Wireless Power Transmission Seminar Report 2019;-converted(1) 6591m

CHAPTER 1 Wireless Power Transmission 1.1: Introduction Power is very important to modern systems. From the smallest sensors, bionic implants, laptops, consumer products to satellites and oil platforms, it is important to be able to deliver power means other than classical wires or transmission lines. Wireless transmission is useful in cases where instantaneous or continuous energy transfer is needed, but interconnecting wires are inconvenient, hazardous, or impossible some times. In the case of biological implants, there must be a battery or energy storage element present that can receive and hold energy. This element takes up valuable space inside a person body. In the case of satellites, UAVs and oil platforms, solar s, fuel cells, or combustion engines are currently used to supply power. Solar s take up a great deal of weight and bulk in of energy density and must have a tracking system to maximize exposure to the sun. Fuel cells and combustion cells needs fuel and maintenance to be delivered on site. Wireless Power Transmission (WPT) is the efficient transmission of electric power from one point to another trough vacuum or an atmosphere without the use of wire or any other substance. The power can be transmitted using Inductive coupling for short range, resonant induction for mid-range electromagnetic wave power transfer. WPT is a technology that can transport power to locations, which are otherwise not possible or impractical to reach. The objective of this report is to design and implant a method to transmit wireless electrical power through space. The system will work by using resonant coils to transmit power from an AC line to a resistive load. Investigation of various geometrical and physical form factors evaluated in order to increase coupling between transmitter and receiver.

1.2: Why Do We Go For WPT System 1.2.1 Losses in the Wired System Professor Rauscher showed that the earth’s magnetosphere contains sufficient potential energy (at least 3 billion kilowatts) so that the resonant excitation of the earth- ionosphere cavity can reasonably be expected to increase the amplitude of natural

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“Schumann” frequencies, facilitating the capture of useful electrical power. Tesla also knew that the earth could be treated as one big spherical conductor and the ionosphere as another bigger spherical conductor, so that together they have parallel plates and thus, comprise a “spherical capacitor.” Dr. Rauscher calculates the capacitance to be about 15,000 microfarads for the complete earth-ionosphere cavity capacitor. W.O. Schumann is credited for predicting the “self-oscillations” of the conducting sphere of the earth, surrounded by an air layer and an ionosphere in 1952, without knowing that Tesla had found the earth’s fundamental frequency fifty years earlier. In comparison to the 3 billion kW available from the earth system, it is possible to calculate what the U.S. consumed in electricity. In 2000, about 11 Quads (quadrillion Btu) were actually used by consumers for electrical needs, which is equal to 3.2 trillion kWh. Dividing by the 8760 hours in a year, we find that only 360 million kW are needed on site to power our entire country. This would still leave 2.6 billion kW for the rest of the world! The really shameful U.S. scandal, unknown to the general public, is that out of the total electrical power generated using wire transmission (about 31 Quads), a full 2/3 is totally wasted in “conversion losses.”

Fig 1.1: Losses in the Wired System

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No other energy production system of any kind in the world has so much wastefulness. Instead of trying to build 2 power plants per week (at 300 MW each) for the next 20 years (only to have a total of additional 6 trillion kWh available by 2020), as some U.S. government officials want to do, we simply need to eliminate the 7 trillion kWh of conversion losses in our present electricity generation modality. Tesla’s wireless transmission of power accomplishes this goal, better than any distributed generation.

1.3: Historical Revolution of Wireless Power Transmission

Fig 1.2: Wireless Power Transmission In 1864, James C. Maxwell predicted the existence of radio waves by means of mathematical model. In 1884, John H. Pointing realized that the Pointing vector would play an important role in quantifying the electromagnetic energy. In 1888, bolstered by Maxwell's theory, Heinrich Hertz succeeded in showing experimental evidence of radio waves by his spark gap radio transmitter. The prediction and evidence of the radio wave in the end of 19th century was start of the wireless power transmission. During the same period of Marches G. Marconi and Reginald Fessenden who are pioneers of communication via radio waves, Nicola Tesla suggested an idea of the wireless power transmission and carried out the first WPT experiment in 1899. He said “This energy will be collected all over the globe preferably in small amounts, ranging from a fraction of one to a few horse powers. One of its chief uses will be the illumination of isolated homes”. His actual y built a gigantic coil which was connected to a high mast of 200 ft. with a 3 ft. diameter ball at its top. He fed 300 Kwan power to the Tesla coil resonated at 150 kHz. The RF potential at the top sphere reached 100

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MV. Unfortunately, he failed because the transmitted power was diffused to all directions with 150 kHz radio waves whose wave length was 21 km. To concentrate the transmitted power and to increase transmission efficiency, we have to use higher frequency than that used by Tesla. In 1930s, much progress in generating high power microwaves, namely 1-10 GHz radio waves, was achieved by invention of the magnetron and the klystron. After World War II, high power and high efficiency microwave tubes were advanced by development of radar Technology. We can concentrate a power to receiver with microwaves. We call the wireless power transmission with microwaves as microwave power transmission (MPT). Based on the development of the microwave tubes during the World War II, W. C. Brown started the First MPT research and development in 1960. First of all, he developed a retina, rectifying antenna which he named, for receiving and rectifying microwaves. The efficiency of the first retina developed in 1963 was 50 % at output 4WDC and 40% at output 7WDC, respectively.

Fig 1.3: MPT Demonstration with Helicopter by W.C.Brown

With the retina, he succeeded in MPT experiments to wire helicopter in 1964 and to free flied helicopter in 1968 (Fig. 1.3). In 1970s; he tried to increase DC RF transmission RF DC total efficiency with 2.45 GHz microwave. In 1970, overall DC total efficiency was only 26.5 % at 39WDC in Marshall Space Flight Centre.

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Fig 1.4: 1sty Ground To Ground MPT Experiment in 1975 At The Venous Site. In parallel, he and his team succeeded in the largest MPT demonstration in 1975 at the Venus Site of JPL Goldstone Facility (fig 1.4). Distance between a transmit ting parabolic antennas, whose diameter was 26m, and a retina array, whose size was 3.4 m x 7.2 m, was 1 mile. After 1990s, many MPT laboratory and field experiments were carried out in the world. We often use 2.45 GHz or 5.8 GHz of the ISM band (ISM=Industry, Science, and Medical) for the MPT system. A Canadian Group demonstrated fuel free airplane flight experiment with MPT in 1987 which was called SHARP (Stationary High Altitude Relay Platform) with 2.45 GHz.

Fig 1.5: Stationary High Altitude Relay Platform. In USA, there were many MPT research and development projects after W. C. Brown: for instance, retro directive microwave transmitters, retina, and microwave circuit technologies.

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In Japan, there were many field MPT experiments such as fuel free airplane flight experiment with MPT phased array with 2.411 GHz in 1992, ground to ground MPT experiment with Power Company and universities in 1994-95.

Fig 1.6: Ground To Ground MPT Experiment In Japan In 1994-95. In the early 1970s, experiments with RFID tags began and by the early 2000’s Professor She Yuen (Ron) Hue and S.C. Tang developed a charger to provide resonant power transfer for small electronics. Today wireless power is used for everything from industrial motors to charging smart phones and tablets. Researchers predict that wireless power will be making a signify ant contribution to energy supplies by the end of this decade.

1.4: What Is WPT? WPT is nothing but wireless electricity. Transmission of electrical energy from one object to another without the use of wires is called as WPT. WPT will ensure that the cell phones, laptops, iPods and other power hungry devices get charged on their own, eliminating the need of plugging them in. WPT technology is transferring electric energy or power over distance without wires. With the basics of electricity and magnetism, and work our way up to the WPT technology. Even better, because of WPT some of the devices won't enquire batteries to operate. No, this concept of wireless electricity is not new. In fact Nikola Tesla used resonance magnetic fields to transfer wireless power.

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1.5: How Does Wireless Power Work? The basics of WPT involve the transmission of energy from a transmitter to a receiver via an oscillating magnetic field. To achieve this, Direct Current (DC) supplied by a power source, is converted into high frequency AC by specially designed electronics built into the transmitter. The AC energizes a copper wire coil in the transmitter, which generates a magnetic field. Once a second (receiver) coil is placed within proximity of the magnetic field, the field can induce an alternating current in the receiving coil. Electronics in the receiving device then converts alternating current back into direct current, which becomes usable power. The diagram FIG. 1.8 simplifies this process into four key steps.

1.6: Need of WPT Now a days there is a Rapid development of autonomous electronics like Laptops, Cell phones, House hold robots and all those devices typically relay on chemical energy storage(Battery) As they are becoming daily needs to present generation, Wireless energy transfer would be useful for many applications and they need midrange energy.

Fig 1.7: Wireless Energy Transfer

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Fig. 1.8: Simple Wireless Power Transmission Diagram

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CHAPTER 2 The Basic Idea of Transforming Electricity to WPT 2.1: Electricity The flow of electrons (current) through a conductor (like a wire), or charges through the atmosphere (like lightning). A convenient way for energy to get from one place to another.

Fig 2.1: An Illustration Representing the Earth's Magnetic Field

2.2: Magnetism A fundamental force of nature, which causes certain types of materials to attract or repel each other. Permanent magnets, like the ones on your refrigerator and the earth‘s magnetic field, are examples of objects having constant magnetic fields. Oscillating magnetic fields vary with time, and can be generated by alternating current (AC) flowing on a wire. The strength, direction, and extent of magnetic fields are often represented and visualized by drawings of the magnetic field lines.

2.3: Electromagnetism A term for the interdependence of time varying electric and magnetic fields. For example, it turns out that an oscillating magnetic field produces an electric field and an oscillating electric field produces a magnetic field.

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Fig 2.2: B Represents Magnetic Field When Current Flows Through a Coil.

As electric current, I, flows in a wire, it gives rise to a magnetic field, B, which wraps around the wire. When the current reverses direction, the magnetic field also reverses its direction.

2.4: Magnetic Induction A loop or coil of conductive material like copper, carrying an alternating current (AC), is a Very efficient structure for generating or capturing a magnetic field. If a conductive loop is connected to an AC power source, it will generate an oscillating magnetic field in the vicinity of the loop. A second conducting loop, brought close enough to the first, may capture some portion of that oscillating magnetic field, which in turn, generates or induces an electric current in the second coil. The current generated in the second coil may be used to power devices. This type of electrical power transfer from one loop or coil to another is well known and referred to as magnetic induction. Some common examples of devices based on magnetic induction are electric transformers and electric generators.

2.5: Energy/Power Coupling An electric transformer is a device that uses magnetic induction to transfer energy from its primary winding to its secondary winding, without the windings being connected to each other. It is used to transform AC current at one voltage to AC current at a different voltage. Energy coupling occurs when an energy source has a means of

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Transferring energy to another object. One simple example is a locomotive pulling a train car the mechanical coupling between the two enables the locomotive to pull the train, and overcome the forces of friction and inertia that keep the train still and, the train moves.

Fig 2.3: Magnetic Induction

Magnetic coupling occurs when the magnetic field of one object interacts with a second object and induces an electric current in or on that object. In this way, electric energy can be transferred from a power source to a powered device. In contrast to the example of mechanical coupling given for the train, magnetic coupling does not require any physical between the object generating the energy and the object receiving or capturing that energy.

2.6: WPT Technology WPT power sources and capture devices are specially designed magnetic resonators that efficiently transfer power over large distances via the magnetic near field. These proprietary source and device designs and the electronic systems that control them efficient energy transfer over distances that are many times the size of the sources/devices themselves. The WPT power source, left, is connected to AC power. The blue lines represent the magnetic near field induced by the power source. The yellow lines represent the flow of energy from the source to the WPT capture coil, which is shown powering a light bulb. Note that this diagram also shows how the magnetic field (blue lines) can wrap around a conductive obstacle between the power source and the capture device.

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Fig 2.4: WPT Power Source

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CHAPTER 3 Theories on WPT 3.1: Near Field Theory Near field are wireless transmission techniques over distances comparable to, or a few times the diameter of the device(s), and up to around a quarter of the wavelengths used. Near field energy itself is non radioactive, but some radioactive losses will occur. In addition there are usually resistive losses. Near field transfer is usually magnetic (inductive), but electric (capacitive) energy transfer can also occur. The magnetic near field has several properties that make it an excellent means of transferring energy in a typical consumer, commercial, or industrial environment. Most common building and furnishing Materials, such as wood, gypsum wall board, plastics, textiles, glass, brick, and concrete are essentially transparent to magnetic fields enabling WPT Technology to efficiently transfer power through them. In addition, the magnetic near field has the ability to wrap around many metallic obstacles that might otherwise block the magnetic fields. 3.2: Electrical Conduction Principle Electrical energy can be transmitted by means of electrical currents made to flow through naturally existing conductors, specifically the earth, lakes and oceans, and through the upper atmosphere starting at approximately 35,000 feet (11,000 m) elevation — a natural medium that can be made conducting if the breakdown voltage is exceeded and the constituent gas becomes ionized. For example, when a high voltage is applied across a neon tube the gas becomes ionized and a current es between the two internal electrodes. In a wireless energy transmission system using this principle, a high-power ultraviolet beam might be used to form vertical ionized channels in the air directly above the transmitter-receiver stations. The same concept is used in virtual lightning rods, the electro laser electroshock weapon and has been proposed for disabling vehicles. A global system for "the transmission of electrical energy without wires" dependent upon the high electrical conductivity of the earth was proposed by Nikola Tesla as early as 1904.

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"The earth is 4,000 miles radius. Around this conducting earth is an atmosphere. The earth is a conductor; the atmosphere above is a conductor, only there is a little stratum between the conducting atmosphere and the conducting earth which is insulating. Now, you realize right away that if you set up differences of potential at one point, say, you will create in the media corresponding fluctuations of potential. But, since the distance from the earth's surface to the conducting atmosphere is minute, as compared with the distance of the receiver at 4,000 miles, say, you can readily see that the energy cannot travel along this curve and get there, but will be immediately transformed into conduction currents, and these currents will travel like currents over a wire with a return. The energy will be recovered in the circuit, not by a beam that es along this curve and is reflected and absorbed, but it will travel by conduction and will be recovered in this way." Researchers experimenting with Tesla's wireless energy transmission system design have made observations that may be inconsistent with a basic tenet of physics related to the scalar derivatives of the electromagnetic potentials, which are presently considered to be nonphysical. The intention of the Tesla world wireless energy transmission system is to combine electrical power transmission along with broadcasting and point-to-point wireless telecommunications, and allow for the elimination of many existing high-tension power transmission lines, facilitating the interconnection of electrical generation plants on a global scale. One of Tesla's patents suggests he may have misinterpreted 25–70 km nodal structures associated with cloud - ground lightning observations made during the 1899 Colorado Springs experiments in of circum globally propagating standing waves instead of a local interfere nice phenomenon of direct and reflected waves. Regarding the recent notion of power transmission through the earthionosphere cavity, a consideration of the earth- ionosphere or concentric spherical shell waveguide propagation parameters as they are known today shows that wireless energy transfer by direct excitation of a Schumann cavity resonance mode is not realizable. "The conceptual difficulty with this model is that, at the very low frequencies that Tesla said that he employed (1-50 kHz), earth- ionosphere waveguide excitation, now well understood, would seem to be impossible with the either the Colorado Springs or the Long Island apparatus (at least with the apparatus that is visible in the photographs of these facilities)."

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Fig 3.1: Tesla Coil Transformer Wound in the Form of a Flat Spiral. This Is The Transmitter Form As Described In U.S. Patent 645,576. On the other hand, Tesla's concept of a global wireless electrical power transmission grid and telecommunications network based upon energy transmission by means of a spherical conductor transmission line with an upper three-space model return circuit, while apparently not practical for power transmission, is feasible, defying no law of physics. Global wireless energy transmission by means of a spherical conductor “single-wire” surface wave transmission line and a propagating TM00 mode may also be possible. 3.3: Induction Principle (Non Resonant Energy Transfer) The action of an electrical transformer is the simplest instance of wireless energy transfer. The primary and secondary circuits of a transformer are not directly connected. The transfer of energy takes place by electromagnetic coupling through a process known as mutual induction. (An added benefit is the capability to step the primary voltage either up or down.) The Battery chargers of a mobile phone or the transformers on the street are examples of how this principle can be used. Induction cookers and many electric toothbrushes are also powered by this technique. The main

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Drawback to induction, however, is the short range. The receiver must be very close to the transmitter or induction unit in order to inductively couple with it. 3.4: Electrostatic Induction Principle

FIG 3.2: (Tesla Illuminating Two Exhausted Tubes By Means Of A Powerful, Rapidly Alternating Electrostatic Field Created Between Two Vertical Metal Sheets Suspended From The Ceiling On Insulating Cords.) The "electrostatic induction effect" or "capacitive coupling" is an electric field gradient or differential capacitance between two elevated electrodes over a conducting ground plane for wireless energy transmission involving high frequency alternating current potential differences transmitted between two plates or nodes. The electrostatic forces through natural media across a conductor situated in the changing magnetic flux can transfer energy to a receiving device (such as Tesla's wireless bulbs).Sometimes called "the Tesla effect" it is the application of a type of electrical displacement, i.e., the age of electrical energy through space and matter, other than and in addition to the development of a potential across a conductor. Tesla stated, "Instead of depending on [electrodynamics] induction at a distance to light the tube . . . the ideal way of lighting a hall or room would . . . be to produce such a condition in it that an illuminating device could be moved and put anywhere, and that it is lighted, no matter where it is put and without being electrically connected to anything. I have been able to produce such a condition by creating in the room a powerful, rapidly alternating electrostatic field. For this purpose I suspend a sheet of metal a distance from the ceiling on insulating cords and connect it to one terminal of the induction coil, the other terminal being preferably connected to the ground.

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I suspend two sheets .each sheet being connected with one of the terminals of the coil, and their size being carefully determined. An exhausted tube may then be carried in the hand anywhere between the sheets or placed anywhere, even a certain distance beyond them; it remains always luminous.” And “In some cases when small amounts of energy are required the high elevation of the terminals, and more particularly of the receiving- terminal D' may not be necessary, since, especially when the frequency of the currents is very high, a sufficient amount of energy may be collected at that terminal by electrostatic induction from the upper air strata, which are rendered conducting by the active terminal of the transmitter or through which the currents from the same are conveyed. 3.5: Electro-Dynamic Induction (Resonant Inductive Coupling Method/ Evanescent Coupling Method) An inductive transformer is a device commonly used in power circuits and electromechanical motors (for example electrical toothbrushes and chargers). A transformer typically operates up to mid-kHz frequencies. It essentially transfers electrical energy from one circuit to another via induction: the time-varying magnetic flux produced by a primary coil crosses a secondary coil and induces in it a voltage. The primary and the secondary coils are not physically connected, hence the method is wireless. Transformers can be very efficient but the distance between the coils must be very small (typically a few millimeters). For distances a few times the size of the coils, the efficiency drops significantly. Part of the underlying physics for most of the existing methods for the wireless transfer of electricity is the fundamental principle of resonance: the property of certain physical systems to oscillate with maximum amplitudes at certain frequencies. It follows that, for any type of excitation (mechanic an l, acoustic, electromagnetic, nuclear) with a given frequency, a receiver will pick up the transmitted energy efficiently only when designed to resonate at the excitation frequency. Only then do successive excitations after each oscillation period add coherently in phase and lead to a buildup of energy within the receiver. To illustrate, consider 100 glasses filled with wine at different levels so that they acoustic resonances at different frequencies. Now let electric-guitar players produce and sustain a very well-defined note. Only one of the glasses, the one resonant with the frequency of this note, will respond to the excitation, to the extent that it may even break, while the rest will remain unaffected. Similarly, we tune the electromagnetic

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Antenna of a radio to be resonant with the frequency of the station we want to listen to. Many transformers used in power circuitry and elsewhere are also designed to employ resonance to enhance the power transmission.

3.6: Experimental Demonstration of Evanescent Coupling at MIT Based on their theory, they started experiments in late 2006.The main challenges consisted of deg a driving circuit that would operate in our desired low-MHz regime and constructing coils that would resonate with high enough value of Q. After a trial-and-error phase, they realized that a simple coil design without a separate capacitor, but using the coil’s self-capacitance to achieve resonance was best option in of Q. We made two copper-pipe coils with 60 cm diameters and with five turns, such that they resonate at 10MHz and have Q=1000. A 60 W light bulb was the chosen device, since it operates at tested frequencies (and what can be a clearer sign of the functionality of a system than the switch on of a light bulb?). They suspended the coils from the ceiling with fishing wire, at distance of 2m from each other, tuned them up, turned them on and…there was light. At an efficiency of 45%, this was, to our knowledge, the first-ever demonstration of midrange efficient wireless energy transfer.

Fig 3.3: Lightening a 60 Watt Bulb Around 2m Away From the Source at MIT

3.7: Far Field Theory Far field methods achieve longer ranges, often multiple kilometer ranges, where the distance is much greater than the diameter of the device(s). With radio wave and optical devices the main reason for longer ranges is the fact that electromagnetic radiation in the farfield can be made to match the shape of the receiving area (using high directivity antennas or well-collimated Laser Beam) thereby delivering almost all

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Emitted power at long ranges. The maximum directivity for antennas is physically limited by diffraction. The Raytheon Company did the first successful WPT experiment in 1963. In this experiment energy was transmitted with a DC-to-DC efficiency of 13%. This company also demonstrated a microwave-powered helicopter in 1964. The Jet propulsion lab of NASA carried out an experiment and demonstrated the transfer of 30 kW over a distance of 1 mile in 1975. They used an antenna array erected at the Goldstone facility. This test demonstrated the possibilities of wireless power outside the laboratory. Rockwell International and David Sarnoff Laboratory operated in 1991 a microwave powered rover at 5.86 GHz. Three kilowatts of power was transmitted and 500 watts was received. 3.8: Microwave Power Transmission (MPT) In order to transport electricity is has to be transformed into a suitable energy form. For wireless transmission, this has to be a form that can travel through air. Microwave frequencies hold this ability. The microwave spectrum is defined as electromagnetic energy ranging from approximately 1 GHz to 1000 GHz in frequency, but older usage includes lower frequencies. Most common applications are within the 1 to 40 GHz range. A complete microwave transmission system consists of three essential parts: •

Electrical power to microwave power conversion

•

Absorption antenna that captures the waves

•

(Re)conversion to electrical power

Fig 3.4: Microwave Transmitter and Retina The components include a microwave source, a transmitting antenna and a receiving antenna. The microwave source consists of an electron tubes or solid-state devices with electronics to control power output. The slotted waveguide antenna, parabolic dish and micro strip patch are the most popular types. Due to high efficiency (>95%) and high power handling capacity, the slotted waveguide antenna seems to be

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The best option for power transmission. The combination of receiving and converting unit is called retina. The retina is a rectifying antenna that is used to directly convert microwave energy into DC electricity. It is an antenna includes a mesh of dipoles and diodes for absorbing microwave energy from a transmitter and converting it into electric power. Its elements are usually arranged in a multi element phased array with a mesh pattern reflector element to make it directional. The Rayleigh criterion dictates that any beam will spread (microwave or laser), become weaker, and diffuse over distance. The larger the transmitter antenna or laser aperture, the tighter the beam and the less it will spread as a function of distance (and vice versa). Therefore, the system requires large transmitters and receivers. The used power density of the microwave beam is normally in the order of 100 W/m2. This is relative low compared to the power density of solar radiation on earth (1000 W/m2) and chosen this way for safety reasons.

Applications WPT for Space Solar The largest application for microwave power transmission is space solar power satellites (SPS). In this application, 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 electric it y. NASA is still investigating the possibilities of SPS. One of the problems is the high investment cost due to the space transport. The current rates on the Space Shuttle run between $7,000 and $11,000 per kilogram of transported material. Recently the idea of Space Solar Power caught again the public attention e.g. by the Osama transition team and The Economist.

Fig 3.5: Space Solar Power Satellite

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Power Transfer, Bridging Applications Using a powerful focused beam in the microwave or laser range long distances can be covered. There are two methods of wireless power transmission for bridging application. First is the direct method, from transmitting array to retina. A line of sight is needed and is therefore limited to short (< 40 km) distances. Above 40 kilometers, huge structures are needed to compensate for the curvature of the earth. The second method is via a relay reflector between the transmitter and retina. This reflector needs to be at an altitude that is visible for both transmitter and retina. Next one bridging applications of WPT are discussed.

Alaska '21 WPT can be an option for power supply to rural areas. In 1993 was a project presented about wireless power supply in Alaska. Because of limited infrastructure, hundreds of small rural communities in Alaska must provide their own electric it y. These systems can be expensive not standard or just not available. At the moment, the small communities produce their own power with mainly diesel engines. These produce noise and pollution. Also the needed fuel has to be transported over long distances. All this results in an electricity price in excess of $40 /kWh .Cable connections trough water is no option because of ice. With the help of WPT, the needed power production of the communities can be combined. This can reduce noise, pollution and transportation of fuel. WPT may be capable of transmitting electrical energy to Alaska’s remote villages. To investigate these possibilities, a pilot project was conducted named "Alaska'21”. The system used for the pilot project consisted of a2.45 GHz phased array design. The distances that should be bridged are between 1 and 15 miles. The status of the project is unknown.

Fig 3.6 :( Alaska’21).

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Safety Issues Bio-Effects A general public perception that microwaves are harmful has been a major obstacle for the acceptance of power transmission with microwaves. A major concern is that the long-term exposure to low levels of microwaves might be unsafe and even could cause cancer. Since 1950, there have been thousands of papers published about microwave bio-effects. The scientific research indicates that heating of humans exposed to the radiation is the only known effect. There are also many claims of low-level non thermal effects, but most of these are difficult to replicate or show unsatisfying uncertainties. Large robust effects only occur well above exposure limits existing anywhere in the world. The corresponding exposure limits listed in IEEE standards at 2.45 or 5.8 GHz are 81.6 W/m2 and 100 W/m2 averaged over 6 minutes, and 16.3 or 38.7 W/m2 averaged over 30 minutes.

Fig 3.7: Graph Showing Safety Level to Different Range Of Frequencies

This low compared to average solar radiation of 1000 W/m2. A clearly relevant bioeffect is the effect of microwave radiation on birds, the so-called "fried

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Bird effect". Research is done on such effect at 2.45 GHz. The outcome showed slight thermal effects that probably are welcome in the winter and to be avoided in the summer. Larger birds tend to experience more heat stress then small birds. The overall conclusion of bioeffects research is that microwave exposures are generally harmless except for the case of penetrating exposure to intense fields far above existing exposure limits.

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CHAPTER 4 Transmitters, Antennas and Receivers 4.1: Antennas for Microwave Power Transmission All antennas can be applied for both the MPT system and communication systems, for example, Yogi Due antenna, horn antenna, parabolic antenna, micro strip antenna, phased array antenna or any other type of antenna. To fixed target of the MPT system, we usually select a large parabolic antenna, for example, in MPT demonstration in 1975 at the Venus Site of JPL Goldstone Facility and in ground to ground MPT experiment in 1994-95 in Japan. In the fuel free airship light experiment with MPT in 1995 in Japan, they changed a direction of the parabolic antenna to chase the moving airship. In some MPT experiments in Japan, the phased array antenna was adopted to steer a direction of the microwave beam (FIG. 4.1). All SPS is designed with the phased array antenna.

Fig 4.1: Phased Array Used In Japanese Field MPT Experiment 4.2: Recent Technologies for Transmitters The technology employed for generation of microwave Radiation is an important subject for the MPT system. We need higher efficient generator/amplifier for the MPT system than that for the wireless communication system. For highly efficient beam collection on retina array, we need highly stabilized and accurate phase and amplitude of microwaves for phased array system for the MPT .There is two types of

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Microwave generators/amplifiers. One is a microwave tube (magnetron) and the other is semiconductor amplifier. 4.3: Magnetron Magnetron is a crossed field tube in which electrons emitted from the cathode take cyclical path to the anode. The magnetron is self-oscillatory device in which the anode contains a resonant RF structure. The magnetron has long history from invention by A. W. Hull in 1921. The practical and efficient magnetron tube attracted worldwide interest only after K. Okabe proposed divided anode type magnetron in 1928. Magnetron technologies received a boost during the World War II, especially with the Japanese Army. The magnetrons were also useful for microwave ovens. As a result, the magnetron of 500 – 1,000 W is widely in use for microwave ovens in 2.45 GHz, and is a relatively inexpensive oscillator (below $5). There is a net global capacity of 45.5GW/year for all magnetrons used in microwave ovens whose production is 50– 55 millions. It was W. C. Brown who invented a voltage controlled oscillator with a cooker type magnetron in PLL. 4.4: Semiconductor Amplifier After 1980s, semiconductor devices became dominant in microwave world instead of the microwave tubes. This was driven by advances in mobile phone networks. The semiconductor device is expected to Expand microwave applications, for example, phased array and active integrated antenna (AIA), because of its manageability and mass productivity. After 1990s, some MPT experiments were carried out in Japan with phased array of semiconductor amplifiers . Typical semiconductor devices for microwave circuits are FET (Field Effect Transistor), HBT (Hetero junction Bipolar Transistor), and HEMT (High Electron Mobility Transistor). Present materials for the semiconductor devices are Si for lower frequency below a few GHz and Gas for higher frequency. It is easy to control phase and amplitude through the microwave circuits with semiconductor devices, for example, amplifiers, phase shifters, modulators, and so on. Currently, new materials are under development to enable semiconductor devices yield increased output power and efficiency.

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4.5: Wireless Power Transmission – Receivers and Rectifiers Point to point MPT system needs a large receiving area with a retina array because one retina element receives and creates only a few W. Especially for the SPS, we need a huge retina site and a power network connected to the existing power networks on the ground. On contrary, there are some MPT applications with one small retina element such as RF ID. Recent Technologies of Retina The word “retina” is composed of “rectifying circuit” and “antenna”. The retina can receive and rectify a microwave power to DC. The retina is ive element with a rectifying diode, operated without any power source. The circuit, especially diode, mainly determines the RF DC conversion efficiency. Silicon Scotty barrier diodes were usually used for earlier retina. New devices like Sic and Gann are expected to increase the efficiency. The retina with FET or HEMT appeared recently. The single shunt full wave rectifier is always used for the retina. It consists of a diode inserted in the circuit in par all, a λ/4 distributed line, and a capacitor inserted in parallel. In an ideal situation, 100% of the received microwave power should be converted into DC power. Recent Technologies of Retina Array The retina will be used as an array for high power MPT because one retina element rectifies a few W only. For usual phased array antenna, mutual coupling and phase distribution are problems to solve. For the retina array, problem is different from that of the array antenna because the retina array is connected not in microwave phase but in DC phase. When we connect two retina in series or in parallel, they will not operate at their optimum power output and their combined power output will be less than that if operated independently. This is theoretical prediction. Efficiency We classify the MPT efficiency roughly into three stages; •

DC RF conversion efficiency which includes losses caused by beam forming.

•

Beam collection efficiency which means ratio of all radiated power to collected power on a receiving antenna, and

•

RF DC conversion efficiency.

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RF DC Conversion Efficiency The RF DC conversion efficiency of the retina or the CWC is over 80 % of experimental results as shown. Decline of the efficiency is caused by array connection loss, change of optimum operation point of the retina array caused by change of connected load, trouble of the retina, and any losses on the systems, for example, DC/AC conversion, cables, etc. However, it is easier to realize higher efficiency than that on the other two Beam Collection Efficiency The beam collection efficiency depends on the transmitter and receiver aperture areas, the wavelength, and the separation distance between the two antennas.

Fig 4.2: Efficiency of Retina Element.

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CHAPTER 5 Recent Technological Trends There are several technological trends which are going to be concerned for wireless power transmission which are as follows: 5.1: Retro Directive Beam Control A microwave power transmission is suitable for a power transmission from/to moving transmitters/targets. Therefore, accurate target detection and high efficient beam forming are important. Retro directive system is always used for SPS. A corner reflector is most basic retro directive system. The corner reflectors consist of perpendicular metal sheets, which meet at an apex. Incoming signals are reflected back in the direction of arrival through multiple reflections off the wall of the reflector. Van Atta array is also a basic technique of the retro directive system. This array is made up of pairs of antennas spaced equidistant from the centre of the array, and connected with equal length transmission lines. The signal received by an antenna is re-radiated by its pair, thus the order of re-radiating elements are inverted with respect to the centre of the array, achieving the proper phasing for retro directivity. Usual retro directive system

have phase

conjugate circuits in each

receiving/transmitting antenna, which play same role as pairs of antennas spaced equidistant from the centre of the array in Van Atta array. The signal is called a pilot signal. We do not need any phase shifters for beam forming. The retro directive system is usually used for satellite communication, wireless LAN, military, and so on. 5.2: Environmental Issues One of the characteristics of the MPT is to use more intense microwave than that in wireless communication systems. Therefore, we have to consider MPT safety for humans. Interaction with Atmosphere In general, effect of atmosphere on microwaves is quite small. There are absorption and scatter by air, rain, and irregularity of air refraction ratio. In 2.45 GHz

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and 5.8 GHz, the absorption by water vapor and oxygen Dominate the effect in the air. Especially, it is enough to consider only absorption by the oxygen in the microwave frequency. It is approximately 0.007 dB/km. In the SPS case, the amount of total absorption through the air from space is approximately 0.035 dB. 5.3: Interaction with Space Plasmas When microwaves from SPS propagate through ionosphere plasmas, some interaction between microwaves and the ionosphere plasmas occurs. It is well known that refraction, Faraday rotation, scintillation, and absorption occur between weak microwave used for satellite communication and the plasmas. However, influence on the MPT system is negligible. It is nonlinear interaction between intense microwave and the space plasmas that we have to investigate before the commercial SPS. We theoretically predict that the following may occur: heating of the plasmas, plasma hall effect, thermal self-focusing effect of the microwave beam, and three wave interactions and excitation of electrostatic waves in MHz bands. These interactions don’t occur in existent satellite communication systems because microwave power is very weak. Generating power by placing satellites with giant solar arrays in Geosynchronous Earth Orbit and transmitting the power as microwaves on the earth called Solar Power Satellites (SPS) will be the largest application of WPT.

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CHAPTER 6 Applications, Advantages and Future 6.1: Applications WPT wireless power transfer technology can be applied in a wide variety of applications and environments. The ability of our technology to transfer power safely, efficiently, and over distance can improve products by making them more convenient, reliable, and environmentally friendly. WPT technology can be used to provide: Automatic Wireless Power Charging When all the power a device needs is provided wirelessly, and no batteries are required. This mode is for a device that is always used within range of its WPT power source. When a device with rechargeable batteries charges itself while still in use or at rest, without requiring a power cord or battery replacement. This mode is for a mobile device that may be used both in and out of range of its WPT power source. Consumer Electronics Automatic wireless charging of mobile electronics (phones, laptops, game controllers, etc.) in home, car, office, We If hotspots, while devices are in use and mobile. Direct wireless powering of stationary devices (flat screen TV‘s, digital picture frames, home theater accessories, wireless loud speakers, etc.) eliminating expensive custom wiring, unsightly cables and wall wart power supplies. Direct wireless powering of desktop PC peripherals: wireless mouse, keyboard, printer, speakers, display, etc… eliminating disposable batteries and awkward cabling. 6.2: Industrial Direct wireless power and communication interconnections across rotating and moving ts (robots, packaging machinery, assembly machinery, machine tools) … eliminating costly and failure prone wiring. Direct wireless power and communication interconnections at points of use in harsh environments (drilling, mining, underwater, etc.) … where it is impractical or impossible to run wires.

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Wireless sensors and actuators, eliminating the need for expensive power wiring or battery replacement and disposal. 6.3: Transportation Automatic wireless charging for existing electric vehicle classes: golf carts, industrial vehicles. Automatic wireless charging for future hybrid and all electric enger and commercial vehicles, at home, in parking garages, at fleet depots, and at remote kiosks. Direct wireless power interconnections to replace costly vehicle wiring harnesses and slip rings.

Other Applications a) Direct wireless power interconnections and automatic wireless charging for implantable medical devices (ventricular assist devices, pacemaker, defibrillator, etc.). b) Automatic wireless charging and for high tech military systems (battery powered mobile devices, covert sensors, unmanned mobile robots and aircraft, etc.). c) Direct wireless powering and automatic wireless charging of smart cards.

Advantages and Disadvantages There are so many advantages with this WPT concept, some of those are: d) Unaffected by the day night cycle, weather or seasons. e) This is an ecofriendly. f) It is a boon for the devices which use midrange power. g) At places where economic competition is not the prime consideration, it can be an option. Wireless power transmission can supply power to places that are difficult to reach. Especially small communities in rural areas could be supplied with power using WPT. h) First of all the wireless electrical transmission of data removes the need for physical infrastructure like grids and towers. In this way the cost associated with deploying towers and cables can be saved.

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i)

During the rains and after natural disasters it is often hard to manage the cables and towers .by using WPT technology this problem can be eliminated.

j)

The transmission and distribution loss associated with traditional electricity grids can be overcome.

k) Today two words are ruling the world “efficiency” and “speed”. These two words have become the base for the development in the technology. l)

The electricity generation using microwaves is more environments friendly. Moreover it does not involve any emission of carbon gases.

m) The monthly electricity bills using conventional electricity supply can be cut to very low. n) Use of battery for charging electrical and electronics devices can totally be eliminated. Some of the disadvantages are as follows: 1. High capital cost for practical implementation of wireless power transmission. 2. Another potential disadvantage is the interference of the microwaves with the present wireless communication system. 3. The effect of microwave radiations at high doses received is not suitable to human health.

Safety and Future Scope Is WPT Technology Safe? WPT technology is a non radioactive mode of energy transfer, relying instead on the magnetic near field. Magnetic fields interact very weakly with biologic a l organism’s people and animals and are scientifically regarded to be safe. Professor Sir John Penury of Imperial College London, a world renowned physicist, explains: The body really responds strongly to electric fields, which is why you can cook a chicken in a microwave. But it doesn't respond to magnetic fields. As far as we know the body has almost zero response to magnetic fields in of the amount of power it absorbs." Evidence of the safety of magnetic fields is illustrated by the widespread acceptance and safety of household magnetic induction cook tops. Through proprietary design of the WPT source, electric fields are almost completely contained within the source.

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Risk to people or animals. Limits for human exposure to magnetic fields are set by regulatory bodies such as the FCC, ICNIRP, and are based on broad scientific and medical consensus. Future Scope of WPT MIT's WPT is only 40 to 45% efficient and according to Solace, they have to be twice as efficient to compete with the traditional chemical batteries. The team's next aim is to get a robotic vacuum or a laptop working, charging devices placed anywhere in the room and even robots on factory floors. The researchers are also currently working on the health issues related to this concept and have said that in another three to five years’ time, they will come up with a WPT system for commercial use. WPT, if successful will definitely change the way we live. Imagine cell phones, laptops, digital camera's getting self-charged! Wow! Let's hope the researchers will be able to come up with the commercial system soon. Till then, we wait in anticipation! Human beings or other objects placed between the transmitter and receiver do not hinder the transmission of power. However, does magnetic coupling or resonance coupling have any harmful effects on humans? MIT's researchers are quite confident that WPT's 'coupling resonance' is safe for humans. They say that the magnetic fields tend to interact very weakly with the biological tissues of the body, and so are not prone to cause any damage to any living beings.

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CONCLUSION Today we do live in the “wireless age”, in which the air that we breathe probably contains more information than oxygen. However, this is also an age where mobile phones, MP3 players, laptop computers and domestic robots exist alongside old-fashioned power wires and bulky batteries. Unlike information, electrical energy is still physically confined to these borderline anachronistic appliances. Overcoming these last obstacles would finally make this a truly wireless world. Transfer of power via microwaves has long been the focus of study and experimentation. In the early 1900s, Nikola Tesla experimented with transmission of power wirelessly,

through

microwaves.

His work, however, was largely left

unimplemented, as his experiments were vastly ahead of their time and the technology did not yet exist to make WPT via microwaves feasible. Advances in wireless technologies since Tesla, however, have made possible that which was not in the early 20th century. Described in this section are the details of those technologies behind MPT as a mechanism for WPT.

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REFERENCES 1. Tesla, N. “Apparatus for transmitting electrical energy.” U.S. patent number 1,119,732, issued in December 1914. 2. Ka-Lai, L., Hay, J. W. and Beard, P. G. W. “-less power transfer.” U.S. patent number 7,042,196, issued in May 2006. (Splash Power Ltd., www.splashpower.com) 3. Hirai, J., Kim, T.-W. And Kawamura, A. “Wireless transmission of power and information and information for cable less linear motor drive.” IEEE Trans. on power electronics 15, 21 (2000). 4. G. Landis and R. Cull , “Integrated Solar Power Satellites: An Approach to LowMass Space Power, “Space Power, Vol. 11, No. 3–4, 303–218 (1992); presented at SPS-91: Power From Space, Aug. 27–30, 1991, Paris , pp. 225–232 5. www.WPT.com 6. http://www.cse.wustl.edu/~jain/cse574-14/ftp/power.pdf } 7. Electricity Flow Chart 1999, which contains US DOE/EIA data, updating the Toby Grosz article in this book.) 8. http://ijtir.hctl.org/vol8/IJTIR_Article_201403012.pdf 9. http://www.seminarreports.in/2014/09/wireless-electricity-or-witricity.html 10. http://www.collegelib.com/t-witricity-wireless-electricity-seminar-abstractreport.html

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