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  1. 1. Senthil Nathan.M1, Pandiarajan.K / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 3, Issue 1, January -February 2013, pp.1125-1130 A Review Of Wireless Power Transmission Senthil Nathan.M1, Pandiarajan.K2 1 Student, II year Electronics & Communication,Karpagam College of Engineering,Coimbatore,India. 2 Student, II year Electronics & Communication,Karpagam College of Engineering,Coimbatore,India.ABSTRACT In the present article some of the latest 1891[2].In 1893, Tesla demonstrated theadvances and the concept of transmitting power illumination of vacuum bulbs without using wireswithout wires are reviewed.The methods applied for power transmission at the World Columbianfor the wireless power transmission such as - Exposition in Chicago. The Wardenclyffe towerinduction, electromagnetic transmission, radio shown in Figure 1 was designed and constructed byand microwave and evanescent wave coupling Tesla mainly for wireless transmission of electricalare discussed here. Furthermore, the various power rather than telegraphy [1].technologies available so far for wireless Tesla wanted to make use of the Niagaratransmission of electricity and the need for a Falls to transmit electricity from this Tower to thewireless system of energy transmission is whole globe without wires using the Ionosphere [1].presented.The study also focuses on the latest The most popular concept known is Tesla Theory intechnologies, merits, demerits and economical which it was firmly believed that Wardenclyffe, asaspects in this field. shown in figure 1, would permit wireless transmission and reception across large distancesI. INTRODUCTION with negligible losses [2]. But it was so unfortunate One of the major issues in power system is that people of that century was not in a position tothe losses during the transmission and distribution of recognize his splendid work.electrical energy. As the demand increases day byday, the power generation increases and the powerlosses during transmission is also increased. In thepresent electricity generation system more than halfof our resources are wasted due to the variousreasons particularly during transmission. Theresistance of the wire used in the electrical griddistribution system causes a loss of 26-30% of theenergy generated. This loss implies that the presentsystem of is only 70-74% efficient. We have tothink of Hence, an alternate technology to transmitand distribute the electricity is to developed Fig.1. 187-foot Wardenclyffe Tower (Tesla[3].Using a wireless system for the transmission of Tower)electricity is a prominent method to increase theefficiency. Wireless power transmission(WPT) is the III. METHODS OF WIRELESS POWERmethod of transmitting the power from one place to TRANSMISSIONanother without the means of wires through A. MICROWAVE METHOD (MPT)atmosphere or vacuum. This can be used for Power transmission via radio waves can beapplications where either an instantaneous amount made more directional, allowing longer distanceor a continuous delivery of energy is needed, but power beaming, with shorter wavelengths ofwhere conventional wires are unaffordable, electromagnetic radiation, typically in theinconvenient, expensive, hazardous, unwanted or microwave range.impossible. There are various methods of powertransmission which are discussed further in the COMPONENTS OF MPTfollowing sections William C. Brown, the pioneer in wireless power transmission technology has designed,II . WIRELESS POWER TRANSMISSION developed a unit and demonstrated to show howA. TESLA THEORY power can be transferred through free space by Nikola Tesla, the father of wireless, microwaves. The concept of Wireless Powerinvented the radio. He conceived the idea of Transmission System is explained with functionalwireless power transmission and demonstrated thetransmission of electrical energy without wires thatdepends upon electrical conductivity as early as 1125 | P a g e
  2. 2. Senthil Nathan.M1, Pandiarajan.K / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 3, Issue 1, January -February 2013, pp.1125-1130 stress caused by a thermal gradient). But it has many drawbacks such as: 1. Conversion to light, such as with a laser, is moderately inefficient 2. Conversion back into electricity is moderately inefficient, with photovoltaic cells achieving 40%-50% efficiency 3. This method requires a direct line of sight with the target. However, it is argued that due to recent advances in direct solar pumped lasers,laser-based wireless power transmission concepts should be matured further in order to represent a credibleFig 2. Flow and components of Wireless power alternative.System block diagram shown in Figure 2 [3]. In thetransmission side, the microwave power sourcegenerates microwave power and the output power iscontrolled by electronic control circuits. The waveguide ferrite circulator which protects themicrowave source from reflected power isconnected with the microwave power sourcethrough the Coax Waveguide Adaptor. The tunermatches the impedance between the transmittingantenna and the microwave source. The attenuatedsignals are then separated based on the direction ofsignal propagation by Directional Coupler. Thetransmitting antenna radiates the power uniformly fig. 3: fully laser powered autonomous rover.through free space to the rectenna. In the receiving side, a rectenna receives C. INDUCTIVE COUPLINGthe transmitted power and converts the microwave Inductive coupling uses magnetic fieldspower into DC power.The rectifying circuit consists that are a natural part of currents movement throughof Schottky barrier diodes which converts the wire. When electrical current moves through a wire,received microwave power into DC power. it creates a circular magnetic field around the wire. Bending the wire into a coil amplifies the magnetic field. The more the loops the coil makes, the biggerB. ELECTROMAGNETIC TRANSMISSION Lasers generate phase-coherent the field will be generated. When the coil of wire iselectromagnetic radiation at optical and infrared introduced in the magnetic field already generated,frequencies from external energy sources by the field can induce a current in the wire. In generalpreferentially pumping excited states of a “lasant" to in inductive coupling method, it consists of twocreate an inversion in the normal distribution of coils of wire which are close enough to each otherenergy states. Photons of specific frequency emitted such that they act like a weakly coupled air-coreby stimulated emission enter and are amplified as transformer. Coiling must be tight to achieve highstanding waves in a resonant optical cavity. The efficiency.most efficient DC-to-laser converters are solid-statelaser diodes commercially employed in optic andfree-space laser communication [8].Alternatively,direct solar-pumping laser generation has a majoradvantage over conventional solid state or gaslasers, which rely on the use of electrical energy togenerate laser oscillation since the generation ofelectricity in space implies automatically a system Fig 4.Induction Coupling Block Diagramlevel efficiency loss of roughly 60%. To generate alaser beam by direct solar pumping, solar energy D. RESONANCE INDUCTIVE COUPLINGneeds to be concentrated before being injected into (EVANESCENT WAVE COUPLING)the laser medium. The required concentration ratio It is a combination of inductive couplingis dependent on the size of the laser medium, the and resonance.Resonance improves the efficiencyenergy absorption ratio and the thermal shock by tunneling magnetic field to a receiver coil whichparameter (weakness of the material to internal 1126 | P a g e
  3. 3. Senthil Nathan.M1, Pandiarajan.K / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 3, Issue 1, January -February 2013, pp.1125-1130resonates at the same frequency.When resonant using so many panels requires power transmissioncoupling is used the two inductors are technology with high precision phase control at atuned to a mutual frequency and the input current is target level of less than 100 for economic viabilitymodified from sinusoidal to non sinusoidal and safety. Mitsubishi Heavy Industries isrectangular or transient waveform so as to drive the developing two transmission-controlsystem more aggressively. technologies:the position and angle correction A capacitance plate which can hold a (PAC) and parallel methods [6]. In the PAC method,charge attaches to each end of the coil. As electricity the unique position gap of each panel is estimatedtravels through this coil the coil begins to resonate. by comparing the reaching-phase angle of pilot-Its resonant frequency is a product of the inductance signal from Earth,and the microwave beam phaseof the coil and the capacitance of the plate [4]. angle is corrected accordingly. In the parallelUnlike multiple layer secondary of non-resonant method, microwave phase modulation occurs attransformer single layer solenoids with closely each panel. When the phase-modulated microwavespaced capacitor plates on each end as shown in is compared to a reference signal at the rectenna, thefigure 5 is used as transmitter and receiver. resulting phase deviation is equivalent to the modulation frequency output. Based on this principle, the phase deviation for each panel is corrected individually. B. WITRICITY Witricity, standing for wireless electricity, is a term coined by MIT researchers, to describe the ability to provide electricity to remote objects Fig.5 Transmitter and receiver [4] without wires. Witricity is based upon coupled resonant objects to transfer electrical energyIV. CURRENT TECHNOLOGIES IN THE between objects without wires. Two objects of theFIELD OF WPT same resonant frequency tend to exchange energyA. SOLAR POWER SATELLITES (SPS) efficiently [7]. A child on a swing is a good example It is a gigantic satellite designed as an of mechanical resonance. According to the theory,electric power plant orbiting the earth which uses one coil can recharge any device that is in range ofwireless power transmission of space based solar the coil, as long as the coils have the same resonantpower. The SPS satellites would be put in high earth frequency.orbit at geosynchronous location. It consists ofmainly three segments; solar energy collector toconvert the solar energy electrical energy which canbe either photovoltaic cells or solar thermal turbine;a DC-to-microwave converter for which microwaveoscillator like klystrons, magnetrons can be usedand the transmitiing antenna which transmits themicrowaves to the earth’s receiving antenna [5]. Fig. 7 Experiment at MIT for WPT. The system developed by MIT uses two copper coils, each a self-resonant system, as shown in fig.7. One of them, attached to the power source which is a sending unit. It fills the surrounding space with a non-radiative magnetic field. The non-Figure 6. Solar Power Satellite (SPS) [3]. radiative field mediates the power exchange with the other, receiving coil, specially designed to The SPS targeted for commercial launch in “resonate” with the field. With such a design, power2030 is capable of a power output equivalent to a transfer still has a limited range. But researches400-MV thermal plant unit and able to supply expected that power levels more than sufficient toelectricity at a price similar to that of publicly run a laptop can be transferred over room-sizedsupplied power [6]. Generating a microwave beam distances, even when environmental objects 1127 | P a g e
  4. 4. Senthil Nathan.M1, Pandiarajan.K / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 3, Issue 1, January -February 2013, pp.1125-1130completely obstruct the line of sight between thetwo coils [7].V. RECENT INVENTIONS AND RESEARCHESA. IMPLANTABLE BIOMEDICAL APPLICATIONS Biomedical implants require a clean andmedically safe source of energy to perform the Fig. 8 block diagram of wireless biomedicaloperation. Early implants such as pacemakers Implantationsourced their power from small lithium ion batterywhich had some drawbacks like limited battery life B. POWER WITHOUT THE CORDwhich causes the impracticality, health risks and Researchers at the Fraunhofer institute forexpense of operating on patients. While this solution ceramic technologies and systems IKTS inallows for the operation of the implantable device Hermsdorf succeeded in wirelessly transmittingwithout a wire connecting the internal and external power from a portable transmitter module to acircuitry which avoids the usage of lithium ion mobile generator module the receiver,shown inbattery for the implants. figure.9 .The cylindrical shaped transfer module is For implanted devices, wireless power and so small and compact that it can be attached to adata transmission is preferred to avoid changing belt. The transmitter provides an electric current ofbattery frequently through surgery so as to reduce over 100 mW and has a range of about 50cm.Sothe cost and the risks in the surgery. The external that, the receiver can be placed almost anywhere inpower and signal transmission module as shown in the body [10].Figure.8 transmits the power and data to the In the transfer module, a rotating magnetimplanted devices in the human body through a driven by an EC motor generates a magnetic rotatorwireless link of inductive coupling. The implanted field. A magnetic pellet in the receiver connects todevices interact with the targeted tissues and cells the alternating exterior magnetic field and as afor biological prosthesis, health monitoring and result, is set in rotation itself. The rotationaladvanced biomedical treatment such as pain control, movement is transformed into electricity, thus themood regulation and remote microsurgery. These power is produced right in the generate and operation can be monitored and With magnetic coupling, power can be transportedcontrolled through a handheld device [9]. Among through all non-magnetic materials, such asthe technologies used for the wireless power biological tissue, bones, organs, water, plastic ortransmission inductive coupling method is the even a variety of metals. Moreover , the magneticmostly used for the biomedical implantation. field produced has no harmful side effects on The external power transmission module humans. It does not even heat up tissue.Because theconsists of one power amplifier and a primary modules available as prototypes are scalable in terminductive coil. The power receiving block of the of range, size and performance capacity, they can beimplanted device consists of the secondary inductive used for more than medical technology applications.coil, matching network, rectifier and low drop-out They can also supply power wirelessly toregulator. The primary and the secondary coils are hermetically sealed sensors- such as those insidedesigned to have a resonant frequency.The walls or bridges [10]. With this portable device, weconventional efficiency-boosting technique adds a can remotely supply power to implants, medicationcapacitor Ct to form the resonance at power carrier dosing systems and other medical applicationsfrequency. The rectifier is used to convert the without touching them.differential alternating voltage signal (AC)appearing across the two terminals of secondary coilinto a direct voltage signal (DC). To obtain a stableDC supply, one low drop-out voltage regulator(LDO) is followed after the rectifier to provide aregulated DC output to power the entire implanteddevice [9]. Fig.9 wireless power transmitter designed by Fraunhofer institute for ceramic technologies [10]. 1128 | P a g e
  5. 5. Senthil Nathan.M1, Pandiarajan.K / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 3, Issue 1, January -February 2013, pp.1125-1130VI. LATEST EXPERIMENTS each other as well as with the transmitting coil, andA. JAPAN’S EXPERIMENT help to reinforce the strength of the magnetic field. Japan is now planning to perform a kW- Researchers says that the efficiency should continueclass microwave power transmission experiment in to rise as more devices are added, climbing toward athe range around 50 m as shown in Figure.10. It will theoretical limit of 100% [12]. The amount of powerbe the first experiment in the world as a high power transmitted in the latest experiment was on the orderand long-range microwave transmission experiment of 100 watts, but researchers says that is onlywith a capability of retro-directive beam control limited by the amplifier used for the transmitting[11].The microwave transmitter consists of 4 coil, and easily can be increased.individual panels,which are movable to each otherto simulate antenna motion in orbit. Each panel, VII. FUTURE ASPECTS0.6m x 0.6m, has an array consisting of hundreds of A. SPS RESEARCH IN CHINAtransmitting antennas, receiving antennas for the Chinas first SPS research started in the latepilot signal, phase controllers, and power systems. 20th century. In the new millennium, when theThe power level from each panel will be several energy issue became a constraint on sustainablehundreds of watts, totally one kW level, at 5.8 GHz. development in China, the China Academy of SpaceThe frequency of the local oscillator in each panel is Technology (CAST) submitted to the government asynchronized by a master oscillator. The phase of “Necessity and Feasibility Study Report of SPS”local oscillator in each panel is adjusted by a [13]. The CAST SPS research team conceives thatRotating Element Electric Field Vector (REV) there are four imperative sections for SPSmethod so as that the power at the receiving site gets development in china:launching approach, in-orbitmaximum. In the demonstration experiment , the construction, high efficiency solar conversion andoutput dc power will be several hundreds of watts wireless transmission. Except for launch, the otherfrom the rectenna. aspects do not seem to be insurmountable issues for China in the upcoming years. Based on Chinas SPS scenario, there are 5 steps to achieving the first commercial SPS system. In 2010, CAST will finish the concept design; while the industrial level testing of in-orbit construction and wireless transmissions could be finished in 2020. the first 100kW SPS demonstration at LEO is expected to be finished by 2025; and in 2035, the 100mW SPS will have electric generating capacity. Finally in 2050, the first commercial level SPS system will be in operation at GEO [13].Fig.10 wireless power transmission on ground[11].B. MORE EFFICIENT WPT In 2007, MIT researchers announced thatthey had discovered a novel way of transmittingelectricity without the use of wires. by which theywere able to produce a power of about 60watts [7].Now, the researchers have demonstrated that thesystem’s efficiency at transmitting energy improvessignificantly when it is used to charge multipledevices at the same time [12]. A number of othercompanies have independently begun to develop Fig.11 China’s research on Solar Power Satellitessimilar wireless power systems, including large (SPS)companies such as microchip maker Intel ® andelectronics giant Sony® because this type of wireless VIII. MERITS AND DEMERITSpower transmission produces a greater power of A. MERITSabout 100 watts. 1. It has been predicted that by 2030, the The team that carried out on the recent world needs 30TW power from renewable energywork- Kurs, Moffat and Soljacic found that when sources and solar energy alone has the capability ofpowering two devices at once, which individually producing around 600TW.The levels of CO2 gascould achieve less than 20% efficiency in power emission can be minimized and brought undertransfer, the combined efficiency climbed to more control. Thus the problem of global warming will bethan 30% . the two receiving coils resonate with solved to a great extent. 1129 | P a g e
  6. 6. Senthil Nathan.M1, Pandiarajan.K / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 3, Issue 1, January -February 2013, pp.1125-11302. The system would reduce the cost of electrical transmission system,” Internationalenergy used by the consumer and rid the landscape journal of computer applications(0975-of wires, cables, and transmission towers. The 8887),vol.1-no.13,pp.100-103,2010.electrical energy can be economically transmitted [4] Vikash choudhary,Abdul Kadir andwithout wires to any terrestrial distance, so there Satendar pal singh“ wireless powerwill be no transmission and distribution loss. The transmission-a novel idea ”, Int.efficiency of the transmission can be as high as 96 Journal of scientific and engineeringor 97 per cent, and there are practically no losses. research.vol.2 Issue.9,ISSN 2229- 5518,pp.1-7,sep 2011.B. DEMERITS [5] Barathwaj.G,Srinag.K,” wireless power Common beliefs fear the effect of transmission of space based solar power ”,microwave radiation. But the studies in this domain Int. conference on Environmental sciencerepeatedly proves that the microwave radiation level and technology.IPCBEE vol.6 pp.V2.227-would be never higher than the dose received while V2.231,2011.opening the microwave oven door, meaning it is [6] Takanori Narita,Toshihiro Kamiya,Keijislightly higher than the emissions created by cellular Suzuki Kenichi Anma,Mayukitelephones [14]. Calculating the circulating Niitsu,Nobuhiko Fukuda“ Thereactive power, it was found that the frequency is development of solar power systemvery small and such frequency is very biologically Technologies ”,Mitsubishi heavy industriescompatible. technical Review.vol.48,no.4,pp.17- 22,dec.2011.IX . ECONOMIC ASPECTS [7] MIT news office In terms of economic theory many will be benefited by this wireless power s- 0607.html.transmission method.By keeping a receiver module [8] Sourabh Pawade,Tushar Nimje,Diptiat any point or inside any devices.The receiver can Diwase“ goodbye wires:approach toreceive power without the use of any cords.The wireless power Transmission ”.Int. journalcapital cost of the practical implementation of of emerging technology and advancedwireless power transmission seems to be very engineering.ISSN 2250-2459,vol.2high.But the maintanence cost of the WPT is very issue 4,pp.382-387,apr 2012.low when compared to the conventional power [9] Lei Yao,Jia Hao Cheong,Rui-Fengtransmission system. Xue,Minkyu Je “ An inductive coupling based CMOS wireless Powering link forX . CONCLUSION implantable biomedical Application The transmission of power without wires is ”.world academy of science,engineeringnot a theory or a mere possibility, it is now a reality. and technology 69 2012.pp.456-459.The electrical energy can be economically [10] Fraunhofer institute for ceramictransmitted without wires to any terrestrial distance. technologies and systems IKTS. “ powerDr.N.Tesla is the pioneer of this invention.Wireless without the cord ”,Research newspower transmission of electrical power can be 04/2012,topic 1.ISSN 0948-8383.considered as a large scope in electrical engineering www.ikts.fraunhofer.defor future prospects of power generation and [11] Susumu Sasaki,Koji Tanaka and Advancedtransfer. The various methods and aspects regarding mission research group “ WPTwireless transmission of electrical power are technologies for solar power satellitediscussed. The evolution of the technology from the ”,IWMS-IWPT 2011 proceedings,2011.time of Tesla has been overviewed. pp.3-6. [12] MIT news officeREFERENCES [1] Nikola Tesla “ The transmission of power- 0409.html. electrical energy without wires as a means [13] Gao Ji,Hou Xinbin and Wang Li “ solar for furthering peace ”, electrical world and power Satellites research in china engineer.Jan 7, pp.21,1905. ”,issue 16:china SPS Strategy and [2] Nikola Tesla,my inventions,Ben schedule,Online journal of space Johnston,Ed. Austin,Hart Brothers,p.91,1982 travel,p.2007 e 16/ji.html. Modeling and simulation design.Ak peters [14] (how microwave ltd. works-A cooking oven for the 21st [3] S.Sheik Mohammed, K.Ramasamy, century:by Gabriel Gache). T.Shanmuganatham “ Wireless power transmission-A next generation power 1130 | P a g e