微机电系统在仿生学生学上的应用.docx

微机电系统在仿生学生学上的应用.docx

《微机电系统在仿生学生学上的应用.docx》由会员分享，可在线阅读，更多相关《微机电系统在仿生学生学上的应用.docx（16页珍藏版）》请在冰豆网上搜索。

微机电系统在仿生学生学上的应用

Design,andpreliminarycharacterizationofanovelMEMSbionicvectorhydrophone

HuaMingya

（SchoolofmechanicalengineeringandautomationShanghaiUniversity,Shanghai200072,China）

Abstract:

Accordingtothe principleof thefish laterallineorgan ofhearing, anovelmicroelectromechanicalsystems （MEMS） bionicvectorhydrophone usedforobtainingvector informationofunderwatersoundfield isintroduced. Itisdesirablethat theapplicationofMEMS piezoresistiveeffect andbionic structurecanimprovethe lowfrequency sensitivity ofvectorhydrophone and itsminiaturization basedon. Bionic structureiscomposedoftwoparts:

highprecision four beamstructureandthe rigid plastic barrelisfixedon themicrostructureofthe center. Haircells locatedinthe lateral line varistors beamsimulation and rigidplasticcylindrical simulation cilia. Whentheplastic tube isbyvoice, strain varistor totransformthe differentialvoltage output signalthroughthe Wheastonebridge circuit. Microfabricationtechniqueshavebeen usedtomeasure tissue results made.

Keywords:

MEMS;Bionic;Vectorhydrophone;Lowfrequency

1.ThecharacteristicsofMEMS

Miniature:

MEMSdevices hastheadvantagesofsmallvolume, lightweight, lowenergyconsumption, smallinertia, highresonancefrequency, shortresponsetime.

Siliconasthemain material, mechanicalandelectrical propertiesof silicon fine:

strength, hardnessandYoung'smodulus and densityof iron, likealuminum, heatconduction rate closetothe molybdenumandtungsten.

Massproduction:

 micromachining with silicon also making hundredsof microelectromechanical deviceora completeMEMS in apieceofsilicon technology.Massproduction cangreatlyreducetheproduction cost.

Integration:

 cantake differentfunctionsand sensitive directionorthe actuatingdirection ofmultiple sensorsoractuators areintegrated, or theformationofmicrosensorarray, microactuator array, eventothe device ofmultiplefunctions areintegratedtogether, forminga complexmicrosystems. Microsensors, microactuators andmicro integration canproduce reliability, highstability MEMS.

2.Introduction

Inunderwateracoustics,theapplicationofvectorhydrophoneendowsseveraladvantagesfordetectionofsubmarines:

Itcanobtainboththesoundpressureandparticlevelocityofsoundfieldsimultaneously,effectivelyreducereceivedintensityofisotropichindrance,andsoon.

Therefore,allcountrieswithnoticeablenavyforcehavedrawnunprecedentedattentiononthevectorhydrophoneandmanyworkshavebeendoneaboutit.Althoughgreatachievementshavebeenmade,therearestillsomelimitationsinlow-frequencydetection,miniaturization,andhighsensitivity.

Theminiaturizationofmechanicalsystemsoffersuniqueopportunitiesforscientificandtechnologicalprogress,andwillalmostcertainlyopenanentirelynewindustry[1].Microelectromechanicalsystems（MEMS）refertomicroscopicdevicesthathaveacharacteristiclengthoflessthan1mmbutmorethan100nmandcombineelectricalandmechanicalcomponents[2].MEMSdevicesandsystemsareinherentlysmaller,lighter,morereliable,andfasterthantheirmacroscopiccounterparts,andareusuallymoreprecise[1].Thesmalldimensionsofmicrocantileversmakethemexcellentsensorsforverysensitivedetectionofmanyphysical,chemical,andbiologicalphenomena,includingacousticsignals[3–5].

Engineers,designersandarchitectsoftenlooktonatureforinspiration.Biologyhasperfecteditsdesignsandformedmanyfruitfulabilitiessuchasitsexquisitesensitivity,effectiveness,andreliability,throughbillionsofyearsofevolution.Somimickingitscreationsisasurewayofproducingnewtechnologiesandnewachievementthatarebothefficientandreliable[6].

Theadvantageofpiezoresistiveeffectisthatitcanbeusedtodetectlow-frequencysignalevenat0Hz.Therefore,itisofgreatadvantageforresearchonvectorhydrophonebasedonpiezoresistiveeffect.Inthispaper,anovelMEMSvectorhydrophonebasedonthetheoryofbionicsandpiezoresistiveeffectwillbepresented,withrespecttothedesign,fabrication,andpreliminarycharacterization.Thetargetedapplicationregionforthesesensorsislow-frequencydetectionofsubmarinesound

Fig.1.Laterallineofthefish.Fig.2.Schematicviewoffish’sneuromastorgan.

3.Basicprinciple

3.1bionicsprinciple

Anextraordinarybutlesserknownsensorysystemisthemechanosensorylaterallineorganthatenablesthedetectionofminutewatermovementsintheimmediateenvironment[7].Thelaterallinerunsfromtheheadtothetailofthefishandresemblesatowedarraywithsensingorgans（stitches）spacedatintervalsalongthenervefiber（Fig.1）.Eachstitchcontainsseveralneuromasts.Eachneuromastcomprisesuptoseveralhundredmechanosensoryhaircells,moreorlessseparatedbysupportingcells,andsurroundingmantlecells.Theapicalpartofthehaircellpresentsitsstereocilia（mechanoreceptorstructure）andkinociliumtotheoutsideenvironmentthroughthegelatinouscupulathatcoverstheneuromastandmakescontactwithwater[8,9].Fig.2istheschematicviewoftheneuromast.

Thestereociliavibrateandactassensorsforflownoiseasthefishswimsthroughwater.Whenstimulatedbyturbulence,themotionofthehaircellproduceschangesinthesynapseswhichareinturnconnectedtothenervefiber.TheelectricsignaloriginatesfromimpedancechangesincellwallswhichmodulatetheflowofK+ions.Thelaterallineisespeciallysensitivetolowfrequencyfluidmotionparalleltothelengthofthefish.Sound,especiallylowfrequencysound,travelsfasterandfartherthaninair.‘‘Near-field’’soundconsistsofsmallfluidmotionsorvibrationsandarecharacterizedbyadisplacementdirection.Theyaredetectedbytheinnerearorbythelateralline[10].

3.2.Acousticstheoryofcylinder

Acousticstheoryresearchindicatesthatforanacousticallysmallcylinderimmersedinfluidwhenthesizeoftheacousticscylinderisfarsmallerthanthelengthofsoundwave,undertheactionofsoundwave,therelationofthevelocitybetweenthecylinderandthefluidparticleisV

（1）

whereVistheamplitudeofthecylindervelocity,V0theamplitudeoftheparticlevelocity,

thedensityofthefluid,

thedensityofcylinder,k=w/cthewavenumber,andathecrustaceousradiusofthecylinder.When

（2）

Thisshowsthatatlowfrequenciesthemotionofacylinderwhosedensityisequaltothatofthefluiditdisplacesisidenticaltothemotionofthefluidparticlesatthislocationwhenthecylinderisremoved[11–13].Consequently,ifthecylinderisfixedonaninertialtransducer,asignalisproducedandcanberelatedtotheacousticparticlemotion.

4.Theprocessofdesignthought[14]

Accordingtotheauditoryprincipleoflaterallineorgan,wecanseethatthemechanoreceptorstructureisthestereociliawhichactsassensorsforflownoisebystimulatingthehaircell.Therefore,thebionicstructuremainlyincludesthedesignofhaircellanditsstereocilia.Inthispaper,thepiezoresistorissimulatedtohaircellandtherigidplasticcylinderissimulatedtostereocilia.

Thestructureofhydrophoneconsistsoftwoparts:

fourbeammicrostructureandrigidplasticcylinderwhichhasthesamedensityasthatofwater.Fig.3showstheactualdesignofthisstructure.Fig.3（a）isthethree-dimensional（3D）modelofthedesignandFig.3（b）givesthetwodimensional（2D）topviewofthedesign.Thefour-beammicrostructureconsistsoffourverticalcantileverbeams.Therigidplasticcylinderisfixedatthecenterblockofthefour-beammicrostructure.Boththecenterblockandthebeamshavethesamethickness.Thewholestructurehascompleteaxialsymmetryinthexozplaneandyozplanes.

Accordingtoacousticstheory,onlywhenthecylinderandthesurroundingmediumhavethesamedensitycanthecylinderandthemediumparticlehavesynchronousvibration,orelsetheacousticinformationcannotbeexactlymemorized.Inthispaper,therigidplasticcylindernotonlyhasthesamedensityasthatofwaterbutalsohassmallgeometricsize（diameter:

200mm,length:

5000mm）,meetingthevibrationconditionswell.

Whentheplasticcylinderrespondsdirectlytotheacousticparticlemotion,thecenterblockwillhaveahorizontaldisplacementandanangularrotation.Therefore,thestructurewillbesubjecttodeformation,anamplifiedandconcentratedstrainisgeneratedontheslimsensingbeams.Afull-activeWheatstonebridgeislogicallyformedbylocatingeightpiezoresistorswhichisusedtosensethedeformationofthebeams.Thisbridgestructurecanincreasethehydrophone’ssensitivitybyabouttwoordersofmagnitudewithoutsacrificingthenaturalfrequencyofthehydrophone.Theresistanceofthepiezoresistorimplantedintosensitivestructureischangedwhenthesignalistransmittedtoit.Whenthereisincentivedirectcurrent,thebridge’schangewillbedetected.Therefore,thevectorunderwateracousticsignalwillbedetectedalso.

Consideringthepresentfabricationtechnology,thecenterblockofthemodeledstructureelementis500mmlong,500mmwide,and10mmthick.Thefourbeamsare1000mmlong,120mmwide,and10mmthick.

Toverifytheaccuracyoftheabovemodelandevaluateitsperformance,thestaticbehaviorofthehydrophone’sstructureisstudiedbymeansoffiniteelementmodeling（FEM）inthissection.Weused45solid,3Delements.Alltheelementsarestandardcuboids;theratioamonglength,width,andheightiscloseto1:

1:

1.Fig.4（a）showsthedistributionofsimulatedstressonabeamunderstaticexcitation.Asexpected,themaximalstressislocatedattheedg