CONTENTS

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1.INTRODUCTION......................................................32.HISTORY.......................... 43.CLASIFICATION..5 3.1FAR-FIELD TECHNOLOGY............................ 5 3.2NEAR-FILELD TECHNOLOGY...................... 64.ADVANTAGES AND DISADVANTAGES........... 105.APPLICATION.........................................................126.COMPONENTS....................................................... 137.CONCLUSION.148.REFRANCES....15

ABSTRACT

We cannot imagine the world without electric power. Generally the power istransmitted through wires. This paper describes an original idea to eradicate the hazardous usage of electrical wires which involve lot of confusion in particularly organizing them. Imagine a future in which wireless power transfer is feasible: cell phones, household robots, mp3 players, laptopcomputers and other portable electronics capable of charging themselves without ever being plugged in, freeing us from that final, ubiquitous power wire. Some of these devices might not even need their bulky batteries to operate. This paper includes the techniques of transmitting power withoutusing wires with an efficiency of about 95% with non-radiative methods. Due to which it does not effect the environment surrounding. These techniques Includes resonating inductive coupling in sustainable moderate range. The coupling consists of an inductor along with a capacitor with its own resonating frequency. In any system of coupled resonators there often exists a so-called strongly coupled regime of operation. If one ensures to operate in that regime in a given system, the energy transfer can be very efficient. Another technique includes transfer of power through microwaves using rectennas.This is particularly suitable for long range distances ranging kilometers. With this we can avoid the confusion and danger of having long, hazardous andtangled wiring. This paper as a whole gives an effective, high performancetechniques which can efficiently transmit the power to the required areavarying in distances . .There are two type of technologys can be used in the case of wireless power transmission.They are,

Far-Field Techniques Microwave Power Transmission (MPT) LASER Power Transmission

Near-field techniques Inductive Coupling Resonant Inductive Coupling Air Ionization

Key Words Microwave Power transmission (MPT), Nikola Tesla, Rectenna, Solar Power Satellites (SPS), Wireless Power transmission (WPT).

1.INTRODUCTION

The area of wireless power transmission is veryinteresting. The technology is in its infancy but the overall benefits from its maturation could be significant to society as a whole. World population is expected to continue to grow exponentially. All of these trends point to an energy demand that will grow at even a larger rate. Wireless power transmission could one day allow us to generate solar power on a satellite and beam it down to Earth, transmit power toa water treatment plant for a disaster relief operation or power a flying communication relay station from a terrestrial station. There are a few engineering hurtles yet to overcome to make this technology suitable for todays investors, Especially the transmission and distribution losses are the main concern of the present power technology. Much of this power is wasted during transmission from power plant generators to the consumer. The resistance of the wire used in the electrical grid distribution system causes a loss of 26- 30% of the energy generated. This loss implies that our present system of electrical distribution is only 70-74% efficient. The main reason for power loss during transmission and distribution is the resistance of wires used for grid. The efficiency of power transmission can be improved to certain level by using high strength composite over head conductors and underground Cables that use high temperature super conductor. but, the transmission is still inefficient. According to the World Resources Institute (WRI), Indias 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 (grids inefficiencies) and theft.We have to think of alternate state - of - art technology to transmit and distribute the electricity. Now- a- days global scenario has been changed a lot and there are tremendous development in every field. If we dont keep pace with the development of new power technology we have toface a decreasing trend in the development of power sector.

2.HISTORY

Nikola Tesla,who invented radio and shown us is indeed as the Father of Wireless. Nikola Tesla was 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. In 1893, Tesla demonstrated the illumination of vacuum bulbs without using wires for power transmission at the World Columbian Exposition in Chicago. The worlds 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). 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 in 2007 .In 2008, Intel reproduced the MIT group's experiment by wirelessly powering a light bulb with 75% efficiency at a shorter distance. MIT team experimentally demonstrates wireless power transfer,potentially useful for powering laptops, cell phones without any cords. Imagine a future in which wireless power transfer is feasible: cell phones, household robots, mp3 players, laptop computers and other portable electronics capable of charging themselves without ever being plugged in, freeing us from that final, ubiquitous power wire. Some of these devices might not even need their bulky batteries to operate.A team from MIT's Department of Physics,Department of Electrical Engineering and Computer Science, and Institute for Soldier Nanotechnologies (ISN) has experimentally demonstrated an important step toward accomplishing this vision of the future. Realizing their recent theoretical prediction, they were able to Light a 60W light bulb from a power source seven feet. (more than two meters) away, there was no physical connection between the source and the appliance. The MIT team refers to this concept as "WiTricity" .

3.CLASSIFICATION

Based on the distance between the transmitter and receiver we can classified the wireless power transmission as,

1) Far-Field Techniques2) Near-Field Techniques

1.FAR-FIELD TECHNOLOGYS

Far-field thechnology is a one kind of wireless power transmission.This technologys can be used for log-range wireless power transmission.Far-field technologys mainly contain two type power transmissions.They are,

Microwave Power Transmission (MPT) LASER Power Transmission

Microwave Power Transmission (MPT)

With this method a long range is possible. In this method microwave is sent to the long distances and can be received through rectenna which extract microwave energy back to electrical energy. But the problem with this method is that the diameter of antenna should be order of kilometer.a microwave beaming system was developed to realize wireless power supplay.this system consist of transmitting,tracking and reciving systems.in the transmitting system,a 5.8GHz microwave beam was irradiated from an active phased array antinna.

Working of Microwave Power Transmission in simple words

AC is converted to DC first DC is converted to microwaves using magnetron Electrical energy to microwave energy Capturing microwaves using rectenna Microwave energy to electrical energy Transmitted waves are received at rectenna which rectifies, gives DC as the output DC is converted back to AC

Rectenna: Stands for rectifying antenna Consists of mesh of dipoles and diodes Converts microwave to its DC equivalent Usually multi-element phased array

Laser Power Transmission

In this method, laser is beamed to the photo voltaic cells which extract the electrical energy. This very difficult to implement and manage.the laser method of energy transfer involves shining a laser beam onto a photovoltaic receiver.this requires the ability to precisely track the position of the receiver relative to the laser transmission.recent experiments using commercially obtainable laser sources have generated over 7.2 watts of photovoltaic output from a 70 watts laser beam.This corresponds to a power density of 13.6 watts per squre centimeter of reciver area,as well as a 28% optical to electrical conversion effiency,which is promising for real applications if the experimental result can be scaled to larger systems.

2.NEAR-FIELD TECHNIQUES

Near-field thechnology is a one kind of wireless power transmission.This technologys can be used for short-range wireless power transmission.Near-field technologys mainly contain two type power transmissions.They are,

Inductive Coupling Resonant Inductive Coupling Air Ionization

Inductive Coupling

Inductive coupling occurs when an energy source has means of transferring entering energy to another object .one simple example is a iocomotive pulling a train car the mechanical coupling between the two enables the locomotive to pull the train, and over come the forces of friction and inertia that keep the train still-and,the train moves ,inductive coupling occurs when the magnrtic field of one object intract with a second object and includes an electric current or on that object.in this way,electric energy can be transferd from a power source to a powered device.In contrast to the example of inductive coupling given for the train ,inductive coupling does not require any physical contact between the object reciveing that energy..

Working of inductive coupling in simple words

Primary and secondary coils are not connected with wires. Energy transfer is due to Mutual Induction Wireless Charging Pad(WCP) ,Electric Brushes are some examples.

Ronant Inductive Coupling

Magnetic coupling occurs when two objects exchange energy through their varying or oscillating magnetic fields. Resonant coupling occurs when the natural frequencies of the two objects are approximately the same. WiTricity power sources and capture devices are specially designed magnetic resonators that efficiently transfer power over large distances via the magnetic near-field. The proprietary source and device designs and the electronic systems the control them support efficient energy transfer over distances that are many times the size of the sources/devices themselves. At first glance, WiTricity technology for power transfer appears to be traditional magnetic induction, such as is used in power transformers, where conductive coils transmit power to each other wirelessly, over very short distances. In a transformer, an electric current running in a sending coil (or primary winding) induces another current in a receiving coil (or secondary winding). The two coils must be very close together, and may even overlap, but the coils do not make direct electrical contact with each other. However, the efficiency of the power exchange in traditional magnetic induction systems drops by orders of magnitude when the distance between the coils becomes larger than their sizes. In addition to electric transformers, other devices based on traditional magnetic induction include rechargeable electric toothbrushes, and inductive charging pads which require that the object being charged be placed directly on top of, or very close to, the base or pad supplying the power.

Resonant Inductive Coupling in simple words

The capacitor and inductor forms the resonator. Charge oscillates between inductor (as magnetic field) and capacitor (as electric field.) This type of oscillation is called resonance if the reactance's of the inductor and capacitor are equal.

HOW RESONANCE IN RESONANCE INDUCTIVE COUPLING??

Coil provides the inductance Capacitor is connected parallel to the coil Energy will be shifting back and forth between magnetic field surrounding the coil and electricfield around the capacitor. Radiation loss will be negligible

Air Ionization

Toughest technique under near-field energy transfer techniques Air ionizes only when there is a high field Needed field is 2.11MV/m Natural example: Lightening Not feasible for practical implementation

4.ADVANTAGES AND DISADVANTAGES

Far Field Technology

Advantages Efficient , Easy Need for grid eliminated Low maintenance cost More effective when the transmitting and receiving points are along a line-of-sight Can reach the places which are remote

Disadvantages:

Radiate When LASERs are used,conversion is inefficient Absorption loss is high When microwaves are used,interference may aris

Near-Field Techniques

Advantages:

No wire, No e-waste Need for battery eliminated Efficient & Harmless Disadvantages:

Distance constraint Field should be under safety level High initial cost Tuning is difficult in RIC

4.1 Biological Impacts

Common beliefs fear the effect of microwave radiation. But the 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 higherthan the emissions created by cellular telephones[17]. Cellular telephones operate with power densities at or below the ANSI/IEEE exposure standards [18]. Thus public exposure to WPT fields would also be below existing safety guidelines.

5.APPLICATION

Generating power by placing satellites with giant solar arrays in Geosynchronous Earth Orbit and transmitting the power as microwaves to the earth known as Solar Power Satellites (SPS) is the largest application of WPT. Another application of WPT is moving targets such as fuel free airplanes, fuel free electric vehicles, moving robots and fuel free rockets. The other applications of WPT are Ubiquitous Power Source (or) Wireless Power Source, Wireless sensors and RF Power Adaptive Rectifying Circuits (PARC).

Near-field energy transfer

Electric automobile charging Static and moving Consumer electronics Industrial purposes Harsh environment

Far-field energy transfer

Solar Power Satellites Energy to remote areas Can broadcast energy globally (in future)

Functional Block Diagram of Wireless Power Transmission System

6. COMPONENTS OF WPT SYSTEM

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

6.1 Microwave Genarator 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 (GaAs MESFET, GaN pHEMT, SiC MESFET, AlGaN/GaN HFET, and InGaAS). Magnetron is widely used for experimentation of WPT. The microwave transmission often uses 2.45GHz or 5.8GHz of ISM band. The other choices of frequencies are 8.5 GHz , 10 GHz and 35 GHz . The highest efficiency over 90% is achieved at 2.45 GHz among all the frequencies.

6.2 Transmitting Antenna

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

6.3 Rectenna

The concept, the name rectenna and the rectenna was conceived by W.C. Brown of Raytheon Company in the early of 1960s . The rectenna is a passive element consists of antenna, rectifying circuit with a low pass filter between the antenna and rectifying diode. The antenna used in rectenna may be dipole, Yagi Uda, microstrip or parabolic dish antenna. The patch dipole antenna achieved the highest efficiency among the all. The performance of various printed rectenna is shown in Table I. Schottky barrier diodes (GaAs-W, Si, and GaAs) are usually used in the rectifying circuit due to the faster reverse recovery time and much lower forward voltage drop and good RF characteristics.

7. CONCLUSION The concept of Microwave Power transmission (MPT) and Wireless Power Transmission system is presented. The technological developments in Wireless Power Transmission(WPT), the advantages, disadvantages, biological impacts andapplications of WPT are also discussed.This concept offers greater possibilities for transmitting power with negligible losses and ease of transmission than any invention or discovery heretofore made. Dr. Neville of NASA states You dont need cables, pipes, or copper wires to receive power. We can send it to you like a cell phone call where you want it, when you want it, in real time. We can expect with certitude that in next few years wonders will be wrought by its applications if all theconditions are favourable.

8. REFERENCES

[1] http://cleantechindia.wordpress.com/2008/07/16/indiaselectricity- transmission-and-distribution-losses/[2] Nikola Tesla, My Inventions, Ben Johnston, Ed., Austin, Hart Brothers, p. 91,1982.[3] Nikola Tesla, The Transmission of Electrical Energy Without Wires as a Means for Furthering Peace, Electrical World and Engineer. Jan. 7, p. 21, 1905.[4] The Electrician (London), 1904).[5] W.C. Brown, J.R. Mims and N.I. Heenan, An Experimental Microwave-Powered Helicopter, 965 IEEE International Record, Vol. 13, Part 5, pp.225-235.[7]POINT-TO-POINT WIRELESS POWERTRANSPORTATION IN REUNION ISLAND 48th International Astronautical Congress, Turin, Italy, 6-10 October 1997 - IAF-97-R.4.08 J. D. Lan Sun Luk, A. Celeste, P. Romanacce, L. Chane Kuang Sang, J. C. Gatina - University of La Runion - Faculty of Science and Technology. [8] Matsumoto, H.N. Kaya, I. Kimura, S. Miyatake, M. Nagatomo, and T. Obayashi, MINIX Project toward the SolarPower Satellites --- Rocket experiment of microwave energy transmission and associated plasma physics in the ionosphere, ISAS space energy symposium, pp 69-76, 1986. [9] J.J. Schelesak, A. Alden and T. Ohno, A microwave powered high altitude platform, IEEE MTT-S Int. Symp. Digest, pp - 283-286, 1988.[10] "CES Best of 2007"[11] "Goodbye wires". MIT News. 2007-06-07. http://web.mit.edu/newsoffice/2007/wireless-0607.html.[12] www.tgdaily.com[13] L.W. Epp, A.R. Khan, H.K. Smith, and R.P. Smith, A compact dual-polarized 8.51-GHz rectenna for high-voltage (50 V) actuator applications, IEEE Trans. Microwave Theory Tech., vol. 48, pp. 111-120, 2000.

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