磁共振(磁谐振耦合)无线充电技术鼻祖级文章-英文原文

/éKurs,1*AristeidisKaralis,2RobertMoffatt,1J.D.Joannopoulos,1PeterFisher,3MarinSoljačić11DepartmentofPhysics,MassachusettsInstituteofTechnology,Cambridge,MA02139,USA.2DepartmentofElectricalEngineeringandComputerScience,MassachusettsInstituteofTechnology,Cambridge,MA02139,USA.3DepartmentofPhysicsandLaboratoryforNuclearScience,MassachusettsInstituteofTechnology,Cambridge,MA02139,USA.*Towhomcorrespondenceshouldbeaddressed.E-mail:[e-mail]-resonantcoilsinastronglycoupledregime,weexperimentallydemonstrateefficientnon-radiativepowertransferoverdistancesofuptoeighttimestheradiusofthecoils.Wedemonstratetheabilitytotransfer60Wwithapproximately40%efficiencyoverdistancesinexcessoftwometers.Wepresentaquantitativemodeldescribingthepowertransferwhichmatchestheexperimentalresultstowithin5%.Wediscusspracticalapplicabilityandsuggestdirectionsforfurtherstudies.Atfirstglance,suchpowertransferisreminiscentoftheusualmagneticinduction(10);however,notethattheusualnon-resonantinductionisveryinefficientformid-rangeapplications.Overviewoftheformalism.Efficientmid-rangepowertransferoccursinparticularregionsoftheparameterspacedescribingresonantobjectsstronglycoupledtooneanother.Usingcoupled-modetheorytodescribethisphysicalsystem(11),weobtainthefollowingsetoflinearequationsIntheearly20thcentury,beforetheelectrical-wiregrid,NikolaTesla(1)devotedmuchefforttowardsschemestoa&m(t)(iωmm)am(t)iκmnan(t)Fm(t)nm(1)transportpowerwirelessly.However,typicalembodiments(e.g.Teslacoils)involvedundesirablylargeelectricfields.Duringthepastdecade,societyhaswitnessedadramaticsurgeofuseofautonomouselectronicdevices(laptops,cell-phones,robots,PDAs,etc.)Asaconsequence,interestinwirelesspowerhasre-emerged(2–4).Radiativetransfer(5),whileperfectlysuitablefortransferringinformation,posesanumberofdifficultiesforpowertransferapplications:theefficiencyofpowertransferisverylowiftheradiationisomnidirectional,andrequiresanuninterruptedlineofsightandsophisticatedtrackingmechanismsifradiationisunidirectional.Arecenttheoreticalpaper(6)presentedadetailedanalysisofthefeasibilityofusingresonantobjectscoupledthroughthetailsoftheirnon-radiativefieldsformid-rangeenergytransfer(7).Intuitively,tworesonantobjectsofthesameresonantfrequencytendtoexchangeenergyefficiently,whileinteractingweaklywithextraneousoff-resonantobjects.Insystemsofcoupledresonances(e.g.acoustic,electro-magnetic,magnetic,nuclear,etc.),thereisoftenageneral“stronglycoupled”regimeofoperation(8).Ifonecanoperateinthatregimeinagivensystem,theenergytransferisexpectedtobeveryefficient.Mid-rangepowertransferimplementedthiswaycanbenearlyomnidirectionalandefficient,irrespectiveofthegeometryofthesurroundingspace,andwithlowinterferenceandlossesintoenvironmentalobjects(6).Considerationsaboveapplyirrespectiveofthephysicalnatureoftheresonances.Inthecurrentwork,wefocusononeparticularphysicalembodiment:magneticresonances(9).Magneticresonancesareparticularlysuitableforeverydayapplicationsbecausemostofthecommonmaterialsdonotinteractwithmagneticfields,sointeractionswithenvironmentalobjectsaresuppressedevenfurther.Wewereabletoidentifythestronglycoupledregimeinthesystemoftwocoupledmagneticresonances,byexploringnon-radiative(near-field)magneticresonantinductionatMHzfrequencies.wheretheindicesdenotethedifferentresonantobjects.Thevariablesam(t)aredefinedsothattheenergycontainedinobjectmis|am(t)|2,mistheresonantfrequencyofthatisolatedobject,andmisitsintrinsicdecayrate(e.g.duetoabsorptionandradiatedlosses),sothatinthisframeworkanuncoupledandundrivenoscillatorwithparameters0and0wouldevolveintimeasexp(i0t–0t).Themn=nmarecouplingcoefficientsbetweentheresonantobjectsindicatedbythesubscripts,andFm(t)aredrivingterms.Welimitthetreatmenttothecaseoftwoobjects,denotedbysourceanddevice,suchthatthesource(identifiedbythesubscriptS)isdrivenexternallyataconstantfrequency,andthetwoobjectshaveacouplingcoefficient.Workisextractedfromthedevice(subscriptD)bymeansofaload(subscriptW)whichactsasacircuitresistanceconnectedtothedevice,andhastheeffectofcontributinganadditionaltermWtotheunloadeddeviceobject'sdecayrateD.TheoveralldecayrateatthedeviceisthereforeD=D+W.Theworkextractedisdeterminedbythepowerdissipatedintheload,i.e.2W|aD(t)|2.MaximizingtheefficiencyofthetransferwithrespecttotheloadingW,givenEq.1,isequivalenttosolvinganimpedancematchingproblem.Onefindsthattheschemeworksbestwhenthesourceandthedeviceareresonant,inwhichcasetheefficiencyisTheefficiencyismaximizedwhenW/D=1+2/SD)1/2.Itiseasytoshowthatthekeytoefficientenergytransferistohave2/SD1.Thisiscommonlyreferredtoasthestrongcouplingregime.Resonanceplaysanessentialroleinthis/2/D2(~106fortypicalparameters)comparedtothecaseofinductivelycouplednon-resonantobjects.Theoreticalmodelforself-resonantcoils.Ourexperimenta