Investigation and Comparison of Two Models in.docx
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Investigation and Comparison of Two Models in.docx
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InvestigationandComparisonofTwoModelsin
InvestigationandComparisonofTwoModelsin
GalvanicCouplingIntra-bodyCommunications
PUNSiohang[1,2],GAOYueming[2,3],WONGKuokkit[1],MAKPengun[1,2],
VAIMangi1[2,3],DUmin[2,3]
1.DepartmentofElectricalandElectronicsEngineering,FacultyofScienceandTechnology,UniversityofMacau,Macau,China
2.KeyLaboratoryofMedicalInstrumentation&PharmaceuticalTechnology,FujianProvince,China
3.InstituteofPrecisionInstrument,FuzhouUniversity,Fuzhou,China
Abstract:
Intra-bodycommunication(IBC)isanew,emerging,short-rangeandhumanbodybasedcommunicationmethodology.Itisatechniquetonetworkvariousdevicesonhumanbody,byutilizingtheconductingpropertiesofhumantissues,suitableforcurrentlyfastdevelopingBodyareanetwork(BAN)/Bodysensornetwork(BSN).IBCisbelievedtohaveadvantagesinpowerconsumption,electromagneticradiation,interferencefromexternalelectromagneticnoise,security,andrestrictioninspectrumresource.Inthisarticle,theauthorsdeveloptwomodels,whichareanalyticalandempiricalapproaches,forcomparingtheperformanceandaccuracyofIBConahumanlimb.Throughinvivoexperimentoffivevolunteers,bothmodelsbasicallymatchwiththeexperimentalresultwithequivalentcircuitmodelsuperiorthanelectromagneticmodelintermofmaximumerror.
Keywords:
Intra-bodyCommunication;AnalyticalModel;Empiricalcircuitmodel
I.INTRODUCTION
Intra-bodycommunication(IBC)isanew,emerging,short-rangeandhumanbodybasedcommunicationmethodology.Itisatechniquetonetworkvariousdevicesonhumanbody,byutilizingtheconductingpropertiesofhumantissues.AtypicalIBCisachievedbycouplingasmallamountofelectriccurrent,whichisbelowthesafethreshold,intothehumanbody.Then,thereceiverpicksuptheelectricsignalinanotherlocationonthehumanbody.Nowadays,inthefastdevelopmentadhocBodyareanetwork(BAN)andBodysensornetwork(BSN),IBCisbelievedtoownadvantagesinlowerpowerconsumption,reducedelectromagneticradiation,lessinterferencefromexternalelectromagneticnoise,increasedsecurity,andincreasedspectrumefficiency.
SinceIBCappearedin1995[1],twoimplementationapproacheshavebeendeveloped:
Capacitivecouplingtechniquearetwoelectrodesapproachwithcommoncoupling[2]andGalvaniccouplingtechniquewithfourelectrodes[3].
ThereareseveralapplicationsdevelopedwithIBC,forexample,prototypesforbusinesscardexchange[4],electrocardiography(ECG)monitoring[5],virtualtypingsystem[6],andcommunicatingwithimplanteddevices[7].
Fortheoreticalinvestigation,thedirectionsofmodelingIBCarediverse.Recently,K.Hachisukaetal.conductedexperimentstocomparetheperformancebetweenGalvaniccouplingtechniqueandCapacitivecouplingtechnique[2].In2009,RyoyuXuetal.alsoreportedanexperimentsetupformeasuringthechannelofIBC.TheyfoundthatthecharacteristicsoftheCapacitivecouplingtechniqueshowsabandpassprofilewithcenterfrequencyataround42MHz[8].
EquivalentcircuitdevelopmentisanotherpopularapproachtomodeltheIBC.ThroughouttheresearchofIBC,manyequivalentcircuitsforIBCareproposed.ThelatestisdevelopedbyN.Choetal.Byusingthreecylinderstorepresentthehumanbody,ancircuitmodelofthebodychannelisformedandsatisfactoryresultsareobtainedincomparisonwiththemeasurements[9].
NumericalsimulationisalsoapowerfultoolfortheanalysisofIBC,therepresentativeistheworkreportedbyK.Fujiietal.TheysimulatedtheIBConawholebodyhumanmodelbyusingthefinitedifferencetimedomain(FDTD)method.Interestingly,theyconcludedthatasimplehomogeneouscalculationmodelissufficientfortheCapacitivecouplingIBC[10].ItisworthnotingthatT.Sasmorietal.reportedananalyticalmethodofmodelingtheCapacitivecouplingIBCforhighfrequenciesin2009.
Inthisarticle,amodelbasedontheelectromagnetictheoryandanequivalentcircuitmodelaredeveloped.Incontrastwiththeotherapproaches,ananalyticalmodelshowsflexibilityindiverseparametersofthehumanbody.Thedevelopedmodelalsoconsiderstheinhomogeneouspropertyofthehumanbodytosomedegree.InSection2,thedetailsoftheelectromagneticmodelaredescribed.Section3depictstheequivalentcircuitmodel.TheexperimentforcomparingtheperformanceofbothmodelscanbefoundinSection4.TheresultdiscussionandconclusionaremadeonSection5.
Ⅱ.ELECTROMAGNETICMODEL
TheIBCofhumanlimbisfirstapproximatedbyacylinderandformedthebasisofthelimbmodel.Thisarrangementenablesthecomplexstructureofahumanlimbtobemathematicaldescribed.ConcentriclayersoftissueareemployedtoexpresstheconstituentsofthehumanlimbasshowninFig.1,wherehdepictsthelengthofthelimb,r1…rnrepresenttheradiiofvarioustissues,andσ1…σnrepresenttheconductivitiesoftissues,startingfrominsideoutrespectively.
Fig.1RepresentationofIBClimbmodel
Assumingquasistaticapproximationandlimitingtheoperatingfrequencylessthan1MHz,theelectricandmagneticfieldsaredecoupled[11].Thehumantissues,underthevolumeconductortheory,areconsideredasconductingmedia[11].Thus,thelimbmodelcanbeconsideredassource-free,multilayer,conductingcylindricalmediumandthegoverningequationcanbereducedtoEq.1
∇⋅σs∇V=0s=1N
(1)
whereVdepictsthevoltagewithinlimbmodel,σsdepictsConductiviesoftissues,andNrepresentsthetotalnumberoflayers.
Togetherwithboundaryconditions(Eq.2,Eq.3,andEq.4),themathematicalmodelfortheIBCofthelimbisformed.Inthismodel,Eq.4representsthesignalcouplingbythetransmitterelectrodesatthesurfaceofthelimbandexpressesascurrentdensity.RegularelectrodeshapescanalsobeintroducedintothemodelbydefiningJninEq.4.Eq.5andEq.6arethecontinuitypropertiesdefinedfortheinterfacebetweenadjacenttissues.
whereJn(θ,z)depictsthenormalcomponentofthecurrentdensityinjectedintothelimb
Jns(θ,z)=Jn(s+1)(θ,z)(5)
Vs(θ,z)=Vs+1(θ,z)(6)
wheres=1N−1
BysolvingthemathematicalmodelwithEq.2toEq.6,ananalyticalsolutionfortheIBClimbmodelcanbeexpressedasEq.7,whereInisthemodifiedBesselfunctionofthefirstkindofordernandKnisthemodifiedBesselfunctionofthesecondkindofordern.TheconstantsEsmn,Fsmn,Gsmn,andHsmninEq.7canthenbefoundbyusingEq.8andEq.9.SinceVisfiniteatr=0,thus,F1mnandH1mnareequaltozero.
Withthismathematicalmodel,theauthorsattemptedtoevaluatethepropertiesofIBC.Thedimensionofthelimbistakenas25cminlengthwith32.5mminradiuswithfourlayersoftissue,namely:
bone,muscle,fat,andskin.Thesizeofthesquaredtransmitterelectrodeis40mmby40mmlocated50mmfromoneendofthelimb.TheconductivitiesofthetissuesarederivedfromtheparametricmodelsproposedbyS.Gabrieletal.in1996[5].Thestudiedlocationissupposedat60mmawayfromtheedgeofthetransmitterelectrodes,matchingwiththeproposedreceiver.Onthehumanlimb,theelectromyography(EMG)isthemajorendogenoussignalandtheupperfrequencylimitofsurfaceEMGingeneralwouldbe500Hz[12].Thus,avoidingtheinterferencefromthebiomedicalsignalofthehumanbody,theinvestigatingfrequencyrangeofIBCischosenfrom1kHzto1MHz.ThecalculationresultscanbefoundfromFig.2.
Fig.2CalculationsandmeasurementsofIBC
Ⅲ.EQUIVALENTCIRCUITMODEL
Inthissection,theauthorsproposedanequivalentcircuitmodel,asanalternationforexploringthepropertiesofIBC.Itisarelativelysimplemethodformodeling,reducingthecomplexityofelectromagneticmodel,butitisanempiricaltypetechniquewhilescarifyingthemodelgenerality.InFig.3,asimpleequivalentcircuitisproposedbyconcludingfromtheinvivomeasurementinthelaboratory.Inthecircuit,asecondorderhighpassfilterconstitutedthebasicstructureoftheequivalentcircuitwithasimplecircuitryforrepresentingthevariationofdistancebetweentransmitandreceiverelectrodes.
Fig.3Schematicdiagramoftheequivalent
circuitmodelwithtypicalvalues
Theequivalentcircuitmodelisneededtoundergoatrainingphase,inwhich,parameters(i.e.valueoftheresistorsandcapacitors)aredeterminedbythemeasurementdata,beforebeingcapableofrepresentingtheelectricalpropertiesofIBC.Thus,adoptingthesamemeasurementconfigurations,procedures,andmethodologiesmentionedinSection4,fourvolunteershavebeenrecruitedandtheirmeasurementdataareconcludedanddevelopedfortheequivalentcircuit.
Afterfixingtheparametersoftheequivalentcircuit,thecapabilityofthemodelistestedagainstthemeasurementresult.InFig.4,theresultobtainedfromtheequivalentcircuitmodelisplotted.
Fig.4Comparisonofmeasurementsand
equivalentcircuitmodel
Ⅳ.INVIVOEXPERIMENT
Fivehealthymalevolunteershavebeenchosenforexperiment.Duringthemeasurement,stimulatingsurfaceelectrodes(40mmby40mminarea)wereusedforcouplingthesignalintothehumanbodyandpickedupthesignalatthereceivingelectrodes.AsshowninFig.5,twoelectrodeswereattached50mmawayfromtheelbowastransmitterandthereceiverwas60mmawayfromtransmitter.ThisformedasimplegalvaniccouplingIBCwithupperarmasthecommunicationmedium.AcalibratedAgilent4395ANetwork/Spectrum/ImpedanceAnalyzerwasusedtomeasurethecharacteristicsofthechannel.Priortotheinvivomeasurements,thetransfercharacteristicofthemeasurementsetupwastakenasthebaselineforlatercompensation.
Fig.5Placementofelectrodesinthe
ex
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