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IJEEE, Vol. 1, Spl. Issue 2 (May, 2014) e-ISSN: 1694-2310 | p-ISSN: 1694-2426GV/ICRTEDC/01

WIRELESS ELECTRICAL POWERGENERATION

Kevin BasenooUniversity of Mauritius, Republic of Mauritius

kervin005@hotmail.com

Abstract : Wireless energy transfer or Wireless Power isthe process that takes place in any system where it istransmitted from a power source to an electrical loadwithout interconnecting wires. Wireless transmission isuseful in cases where instantaneous or continuous energytransfer is needed but interconnecting wires areinconvenient, hazardous, or impossible. In this paperdifferent Wireless energy transfer methods are studied.The objective of the paper discussed herein is to developan approach that maximizes the power transferred.

Keywords: Wireless, Energy Transfer.

I. INTRODUCTIONWith the recent advances in wireless and microelectromechanical systems (MEMS) technology, thedemand for portable electronics and wireless sensors isgrowing rapidly. Because these devices are portable, itbecomes necessary that they carry their own power supply.In most cases this power supply is the conventionalbattery; however, problems can occur when using batteriesbecause of their finite lifespan. For portable electronics,replacing the battery is problematic because the electronicscould die at any time and replacement of the battery canbecome a tedious task. In the case of wireless sensors,these devices can be placed in very remote locations suchas structural sensors on a bridge or global positioningsystem (GPS) tracking devices on animals in the wild.When the battery is extinguished of all its power, thesensor must be retrieved and the battery replaced. Becauseof the remote placement of these devices, obtaining thesensor simply to replace the battery can become a veryexpensive task or even impossible. For instance, in civilinfrastructure applications it is often desirable to embedthe sensor, making battery replacement unfeasible [1]. Ifambient energy in the surrounding medium could beobtained, then it could be used to replace or charge thebattery. One method is to use piezoelectric materials toobtain energy lost due to vibrations of the host structure.This captured energy could then be used to prolong the lifeof the power supply or in the ideal case provide endlessenergy for the electronic devices lifespan.

Piezo- Electric MethodPiezoelectric materials[1] have a crystalline structure thatprovides them with the ability to transform mechanicalstrain energy into electrical charge and, vice versa, toconvert an applied electrical potential into mechanicalstrain. This property provides these materials with theability to absorb mechanical energy from their

surroundings, usually ambient vibration, and transform itinto electrical energy that can be used to power otherdevices.The piezoelectric effect exists in two domains: the first isthe direct piezoelectric effect that describes the material’sability to transform mechanical strain into electricalcharge; the second form is the converse effect, which isthe ability to convert an applied electrical potential intomechanical strain energy. The direct piezoelectric effect isresponsible for the material’s ability to function as asensor and the converse piezoelectric effect is accountablefor its ability to function asan actuator.

Fig. 1. Piezoelectric Sensor [2]Most piezoelectric electricity sources produce power in theorder of milliwatts, too small for system application, butenough for hand-held devices such as some commerciallyavailable self-winding wristwatches. One proposal is thatthey are used for micro-scale devices, such as in a deviceharvesting micro-hydraulic energy. In this device, the flowof pressurized hydraulic fluid drives a reciprocating pistonsupported by three piezoelectric elements which convertthe pressure fluctuations into an alternating current.Aspiezo energy harvesting has been investigated only sincethe late '90s, it remains an emerging technology.Nevertheless some interesting improvements were madewith the self-powered electronic switch at INSA school ofengineering, implemented by the spin-off Arveni. In 2006,the proof of concept of a battery-less wireless doorbellpush button was created, and recently, a demonstratorshowed that classical TV infra-red remote control can bepowered by a piezo harvester. Other industrial applicationsappeared between 2000 and 2005, to harvest energy fromvibration and supply sensors for example, or to harvestenergy from shock.Piezoelectric systems can convert motion from the humanbody into electrical power. DARPA has funded efforts toharness energy from leg and arm motion, shoe impacts,

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and blood pressure for low level power to implantable orwearable sensors. The nanobrushes of Dr. Zhong LinWang are another example of a piezoelectric energyharvester [2]. They can be integrated into clothing. Carefuldesign is needed to minimise user discomfort. Theseenergy harvesting sources by association have an impacton the body. The Vibration Energy Scavenging Project isanother project that is set up to try to scavenge electricalenergy from environmental vibrations and movements.Pyroelectric energy harvestingThe pyroelectric effect[2] converts a temperature changeinto electric current or voltage. It is analogous to thepiezoelectric effect, which is another type of ferroelectricbehavior. Like piezoelectricity, pyroelectricity requirestime-varying inputs and suffers from small power outputsin energy harvesting applications. One key advantage ofpyroelectrics over thermoelectric is that many pyroelectricmaterials are stable up to 1200 C or more, enabling energyharvesting from high temperature sources and thusincreasing thermodynamic efficiency. There is apyroelectric scavenging device that was recentlyintroduced, which doesn't require time-varying inputs. Theenergy-harvesting device uses the edge-depolarizingelectric field of a heated pyroelectric to convert heatenergy into mechanical energy instead of drawing electriccurrent off two plates attached to the crystal-faces.Moreover, stages of the novel pyroelectric heat engine canbe cascaded in order to improve the Carnot efficiency[16].

II. INDUCTION METHODThe action of an electrical transformer is the simplestinstance of wireless energy transfer. The primary andsecondary circuits of a transformer are not directlyconnected. The transfer of energy takes place byelectromagnetic coupling through a process known asmutual induction. (An added benefit is the capability tostep the primary voltage either up or down.) The batterycharger of a mobile phone or the transformers on the streetare examples of how this principle can be used. Inductioncookers and many electric toothbrushes are also poweredby this technique. A magnetic resonance[3] wirelesspower supply system was discussed in one paper that’sprototyped by the Arakawa & Komurasaki Laboratory ofthe University of Tokyo together with DENSO Corp. ofJapan [3]. Professor Kimiya Komurasaki of theDepartment of Advanced Energy, Graduate School ofFrontier Science at the University, stated: "The system cansupply power not only to mobile phones and notebookPCs, but also objects moving freely in free space."

Fig. 2. Induction Principle [4]With the prototype system researchers studied therelationship of the resonator’s position within three-dimensional space to transfer efficiency. Both simulatedand actual measurements are shown in figure below.

In order to achieve optimal power transfer, impedancematching between coils is a key factor [4]. By changingthe distance between the transmitter and receiver causes achange in the coupling constant (K) which causes a changein the optimal impedance ratio.Transfer Efficiency Affected by Impedance Matching.Credit: Nikkei Electronics based on material courtesyUniversity of Tokyo and DENSO.ELECTRODYNAMIC INDUCTIONThe "electrodynamic inductive effect" or "resonantinductive coupling" has key implications in solving themain problem associated with non-resonant inductivecoupling for wireless energy transfer; specifically, thedependence of efficiency on transmission distance.Electromagnetic induction works on the principle of aprimary coil generating a predominantly magnetic fieldand a secondary coil being within that field so a current isinduced in the secondary. Coupling must be tight in orderto achieve high efficiency. As the distance from theprimary is increased, more and more of the magnetic fieldmisses the secondary. Even over a relatively small rangethe simple induction method is grossly inefficient, wastingmuch of the transmitted energy.ELECTROSTATIC INDUCTIONThe "electrostatic induction effect" or "capacitivecoupling" is an electric field gradient or differentialcapacitance between two elevated electrodes over aconducting ground plane for wireless energy transmissioninvolving high frequency alternating current potentialdifferences transmitted between two plates or nodes. Theelectrostatic forces through natural media across aconductor situated in the changing magnetic flux cantransfer energy to a receiving device.ELECTRICAL CONDUCTIONElectrical energy can be transmitted by means of electricalcurrents made to flow through naturally existingconductors, specifically the earth, lakes and oceans, andthrough the upper atmosphere starting at approximately35,000 feet (11,000 m) elevation— a natural medium thatcan be made conducting if the breakdown voltage isexceeded and the constituent gas becomes ionized. Forexample, when a high voltage is applied across a neontube the gas becomes ionized and a current passes betweenthe two internal electrodes. In a wireless energytransmission system using this principle, a high-powerultraviolet beam might be used to form vertical ionizedchannels in the air directly above the transmitter-receiverstations.

III. APPLICATIONSFuture applications may include high power outputdevices (or arrays of such devices) deployed at remotelocations to serve as reliable power stations for largesystems. Another application is in wearable electronics,where energy harvesting devices can power or rechargecellphones, mobile computers, radio communicationequipment, etc.Such as at train stations piezo elements that wouldgenerate electricity as commuters walk through, this sortof human-powered electricity generation system mayprovide a portion of the electricity consumed at station.

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Energy harvesters could be used extensively, for example,to provide power for wireless monitoring and diagnosticsensors that generate data on:

A person’s heart rate, body temperature or bloodpressure;

Stresses experienced by engine components,structural elements in buildings etc;

Brake temperatures in railway rolling stock.

IV. CONCLUSIONExisting devices can only exploit vibrations that have anarrow range of frequencies (the frequency is the numberof vibrations occurring per second). If the vibrations don’toccur at the right frequency, very little power can beproduced and it will be too low to be useable. This is a bigproblem in applications like transport or human movementwhere the frequency of vibrations change all the time.

REFERENCES1. https://secure.wikimedia.org/wikipedia/en/wiki/Energy_harves

ting2. Adaptive Piezoelectric Energy Harvesting Circuit for Wireless

Remote Power Supply, IEEE TRANSACTIONS ON POWERELECTRONICS, VOL. 17, NO. 5, SEPTEMBER 2002

3. Arakawa & Komurasaki Laboratory of the University ofTokyo together with DENSO Corp. of Japan.

4. IEEE Electron Devices Meeting, 2007. IEDM 2007.International Energy Harvesting - A Systems Perspective, J.Rabaey, F. Burghardt, D. Steingart, M. Seeman, and P. WrightBerkeley Wireless Research Center University of California,Berkeley.