSM), Broadcasting (DTV) and WiFi. The signal amplitudes will generally be at least one order of magnitude lower than what may be expected in a radiative WPT system. Energy out of Thin Air 19

Therefore, we need larger collecting apertures for these applications. Using our frequency selective surface (FSS) based harvester, we will investigate other and cascaded RF harvesting FSS structures.

National and international cooperation All the research lines mentioned cannot be executed simultaneously by a single person on a part-time basis. Therefore, I strive to attract and fund MSc and PhD students from our own and other universities through national and international cooperation. National cooperation is directly available through my employment by imec Netherlands and through the Netherlands Antenna Research Framework (NARF). International cooperation may enable student exchanges and (partial) funding. Plans for national and international funded and executed cooperation are in several stages of preparation.

An important international cooperation in the field of WPT is the European Cooperation in Science and Technology (COST) Action IC1301 Wireless Power Transmission for Sustainable Electronics (WIPE). In the symposium preceding this inaugural speech, the work of COST Action IC1301 WIPE participants, including the chairman, professor Carvalho, was presented. WIPE brings together everyone working in the field of WPT in Europe and beyond and has already proved to be the starting point of many bilateral cooperations. 20

Education

“Education is that what remains after one has forgotten what one has learned in school” Albert Einstein

I am very proud to be appointed as part-time professor at Eindhoven University of Technology, being hailed as best Dutch university of technology for the eleventh time in a row and now third in the overall ranking of Dutch universities. This ranking is predominantly based on the student’s assessment of the education and therefore shows that we are doing a good job in this respect. After all, this is, I think, the core business of a university. If we educate the students well in class, we can profit from their input in our scientific research when we assign them their final educational assignments. The fact that we are doing a good job does not mean that we can relax. Being good means that we need to work extra hard to remain good or even become better.

I have the pleasure to teach two courses at the moment: ‘Electromagnetic waves and antennas’ and ‘Microstrip antenna analysis, design and realization’. Through slightly modifying the course over the years the former has been made more appealing for students, guiding them through the major observations and discoveries discussed at the beginning of this lecture and using the element of summarizing repeatedly.

The latter course has been popular due to the practical work involved: students need to make an antenna by hand, measure that antenna and tune it mechanically to obtain the desired characteristics. Afterwards they can take the antenna home. Before they reach that stage they have to design the antenna by studying an approximate analysis model and implementing this model in software. Then they have to compare the analysis results with results obtained by commercially available full-wave analysis software.

What we see lately is that students try to take a short-cut and design the antenna through trial and error using the commercial software only. Allowing that would throw us back more than a century in time. Remember that up till the 1920s – Energy out of Thin Air 21

in Marconi’s time – it was customary to design an antenna through trial and error and, once the antenna was made, to come up with a physical explanation of the functioning. So, I allow the full-wave software-based trial-and-error design but demand that the approximate model is implemented in software and used afterwards. The functioning needs to be understood and explained. What the student then learns – the hard way – is that it would have worked better the other way around. I find that I have to be firm about that since allowing the use of full- wave software on a trial-and-error basis does not fit in an academic education. Provided that you have enough bananas you could teach a monkey to do that. Full-wave software is only a big help if we understand the basic functioning of the antenna we try to design so that we can do it faster a second time for changed conditions like different frequencies or different materials to be used. Keeping the quote of Einstein in mind, we need to teach the students a way of thinking rather than let him or her memorize equations. Besides we need to allow the students to make errors and we must let him or her make their own design and measure it. By doing that we will live up to another quote of Einstein: “The only source of knowledge is experience”.

So we see that students try to take a short cut. Can we conclude then, like many generations of teachers before us, that the new students are lazier or even less smart than their predecessors? No, certainly not. Can we conclude that their background education is not sufficient? That’s a hard one. At least we can conclude that their education is different and that we need to adapt our teaching to that.

Right now we are preparing to renew the electromagnetic Master courses giving an opportunity to incorporate lessons learned. Among the things we will be doing is to combine microwave engineering and antenna theory courses and bring in practical work to adapt to the new generation of students and the requirements from industry. It is my strong belief that a part-time professor, coming from industry, should be actively involved in education. Giving lectures is a way of communicating the requirements of industry to the next generation of engineers and attracting MSc research students. Both the lecturing and the guidance of MSc and PhD students strengthen the interaction between the university and the industry. Also that will contribute to keeping a high university ranking. 22

Acknowledgements

“The lecturer should give the audience full reason to believe that all his powers have been exerted for their pleasure and instruction” Michael Faraday

Having come to the end of my inaugural lecture, it is time to acknowledge the people who have made my appointment possible.

To start with, I would like to express my gratitude to the Executive Board of the university and the board of the Department of Electrical Engineering for giving me this opportunity.

I would like to express my gratitude to Will Keizer and Frank van den Bogaart, leading the Antennas and Front-End group of the former TNO Physics and Electronics Laboratory in The Hague. Fresh from university I started working in your group, first as part of my military service, later as a civilian. I thank you for the freedom and stimulating environment you provided. Your group has turned out to be the cradle of part-time professors in microwave and antenna technology, producing prof. Zwamborn, prof. Smolders, prof. Gerini, prof. van Vliet and now me, who all started their careers in your group.

I would also like to express my gratitude to the management of imec Netherlands, especially Harmke de Groot, Rob van Schaijk and Guido Dolmans, for supporting me and providing the opportunity for me to hold this position.

Hooggeleerde Tijhuis, beste Anton. We have known each other a long time, starting from the period that I worked for TNO in The Hague. When I moved to TNO in Eindhoven in 2001 you gave me a part-time position in your group and trusted me with giving antenna lectures, which is something for which I’m still grateful. Your deep theoretical understanding of physics and electromagnetics and your ability to explain complex matter in an understandable way continue to be a source of inspiration. You have been my promoter and recently we have been promoters together, a situation that I hope will be repeated many times. Energy out of Thin Air 23

Hooggeleerde Smolders, beste Bart. We became friends more than a quarter of a century ago when we both did an internship supervised by the late Dr. Martin Jeuken. Then we both performed our MSc thesis work supervised by him and we both ended up doing our military service at TNO Physics and Electronics Laboratory. Our ways then parted, but we kept on meeting each other for work related activities. Our contacts intensified with your appointment as professor at Eindhoven University of Technology and it is through you that I have been appointed as part-time professor now, for which I’m very grateful. I admire your no-nonsense, engineering approach to transforming scientific knowledge into applied science and the way you incorporate this in the education of students. I’m looking forward to an intensified educational and applied scientific cooperation, starting with the renewing of the electromagnetic Master courses.

Lieve Lotte, Noa en Dianne. Mijn grootste dank gaat uit naar jullie. Voor de ruimte die jullie mij geven. Voor het accepteren dat ik weer eens een avond of een deel van een weekend moet werken omdat iets perse af moet voor een bepaalde deadline. Voor het verdragen van mijn humeur dat daar wel eens mee gepaard gaat. Voor al die keren dat ik van huis ben. Maar weet dat als ik van huis ben ik gelukkig ben in de wetenschap dat als ik thuiskom jullie daar zijn. Dat is niet uit de lucht gegrepen.

Ik heb gezegd. 24

References

[1] Hubregt J. Visser, Array and Antenna Basics, John Wiley & Sons, Chichester, UK, 2005. [2] James Clerk Maxwell, A Treatise on Electricity and Magnetism, Dover Publications, 1954. [3] Guglielmo Marconi, “The Most Recent Developments of Wireless Telegraphy”, De Ingenieur, Nr. 22, May 1909, pp. 431-439. [4] “The Nobel Prize in Physics 1909”. Nobelprize.org. Nobel Media AB 2014. Web. 30 Oct 2014. http://www.nobelprize.org/nobel_prizes/physics/ laureates/1909/ [5] Nikola Tesla, “The True Wireless”, The Electrical Experimenter, May 1919, pp. 28-13, 61-63, 87. [6] Nikola Tesla, System of Transmission of Electrical Energy, USA Patent No. 645,576, March 20, 1900. [7] Nikola Tesla, Apparatus for Transmission of Electrical Energy, USA Patent No. 649,621, May 15, 1900. [8] “Guglielmo Marconi - Nobel Lecture: Wireless Telegraphic Communication”.Nobelprize.org. Nobel Media AB 2014. Web. 30 Oct 2014. http://www.nobelprize.org/nobel_prizes/physics/laureates/1909/ marconi-lecture.html [9] Justia US Supreme Court, Marconi Wireless Tel. Co. v. United States 320 U.S. 1 (1943), Web. 30 Oct 2014. https://supreme.justia.com/cases/federal/us/ 320/1/case.html [10] W. C. Brown, J.R. Mims, and N.I. Heeman, “An Experimental Microwave- Powered Helicopter”, Proceedings IRECON, 1965, pp. 225-235. [11] William, C. Brown, “The History of Power Transmission by Radio Waves”, IEEE Transactions on Microwave Theory and techniques, Vol. MTT-32, No. 9, 1984, pp. 1230-1242. [12] Peter Glaser, “Power from the Sun: Its Future”, Science Magazine, Vol. 162, November 1968, pp. 857-861. [13] Lene Sørensen and Knud Erik Skouby, “User Scenarios 2020 – a Worldwide Wireless Future”, WWRF Outlook, Wireless World Research Forum, No. 4, July 2009. Energy out of Thin Air 25

[14] Aristeidis Karalis, J.D. Joannopoulos, and Martin Soljacic, “Efficient Wireless Non-Radiative Mid-Range Energy Transfer”, Annals of Physics, Vol. 323, No. 1, January 2008, pp. 34-48. [15] Wireless Power consortium. Web. 30 Oct 2014. http://www.wirelesspowerconsortium.com/ [16] Hubregt J. Visser, Antenna Arrangement for Wireless Powering, United States Patent Application US 2014/0176082 01, 26 June 2014. 26 27

Curriculum Vitae

On February 1, 2014, prof.dr.ir. Huib Visser has been appointed part-time professor Wireless data and power transfer for miniature and environment-independent electronics at the Department of Electrical Engineering of the Eindhoven University of Technology (TU/e).

Huib Visser (1964) gained his MSc degree in Electrical Engineering from Eindhoven University of Technology (TU/e) in 1989. In 1990, after doing his military service as an officer in the Royal Netherlands Army at the former TNO Physics and Electronics Laboratory in The Hague, he continued working here. He specialized in the modeling and design of antennas and antenna systems and participated in projects including near-field antenna measurement, Monolithic Microwave Integrated Circuit (MMIC) design and phased array antenna modeling. In 1997 he was assigned to ESA-ESTEC in Noordwijk where he worked on the modeling of open-ended phased array antennas. In 2001 he moved to TNO Science and Industry in Eindhoven where he specialized in antenna miniaturization. From TNO he was assigned part-time to TU/e, the Department of Electrical Engineering where, to this day, he has taught antenna theory and design and supervised BSc, MSc and PhD research projects. Since 2006 he has also been assigned part-time to the Holst Centre in Eindhoven and in 2009 he started working in the Holst Centre as an employee of imec Netherlands where he leads the research in the field of Wireless Power Transfer. In 2009 he gained his PhD from Eindhoven University of Technology and Katholieke Universiteit Leuven in Belgium. Huib Visser is author of the books “Array and Phased Array Antenna Basics” (Wiley, 2005), “Approximate Antenna Analysis for CAD” (Wiley, 2009) and “Antenna Theory and Applications” (Wiley, 2012). Huib has been chief editor of the Journal of the Netherlands Electronics and Radio Society (NERG) and was a member of the NERG board. He holds four patents. 28 prof.dr.ir. Huib Visser

Colophon

Production Communicatie Expertise Centrum TU/e

Cover photography Rob Stork, Eindhoven

Design Grefo Prepress, Sint-Oedenrode

Print Drukkerij Snep, Eindhoven

ISBN 978-90-386-3764-8 NUR 959

Digital version: www.tue.nl/bib/ Intreerede prof.dr.ir. Huib Visser 19 december 2014

Bezoekadres Den Dolech 2 5612 AZ Eindhoven

Postadres Postbus 513 5600 MB Eindhoven

Tel. (040) 247 91 11 www.tue.nl/plattegrond / Faculteit Electrical Engineering

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