Research Activities and Future Trends of Microwave Wireless Power Transmission

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SIXTH INTERNATIONAL SYMPOSIUM NIKOLA TESLA October 18 20, 2006, Belgrade, SASA, Serbia Research Activities and Future Trends of Microwave Wireless Transmission Djuradj Budimir 1 and Aleksandar

1 SIXTH INTERNATIONAL SYMPOSIUM NIKOLA TESLA October 18 20, 2006, Belgrade, SASA, Serbia Research Activities and Future Trends of Microwave Wireless Transmission Djuradj Budimir 1 and Aleksandar Marincic 2 Abstract One of the key technologies throughout the 20 th century was the application of radio for telecommunications. However, radio can be also used for other purposes such as human welfare. Due to a lack of energy supply during the next fifty years, Space Solar Station (SPS) could help solve the problem. Microwave wireless transmission (MPT) is a promising technique for the long term supply for places where it is difficult to install transmission lines. This technology was proposed by W. C. Brawn in In 1968 the initial idea of the SPS was proposed by P. E. Glaser. In this paper we describe a review of the research activities and future trends of microwave wireless transmission (MPT) technology and its application. Keywords Microwave wireless transmission, Solar station, Rectenna, Nikola Tesla. I. INTRODUCTION The transmission of large amounts of electric is one possible future application of microwaves that has not proved very popular so far. In 1900, Nikola Tesla, an inventor and scientist from our neighborhood, proposed the use of radio waves to transmit instead of using high-voltage lines. Nikola Tesla was born in Smiljan, a village in a mountainous area of the Balkan Peninsula known as Lika, which at that time was part of the Military Frontier, border country of Austro-Hungary [1]. On page 193 of Prodigal Genius [2], J. J. O'Neill relates a story of Tesla testing his wireless -transmission system by illuminating two hundred incandescent lamps at a distance of 26 miles, "with electrical energy extracted from the earth." However, while it would seem that such a feat is possible, no documentation from Tesla's own records has been published confirming that such a demonstration actually took place. In 1899, Nikola Tesla performed a wireless transmission in Colorado. [3] He said the energy could be collected all over the globe, preferably in small amounts, ranging from a fraction of one to a few horse s [4]. In the late 1930 s, engineers and D.Budimir is with the Wireless Communication Research Groups, Department of Electronic, Communication and Software Engineering, University of Westminster, London W1W 6UW, UK, d.budimir@wmin.ac.uk 2 A. Marincic is with Department of E&E. Eng., University of Belgrade, Serbia. emarinci@etf.bg.ac.yu scientists used the original Tesla idea of transmitting electric via radio waves, but instead of using a low frequency, they thought about using microwave beams. The people who were interested in wireless energy transmission had to wait for the invention of a high microwave device to generate electromagnetic energy of reasonable short wavelength, since efficient focusing toward the receiving destination is strongly dependent upon the use of narrow beam formation technology by small size antennas and reflectors. World War II developed the ability to convert electricity (energy) to microwave using a magnetron and a klystron. After World War II, high- microwave transmitters became efficient enough to send thousands of watts over distances of a mile or more. The post-war history of research on free-space transmission is well documented by Willian C. Brown [5], who was a pioneer of practical microwave transmission. It was he who first succeeded in demonstrating a microwave-ed helicopter in 1964, using 2.45 in the frequency range of reserved for the ISM (Industrial, Scientific and Medical) applications of radio waves. A conversion device from microwave to DC, called a rectenna, was invented and used for the microwave-ed helicopter. In 1963 the first rectenna was built and tested at Perdue University with an estimated 40% efficiency and output of 7 W. In 1975 at the JPL Goldstone Facility the 84% of microwave to dc efficiency was achieved in the demonstration of WPT. In 1968, Peter Glaser [6] had calculated that if several large solar- satellites were placed in geosynchronous orbit, the energy they collected could be beamed to earth and gathered by arrays of receiving antennas covering many square miles. These satellites would be in cloudless space and receive sunlight every day. received this way would be more reliable than other renewable sources of energy such as solar-ed or wind-ed generators. However, until energy becomes a great deal more expensive than it is, the idea of receiving microwave from space satellites is likely to remain just that an idea. II. C OLORADO SPRINGS LABORATORY Under a $30,000 grant from Colonel John Jacob Astor, the owner of the Waldorf-Astoria Hotel in New York City, in mid-1899, Tesla finally decided on Colorado Springs, a

plateau about 2000 meters above sea level, where he erected a shed large enough to house a high-frequency transformer with a coil diameter of 15 meters.

In his article The transmission of electric energy without wires, [5] written in 1904 in the Electrical World and Engineer, Tesla writes that he came to Colorado Springs with the following goals:

2 plateau about 2000 meters above sea level, where he erected a shed large enough to house a high-frequency transformer with a coil diameter of 15 meters. This gigantic coil was placed in a large square shed over which rose a 200-ft (61 m) mast with a 3-ft (91.4 cm) diameter copper ball positioned at the top. In his article The transmission of electric energy without wires, [5] written in 1904 in the Electrical World and Engineer, Tesla writes that he came to Colorado Springs with the following goals: Tesla s double circuit system is in a way a predecessor of the modern spread spectrum radio system. a) to develop a transmitter of great b) to perfect means for individualizing and isolating the energy transmitted. c) to ascertain the law of propagation of currents through the earth and the atmosphere. In Colorado Springs Tesla (Fig. 1) certainly thought a lot about his wireless transmission of energy but did not write much about it in his diary. He described some wireless energy transmission, but all one could see in the diary points to transmission over short distances. Fig. 2. Colorado Springs laboratory ( ) III. M ICROWAVE WIRELESS POWER TRANSMISSION ACTIVITIES IN THE WORLD Over the last two decades, there has been a substantial amount of work around the world, particularly in the USA, Japan, Russia, Canada, Germany, and France on microwave wireless transmission [7]-[8]. Here, only the most important microwave wireless transmission activities in the world will be presented. It is hoped that the references included at the end of this paper will direct the interest reader to sources of more detailed information on particular subjects. A. US and Canadian Activities Fig.1. Nikola Tesla in his Colorado Springs laboratory Tesla himself claimed to have succeeded in transmitting a small amount of wireless and setting up electrical waves with high-voltage discharges from the Tesla coil. He also experimented with a sophisticated construction of a multicarrier transmitter with a special receiver tuned to all carriers (Fig. 2). It is stated in [6] that this invention consists in generating two or more kinds or classes of disturbances or impulses of distinctive character with respect to their effect upon a receiving circuit and operating thereby a distant receiver which comprises two or more circuits, each of which is tuned to respond exclusively to the disturbances or impulses of one kind or class and so arranged that the operation of the receiver is dependent upon there conjoint or resultant action. In the United States an important milestone in the history of microwave transmission was the three-year study program called the NASA/DOE Satellite System Concept Development and Evaluation Program or NASA/DOE reference model [9], started in The next program was published in 1997 as an improved SPS reference system, called the Fresh-Look-SPS concepts as the Sun Tower SPS concept which was one of their new models [10]. In 1998 SSP Concept Def. Study was examined. The SSP Exploratory Research and Technology (SERT) program was examined in From 2001 to 2002 an SSP Concept and Technology Maturation (SCTM) program has been pursued by NASA. In Canada, the world s first flight of a fuel-less airplane ed by microwave energy from the ground was reported in This system was called Stationary High Altitude Relay Platform (SHARP). Based on this concept, the airplanes would circle slowly at an operating altitude of 21 km and relay radio signals within a diameter of 600 km for many months. An operating frequency of this system was The rectenna is comprised of a custom printed circuit array of

3 dipole antennas with associated rectifying diodes coating the underside of the plane and converts the microwave energy to direct current to the electric motor. B. European Activities A Sail Tower SPS was proposed by Europeans in 2001 [11]. The characteristics of the European Sail Tower SPS are shown in Table I. In 2003 a point to point wireless transmission system was examined to deliver 10 kw of electricity to a small isolated village in Reunion Island, France [12-13]. TABLE I. CHARACTERISTICS OF THE EUROPEAN SAIL TOWER SPS 2.45 SPS Tx 400 MW SPS Tx (radius) 510 m Orbit GEO Final number of SPS 1870 Receiving antenna site: Final number 103 size 11 x 14 Site including safety 27 x 30 km zone delivered per SPS SPS tower Length: Electricity prod. C. Russian Activities 275 MW 15 km 450 MW In Russia, there has been much work on the SPS, including microwave technology required for the SPS and many systems studies [14]. The group at Moscow State University has reported many advances in antenna design, design of microwave components and system design. Also, the later work in collaboration with the group at Kyoto University developing a cyclotron wave converter (CWC) tube. The 83 % of RF to dc efficiency was obtained at the Istok Tube Company, with an output dc voltage of kv and of 10 kw. D. Japanese Activities In the early 1980 s, the Japanese engineers and scientists started their SPS research activities. Here are some of their programs [15]. 1983: Microwave Ionosphere Nonlinear Interaction Experiment (MINIX) [16] 1992: Microwave Lifted Airplane experiment (MILAX) [17] 1993: International Space Year-Microwave Energy Transmission in Space (ISY-METS) [18] Two Japanese organizations have recently proposed their models. JAXA (Japan Aerospace Exploration Agency) proposed a 5.8, 1 SPS model [19], and USEF (Institute for Unmanned Space Experiment Free Flyer) proposed a simpler model [20] IV. MICROWAVE POWER TRANSMISSION AND ITS APPLICATION A block diagram of the microwave wireless transmission demonstration components is shown in Fig. 3. The primary components include a microwave source, a transmitting antenna, and a receiving rectenna. A combination of an antenna and a rectifying circuit is a rectenna. The antenna receives electromagnetic and the rectifying circuit converts it to electric. The microwave source consists of a electron tubes (klystron, TWT or microwave oven magnetron) or solid state devices (GaAs MESFET, GaN phemt, SiC MESFET, AlGaN/GaN HFET, and InGaAs) with electronics to control the output. A coax-towaveguide adapter is connected to a waveguide ferrite circulator which protects the microwave source from reflected. In order to match the waveguide impedance to the antenna input impedance the circulator is connected to a tuning waveguide section. Microwave Source Tx Slotted WG Coax/WG ) WG circulator R LPF for DC LPF for Fundamental C GaAs Schottky barrier diode Free space Rx Rectenna Fig. 3. Block diagram of the microwave wireless transmission system The slotted waveguide antenna, parabolic dish, and microstrip patch are most popular type of tx antennas. Due to high aperture efficiency (> 95%) and high handling capability, the slotted waveguide antenna is an ideal antenna for transmission. The typical parameters of the transmitting antenna for the SPS are shown in Table II. A rectenna which was invented by W. C. Brown in 1960 s [21] is composed of a rectifying circuit and antenna. A rectenna is passive element with a rectifying diode (Si or GaAs Schottky barrier, SiC and GaN) and low pass filter between the antenna (dipole, Yagi- Uda, microstrip or parabolic dish) and the rectifying diode to suppress re-radiation of higher harmonics for absorbing transmitted microwave energy from a transmitter and converting it into direct current (DC). The first rectenna was composed of 28 half-wave dipoles terminated in a bridge rectifier using point-contact semiconductor diodes. Later, the point contact semiconductor diodes were replaced

4 by silicon Schottky-barrier diodes which raised the microwave-to-dc conversion efficiency from 40 % to 84 %, the efficiency being defined as the ratio of DC output to microwave absorbed by the rectenna. In the demonstration of microwave transmission at the Jet Propulsion Laboratory (JPL) Goldstone Facility in 1975, an efficiency of 84 % was obtained and of 30 kw was successfully transferred from the transmitting large parabolic antenna dish to the distant rectenna site over a distance of 1.6 km at the 2.5 band. The microwave transmission systems using electron tubes and semiconductors are shown in Fig. 4 and Fig. 5, respectively. The characteristics of semiconductor radio transceivers for space and earth application are shown in Tables III and IV, respectively. TABLE II TYPICAL PARAMETERS OF THE TRANSMITTING ANTENNA FOR THE SPS SYSTEM Model NASA/ DOE JAXA1 JAXA2 OLD JAXA 2.45 Efficiency 89% 86% 87% 96.7% 6.72 Diameter of 1.0 km 1.0 km km transmitting antenna km Rectenna diameter 1.0 km 3.4 km 3.4 km 2.0 km Electronics High Voltage Supply Multiple Divider Fig. 4. Microwave transmission system using electron tubes Multiple Divider Oscillator Fig. 5. Microwave transmission system using semiconductors Tubes TABLE III. CHARACTERISTICS OF ELECTRON TUBES Klystron TWT Magnetron Microwave Module Efficiency 76% 60-67% 60-75% 50% 100 several Several 100 W Several W 10 7 W Weight g/w Harmonics Less than -70 dbc 1000 W 20 g/w 45 g/ W (2.45 ) 2030 g/w (5.8 ) Less than -70 dbc Second:- 55 dbc Third: -80 dbc Fourth: -70 dbc Fifth: -75 dbc 6.4 g/w TABLE IV. CHARACTERISTICS OF SEMICONDUCTOR RADIO TRANSCEIVERS FOR SPSCE APPLICATION Satellite INT-7 NSTAR TDRSS ETS Efficiency 29% 36% 32% 31% 30 W 40 W 24 W 14 W Weight 1.7 kg 2.5 kg 3.4 kg 1.2 kg The largest application of the WPT via microwave is a Space Solar Satellite (SPS). The typical parameters of retro directive space and ground SPS system are shown in Tables V and VI, respectively. The other application of the WPT are moving targets, ground to ground transmission, wireless source and mobile devices with low consumption such as long range RFID, wireless sensors (see Table VII) and RF adaptive rectifying circuits (PARC). The most popular MPT sub-systems are Space Radio Transmitter System (SPORTS) and Solar Radio Integrated Transmitter (SPRITZ). The typical physical parameters of this transmitter are shown in Table VIII. TABLE V TYPICAL PARAMETERS FOR RETRODIRECTIVE SPS SYSTEM SPS orbit diameter transmitted to earth Total/one element GEO (36,000 km) m 1340 MW/0.175 W

5 TABLE VI TYPICAL PARAMETERS FOR RETRODIRECTIVE GROUND STATION SYSTEM Signal (Pt) 1 KW (60 dbm) EIRP 114 dbm Free space loss (36,000 km) 199 db gain Gt (D=10m, 54 dbi η=0.7) SPS transmitter antenna -80 dbm element received (Pr) SPS transmitter antenna 6 dbi element gain Gr (circular microstrip antenna) Atmospheric loss 1 db TABLE VII. ELECTROMAGNETIC SPECTRUM FOR RFID AND WIRELESS SENSORS Wireless sensors and RFID KHz LF RFID: Passive IC tag KHz MF RFID: Passive IC tag 3-30 MHz HF RFID: Passive IC tag (6.78/13.56/ MHz) MHz Wireless sensor and Active RFID MHz Wireless sensor and Active RFID: Transeivers (315/433/868/915 (5m)/2450(1m) MHz) Active RFID Beamed microwave Transmission TABLE VIII. PHYSICAL PARAMETERS OF SPRITZ SPS TRANSMITTER Tx 25 W Tx Microstrip Array (10 x 10) Beam width 7.3 o Loss # Feed line 6 db Tx Gain Maximum 17.6 dbi Tx EIRP 58 dbm Size in mm 2000 x 2300 x 2850 VI. C ONCLUSION Radio, the core technology of the 20 th century used especially for wireless communications could also be used for human welfare purposes. The problems of a possible lack of energy during the next fifty or hundred years could be solved by the Space Solar Station (SPS), which was originally proposed by P. E. Glaser in A promising technique for the long term supply for places where it is difficult to install transmission lines is Microwave wireless transmission (MPT), which was proposed by W. C. Brawn in A review of the research activities and future trends of microwave wireless transmission (MPT) technology and its application has been described. REFERENCES [1] R. G. D., Laffan, The Serbs: The Guardians of the Gate, 1989 Dorset Press, ISBN [2] J. J. O Neill, Prodigal Genius-The Life of Nikola Tesla, New York: Washburn, [3] Nikola Tesla; Colorado Springs Notes, , Nolit, Belgrade, Serbia, (published by the Nikola Tesla museum, Belgrade, Serbia, [available at the UEC Library, 345 East 47 Street, New York, NY 10017]). [4] N. Tesla, The transmission of electrical energy without wires, Electrical World and Engineer, New York, USA, 5 th March [5] William C. Brown;, A survey of the elements of Transmission by microwave beam, in 1961 IRE Int. Conf. Rec., vol.9, part 3, pp [6] P. Glaser, " From The Sun; Its Future," Science, Vol. 162, pp , Nov. 22, [7] URSI White Paper on a Solar Satellite (SP), October [8] J. O. McSpadden and J. C. Mankins, Space Solar Programs and Microwave Wireless Transmission Technology, IEEE Microwave Magazine, pp.46-57, December [9] U.S. Dept. of Energy & NASA, "Satellite System, Concept Development and Evaluation Program," Reference System Report, DOE/ER-0023, Oct. 1978, Published Jan [10] J. Mankins, et. al, Space Solar : A fresh look at the feasibility of generating solar in space for use on Earth, Tech. Report SAIC 97/1005, April 4, [11] W. Sebolth, M. Klimke, M. Leipold, and N. Hanowski, European Sail Tower SPS Concept, Acta Astronautwa, Vol.48., No.5-12, pp , [12] G. Pignolet, designs for wireless transportation, The Grand Bassin case study in Reunion island. Proc ISAP'96, Chiba. p [13] G Pignolet, " Design of a low- rectenna for a low-cost SPS-2000/WPT demonstration model ", ISAS Note No.573, Institute of Space and Astronautical Science, [14] V. A. Vanke, H. Matsumoto, N. Shinohara and A. Kita, High Converter of Microwave into DC, Journal of Radioelectronics, no.9, [15] H. Matsumoto, Research on Solar Satellites and Microwave Transmission in Japan, IEEE Microwave Magazine, pp.46-57, December [16] H. Matsumoto, N. Kaya, I. Kimura, S. Miyatake, M. Nagatomo, and T. Obayashi, MINIX project toward solar satellite Rocket experiment of microwave energy transmission and associated nonlinear plasma physics in the ionosphere, in ISAS Space Energy Symp., 1982, pp [17] H. Matsumoto, N. Kaya, M. Fuyita, T. Fujtwara, and T. Sato, Microwave lifted airplane experiment with active phased array antennas, Kyoto University, Kyoto, Japan, MILAX, [18] R. Akiba, K. Miura, M. Hinada, H. Matsumoto, and N. Kaya,, ISY-METS rocket experiment, Int. Space Astronaut Sci, no. 652, pp. 1-13, [19] M. Mori, H. Kagawa, H. Nagayama, and Y. Saito, Proc. of the 4 th Int. Conf. on Solar from Space SPS 04, July 2004, Granada, Spain (ESA SP-567, December 2004). [20] Y. Kobayashi, T. saito, K. Ijichi, and H. kanai, Proc. of the 4 th Int. Conf. on Solar from Space SPS 04, July 2004, Granada, Spain (ESA SP-567, December 2004). [21] William C. Brown; The History of the Development of the Rectenna, Proc. of SPS microwave systems workshop, pp , Jan , 1980, at JSC-NASA [22] William C. Brown; The History of Transmission by Radio Waves, IEEE Transaction on Microwave Theory and Techniques, Vol. MTT-32, No.9, September 1984, pp

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