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Direct-CurrentExcitationBasedActiveUnderwater WANGShi-jie,PENGJie-(SchoolofAutomationEngineering，UniversityofElectronicScienceandTechnology Chengdu，:Inthemiddleoflastcentury,biologyresearchersfoundthatweaklyelectricfishcouldsenseweakelectricfieldchangesoftheenvironmenttonavigateandprey,commonlyknownas10electricfieldlocation.Inthispaper,webuiltanexperimentsystemforactiveelectrolocationbysimulatingweaklyelectricfish.UnderDC(directcurrent)excitation,wedidseveralexperimentsoncharacteristicsofactiveunderwaterelectrolocationsystem.Finally,withDCexcitationweachievedunderwaterlocationbyactiveelectrolocationsysteminbothX-axisdirectionandY-axisdirection.:active,directcurrent,electrolocation, Theabilityofsomemarineanimalstosenseelectricfieldswasdiscoveredinthelate1950s[1]andthereisanincreasinginterestinthemechanismsofbiologicalsensingfortheseyears.Theelasmobranchfish,e.g.sharks,raysandskates[2]areabletodetecttheelectricfieldchanges inthesurrounding.Thisabilityistermed“passiveelectrolocation”.Insteadofpassivelydetecting,somekindsofdeepwaterfishesdeveloptheabilitytogenerateaweakelectricfieldactivelyanddetectitschangeduetothepresenceorabsenceofobjectsintheirsurroundings(figure1).TheybothemitandsenseanelectricfieldbyEODs(ElectricOrganDischarge),whichissimilartotheactivesensingsystemssuchasradarandsonar.Suchabilityisanactive electrolocationsystem[3].Andsincetheelectricfieldgeneratedisweakenoughnottokillotherlivingbeings,thefishisknownasweaklyelectricfish.Thisisdifferentfromthegymnotus,whokillspreysbyemittinghigh-voltage.Activeelectrolocatorshuntintotaldarknessandclutteredandturbidenvironmentswherevisionisuseless[4-6].Biologistsaimatunderstandingthissensorymechanismoffishwhileengineersontheotherhandfocuson howtoimitatethismechanismtodesignlocationsystems.Recentpapersbymanyresearchersshowthattheycanbuildsystemswithanelectricsensetolocate,trackandimageobjectsunderwater[7-12].Analternatingelectricfieldwiththefrequencyabout1000Hz(sinewaveorsquarewave)wasusedasweaklyprobeelectricfieldintheirwork.Intheelectromagnetismtheory,sincewaterisconductive,electromagneticwaveswillbeattenuatedaccordingtothe skineffectmechanism[13].Theskineffectmechanismwillbeweakenedatlowerfrequency.Ifweusedanelectrostaticfield,theDirect-Current(DC)excitationelectricfieldforexample,theskindepthofwaterwillbeum.Sotheprobescopewillbeextendedbyelectrostaticfield.Ontheotherhand,directcurrentsignalcanbeconsideredastheextremecaseofalternatingcurrent,theperiodofwhichisindefiniylong.SotheresultofDCexcitation electricfieldisthebasisofalternatingelectricfield.Andmanyresultscanbeextendedtoalternatingelectricfield.Inthispaper,wehavebuiltanexperimentsystemforactiveelectrolocationandthecharacteristicsofactiveelectrolocationsystemwithDCexcitationwereinvestigated.Briefauthorintroduction:WANGShi-jie（1988-）,male,Masterdegreecandidate,sensorCorrespondanceauthor:PENGJie-gang（1971-），male,associateprofessor，sensor.E-mail:Figure1activeelectrolocationsystemmodelofweaklyelectric Thediagramofexperimentdeviceusedinthispaperisshowninfigure Figure2thesystemstructurediagramofactiveelectricfieldTheexcitationsourceinfigure2isaDC(directcurrent)supply(5V±3%),whichisusedtoemittheactivedetectionelectricfield.Inourpreviousstudy,wehavedoneahugenumberofexperimentsontheelectrodes.Finally,atinumelectrodewasusedastheanodeandacalomelelectrodewasusedasthecathode,whichiselectrochemicalstableandlowinelectrochemical55noise.Asilver–silverchlorideelectrodewasusedasareceiverelectrode.Ametalcylinderweight(diameter4cm)wascedunderwaterastheobjecttobelocated.Theexcitationsource,electrodesandDAQ(dataacquisition)boardwereconnectedbyaninterfacepanel.Inordertoobservetherelativepositionbetweendetectionelectrodesandtheobject,thewasmadeofglass.Apositiondevicehasbeendesigned,whichcanbemovedintwo-dimensionoverthe.60Intheexperimentthoseelectrodeswerefixedintheinterfacepanelandtheinterfacepanelwasfixedinthepositiondevice.Whenthepositiondevicewasmoved,therelativepositionbetweenelectrodesandtheobjectwaschanged.Toshowthepositionbetweenelectrodesandtheobjectclearly,anXscaleandaYscalewerelabeledonthesidesofthepositiondevice.Inordertoreduceinterference,coaxialshieldedcablewasusedfordatatransmission.Thephysical65connectionisshowninfigure3.Intheexperiment,thedirect-currentexcitationsourcegeneratesanunderwaterprobeelectricfieldbyemissionelectrodesandthereceivingelectrodesareusedtodetectthechangesoftheprobeelectricfield.Ifthereisanobjectintheeffectivedetectionarea,thestaticbalanceoftheprobeelectricfieldisbrokenandanewstaticbalanceisreformed.TheinformationofunderwaterelectricfieldissenttoDAQ.Thedistributionofelectrodesinthisexperimentisshowninfigure4.Respectively,atinumelectrodeandacalomelelectrodewereusedastheanodeandcathodeofemissionelectrodes;threesilver–silverchlorideelectrodeswereusedasthereceivingelectrodes,whichwereconnected75totheDAQboardintheformofdifferentialinput.Separay,theleftandrightreceivingelectrodeswereconnectedtoai1channelandai0channeloftheDAQ.Thereceivingelectrodeinthemiddlewasusedasreferenceelectrode.Ametalcylinderwascedinthewater,whichwasusedastheobjecttobelocated.Therelativedistancebetweenelectrodesandtheobjectwaschangedbymovingtheinterfacepanelalongsliderailsofthepositiondevice.80Therearetworeasonswhyweadoptedthedifferentialinputmode.First,theintensityoftheprobeelectricfieldisveryweak,sothechangesoftheprobeelectricfieldareweaker.Thedifferentialinputmodecansuppresscommonmodeinterferenceinsystem.Ifwechoosesingle-endedinputmode,thechangesofweaksignalswillbetoosmalltocaptureundercommonmodeinterference.Secondly,thedifferentialinputmodecanjustamplifytheweaksignalsinsomeextent.Inorderto85facilitatethestudyonresponsecharacteristicsindifferentdetectionprocesses,wedefinetheprocesswhenelectrodesgetclosetotheobjectaspositiverouteandtheprocesswhenelectrodesleavetheobjectawayasnegativerouteinthispaper.Figure4thediagramofthedistributionof Thispaperfocusesonthestudyofdirectcurrentexcitationbasedunderwaterlocation.Wehavedesignedtwoexperimentstostudycharacteristicsofactiveelectricfieldlocationsystemindifferentdirections.Uniformly,adirect-currentexcitationsource(5V±3%)wasusedtogenerateaprobeelectricfield.

ExperimentinX-axisIntheexperiment,thevalue(Y)ofelectrodeswasfixedandhorizontalvalue(X)ofelectrodeswaschangedbymovingelectrodesalongtheX-axisofsliderailonthepositiondevice,sothedistancebetweenelectrodesandtheobjectwaschanged.Inthisexperiment,thedistanceinY-axisbetweenelectrodesandtheobject(Y)is1cm.Wemovetheelectrodesfromtheleftmostsidetorightmostsidepassingtheobjectthenbacktothebeginningpoint,asshowninfigure5.Theresultsareshowninfigure6.Figure5X-axis--

ai0positiverouteai1positiverouteai1negative-12-10ai0positiverouteai1positiverouteai1negative-

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Figure6reciprocatingmotioninX-axisInfigure6,theordinateisvoltagevalue,theabscissaisdistance.Thezerodatummarkofhorizontalaxisisrightmostpositioninreciprocatingmotion.Inreciprocatingmotionwesampleddataeveryother2cminX-axisdirection.Thedistancebetweentheleftmostsideandtherightmostsideis20cm.Inthefigure,thepositiveandnegativeoftheabscissastandfordirectionsofreciprocatingmotion.Forexample,thepositivemotionmeansthattheelectrodesweremovedfromtheleftmostsidetotherightmostside,viceversa.Asshowninthefigure,forthedatafromai0electrode,apeakappearedatX=5cm,whileforthedatafromai1electrodeatroughappearedatX=5cm,too.Wecaninferthatwhenelectrodesapproachtheobject,thesignalfromelectrodeswillchangeobviously,apeakoratrough.Inthisway,wecandeterminethepositionoftheobjectfromthevoltagechangesofelectrodes.

ExperimentinY-axisInthisexperiment,thevalue(X)ofelectrodeswasfixedandverticalvalue(Y)ofelectrodeswaschangedbymovingelectrodesalongtheY-axisofsliderailonthepositiondevice,sothedistancebetweenelectrodesandtheobjectwaschanged.Intheexperiment,areciprocatingmotiondetectionmanner(apositiverouteandnegativeroute)wasadopted.Thenegativemotionmeansthattheelectrodesweremovedfromthenearestpointoftheobjecttothefarthestpointoftheobject.Thepositivemotionmeansthattheelectrodesweremovedfromthefarthestpointoftheobjecttothenearestpointoftheobject.First,electrodesweremovedalongthesliderailofthepositiondevicefrom(-14cm)to(0cm)(wheretheobjectwasced)inY-axisdirection.Andthen,electrodesweremovedbacktotheinitialposition(14cm).Theresultisshowninfigurepositiveroutepositiveroute-16-14-12-10-8-6-4-202468101214

Figure7theobjectunderwaterwascedatAsshowninfigure7,whenelectrodesgetclosetothemetalcylinder,thevoltageamplitudeofreceivingelectrodeswillincreaseabout4～6mV.Sounderdirectcurrentexcitationtheobject(aconductor)canbelocatedbytheactiveunderwaterelectrolocationsysteminY-axisdirection. Anactiveunderwaterelectrolocationsystemwasbuiltinthispaper.AndunderwaterlocationwasachievedbyDC(directcurrent)basedactivefieldlocationsystembothinX-axisdirectionandY-axisdirection.SounderwaterlocationwasabletobeachievedwithdirectcurrentH.W.LissmannandK.E.Machin,ThemechanismofobjectlocationinGymnarchusniloticusandsimilarfishExp.Biol.1958,35:451-R.K.Adair,R.D.Astumian,andJ.C.Weaver,Detectionofweakelectricfieldsbysharks,rays,andskates[J}.Chaos.1998,8(3):576-587M.E.NelsonandM.A.MacIver,SensoryacquisitioninactivesensingT.H.BullockandW.Heiligenberg,Electroreception[M].Wiley,NewYork,R.W.Turner,L.MalerandM.Burrows,Specialissueonelectroreception Biol.1999202(10):1167-M.A.MacIver,N.M.SharabashandM.E.Nelson,Prey-capturebehavioringymnotidelectricfish:

ysisandeffectsofwaterconductivity,Exp.Bi