Wireless Power Transmission Using Microwaves

Wireless Power Transmission Using Microwaves

Dhole Patil College of Engineering, Wagholi, Pune. (University of Pune)

[email protected]

Arati A. Dandavate

Dhole Patil College of Engineering, Wagholi, Pune. (University of Pune) [email protected]

Abstract—In this paper, we present the concept of wireless power transmission to cut the clutter or lead to clean sources of electricity. It will eradicate the hazardous usage of electrical wires which involve lot of confusion in particularly organizing them. The plan is transmitting power as microwaves from one place to another in order to reduce the use of clumsy wires & distribution losses. This paper will give the idea about impact on human beings, advantages, disadvantages, & applications of wireless power transmission.

Key Words— Microwave Power transmission (MPT), Nikola Tesla, Rectenna, Wireless Power transmission (WPT).

I. I

Wireless Power Transmission is not new to the world, Nikola Tesla is the one who first Conceived the idea Wireless Power Transmission and demonstrated “the transmission of electrical energy without wires" that depends upon electrical conductivity as early as 1891[1]. He further culminated his efforts in a major breakthrough in 1899 at Colorado Springs by transmitting 100 million volts of high-frequency electric power wirelessly over a distance of 26 miles at which he lit up a bank of 200 light bulbs and ran one electric motor! With this souped up version of his Tesla coil, Tesla claimed that only 5% of the transmitted energy was lost in the process. [43].

The wireless transmission of energy is common in much of the world. Radio waves are energy, and people use them to send and receive cell phone, TV, radio and Wi-Fi signals every day. The radio waves spread in all directions until they reach antennae that are tuned to the right frequency. A similar method for transferring electrical power would be both inefficient and dangerous.

During the world war II, W. C. Brown started the first microwave power transmission (MPT) research and development in 1960s based on the development of the microwave tubes. First of all, he developed a rectifying antenna, for receiving and rectifying microwaves Called rectenna. The efficiency of the first rectifying antenna (rectenna) developed in 1963 was 50 % at output 4WDC and 40% at output 7WDC, respectively [3]. P. E. Glaser proposed a Solar Power Satellite (SPS) in 1968, based on the Brown’s work, [4]. In 1980s, Japanese scientists progressed the MPT technologies and research[5][6]. In 1983 and 1993, Hiroshi Matsumoto’s team carried out the first MPT experiment in space. The rocket experiment were called MINIX (Microwave Ionosphere Nonlinear Interaction experiment) in 1983 and ISY-METS (International Space Year – Microwave Energy Transmission in Space) in 1993, respectively. They focused nonlinear interaction between intense microwave

and ionospheric plasmas. In the MINIX experiment, they used cooker-type 800W-2.45GHz magnetron for microwave transmitter. New wave-wave-particle interaction phenomenons were observed in the MINIX. Plasma theory and computer experiments supported the observations [7][8]. The world’s first fuel free airplane powered by microwave energy from ground was reported in 1987 at Canada. This system is called SHARP (Stationary High –Altitude Relay Platform) [9]. In 2003, Dryden Flight Research Centre of NASA demonstrated a laser powered model airplane indoors. In 2004 Japan proposed wireless charging of electric motor vehicles by Microwave Power Transmission. Powercast, a new company introduced wireless power transfer technology using RF energy at the 2007 Consumer Electronics Show [10]. In 2007 a physics research group, led by Prof. Marin Soljacic, at the Massachusetts Institute of technology (MIT) demonstrated wireless powering of a 60W light bulb with 40% efficiency at a 2m (7ft) distance using two 60cm-diameter coils [11]. Intel reproduced the MIT group's experiment by wirelessly powering a light bulb with 75% efficiency at a shorter distance in 2008 [12].

II. N

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One of the major issue in power system is the losses occurs during the transmission and distribution of electrical power. As the demand increases day by day, the power generation increases and the power loss is also increased. The major amount of power loss occurs during transmission and distribution. The percentage of loss of power during transmission and distribution is approximated as 26%. The main reason for power loss during transmission and distribution is the resistance of wires used for grid. According to the World Resources Institute (WRI), India’s electricity grid has the highest transmission and distribution losses in the world – a whopping 27%. Numbers published by various Indian government agencies put that number at 30%, 40% and greater than 40%. This is attributed to technical losses (grid’s inefficiencies) and theft [2].

III. A

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The pioneer in wireless power transmission technology, William C. Brown, has designed, developed a unit and demonstrated to show how power can be transferred through free space by microwaves. The concept of Wireless Power Transmission System can be explained with functional block diagram as shown in Fig1. In the transmission side, the microwave power source generates microwave power and the output power is controlled by electronic control circuits. The wave guide ferrite circulator which protects the microwave source from reflected power is connected with the microwave power source through the Coax –Waveguide Adaptor. The tuner matches the impedance between the transmitting antenna and the microwave source. The attenuated signals will be then separated based on the direction of signal propagation by Directional Coupler. The transmitting antenna radiates the power uniformly through free space to the rectenna. In the receiving side, a rectenna receives the transmitted power and converts the microwave power into DC power. The impedance matching circuit and filter is provided to setting the output impedance of a signal source equal to the rectifying circuit. The rectifying circuit consists of Schottky barrier diodes converts the received microwave power into DC power.[13].

Fig.1. Functional Block Diagram of Wireless Power Transmission

IV. C

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The Primary components of Wireless Power Transmission are Microwave Generator, Transmitting antenna and Receiving antenna (Rectenna). The components are described as follows.

A. Microwave Generator

The microwave transmitting devices are classified as Microwave Vacuum Tubes (magnetron, klystron, Travelling Wave Tube (TWT), and Microwave Power Module (MPM)) and Semiconductor Microwave transmitters. The highest efficiency over 90% is achieved at 2.45 GHz among all the frequencies [14].

a. Magnetron

It was W. C. Brown who invented a voltage controlled oscillator with a cooker-type magnetron in a phase locked loop[15]. He could control and stabilize a phase of microwave emitted from cooker-type magnetron. It is however confirmed that spurious emissions from the cooker-type magnetron with a stable DC power supply is low enough and this can be applied to the MPT system[16].

b. Semiconductor Amplifier

Because of advance of mobile phone network, after 1980s, semiconductor device played the major in microwave world instead of the microwave tubes. The semiconductor device is expected to expand microwave applications, for instance, phased array and Active integrated antenna (AIA), because of its manageability and mass productivity. Some microwave power transfer (MPT) experiments were carried out in Japan with phased array of semiconductor amplifiers, after 1990s, [17]. Due to the nature of small-size, thinness, lightness and multi-functions in AIA, a power transmission part of the spacetenna (space antenna) can be realized in thin structure. Prof. Kawasaki’s group has developed some AIA system for the MPT application [18]. In present, new materials are developed fore the semiconductor device to increased output power and efficiency. They are called band gap devices such as SiC and GaN. The wide-band gap devices can make over hundreds watt amplifier with one chip. In recent days, there are some development of microwave amplifiers with SiC MESFET [19][20] or GaN HEMT[21][22].

important problem in space. All lost power converts to heat. We need special heat reduction system in space. If we use high efficient microwave transmitters, we can reduce weight of heat reduction system. We should aim for over 80 % efficiency for the microwave transmitter, which must include all loss in phase shifters, isolators, antennas, power circuits. Especially, the SPS is a power station in space, therefore, heat reduction will be a serious problem [25].

B. Transmitting Antenna

Fig. 2. Waveguide Slot Antenna

The most popular type of transmitting antenna are the slotted wave guide antenna, microstrip patch antenna, and parabolic dish antenna [26]. The slotted waveguide antenna is ideal for power transmission because of its high aperture efficiency (> 95%) and high power handling capability.[27].

The front view of the slotted wave guide antenna is as shown in Fig 2 [28]. The slots on the waveguide will assumed to have a narrow width. Increasing the width increases the Bandwidth, each slot could be independently fed with a voltage source across the slot. The position, shape and orientation of the slots will determine how (or if) they radiate. In addition, the shape of the waveguide and frequency of operation will play a major role. If the slots are displaced from the centerline, the x-directed current will not be zero and will need to travel around the slot. Hence, radiation will occur. The distance from the edge will determine the magnitude of the current. As a result, the power that the slot radiates can be altered by moving the slots closer or farther from the edge. In this manner, a phased array can be designed with varying excitation to each element. Antenna arrays made up of hundreds or even thousand elements are often slotted waveguides similar to those described above.[29][30].

C. Rectenna

Fig. 3. Schematic rectenna system.

In the early of 1960s, the concept of rectifying antenna (rectenna), the name ‘rectenna’ and the rectenna was conceived by W.C. Brown of Raytheon Company [31]. A rectenna is a rectifying antenna, a special type of antenna that is used to directly convert microwave energy into DC electricity. Its elements are usually arranged in a multi element phased array with a mesh pattern reflector element to make it directional.[33]. The rectenna is consists of antenna, rectifying circuit with a low pass filter between the antenna and rectifying diode. The rectenna termed as rectifying antenna, is combination of an antenna and a nonlinear rectifying element (Schottky diode, IMPATT diode…etc.) where the two elements are integrated into a single circuit. The schematic of a rectenna system is shown in Fig. 3 [32]. Such a system is capable to receive and detect microwave power and converts the RF power into dc voltage at high frequencies (THz). Rectennas are highly efficient at converting microwave energy to electricity. In laboratory environments, efficiencies of over 85%[34].

Rectifying antennae are usually made of an array of dipole antennae, which have positive and negative poles. These antennae connect to semiconductor diodes. Here's what happens:

1. Microwaves, which are part of the

electromagnetic spectrum, reach the dipole

antennae.

2. The antennae collect the microwave energy and

transmit it to the diodes.

3. The diodes act like switches that are open or

closed as well as turnstiles that let electrons flow

in only one direction. They direct the electrons to

the rectenna's circuitry.

4. The circuitry routes the electrons to the parts and

systems that need them.[37].

The maximum rectenna array in the world is that used for a ground to ground experiment in Goldstone by JPL, USA, in 1975[36].

Fig. 4. Rectenna array

V. B

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A general public perception that microwaves are harmful has been a major obstacle for the acceptance of power transmission with microwaves. The scientific research indicates that heating of humans exposed to the radiation and effect of microwave radiation on birds (fried bird effect) is the only known effect.[40]. However this can happen in a highly intense area, in an area around and above the rectenna, access would need to be carefully controlled to ensure environmental safety and health standards are maintained. Under normal operating conditions, the SPS microwave downlink will need to be monitored continuously to ensure the tightly tuned phased-array techniques and beam control are functioning correctly[46].

Studies in this domain repeatedly proves that the microwave radiation level would be never higher than the dose received while opening the microwave oven door, meaning it is slightly higher than the emissions created by cellular telephones[38]. Cellular telephones operate with power densities at or below the ANSI/IEEE exposure standards [39]. Thus public exposure to WPT fields would also be below existing safety guidelines.

VI. A

& D

WPT

A. Advantages

1. The power could be transmitted to the places where the wired transmission is not possible. 2. Wireless Power Transmission system would

completely eliminate the existing high-tension power transmission line cables, towers and sub

stations between the generating station and consumers and would facilitate the interconnection of electrical generation plants on a global scale.

3. The cost of transmission and distribution would become less and the cost of electrical energy for the consumer would be reduced also.

4. It has more freedom of choice of both receiver and transmitters. Even mobile transmitters and receivers can be chosen for the WPT system. 5. Loss of transmission is negligible level in the

Wireless Power Transmission; therefore, the efficiency of this method is very much higher than the wired transmission.

6. The power failure due to short circuit and fault on cables would never exist in the transmission. 7. Power theft would be not possible at all.

8. Wireless charging would also possible. laptops and cell phones might never need any wires at all.

9. Vehicles would be driven using WPT, no need of fuel.

B. Disadvantages

1. Cost for practical implementation of WPT seems to be very high.

The slightly over 1million dollar Goldstone test in 1975 delivered 34 kW at 1.6 km. The costs of the test in Hawaii in 2008, where just under 1 million dollar and delivered 20 Watts over 148 kilometers.[40].

The very short range (1- l0m), preliminary demonstrations of W at low power levels (< kW) were in general quite costly, however, the cost estimates are coming down for larger power levels and longer ranges. Given the economic disparity andbeam safety concerns, it is doubtful that short range WPT applications involving beams that are near tangent to the Earth’s surface will ever be useful for electric power transmission as compared to wired power delivery. However, this does not preclude research and development tests and demonstrations of WPT from point to point on the Earth’s surface, where economic competition is not the prime consideration[45].

2. Interference of microwave with present communication systems is difficult.

VII. A

WPT

A. WTP for Space Solar

Fig. 5. Solar Power Satellite

Space Solar Power Satellites (SPS) is the largest application of microwave power transmission. In SPS solar power is captured in space and converted into electricity. The electricity is converted into microwaves and transmitted to the earth. The microwave power will be captured with antennas and converted into electricity [40] as shown in .Fig 5[41].

B. To power vehicles

A high powered and efficient rectenna is just the ticket to power vehicles such as this. In this case, the remote fueling is likely accomplished via a MASER rectenna as it is the most developed system.[42]. Also to fuel moving targets such as free airplanes, fuel free electric vehicles, moving robots and fuel free rockets.

C

We come to a conclusion that the day is not so far when there will not be a wire & stop power theft. Even some electronic gadgets will not need batteries at all. And also with solar power satellite the need of the electricity will be fulfilled. The concept is still at the embryonic state of the development. In particular the EMI characteristics of the rectenna must be improved. It will also be necessary to access impact of wild scale use of microwave power transmission on use of the frequency spectrum.

R

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Nikhil B. Dhakeborn in Jalgaon District, India on 5th November 1989 is a student at Dhole Patil College of Engineering, Pune, affiliated to the University of Pune. He is in final year of Information Technology and will be granted the degree of Bachelor of Engineering in July, 2012. He has published three

Articles in International Journal & also presented various papers at National level.