piezoelectric manual

7/27/2019 piezoelectric manual

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MaterialsSystemsInc.NearNet-shapeFabricationofUltrafineScaie PiezoelectricCeramic/PolymerComposites

FinalReport:November1997

ContractNumberN00014-92-C-0212

Submitted to:OfficeofNavalResearchArlington,Virginia

infulf i l lmentofcontractrequirements

Contractor: MaterialsSystemsInc.521GreatRoad Littleton,M A 01460

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Executive SummaryIn thisprogram,new net-shapeformingtechnologiesweredevelopedfor producingfinescale1-3 an d2-2 piezoelectricceramic/polymer composites.iezocomposite materialshavingextremelyfinepiezoceramicelementswereabricatedusinga modifiedceramicinjection moldingprocesssimilartothatdevelopedbyM SI[1 ]fo rcoarsescalepiezocomposite manufacturing.heprincipaltechnicalchallengesweretomakeextremelyfinePZTceramic1-3an d2-2 preformswithoutdefectsor distortion,an dusethesetoan dproducepiezocompositesampleshavingsufficientthicknesstoachievelateralmode-freeresponse.ZT rodsan dstripshavingwidthdimensionsin theorder of25to 600urnan dlength-to-width aspectratiosin excessoftenweredemonstratedon aresearchscale.hesewereusedfo rexperimentaldemonstration ofhighfrequencyacoustic imagingarraysfor medicalultrasoundan dNavyminehuntingapplications.Thenew piezocompositefabrication technologyisfindingapplicationsrangingfrom diver-heldsonarto lowfrequencyminedetectionan dclassification toadvancednet-shapepiezoelectric actuators.heprogram ha sinfluenceddevelopmentofnet-shapeformedaccelerometersfo ractivesurfacecontrol,aswellascoarsereceivearraysfo rsubmarineuse.nderseparateSBIR funding(ONR ContractumberN00014-95-C-0117),thefinescalemoldingtechnologyhas beenscaledup toth epointwherelarge(150x50mm)pieceshavingpitchdimensions below200um can beproducedeveryfewminutes.Priortothiswork,theonlynet-shapeformingapproachavailablefor producingpiezocompositewas onedeveloped bySiemens[2 ]whichutilizedceramicslipcastingintofugitivemoldsproduced byx-rayphotolithography. Thenew finescaleceramicinjectionmoldingapproach developed byM SI has allowedmoldsto bere-used timean dagainfor manufacturingne tshape1-3 an d2-2 piezoelectricceramic/polymercomposites,fferingsignificantcostsavingsoverconventionaldice-and-filltechniquesan dthefugitivemoldapproach.his processha smadepossible th econstruction ofcompositetransducershavingmorecomplexceramicelementgeometries thanthosepreviouslyavailable,allowinggreaterdesignflexibilityfo rimprovedacousticimpedancematching,lateralmodecancellation,an dsuperioractuator performance.Overthecourseofthisprogram,M SIha sshowninjectionmoldingtechnologyto becapableofforming1-3an d2-2 transducer preformson anextremelyfinescale(1-3structureswith


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firstgeneration transducerwas designedbyUltrex,builtbyMSI,an dtested byUDI-Fugroin adevelopmentalimagingsystem.ne unanticipatedoutcomeofthesetestswas theobservationofunusualphasean damplitudeuniformityinth enet-shapeformed arrayelements,whichwas attributedtotightcontroloftheceramicfiringconditionsan dthePZTchemistry.heimpact ofimprovedarrayelementuniformitywas todramaticallyreduceth ebeamformingcomputation requirements an dthusreducesignalprocessingcostan dcomplexity.A stheprogramprogressed,tw onet-shapeapplicationstaskswereadded.hefirstwas to exploitlow costinjectionmoldingofvelocity sensorsfo r potentialuse in theCAVES(ConformalAcousticVElocitySonar)program.orth esecond,two,40element,1-3 hydrophonearraysfo rsurfaceshipminedetectionapplicationswerefabricatedan ddeliveredto NUWCfo rtesting.Overall,theprogram goalsweremet on schedulean dwithin budget.heprogram impactwas extendedbeyondfinescale1-3an d2-2 piezoceramicmolding to includepiezocomposite materialsevaluationan dtransducerfabricationdemonstrations. directlinkwas establishedbetweenceramicprocessing,system costandimagingperformance thatwouldnot havebeenpossiblewithoutfullintegration ofthematerials,transducerdesignan dsystemsfunctionsunderthisprogram.Other defensean d commercialarenasca nbenefitfrom th eavailabilityoffinescalepiezocompositematerials.eedbackon applicationsfrom Navyan dcommercialsystemsend-usershas promptedM SIto performadditionalexploratorydemonstrationsofitsprocessfo rtransducersthatoperatein the1 to5M Hzfrequencyrangefo rtherapeuticultrasound,nondestructive evaluation,an dmedicalimaging.1. Objective and Deliverables

Theprogramwas dividedintotw omajorreas:1 )in escalepiezocomposite synthesis2)iezocompositeevaluation. Otherapplicationsdemonstrationswere:3)owCostAccelerometer Panels4)ydrophoneArraysFinecale PiezocompositeynthesisThe primaryobjectivewas toadvanceth estate-of-the-art in near-netshapefabricationofultrafinescalePZTceramic/polymercomposites.heworkwas aimedat2-2 typecompositeshavingPZT elementdimensions downto10urn.or1-3compositesth eultimatedimensionalgoalwas 25(im roddiameter.iezocomposite processscale-upto producecompositepieces30-50m m squarewas anotherprogram objective. In pursuing theseobjectives,M SIfocusedon formingprocessesthatwereexpectedto becapable,afterscale-up,of economicallymanufacturingultrafinescalepiezoelectric compositesfo rboth Navyan dcommercialapplications.


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Piezocomposite EvaluationThisactivitywas aimedatevaluatingth efinescalepiezocompositetransducermaterialsfo rseveralNavyapplications,includingbuildingan dtesting1-3an d2-2 transducermaterialsan darrays.helatter effortswereaccomplished in conjunction withacousticsystemspartners,includingMSI'sTTCP partnersan dasubcontractor,TetradCorporation.heobjectiveswereasfollows:Hydrophones:TocollaboratewithTTCPpartnersto better understand,through modeling,transducerfabrication,an dtesting,ho w1-3 piezocomposites improveth eperformanceofhydrophonesfo rflankarraysan dotherunderwaterapplications.Multilayer1-3 transducers:ncollaboration with TTCP partners,to developtechniquesfo rfabricatingdoublelayeran dmultilayer1-3compositetransducersfo runderseasensingand actuation.Piezocomposites forUnderseaImaging:odemonstratea prototypeelectronically beam-steeredpiezocompositearrayfo r useinminehunting(TTCP)an dto demonstratethatnet-shapeformedpiezocomposites canbesuccessfully utilized in highfrequencyimaging(withTetrad).TheprimaryroleperformedbyM SIwas to providecompositetransducermaterialsan ddevices,an dtodeveloptechniquesfor fabricatingnew piezocompositetransducerconfigurationsfo r evaluationwithintheTTCPan d byTetrad.M SIalsofabricatedseveralprototypereceivearrayswhichweretestedbyTTCPpartners.OtherpplicationsemonstrationsLowCost AccelerometerPanels:Withth econcurrenceofth eO NR ContractMonitor,MSI,NRL,an dN U W C(M .Moffett)undertookthedevelopmentofvelocitysensorsfo rpotentialuse in th eCAVES(ConformalAcousticVElocitySonar)program.hemotivationwas toexploittheM SIlowcostinjection moldingtechnology to manufacturethesensorsfo rthisapplication.everal100 x100 x18mm (4 "x4"x0.7")panels,each containing16net shapemoldedPZT accelerometer elements,wereproducedan ddeliveredtoNUWC-USRD fo r evaluation.Hydrophone Arrays:Theobjectiveofthistask was tofabricate two,40elementhydrophonearraysusing1-3piezocompositematerialsfo rsurfaceshipminedetectionapplications.hecompletedarraysweredeliveredto theNavalUnderseaWarfareCenter,Newportfo revaluation.

2. AccomplishmentsersusbjectivesFinecale PiezocompositeynthesisThebasicM SIinjectionmoldingprocesswas adaptedsuccessfullyan dnew proceduresweredeveloped,wherenecessary,tofacilitatemoldingofextremelyfine1-3compositedimensions.he1-3toolingapproachwas shownto becapableofachievingdimensionsdowntoatleast50(im,an dthatof th e2-2 toolingdowntoatleast20jxm.M SIdemonstrated fo rthefirsttimethatultrafmescale1-3compositescouldbenet-shapefabricatedin reusabletooling.


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Theultimate1-3 piezocomposite dimensionsachievedwere50u.m diameterPZTrodsat0.25PZTvolumefraction,comparedwitha program goalof25(am roddiameter.or2-2 piezocomposites,th eultimatepitchdimensionsachievedwere45fimfo r 0.5PZTvolumefraction,comparedwith aprogram goalof25Jimfo rthisconfiguration.sth eworkprogressed,itbecameincreasinglyobviousthatachievingth eultimategoalimensionswouldrequiremajor effortan dthattheprimarydefensean dcommercialapplicationrequirements werefo rcoarserpiezocomposites.onsequently,withContractMonitorapprovalthetechnicalemphasisfo r thelatter halfof theprogram was redirectedawayfrom ultrafinescaledimensions,and on todemonstratingtheperformancebenefitsofth efinescalenet-shapepiezocomposites in imagingan dotherapplicationsofgreater interesttotheNavy.The1-3processwassuccessfullyscaledup to3 0m m squarepiecesfo rPZTelementarraysof100-150(imdiameter rodsat25% PZTvolumefraction.his allowedM SIto perform highfrequencytesting,aswellasmakesamplesavailablefo revaluation bytheNavyan dth eprivatesector.nadditionaleffort,aimedatdeveloping fabrication technologyfo r1-3 compositeshavingcoarserelementsin the200-600Jim range,was pursued.heimpetusfo rthisworkwas basedon feedbackfromtheacousticimagingsystemsuser communitywhichindicated thattransducers havingPZTelementsinthatsizerangewereneededfor defensean dcommercialunderseaapplicationsin thefrequencyrange0.5 to3 MHz.heresults ofthisworkprovidedthetechnicalbasisfo r refinementan dscale-upunderasubsequentSBIRprogramONRcontractN00014-95-C-0117). The2-2 work proceededaccordingtoplan.Thesmallestpitchdimensionsproducedwere45 (im,smaller thanthosecommonlyachieved byconventional dicing.hereappearto bemarketsfo rsuchultrafinescale2-2 compositetransducersin intravascularan dendoscopicultrasound.pplicationsincludebothdefense(battlefield medicaldiagnosisan dtreatment)an dcommercialuses,especiallywherelowcostfacilitatesdisposableusage.argeareascale-upan dmanufacturingwas pursuedunderaseparateSBIRfunding.Piezocomposite EvaluationUndertheTTCPportion,M SIsuppliedcustom1-3hydrophonesfo revaluationbyNRL-USRDand DRA. singlowcosttoolingtechnologydevelopedundercontractnumberN00014-95-C-0117,M SIwas ableto fabricate1-3compositeshaving PZTelementsofdiamondand triangular-shapedcross-section. ThesewereevaluatedatStrathclydeUniversity tohelpunderstandinterelementmodesuppression.naddition,severalne w typesofdoublelayer1-3piezocompositewiththicknessmoderesonance frequenciesunder100 kHzweredeveloped,includingsomethatresonated atfrequencies aslowas45 kHz.Theseresultsweresubsequently appliedbyT.HowarthofNRL-DC underseparate fundingto producestacked1-3piezocomposites for Navytransmitapplications[3] .A new moldingtechnology was usedto produce40 volumepercentPZTpreformsfo rfrequency applicationsin th erange250kHzto1MHz.hiscompositewas incorporatedintoth ecurvedreceivearrayfo runderwaterminehunting.woprototypeelectronically beam steeredarrayswerefabricated an ddelivered to UDIfo rsystemsintegration an dtest.Thefirstdeliverablearray(S/N002)was testedin theoutdoortankattheNavyCoastalSystems,Panama City,Florida.Thesecondwillbeevaluatedin th enextphaseoftheprogram.In collaborationwithTetradCorporation,ahighfrequencylineararraywas constructedan dtestedusingfine-scaleinjectionmolded 2-2 composite.Imagesmadeusingthe2-2


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compositearraydemonstratedtheexcellentqualitythatwould beexpectedfrom anarraywith85%fractionalbandwidth.Nounusualbehavioror artifactswereobserved.OtherpplicationsemonstrationsSeveral1 00 x100 x8mm accelerometerpanelswithintegrallownoisepre-amplifierswereproducedan dtestedbyNUWC-Newport .hefirstgenerationpanelsshowedgoodaccelerationsensitivity whentestedin ai r on ashakertable.owever,initialin-waterevaluationrevealedpressuresensitivitythatwas attributedtostraintransmittedto thePZT elementsfrom th ecircuitboardmounting.hisha ssincebeenverifiedunderth ene w SmartPanelsprogram (ONR/DARPA contractN00014-97-C-0236).Two40elementhydrophonearrayswerefabricated,testedin-housean ddeliveredto N U W CNewportfor evaluationin shipboardminehuntingapplications.

3. ResultsFinecale Piezocompositeynthesis1-3Piezocompos i tes Molding Process Development:Theinjectionmoldingprocessconditionsusedfo r finescalepiezoceramicpreform fabricationweresimilarto thosereported elsewherefo rfabricating coarsescale1-3 composites[1 ] .hesamewax-basedbindersystem was usedfo rmostofth ework,exceptfo r abriefstudyofalternativebinderswhichwas conducted to determinewhethermoldedpartgreenstrength could beimprovedvia polymeradditionsto thewax bindersystem.incethealternativebinderstesteddidnotresultin an yimprovementto th emoldingprocess,thisactivitywas discontinuedaftercompleting th einitialstudies.Extendingthecoarse1-3moldingprocessto form compositeshavingultrafine1-3 connectivity requiredadjustmentstothegreenprocessstepsaimedatimproving toolcavity fillingan dmoldedpartejection.hangeswereneededin th eareasofpowder processing, molding,an dmoldedpartejection,butno tin binder removalan dsintering.inceal loftheseprocessstepswerehighlyinterdependent,adjustmentsmadein one areawereusuallybalancedbychangesin subsequentprocesssteps,especiallybinder removal.Earlymoldingprocessmodificationscentered principallyaround reducingthemeltviscosity ofthecompounded mix throughbinder modificationan doptimizationofthePZT powderparticle sizedistribution.Moldfillingwas facilitated byreducingth emeltviscositythroughPZTsolidsreductionan dincreasesto themoldingtemperature.nfortunatelythisledtoproblemswithbinderbleedingduringtoolfillingwhichin turncausedunevenfillingan dpartcollapseduringbinder removal.oavoidbinderbleeding,th eprocessconditions wereadjustedto increasethePZT-binder mixviscosity.his necessitatedchangesin moldingproceduresaimedataccommodatingthemoreviscousmixes.hesechangesincludedhigherpressuresan dlowertemperatures,requiringmodifications toth emoldingequipment.woexperimentalmoldersweredesignedtoallowincreasedmoldingpressure,to improvecontrolovertemperature,an dmakelargerareadevicesup to3 0m m square. pproximately150runswerecompletedin thisexperimentalset-up,leadingtoagreaterunderstandingofth emechanismsofmoldingan dejection. singprocedures established in priorwork,severalsetsof1-3toolinsertsweremadeto testth enew


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moldingproceduresan dequipment.-3 insertsvariedin sizefrom 20to 40m m square,withcavitiesdesigned to producegreenPZTelementsrangingin sizefrom50to150fxm.Afterseveralexperimentaliterationsofmoldingtemperature,pressurean dtime,complete toolfillingwas obtainedconsistentlyfo ralloftheseconfigurations. jectionwas thenstudiedasafunctionof temperature,pressure,binderformulationan dbindercontent.Highqualitymoldedpartswereobtainedconsistentlyfo r elementsizesover120 urn,despitetheincreasedtoolarea.nmostcasesth epartswereremovedwithal lelementsintact.Notethatfo ra3 0mm squaretoolinsert,thisamountsto approximately15,000elementsperpart.)roblemsof elementbreakageatthecornersofth earraywereeliminated byapplyingth eejectionpressuremoreuniformlyso thatallelementswerestressedequallyduringejection.igure1 showssuchan array.heaspectratioofth ePZTrodscan beseenclearlyin Figure2,wherean areaofrodswas brokenoffan dtherodsliehorizontally.he rodswereapproximatelyequalin length,uniformly tapered alongth elength,withanaspectratioofabout4-5.or veryfineelementarrays,50|J.min diameter,theyieldofintactelementswas low.ractureusuallyoccurredatth epointwheretheelementscontactthePZTbaseplate,indicating thatthiswas th eregionofmaximumstressduringejection (thetoolingischamferedin thisareato minimizethisstress). ccasionallyrodsfracturedacrossthethinner portionofth ediameteraroundtheirmid-point.hepresencean dlocation ofintactPZTrods(Figure3)indicatedth efeasibility ofejectingthiscompositeconfiguration.

Figure. 1-3 compositePZTpreform having120 jamdiameterelements.

Figure2. AspectratioofPZTrodsin asimilar compositeto Figure1 .


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Figure3. State-of-development1-3composite preform,40volume%PZTrods,70 urndiameter.Other improvementsweremadeto thebinder removalprocedure.hecross-sectionsofthein ultrafine scalecompositepreformswereextremelysmall,greatlyalleviatingth eproblemsnormallyassociatedwithbinderremovalininjection moldedceramicsan dallowingmuch faster burnoutcycles. ccordingly,thebinder removalmechanism was examined to determinehow thevarioustime/temperature stagescould beaccelerated.A multi-holdcycleinvolvingdifferentheatingrateswas established,resultingin a decreasein thebinderremovalt imefrom severaldaysto under16hours.Severalchallengeswithbinder removalin highPZTvolumefraction compositesweresolved.incetheelementsin thesematerialswerearrangedveryclosely,evensmallamountsofwarpageduring binder removalresultedin adjacentelementscomingintocontactan dcollapsing.heproblem was associated withcertaincompositefeatures,in particular PZTelementaspectratiosin excessoften,an dveryfineelementslessthan50[imwide.Concernsaboutexcessiveleadlossduringsinteringfrom thehigh surfacearea1-3 preforms provedunfounded,an dconventionalclosedcruciblesinteringwassufficientto obtainnormalPZT-5Hceramicpiezoelectricpropertiesin thefinecross-sections.Tooling Development:Severaliterations of toolingwererequired before1-3preforms couldbemadereproducibly.hesetoolingdesigniterationswereconductedonspecimenshavingnominally150 |imdiameterrods.onsequently,deviceshavingthesedimensionsshowed th egreatestprogress,resultingin thepreparation and testingof1-3composite specimenswhichwerefinishedtoahighdegreeofperfection.Thedevelopment oftoolingtoallowintactseparationofthegreenPZTpartfrom thedenselypackedfineholesin thetoolreceivedparticular emphasisaspartoftheprocessrefinementfo rultrafinescale1-3PZTpreforms.nthisregard,th edegreeoftaperon thetoolcavities provedimportantin facilitatingpartejection.naddition,thetoolcavitywallsweremadeassmoothaspossibleto permiteasyslidingofthemoldedpreformsduringejectionfrom thetool.igure4isascanningelectronmicrographofanas-moldedPZT


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preform havingnominally150urn rods.sshownbyth emicrograph,thePZTelements havesignificanttaperan dahighaspectratio.heas-moldedro dsurfacewas usuallysmoothan dflaw-freeprovidedthepartfullypackedout duringmolding.

Figure4. SEM micrograph ofas-moldedPZTrodarrayshowingthetaperan dsmoothsurfacefinish ofgreenrods.Establishing processconditionsthatleadtosatisfactory ultrafinescale1-3PZTpreformsrequiredapproximately200moldingiterationsaimedatestablishingthetrade-offsin temperature,pressure,time,toolgeometryan dejection procedure.hemajor processparametersweresufficiently ruggedthatproceduresfo rmolding100 to150Jim PZTrodsprovedto behighlyreproducible.orfinerdimensions,th eprocesswas verified to becapableoffabricatinggreenPZTroddimensionsdownto50|imdiameter,but withconsiderably pooreryieldan dpartquality.Figure5showsan earlypreform in whichtheoutermostPZTrodwereseveredduringejection,whichwas believedto becausedbyexcessivestresson thefibersat thecornersofth earrayastheejection pressurewas applied.heejection processwas refinedto enableth ecompleterodarrayto berecoveredintact.igure6showsasectionofan as-molded1-3preform having150 fimdiameter rods,approximately1mmlongwithaPZTcontentof25%.ngeneral,moldfillingprovedto beveryuniform,witheachcavitypackingout evenly.igure7isascanningelectron micrograph ofthesurfaceofamoldedrod,indicatingthehighsurfacesmoothness,which was importantfo rsuccessfulpartejection.InFigure8thePZTelementarraywas imaged edge-onto illustratetheaspectratiooftheserods,whichwas approximately 6.igure9showsageneralviewofasintered1-3arrayhavingnominalroddiameterof120| im.heas-sinteredsurfaceofaPZTrodisshownat highermagnification in Figure10wherethePZTgrainsizeisseentofallwithintherangeof2to5(im,typicalfo rthisPZT-5Hformulation.


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i siiii}lsl saFigure5.arlyas-moldedPZT preform having70 jim diameter rodsan d40volume% PZT.heoutermostrods,especially thoseatth ecorners,havebeenseveredduringejectionfrom themold.

Figure6. s-moldedpreform consistingof150um diameterrods,25 volume% PZT.


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.45kx 18kw 89Figure7.EM micrograph of150umdiameteras-moldedPZT rod.

07*55kx ekM 03Figure8.EM micrograph ofgreenPZTrods,150urn diameter,showingtherodaspectratio(approx.6).


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1 1

Figure9.intered1-3PZTpreform having120|imdiameterrods.

Figure10. s-sinteredsurfaceof PZTrodfrom Figure9,showingthePZTgrainsize.


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12Figure1 1 isan opticalphotographofapreform havingnominally70umdiameterrodsan d40 % PZTcontent. fterfiring(Figure12)th esinteringshrinkageyieldedrodsthatwereapproximately40um in diameter atth enarrowtipan dnominally80jim diameteratthebase.heaspectratioforthesePZTrodsrangedfrom10to12,an extremelevelthatarosebecauseofth elargethicknessofth etooling.he effectof thisextremeaspectratioon PZT rodshapeisshownon therightin thisfigure,whereon erodha sundergonesomedistortion duringejection from th emold.For productionofhighquality1-3 ceramicpreforms,atoolingthicknesslimitation wasfoundcorrespondingto arodaspectratioofapproximately7.M ost resonantapplications requireaspect ratiovaluesofonly3 to 4togainthetransducer performancebenefitsofth e1-3 compositeconfiguration.owever,in thepiezocompositeapplications task,itwas subsequentlyfoundthatdistortionofth eceramicpreform duringfiringresultedinmuchofth e1-3piezocomposite thicknessbeinglostduringcompositefinishing.Therefore,althoughthisaspectratiowouldappearto be adequatefo rmost1-3piezocompositeapplications,higheraspectratioswouldbenefitth ecompositefinishingoperation byallowingfo r morematerialtoberemovedduringlapping.

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Figure1.Opticalphotograph ofsinteredPZTelementarrayconsistingof70 |im diameterrodsat 40volume%PZT.hehumanhairin thisfigureis60\imin diameter.Figure13showsth eas-sinteredPZTsurfacenearthetipofth eshortestrodseenin Figure12.hematerialwas densean dpore-free eventhoughth eroddiameterwas only40 Jimat thispointalongitslength.pparentlyth eprocesswas capableoffillingveryfinedimensionsan dproducinghighqualityPZTrodarraysofthisdiameterorless.


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13

t46kx 18kv 10

Figure2. SEM micrograph ofsintered PZTrods70 um in diameter.heaspectratiovariesbetween10an d12for theseexamples.

Figure13. s-sinteredsurfaceoftheupperportionofarodfrom Figure12.hero ddiameterisapproximately40 |im.Figure14isan opticalmicrograph of asinteredpreform thatwas encapsulated in epoxyresinan dsectioned toremoveth ePZTbasean dexposeth ePZT ro dends. rindingthe1-3 compositeswithoutdamagingtherodsprovedstraightforward.heefficiencyofpolingwas verifiedbyd33 measurements an dthechangein dielectric constant.Thethicknessmoderesonancespectraobtainedfo rtw o1-3specimenshavingsputteredgoldelectrodesareillustratedin Figures15an d16.heseresonancecurvesshow considerable distortion,precludinganyestimationof thepiezoelectric parametersbasedon thesedata.or thesespecimensthethicknesswas 400to450urn,yieldinga PZT rodaspectratioofapproximately3 ,sufficienttoobtaina cleandilatational thicknessmode


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1 4 resonance.Mostprobably,th edistortion in theresonancecurvesarosefrom interelement (lateral)modesoccurringnearthethicknessmodefo r thisspecimen thickness,PZTvolume fraction an d polymer matrixmaterial.

* **WF * *#" A'* t4 -#;i(..'#M-0ifill :,i\ #w " #0 Hi 4R|'W ;. ' ;HII '.Ip - i f v. *" : ifj'w- ;.l|m .m # '9 HP" W k sM:. Mr 'am *m < W - ? 1, ft4:m-m-M S t f%; m ??

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' ! A * |ll .*# - " 4 P ^ fPFigure4. Opticalmicrograph offinished compositeconsistingof120 |imdiameter PZT rodsinepoxyresinmatrix.eferencediameter is60 (im.

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START1000000.000HzAMPTD15.0dBm STOP7000000.OOOHZ

Figure15 .mpedance plotof1-3 compositeshownin Figure14.


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REFLEVEL /DIV MARKER32 50000.000HZ15.000deg 15.000deg PHASE(S21) 15.S80deg\\ /\' r ^V \/"V \\

\START 00 0OOO.OOOHzAMPTD .15.0dBm STOP7000OOO.OOOHz

Figure16.haseresponseofsampleshownin Figure 14.Overthecourseofth eprogram,M SIreceivednumerousrequestsfrom bothNavyan dcommercialunderseaimagingsystemsmanufacturersfo rintermediatefrequency1-3 piezocomposites,operatingin the1 to3M Hzrange. saresultofthisNavyinterest,an dafterreviewingprogram prioritieswiththeONRContractMonitor,M SIredirectedits1-3 compositeseffortontomaterialshavingPZT elementdimensionsin the200to 600umrange,rather thanpursuingth eearlierobjectiveofachievingunder25urn elementdimensions.henew configurationsalsofacilitated1-3 compositefabricationfo rtheTTCPportionofthisprogramwheretherequirementwas fo r compositesoperatingin thefrequencyrange0.25to1 MHz.Severalnew toolfabricationoptionswerepursuedunderthisprogramfor makingintermediatefrequency1-3 transducers,aimedat both reducingtoolcostand atachievingappropriatecompositedimensions.hese1-3 compositedimensionslayin adifficultprocessregime,not readilyachievedbyMSI'sstandardnjectionmoldingtoolingapproaches. spartofth etoolingdevelopmentactivity,thetoolapplicationemphasiswas focusedon improvingth etoolsurfacequalitytofacilitatemoldedpart ejection,whileutilizinglow cost,readily machinedinsertmaterialsfo r toolfabrication.M SIcontinued theseactivitiesunderaPhaseIISBIRprogramaimedspecifically at developing lowcosttooling(ONR contractnumber N00014-95-C-0117).hematerialsrequiredfo rfabricatingth eTTCParrayswereproducedunder thisprogram usingtechnologiesdevelopedunderth erelatedSBIRprogram.2-2Composi tes:In th e2-2 compositesarea,MSI'sresearchemphasiswas drivenbyth eneedfo rhigh frequency2-2 compositesfo rintravascularan d endoscopicimagingapplicationsfo r both defensean dcommercialapplications.hesecompositesrequireultrafinescalePZT elementdimensions,i.e.pitchesin theorder of 35tolOOum.Technicaleffortsaimedatextendingtheformingprocessto finerdimensionswereparticularlysuccessfulfo r2-2 composites,an dPZTelementwidthsbelow 25jxm wereachieved. singthe1-3moldingequipmentan d2-2 tooling,M SIachieved pitch


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16dimensionsaslowas45 urnin 2-2 composites,lowerthanthosecommonlyachievedreported bydicing.igure17showsasampleofa50volume%PZTpreform manufactured byinjectionmolding.hePZTfeatureswereapproximately22urnwide,an dth eindividualPZTgrainsca nbeclearlyseenin thisSEM photograph.everalmoldingvestigeswereevidenton theas-firedsurface,includingtracesofflashattheupperedgesofthePZTstripswherethetoolinsertscontact.herewas no evidencethatmolding orsintering representbarriersto finer dimensions;rather,thesearecurrentlylimitedonlybyth ebinderremovalprocessand th eavailabilityofsuitabletooling.itchesas lowas20urnappearfeasible,but requirefreshtoolinsertfabricationapproaches.Larger pitcheswerereadilyfabricatedusingthistechnique(seeFigures18an d19).he technicalpproachesidentified fo r2-2 piezocomposite fabrication underthisprogram werescaledup to largeareaarraysundertherelatedPhaseIISBIRprogram.

Figure17.Scanningelectronmicrograph ofas-sintered2-2 compositepreform having 45 um pitchat50volume%PZTcontent.Piezocomposite EvaluationCompos i teFabr icat ionandCharacter izat ion:Controlofinterelement(lateral)spuriousresonantmodesis criticalin both2-2 an d1-3 piezocomposites.heproblem ariseswhenthePZTelementdimensionsan dspacingaresuchthatthethicknessfundamental modefrequencycoincideswithth efirstan dsecondlateralmodefrequencies,whicharedetermined byth epolymer matrixpropertiesan dthenearestan dnext-nearestneighbor interelementspacing.heresonancespectrum thenbecomesa complexmixtureof interferingmodesin which theadvantagesofth epiezocomposite, viz:highcouplingcoefficientan dlowacousticimpedance,aresignificantlyimpaired.Impedance/frequency characterization was utilizedto better understandth eprocessan ddimensionalfactorsthatinfluencelateralmodegenerationin M SIcomposites.Theinjection moldingprocesshas greaterflexibilityfo radjusting theseparametersthanalternative compositefabricationprocesses,suchasdicing,an dwas exploredin detailwithth eobjectiveof bettercontroloflateralmodes.everalmethodsfo rlateralmodesuppression


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17wereidentified an dexplored,includingmodifying thepolymermatrix,interelement spacing,elementshape,an delementdimensions.Topreparethecompositesamplesfo rtesting,severaltechniquesweredeveloped fo rincorporatingviscouspolymermatrixmaterialsintoth efinescalesintered PZT preforms.Forthispurpose,M SIchosepolyurethanes,leveragingoffexperiencegainedin formerNavycontractstoapplythisversatilefamilyof materialsto resonantcompositetransducers.hesepolymersaddedanew dimension to bothundersea imagingan dmedicalultrasound transducertechnology,whichthenweremainlyusedonlyepoxyresinsfo rthecompositematrix.Polyurethanes offeredawiderangeof stiffnesses,rangingfrom elastomerictoShoreD-85hardness,fo rexploringan dcontrollinginterelementmodes.hey tendedto beviscousan dcurerapidly,thereforeth eearlytechnicaleffortsfocusedondeveloping methodsfo rfullyinfiltrating th ematerialsintothefinest2-2 groovedimensions.apping was attempted byoutsidevendors,butM SIeventually broughtthisan dth eelectrodingprocessin-house.nspiteoftheuse ofgentlelappingprocedures,after removingth ebaseplateson 2-2 samplesthelappeddevicesconsistently delaminatedattheceramic/polymer interface.Thiswas resolved bymodifyingtheceramicsurfacetoimproveadhesion,resultingin complete eliminationofthedelaminationproblem.Both1-3 an d2-2 composites becamefullylappablewith practice,an dchrome/goldelectrodeswereapplied withexcellentadhesion.amplesfo rimpedance/frequencycharacterizationwerepreparedin thisform.LateralModeSuppression: Severaloptionsexistfo rcontrollingspuriousmodesin piezocomposites.heseinclude:1.rranging thePZTelementsclosetogetherso that theinterelementmodefrequenciesaresufficiently fa rabovethethicknessmodeto preventinterference.hisistheconventional methodfor interelementmodecontrolusedin medicalultrasoundan dundersea imaging.hesecompositesusuallyrequireeitherhighPZTvolumefraction

an dthereforehighacousticimpedance,or extremelyfineelementdimensionsthataredifficultto fabricate.2.rrangingth ePZT elements to introduceinterelementspacingvariance.his prevents constructiveinterferencefrom occurringwithinthecompositeat th eproblemfrequencies.3 .aryingtheelementshapetoavoidadjacentfacetswhichmay promoteross-couplingbetweenelements.4.djustingthepolymerstiffnessto reducecross-coupling betweenelements.his is effectivein suppressinginterelementmodes,butalsoadverselyaffectsth ethicknessmoderesponsebyallowingtheelementsto moveindependently ofth ematrix.5.odifying thematrixto suppresscross-coupling,whilemaintaining th esurfaceresponse uniformity,e.g.byincorporatingadditivesintoth epolymer matrixphase.Theinjectionmoldingprocessfacilitatestheseoptionsbyallowingvariationsin PZT elementgeometryan dlayout.onsequently,M SIexploredallofth eaboveapproachesundertheTTCPportionofthisprogram.Usingmodified tooling,M SIsucceededin achievingveryhighPZTvolumefractionin both1-3an d2-2 composites(Figure18).nmanycasesthisexceeded80 volumepercent.


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18Someversatility in thePZTelementshapewas alsodemonstrated(Figure19).heprocessofferedconsiderable potentialfo r producing1-3an d2-2 piezocompositesin which lateralmodesweresuppressed.hesematerialswerenot fabricatedintocompositesfo revaluationoftheir electromechanicalproperties becausetheytendedto betooshallow tofillan dlap.

1 I TR8'8. J a f i 5 $ Si 1 a s u m ii vP 1 B f s 1 ' & :; &3$ 1 .I 4W f.'j * ' ' " " *1 W : S s

( ; E " i ii; 1 fe

A * 3 ' f * ' S! E ; SSffi S S i?&

Figure18.High volumefractionsintered2-2 an d1-3piezocompositePZT preforms(pitch~150um).

Figure9.High PZTvolumefraction1-3composites showingshapeversatilityofth einjectionmoldingprocess.Usingconventionalinjectionmoldingtooling,M SIpursuedlowerPZTvolumefraction1-3composites(-25volume%PZT),havingvariouselementshapes.orthiscompositeconfiguration,interelementmodesbecameproblematicalwhenth ePZTrodaspectratiowas between 2an d3fo ran yreasonablystiff polymermatrix.his configuration was,therefore,an excellentchoicefor examininglateralmodeeffects,an dwas adoptedasanormalizingstandardthroughoutthework.igure20showsthiseffectfo ra0.5 mm rodarrayfabricatedunderrelated contractnumberN00014-94-C-0019.igure21 showsth enearlyidealthicknessmoderesonanceobtainedfo rtheSonoPanel configurationdeveloped undercontractN00014-92-C-0010.nthatcase,thePZT volumefraction was 0.3 an dth ero ddimensionswere1.1m m diameter by6.3 m m long(aspectratio:~5).henormalsofthydrophonepolymer matrixan dcover plateswerereplacedwithahard(ShoreD-80)matrix designedtofacilitateuniform resonantresponsewithoutmassloading.Lateralmodesoccurredaround500kHz,wellclear ofthethicknessdilatationalmode.hecompositeconfigurationin Figure22was thesameasinFigure21 exceptthatthematerial


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19was thinnedtoincreasethethicknessresonancefrequencyto1100kHz,resultingin rodsofaspectratio1.5.igure23showstheeffectofamedium hardnessmatrix(ShoreD-70)in controllinglateralmodes.nFigure23 thecompositeelementdimensionswereth esameasthosein Figure21 ,but thespuriousresonanceswereabsent. lthoughthismaterialwouldnot beexpectedto respondasuniformlyasahardermatrixcomposite,lateralmoderesponseswereminimized,showingtheimportanceofpolymermatrixpropertiesoninterelementmodegeneration.

0.5A: \tA MA> 3 MA> TFI( 10< 80BER.B: 90.0.00 2decMATRIXo MKR MAG PHASE SAMPLE #11 288 242.500 Hz92.8947 C J -22.3782 deg

i""E * :t-41 '\x HT ~t \rfi s\/ V ,F= Jv =AMIN 50.00 nB/DIV 20.00 d e cXMKR 4382 1 2H i

START000.000HzSTOP000000.000HZMAG874.5 J PHASE1.42Figure20. Impedance/frequencycharacteristics of0.5 m m diameter rodarray,hardpolyurethane matrix,0.25PZTvolumefraction,PZTrodaspectratio:2.5.

305S PZT HARD-B: 2 INCH DISK;A : IZl: 8M KR A M AX 50.00 KHAG B MAX 100.0eg PHASE TH -0.250225 775.000z40.67497 9.97961egAMIN0.00TART000.000HzB/DIV0.00egTOP000000.000HzKMKR280720HZ MAG4.25K f i PHASE-5.03

Figure21 . Impedance/frequencycharacteristicsof1 . 1 mm diameter ro darray,hardpolyurethane matrix,0.30PZTvolumefraction,PZTro daspectratio:5.


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2 0

fir0%HARDMATRIXDISK DI --r-MKRMAGPHASEMAXBMAX B :1.0001B0.0 Kndeg 2.75 TH-0.04B111 0630.000HZ1.56617 33.B2502 egAMIN 1.000 QTART 000.000HzBMIN-1B0.0 deg STOP 3000000.000Hz*MKR1418027.5HZMAG90.410PHASE-7.41

Figure22. Impedance/frequencycharacteristics of1.1m m diameter ro darray,hardPolyurethane matrix,0.30PZTvolumefraction,PZTro daspectatio:.5 .A : Zl B: aA MAX 10.00B MAX 100.0 O MKR KQ MAG deg PHASE 258 242.500 Hz55.6812 1 -18.8662 degif: f\ /V,k Y * I\ / JA: -V 7\| HK ! \/ai K /a ~TJ~-V' / V i* J r \, -j ^v _A MIN 20.00 f! START 1 000.000 HzB/DIV 20.00 dec STOP 1 000 000.000 Hz30% PZT THICKNESS= 0.250"

Figure23 . Impedance/frequencycharacteristics of1.1m m diameter ro darray,medium-hardpolyurethane matrix,0.30PZTvolumefraction,PZTrodaspectratio:5.Figure24showsan alternativedesignfo rdiamond-shaped PZTelementsarrangedin aregulararrayat25volume%PZTcontent.or thisconfigurationtherewas nooverlapofth efaceson adjacentelements. owever,at higher volumefractions,it can beseenthatsignificantoverlapoccurs.his compositeconfigurationwas builtundercontractnumberN00014-94-C-0019an dtestedunderthisprogram. Theas-sinteredrodarrayisshownin Figure25.hematrixwas ahard(ShoreD-80)polyurethane whichhas beenshownto clearlysupportinterelement modesin otherspecimens.igure26showstheimpedance/frequencycurvefo rthiscomposite(PZT facedimension:0.64mm,aspectratio:2.5).herewas no evidence fo r reducedinterelementmoderesonancein thisconfiguration.


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21

25.4 vo lpercentPZT

32.6 vo lpercentPZ T

36.9 vo lpercent PZ T

Figure24. Designfo racompositeconfigurationwithdiamond-shapedelementsfo r exploringinterelement modesuppression.

Figure25. As-sintered PZTpreform havingdiamond-shapedPZT elements.


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2 2

0.6VmmIAMONDFIBERS;ARD-8;H=0050A - Z l B : MKR 11 1 0630.000HzA ' MAX0.00 KQ MAG 701003 Q BMAX0.00 degPHASE -19.9478 deg

AMIN 5.000 Q START 1000.000HzB/DIV 20.00 deg STOP 3000000.000Hz*MKR1552982HZ MAG100.3QPHASE-38.18Figure26. Impedance/frequencycharacteristicsof0.64mm squarediamond-shapedrodarray,hardpolyurethane matrix,0.25PZTvolumefraction,PZT ro daspectratio:2.5.Furtherwork was conductedon triangular-shapedelementsdesigned byStrathclyde University.heStrathclydedesignisshownin Figure27.nearlierwork,Strathclydehad observedasignificantreduction in interelement moderesonancewiththisPZT elementconfiguration.owever,theStrathclydecompositewas assembledbyhand-arranging dicedtriangular elements,resultingin naturalvariationsin theelementspacingwhichcouldhaveaccountedfo rthelowincidenceofinterelementmoderesonance.ntheinjectionmoldedversion,madeunder contractnumberN00014-95-C-0117,theelementspacingwas moreuniform (Figures28and 29).ompositesweremadefrom th esinteredpreformsusingfourdifferentpolyurethane matrices:elastomeric,ShoreD-80,ShoreD-85,an dShoreD-80withpolymer microballoons.hesewerethinnedbylapping to 3 .25mm (2.5PZTrodaspectratio),an dtestedfo r interelement modes.

Singleelement cross-section

25 volume percentPZ T

AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA

Figure27. StrathclydeUniversitypiezocomposite designusingtriangularPZTpillars.


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23

Figure28. As-sintered arrayoftriangularPZTpillarsmadeunderONR PhaseIISBIRContractNumberN00014-95-C-0117.

Figure29.riangularPZTpillarsin ShoreD-80polyurethane matrix.Figures30-33show th eresultingimpedance/frequency plots.heelastomericmatrixappearedtohavean idealresonanceresponsebecauseth epolymer was so softthattherodswereessentiallycompletelydecoupledan dresonateindependentlyfrom eachotheran dth ematrix.Thismaterialwas no tfunctioning asa composite,but ratherasan arrayofdiscrete piezoelectricceramicresonators.ortheharder matrices,interelement modeswereplainlyin evidence,evenfo rthematrixcontainingmicroballoons.Apparently,fo raperiodicarrayoftriangular elements,interelementmodeswereno tsignificantly reduced bytheelementshapeor th epresenceof uniformlydispersedvoidsin thematrix.Itappearsthatth ePZTelementshapemodificationsalonedidnot significantlyreduceinterelement modesin1-3composites.Decreasingthepolymermatrixstiffnessremainsaviableroutefo rlateralmodesuppression,butatapenaltyin surfaceresponseuniformity[4].nalternative routeinvolvesarrangingthePZTelementsrandomlyorsemi-randomly to controllateralmodegeneration.heinjectionmoldingprocessisaviableroutefo r thefabricationofsuchrandomized1-3arrays.hisapproachwouldrequirefurtherdevelopment,butoffersconsiderable potentialfo rsuppressingcompositelateralmodes.


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2 4

TRIANGLEELEMENTSOIDEDEN-2; X2X0.122A ' P ^ n Z I I :l oMKR 47 0530.000HzAMA X 100.0 KO MAG 19.6407 0BMA X 80.00 degPHASE -8.22329_ deg

1-oiKdt00 0HzMIN 10.00 Q START 100B/DIV 20.00 deg STOP 000000.000Hz*MKR62 7S 7 2HZ MAG1.29KO PHASE-9.92K R62 7S 7 2HZ MAG1.29Kn PHASb-a.BiFigure30. Impedance/frequency characteristicsof triangularPZTelementarray,elastomeric polyurethanematrix.

TRIANGLEELEMENTS:ARD-2;A l E l"" "AMAXBMAX ~BT^100.0ao.oo oMKRK C 5 MAGdegPHASE 2X2X0.13142 5575.000Hz20.7961 0-17.2723 deg b a .** .'i"o*t I'OAm,AMIN0.00TART000.000HzB/DIV0.00egTOP000000.000Hz*MKR52 0480HZ MAG32.26 ! PHASE-9.50

Figure3 1 . Impedance/frequency characteristics oftriangular PZTelementarray,ShoreD-85polyurethanematrix.


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2 5

JfT^pueE L E M E N T S : AMAXBMAX 100.080.00

HARD-8:OMKRK C 3 MAGde gPHASE2XaX0.131400600.000Hz2 1.5B69 0-31.6880 de g

AMI N0.00iTART000.000HzB/DIV0.00egTOP000000.000Hz*MKR48052 0HZ MAG2 1 .380 PHASE-0.260Figure3 2. Impedance/frequency characteristicsoftriangular PZTelementarray,ShoreD-80solidpolyurethanematrix.

LEMENTgOFT-8: MKRAMAX 100.0 KQAGBMAX 80.00 degHASETRIANGLEA :z i X2X0.132445555.000Hz1 9.2 1 1 5 o-10.4337 de gAMIN0.00ITART000.000HzB/DIV0.00egTOP00 0000.000Hz*MKR53 296 7HZ MAG694.4Q PHASE1.24

Figure3 3 . Impedance/frequency characteristicsoftriangular PZTelementarray,ShoreD-80polyurethanematrixwithvoids.Diceand Fill ArrayComparison Several45 elementinjection moldedPZT2-2 preformshavingpitchdiametersofapproximately150|imwereassembledintocompositetransducersfo r evaluationan dcomparisonwith conventionally producedarrays.Conventional arrayswerediced byTetradCorporationfrom Motorola3202HDceramicwithsimilardimensionsto thoseofth einjectionmoldedparts.Severaldifferentpolymer filler materialswerecharacterizedan dusedtofillth espacebetweenthePZTstrips.Thepropertiesfo rthesematerialsaregivenin Table1 .


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26Table1 .Propertiesofpolymer fillermaterials usedin fabricatingth e2-2 arrays.

Material V, long(m/s)vhear(m/s) DensityJ(g/cm

ShearModulus(xlO'")

BulkModulus(xlO'')

Young'sModulus(xlO'')

Poisson'sRatio long(dB/mm

@7.5MHz)

a,.hear(dB/[email protected])

M SI Solid0 2110 728 1.095 5.80 4.101 1.663 0.432 6.6 16.4M SI Solid0 2270 966 1.144 10.88 4.472 2.967 0.389 2 .1 8.9M SI Solid5 2470 1084 1.175 13 .81 5.328 3.813 0.381 2.1 11.8M SI Voided80 1790 854 0.914 6.67 2.040 1.803 0.353 7.8 9.9M SI Voided85 2000 966 0.958 8.94 2.640 2.410 0.348 6.3 11.3TetradEpoxy 2560 1120 1.121 14.06 5.472 3.886 0.382 3.8 6.4TetradUrethane 2425 1050 1.263 13.92 5.571 3.856 0.385 1.35 6.2

Priortoth eadditionofsputteredgoldelectrodes,PZTstrip,polymerwidth,an dcenterto center spacing was measuredat12locationson eachdevicean daveraged.Volumefractionswerecalculatedfrom themeasureddimensions.Eachcompositesamplewas cu tintotw orectangularsections;on epiece(A )had it slongestdimension parallelto thePZT stripswith itslength > 2timesit swidth,theother(B)had itslongestdimensionperpendicular to thestripswithitslengthalittlelonger thanitswidth.Thedimensionswerechosenso thatlowestresonancewouldnot coupleto othermodesan dcouldbeusedto measureth esoundvelocityan dcouplingto thelateralmodesin bothdimensions.In each caseth esmallest lateraldimension was atleast10timesthethicknessto preventinterferencewithth elowestresonantthicknessmode.Capacitance an ddissipationweremeasuredat1 kHz.ResonancemeasurementswerealsomadesingtheHP4194A Impedance/Gain PhaseAnalyzer.Eachimpedance/phaseplotwas madeoverawiderangeoffrequenciesan dmodesidentified.Thelowestresonant modewas characterized bythepositionof th econductance peak(f r)an d th eresistancepeak (fa).Couplingconstantan dlateralvelocity (assuminghalf waveresonance)werecalculated usingIEEE standards[5] .Similarmeasurements weremadefo r th ethicknessmoderesonance an dth ecouplingcalculated.Atthethicknessmoderesonance,th eminimum impedancewas recordedfo rcalculatingQm[6 ]an dtheStopband EdgeResonance(SBER)frequenciesweremeasuredat th ephasepeakasanapproximateindicator oftheirresonance frequency.Figures3 4an d3 5areimpedanceplotsofinjectionmoldedan ddiced-and-filledcomposites.Thetw oplotswerenearlyidentical.Bothcompositesweremadebyfilling with thesamesolid80polymeran dwerecut to th eBdimensions.In eachcaseth elowestresonance mode(atapproximately130Hz)was th elateralmodeofthelargestdimension. Abovethat,at-400kHz,th eotherlateralmodecoupleswiththethirdharmonicofth elowerresonance.Theovertonesoftheselateralmodesdiedout quickly,so thatthethicknessmodefundamentalwas clearlyvisiblebetween6an d8MHz.Abovethethicknessmoderesonance,SBERswerevisible.Thehighestresonance seenat -25M Hzwas th ethirdharmonicofthethicknessmode.


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27A : IZ I B : 9 AAX S.80B KO BAX 100.0 d eg

AMIN 1.000B/D1V 20.00 f t STARTdts STOP 180080.000HE3000 0000.000HzFigure34. Impedanceplot ofa2-2 injectionmolded composite.

Closeexaminationofth eimpedanceplotsshowedthatthelateralmodesin thedirectionsperpendicularan dparallelto thePZTstripswerenearlyidenticalfo r theinjectionmolded an dth edicedsamples.Asexpected,thecouplingin th edirectionofth estripswas substantiallylargerthanin theperpendicular direction.Figures36an d3 7areimpedanceplotsofth ethicknessmodesfo r an injectedmoldedcompositean dadicedsamplecu tin theBdimensions.Theslight roundingofth ephaseploton th eresonance(left)sidewas du eto thethinelectrodesusedfo rcharacterization.Severalsampleswerecoatedwithadditionalelectroplated electrodes,but thecouplingconstantvaluesmeasured beforeand after coatingwereunchanged.

A : IZ I B : 6AA X S.000 KftBA X 100.0 dto

AMINB/DIV 1.00020.00 R STARTdeg STOP 100008.000Hz30080000.800HzFigure35. Impedanceplot ofadiced-and-filled2-2 composite.


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2 8

A : IZ I Bi 8AAX 1.000B MA X 100.0 dfa|- n~"\J/~ -

1 " 1 . . . . . . . . . .

i.U "U- ,AMIN 1.000BM[N-1B0.0 STARTdog STOP 5000000.000Hz10000000.000Hz

Figure3 6. Impedanceplot ofthethicknessmoderesonancefo r an injectionmolded composite.TwomajorSBERscorresponding to th etw omajorSBERsexpectedin 2-2 compositeswereseenin th eimpedanceplots(Figures34an d35).ThelowerSBERisassociated withalaterallongitudinalresonanceoftheceramicstripan dtheupperonewas associatedwiththelateralshearresonanceoftheceramic[7].Thepredictedlateralresonancefo rsample# 1 was12.2M Hzan dthepredictedshear resonancewas at16.3M Hzwhicharenearlyidenticalto th emeasuredvalues.Theresonancesin th edicedsamples,whilelessstronglycoupled,appeared to bemoredistinct.

A: IZ IAAX B M A X B ! 0I.B00100.0 KB da


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29Theinjectionmolded compositesperformedverywellwhen comparedto th edicean dfillsamples.Thebestsampleswerewithin2% ofthepredictedlq .In general,theinjectedmoldedsampleshad slightlylowerk 3 1valuesan dlessdistinctSBERswhichareadvantageousfeaturesfo rthicknessmodetransducers.

Table2.Summaryofmeasuredpropertiesofinjectionmolded(mold)an ddice-and-fill(diced)transducers.Sample Fab. Filler vol% K p (g/cc) k, V z (mm/(is' Qm k3, VX(mm/|J.s k3, V j(mm/us]1 mold 80 82.9 2384 6.463 0.66 4.063 18.2 0.351 2.98 0.208 1 .7162 diced ureth 72.8 2343 6.031 0.66 4.246 14.4 0.386 2.86 0.194 1.703 3 mold 80 80.7 2439 6.355 0.66 4.024 18.6 0.33 2.93 0.238 1.671 4 diced epox 74.8 2520 6.067 0.65 4.047 5 .5 0.299 2.85 0.202 1.682

128 ElementArray Fabrication and Test:Theobjectivefo rbuildingthe128elementarraywas to compareth eprocessabilityan dimagequalityof an injectionmoldedcompositearraywithadicean dfillarray.Unfortunately theinjectionmoldedcompositechosenfo rarrayfabricationdidnot match an ydicean dfillarraysbeingfabricated byTetrad.A headto headcomparisonwas thereforenot possible.Tetradselected a3 .0 M Hzlinearsequencedarraythatitwas buildingfo ranother customerasthetestvehiclefo rthiscomposite.henominalspecificationsfo r thearrayaregivenin Table3.

Table3.Arrayspecifications. Property Value

NominalCenterFrequency: 3 .0M H zNumberofElements: 128 Pitch: 0.35m m Elevation Width: 18m m GeometricFocalDepth: 90m m

Theinjectionmolded compositematerialhad a nominalpolymer width of75 [im an danominalceramicwidthof125um .Usingthecriterionthatth epolymerwidth should besmaller than0.25ofapolymershearwavelength,it was determinedthattheoperatingfrequencyshouldbelessthan3 .2 MHz.Thearraywas designedfo rsteeringatth eedgestoproduceatrapazoidalimage.etrad'simagingsystem isnotcapableof thismode.his madethetotalarraylengthsomewhatshorterthannormalfo ra3 .0 M Hzarrayyieldingan imagethatwas longan dnarrow.hesmallpitch(which was stilllargeenoughto requiresubdicing)alsoyieldsaspectratiosthatarelessthanidealfo r3 .0 MHz.ecauseoftheseconsiderations,Tetraddecidedto us eth esamearraygeometrybuttopush thefrequencyashighasreasonably possible.Thehigherfrequencyismoreappropriatefo ran unsteeredarrayofthislengthan dtheus eofthinner compositeimproves theaspectratio.Theinitialcompositereceivedfrom M SIwasa1"x2.25"x0.015"samplefilledwithM SIEM/R20filler.his samplewas electrodedan dcu ttoarraydimensionsbyTetrad.Uponcarefulinspection,acrackwas discoveredin thecompositeextendingbetweenthe


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3 0 ceramican dpolymerfo rsomedistancean dthenacrossthepolymer.hismadeitunusablefo ran array.Subsequently,M SIprovideTetradwithan unfilled-2 compositepreform.etradfilledth ecompositeusingthematerialthathad beendevelopedfo rdice-and-fillcomposites,groundth esampletothickness,appliedachrome/copper electrodean dcut itto size.hepropertiesof thefilleraregivenin Table4an dthephysicaldimensionsofth ecompositein Table5.

Table4.PropertiesoftheTetradfiller material.Property ValueLongitudinalVelocity 3.02mm/|is

LongitudinalAttenuation 1 .0dB/mm@ 6.5M HzShear Velocity 1.54mm/(isShear A ttenuation 3 .7dB/mm Density 1.161g/cc

Table5.Measureddimensionsofth earraycomposite. Paramet er ValueMeanpolymer width 89urn (0.0035")

Meanceramicwidth 133ur n(0.0052")Meancenter-to-center spacing 222ur n(0.0087")Ceramicvolumefraction 60 %

Thehighershear velocity oftheTetradpolymerallowedthecomposite to bepressedtoadesign frequencyof4. 4MHz.asedonTetraddesigncriteriath ecompositewas groundto athicknessof0.345m m an dcu ttoth efinaldimensionsofthearray.hecompositewas sputteredwith athinlayer ofchrome(exactthicknesswas not known)an dvapor-coatedwithathinlayer ofcopper(thicknessalsonotknown).hecopperthicknesswas increasedtoapproximately1.3|imbyelectroplating.hewraparoundgroundwas isolatedbycutting justthrough th eelectrodewitha dicingsaw.hecompositewas poled in ai rusingan Efieldofapproximately7600V/cm.ThepropertiesofthecompositeweremeasuredusinganHP 4194NetworkAnalyzeran dareshownin Table6.

Table6.Propertiesofth ecomposite.PropertyK,

RelativefreedielectricconstantStiffenedvelocity(m/sec)Density(kg/m J)AcousticImpedance(MRayls)LowestStopBandEdgeResonanceFrequency (MHz) Value0.611 16.3 2351 4056 49402 0 8. 0


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31 Theperformancewas withintherangeofdice-and-fillcomposites whichoftenrangein couplingbetween0.60an d0.64.Thebasicstructureofth earrayca nbeseeninFigure3 8.

OUTERM A T C H I N G INNERAY ER M A T C H I N G L AY ER F R O N T FAC E E L E C T R O O EPIEZOCE RA MIC

FRONT F A C EGROUND FOILFigure38. iagram ofan arraymadeusing2-2 composite.

Thearraywas constructed byTetradusingtheirstandard fabricationtechniques.Thearraydimensionsareshownin Table7.Table7.Thephysicaldimensions usedintheconstruction ofthearray.

Property ValueKerf Width(crossdice): 0.0394mm (1.55mils)CrystalThickness: 0.345mm (13.6mils)IM LThickness: 0.142m m (5.6mils)OM LThickness: 0.109m m (4.3mils)DicingDepth: 0.569(22.4mils)

Thecompositewas electrodedwitha"wrap-around ground configuration."heground electrodecoveredtheentireouter faceof thecomposite,connected to electrodematerialon thelongsides,an dwrappedto coverasmallpartofth einnerface.nunelectrodedsectionseparatedth eground from theactivepartoftheelectrodethatcoveredmostoftheinnerface.hestripsofthe2-2 compositewerearranged so thattheyextendthelengthofthearray.heisolationbetweenhot and groundelectrodeswas alongthestripsrunning th efulllengthofth earrayon bothsidesofthecomposite.Thiswrap-around groundis not shownin thefigure.)Theouterfaceofth ecompositewas bondedtothedoublematchinglayersystem (referredtointh efigureasth einner[IML]an doutermatchinglayers[OML])whichwas attachedto adicingblock.Table8liststhepropertiesofthematchinglayers.


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3 2 Table8.Bulk matching layermaterialproperties.

Property ValueMLLongitudinalVelocity 3.14mm/(isMLLongitudinalAttenuation 1.8dB/mm@ 7.5M H zMLShearVelocity 1.39mm/|0,sMLShear Attenuation 1.8dB/mm@ 2.25M HzMLDensity 2.43g/ccMLAcousticImpedance 7.6 MRaylsOM L LongitudinalVelocity 2.4mm/|isOM L LongitudinalAttenuation 2.6dB/mm@ 7.5M H zOM LShearVelocity 1.05mm/jisOM LShearAttenuation 5dB/mm@ 2.25M H zOM L Density 1.11g/ccOM LAcousticImpedance 2.66MRayls

Thestack ofthreematerialswas dicedonth edicingsawwithth eouter compositefaceon top.heheightofthebladewas adjusted to leaveapproximately27|im ofth eoutermatchinglayer undiced.hedicingpitchwas exactlyonehalfof theelement pitchleavingtw olayers.Thefigureshowsdicingthroughth ecompositeonly.) tthispoint,th ecompositehad smallpillarsmakingthestructuresimilar to that ofa1-3composite. Flexcircuitswithmetalleadsextendingpastthepolyimideweresolderedto th einnerfaceofthecomposite.his was donein suchaway thateachflexleadtiedth etw osubelementstogether. Allod dnumberedelementswereconnectedbyaflexcircuiton one sideofth earrayan dallevennumberedelementswereconnected byaflexcircuitattachedontheoppositeside.A filler materialwas thenplacedin thecutsto improvethemechanicalstabilityofthearray.Thewrap-around grounds,whichwereseparatedinto piecesbyth edicingprocessweresoldered backtogether usinga busswire.A premadebackingmaterialwas bondedto th einnerfaceofth ecompositein such away thatth esolder jointswerethenembeddedan dprotected.The flexcircuitswerefolded90 degreesto exitatth ebackofthearrayan dth egroundconnectionwas madeto thebackoftheflexcircuits.A siliconelenswas castontoth efaceofthearrayan dth eentireassemblywas pottedintoa plastichousing.A cablewithasystem connectorwas attachedto th eexposedflexcircuitleadsan dthefinalcasewas placedover theentireassembly an dbondedintoplace.Thefirstarraycompletedhad127workingelementswithfour thatwere4to10dBlowin amplitude.his isagoodresultfo ran initialru nwithane wmaterial.heperformancewas verygood. summaryisgivenin Table9.


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3 3 Table9.Arrayperformance.

Property Value MeanCenterFrequency 4.18M H zMean6dBBandwidth 3.32M H z79.5%)Mean-6dBPulseLength 0.3is Mean-20dBPulseLength 0.73(isTotalVariation(excludingproblem elements) 3 .1dB FocalLength (flatPlate) 88m m

Thetimewaveforman dspectrum ofatypicalelementisgivenin Figure39.

&eleetaN*er otPloltpelPageam- .

View^PiintOP'**,:ViewSelling ?#&*Elements- '

3c-e

CuttentEfff/oorflMm ,89037 r,V

PuL-cLonglh ~5


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3 4Thecompositearraywas superiortotheceramicarrayin everyparameterexcept-20dB RelativePulseLength.hiswas probablydu etothefactthatthematchinglayersfo rthecompositewerenotoptimized.hesensitivity comparison isslightlymisleading.helower ceramicvolumefractioninthecompositearraywouldordinarilyleadtohigherelectricalimpedancesan danapparentlossof sensitivity.nthiscaseth eincreasein centerfrequencycompensatedthiseffectsothattheelectricalimpedanceswerecomparable.Thearraywas integrated intotheTetrad2200systeman dphantom imagesweremade.Typicalphantom imagesareshownbelow asFigures40 through42 .heceramicarraydidnot haveaconnectorthatwas compatiblewiththeTetrad2200so comparativeimaging was notdone.ve nifitha dbeendone,th edifferenceincenterfrequency wouldhavemadeth eresultsdifficultto compare.etrad'sprimaryimagingengineerhoweverha shad manyyearsofcomparingimagesfrom variousarraysan dconcluded thattheimagequalityproducedbyth earraywas excellent.hisisconsistentwiththetestresultsgivenabove.Figure40 showsthatth eprobepenetrates tothebottom of theRMI414Bwhilestillachievinggoodresolution in thenearfield.igure41demonstratesgoodaxialan dlateralresolutionthroughouttheimage.igure42 showsexcellentaxialan dlateralresolutionin th enearfield.

Figure40 .hantom viewshowingpenetration.


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35

WUW 12:11S B P R O I O ionmo2B.J)t0RW tmammm twamsiO Ro.SUtlEtE N f i U H O O O ,O BOltt

||MM0

z-

f'g

I' - i X

I8-

1* .. . -renwo

Figure41 .hantom viewshowingresolutionthroughoutth eimage.

Figure42 .hantom viewshowinggoodnearfieldresolution.Theconclusion ofth estudywas asfollows:

1.njectionmolded2-2 compositesca n bemadewithperformanceequivalent to thebestdice-and-fill2-2 composites.2.njectionmoldedmaterialsca nbeeasilyprocessed byusingth esamecarean dprecautionsrequiredfor handling2-2 composites.3 .rrayscan beconstructedusinginjection molded2-2 composites thatdisplay exceptionalbandwidths(approximately85%,-6dBroundtrip)an dsensitivity comparabletoceramicarraysifth eeffectsof electricalimpedance mismatchare compensated.4.magesmadeusingthe2-2compositearraysdemonstrateth eexcellentqualitythatwouldbeexpectedfromanarraywith85 %fractionalbandwidth.ounusualartifactswereapparent.


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36

TTCPPiezocompos i tes:In conjunction withotherTTCPgroups,M SI participated inthreeTechnicalCooperationProgram activities:hydrophones,stackedtransducers,an dmine-huntingarrays.heTTCPparticipantswere:Canada: RoyalMilitary College(RMCC):Piezoelectricmeasurements.K:trathclydeUniversity(SU):Piezoelectric compositemodeling,designan dtesting.Fugro-UDI(UDI):Undersea arrayintegrationan dsystem testing.DRA:ydrophonetesting.USA:RL-USRD:Testing,inputon USNavyneeds.Weidlinger Associates(WA):Modelling.Ultrex(formerlyUltraSoundSolutions):Underseaarraydesign.MaterialsSystemsInc.(MSI):Materialsdesignan dfabrication.Afterseveralmeetingsan dsomerevision oftheprogramplan,thecollaborationbecamefullyoperationalin allthreetechnicalareas.heplantookintoaccountthediffering defenseneedsofthevariouscountriestotheextent possiblewithintheavailabletimeframe andfundingconstraints.Hydrophones: 1-3 piezocompositehydrophonesareof considerableinterestto th eUK Navyfo rflankarrays,an dthereforesignificanteffortwas devoted tomodelling,fabricating,an dtesting M SISonoPanelconfigurationsfo rthisapplication.nthefirstsixmonthsofeffort,M SIsuppliedtw oencapsulated 75 m m SonoPaneltransducersto DRA.hesewereRVStestedat lo w frequency (-50Hz)an dfoundto have-185dBrelV/uPasensitivity,thesameasthatmeasuredat1-100kH zon100 an d250mm samples.incethen,tw omoresamplesweresuppliedto DRA fo rfollowuptesting.heseweredemonstrated tohaveflatresponsewithin2dBoverth efrequencyrange10Hzto 80kHz.StrathclydeUniversity performed modellingof th ehydrophonesaspart oftheirTTCP commitment.M SIsupplieddataan ddesign parametersto both SU an dW A fo r modellingpurposes.heonlydatathatwereno tavailablewereth emechanicalproperties ofth eGRPcover platematerials.ocircumvent theproblem,M SImadeaspecial100 m m SonoPaneltransducerwithaluminum cover platesbecauseitwas easilymodeled.Resultsfrom USRD indicatedthatthisdeviceha dinteresting resonancebehavioran ditsbandwidthwas significantlywider thanthat ofGRPcover-plateddevices.hehydrophonedataan dconclusionsweredetailedin aseparateTTCPreportsubmitted byStrathclydeUniversitytoONRan dDRA.USRDha sdevotedconsiderableefforttoevaluatingth eresonance/frequency behaviorofencapsulated SonoPaneltransducers. spuriousresonancewas notedin unencapsulated devicesat100 kHz,lowerthanthethicknessdilatational mode(-220kHz)fo rthecompositecorematerial.hismay havebeenamass-loaded thicknessmoderesonance thatcorresponded to thatof theentirecover-platedstack.po nencapsulation,thespuriousmoderesonancefrequencydroppedtoapproximately70 kHzwhenmeasuredin air.Whenimmersedin water,the70 kHzmodeshifted backto100 kHz,indicatingthattheencapsulationmaterialwas acoustically-transparentatthisfrequency,an dthe


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37transducerwas resonatinglikean unencapsulateddevice.SRD an dM SIpursuedthiswithW A an dSUin anattemptto better characterize th eresonancemodean dimproveRVSan dTVR performanceuniformity.etailsofth echaracterization workwerereportedseparately byUSRD.In related activity,M SIsuppliedsamplesofencapsulatedan dunencapsulatedsoftmatrix materialsto RMCCforacoustic characterization.hisproveddifficultdueto th ehighly absorbingnatureofth eEN2matrix,an dcharacterization ofthismaterialwas discontinued.owever,characterizationofharder m atrixwas performed.oachievethis,M SI builta completese tof1-3compositesampleshavingsolidShoreD80matrixin th estandardSonoPanelconfigurationfo rus ebyRMCCin acompletecharacterization toIEEEStandards.heresultswerereportedunderTTCPauspices.hisisbelievedtobethefirstfullscalematrixdeterminationfo r1-3piezocomposites.StackedComposites:SUan dU DIhaveperformed modelling workon stacked1-3composites,aswellassomematerialstestingon diceddevices. ndertheTTCP,M SImadesomestacked,unipolarpiezocompositeshaving30volume%PZTin ahardpolyurethanematrix,aswellastwo-layerdeviceshavingoppositepolarity.igures43 an d44show datafrom two-layerdevicesshowingexamplesofbothpolarities,fo rwhichth eimpedance/frequencybehaviorwereverysimilaran dthethicknessfundamentalmodeoccursat90 kHz,asexpected fo rawell-bondedcomposite.igure45showsa modifiedmultilayer compositein whichth ethicknessmoderesonance ha sbeenreducedto 45 kHz.

1 5%PZ THARD-2DOUBLETHICKA : I Z l B : oMK RAMAX 100.0 K C 3 MAGBMAX 80.00 degPHASE 90910.000Hz521.900-23.7474 deg

AMI N00.0TART000.000HzB/DIV0.00egTOP000000.000HzMKR 9590 5HZ MAG6.62K f i PHASE17.55Figure 43 . Impedance/frequency characteristics of unipolardoublelayer1-3

piezocomposite inhardpolyurethanematrix.


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3 8

1 5%PZTDOUBLETHICK;A : Z I B : MKRAMAX 500.0 K f l MAGBMAX BO.00 degPHASE 45095.500HZ936.156 31.5 19 76 deg

AMI N 500.0 Q START00.000HzB/DIV 20.00 deg STOP 1000000.000HzMKR 2 0507 9HZ MAG1.13KR PHASE-40.15Figure44 . Impedance/frequency characteristicsofmultilayer1-3piezocomposite in hardpolyurethane matrix.

A : IZ I: SMKR A MAX 500.0 K C 2AG 100.0 deg PHASEMAX 45095.500Hz297.512 042.9036 degAMI N00.0TARTB/DIV0.00egTOP*MKR2 02579HZ MAG34 1 100.000HZ100 0000.000HZ. 20 PHASE-49.09

Figure45 . Impedance/frequency characteristicsofmodified1-3doublelayerpiezocompositein ShoreD-85polyurethanematrix.Piezocompositesfo rUnderseaImaging:A minecounter-measures (MCM)arraydevelopmentteam was formedin1994for thepurposeofdeveloping advanced sonararraydesigns,an din particular,obtaining broad bandwidth,highsensitivityoperation.ea m tasksincludedidentifyingapracticalM CM applicationwhichwouldbenefitfrom advancedcompositearrays,esigningan array(s)to meetthatapplication,simulatingthedesign of thesearraysusingan advanced time-domainfiniteelementcodedevelopedbyWA,developingcompositematerialsan darraystructures to improvearrayperformanceparameters,and buildingan dtesting feasibility ofarraystructuresan dprototypearrays.Following a reviewofpotentialunderseaimagingapplications,a particularforward-looking,slant beam applicationwas selected. tradestudywas conducted byTTCPmembersfo rsystem an darraydesignsthatwouldmeetthesystem requirements fo raminimum 90scansectorand aminimum numberofchannelsthatwouldfi tinsidea23 5 m m widefootprint.A curvedarray(Figure46 )solutionwas adoptedoveraphasedarray,sinceitplaceslessstringentrequirementson theelementacceptanceangleand requiredsystem delays.hegoalarrayspecifications arelistedin Table11.


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3 9

Figure46.Photograph of100 elementrototypecurvedarray.Table 11.Arrayrequirements.

Center FrequencyBandwidth ArrayEnvelopeBeamwidth VerticalBeamwidthScanSectorwith FullBeamwidth

375 kHZ 250kH z23 5mm widex150m m deep1.5at500kHz15 at500kHz90

Therequirementfo r1.5beamsat500kHzyieldeda115mm aperture.From gratinglobeconsiderations,thepitchof thearraywas chosento beone wavelengthatth emaximum frequency,or 3 mmat500kHz. ssumingthatthemaximumacceptanceanglethatca nbeobtained in an arrayofonewavelengthpitchis30 ,theminimumradiusofacurvedarraywith a115m m aperturewas115mm from simplegeometry.Achievinga90sector usingafull115m m apertureovertheentiresector requiredusinga150curvedarray.helengthofthisarraywas 3 00 mm,whichyielded100 elementsona3 mm pitch.heactive lengthofth earrayis120 mm,which yields40 activeelementsfo ran yone scanline.With thispitch,therewere60scanlinesin the90sectorseparatedby1.5,matchingth ebeamwidth parameter.hedesired15verticalbeamwidthat500kH zwas obtainedusingan elevationalapertureof11.5mm.helengthofthis150 ,115m m radiuscurvedarrayprojectedontotheazimuthalaxiswas 23 2mm,meetingthespacerequirement. mainissuewiththeus eofthiscurvedarraywas achievingthetheoretical30 acceptanceanglein acompositearraystructurewhichcouldwithstandsomehydrostaticpressure.TTCP team membersatUDI-Fugrowerealsocharteredto developasystem testbedfo rdemonstrating thisarray.nthelastyearoftheprogram,anon-realtimedigitalbeamformer was builtthatwouldnotonlyswitchbetween elementstoslidetheactiveaperturearoundthearray,butalsoprovidefocusingfo rnear-field imaging.his system


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40was usedwithth ecurvedreceiverarraydescribed,and asingleelementcurvedtransmitterin imagingtests.Compositeand Array Design:Thepiezoelectricmaterialusedinthearraywas a1-3compositeofPZT ceramicinapolyurethane matrix.MSI'sinjection-moldedcompositetechnology,whichwas expected tolowerth emanufacturingcostofarrays,was chosen.hedesignofth ecompositewas adjustedtofi t MSI'scapabilityin fine-scalecomposites.everaldesignswereconsideredbasedon somerulesofthumbdevelopedattheUniversityof Strathclyde.Originally,twas desiredtohaveatleast5ceramicpillarsin azimuthper element,an da50% volumefractionratio.Severalnew compositeconfigurationswhichwereconsistentMSI'smoldingtechnology at thattimeweredesigned,fabricatedan dtestedunderthistask.hey areshownschematically in Figure47 .he2x8 configuration(Figure47a)wasinvestigatedfirstbecauseitcouldbefabricatedfrom existingtooling.he3x12an d4x16designs(Figures47ban d47c)requiredconsiderable effortin new toolingdesignsan dmoldingprocesses.

3x22 TV'Sdin2x8

! !f3 i & m

H L p U il" r50 volume% PZ T Pitch:l500umPillarwidth:061rnExistingtooling

3x12PUB!BIB! MlHUH mmlamm-mxmm was* nunmm

40volume% PZ T Pitch:992Mm Pillarwidth:624umNewtoolingapproach

4x16 mmmwmaaanoPI

40volume% PZTPilch:750llmPillarwidth:474umNewtoolingapproach

WwwmndHHB tanippdama40volume%PZ T Pitch:992umPillarwklth:624|tmTwilinj:modification

Figure47 .-3compositedesignsinvestigatedunderth eTTCP portionofthisprogram.Initial3x12moldedpreformssuffered from ejectionproblems,which ledto brokenpins.A varietyoftoolingmodificationswereimplementedtosolvethisproblemand producegoodceramic preforms(Figure48).hemostsignificantchangeswhereth eadjustmentofth edraftanglean dcarefulpolishingof themoldinserts.imilardevelopmentwas performedwithth e4x16configurations withgoodresults(Figure47c).owever,theywerenot readyat th etimeof th edesigndown-selection,so 3x12 compositewas usedin arrayfabrication.hemoldingtechnologyfo rthisconfigurationisnow maturean dcompositemadefrom thesepreformsisbeingusedin avarietyofcommercialapplications.Thecompositepillarsin the3x12configurationwerechosento be0.63m m squarean dregularlyspacedon a1m m pitch,leaving3 pillarsinazimuthan d12pillarsin elevation


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41 undereachlementelectrode.he elementelectrodeswereseparated bythe0.37mm spacing betweenadjacentpillarsascanbeseenin Figure47b.Maximumsensitivity ofatransducerisobtained byoperatingat resonance;manysonardeviceshavelargebandwidths,obtainedbyoperatingbelowresonance,sacrificingsensitivityasaresult.ollowingtheusualpracticein commercialapplications,thisarraywas designed to operateatresonanceformaximumsensitivityan dto us eamatchinglayertoachieveup to oneoctaveofbandwidth[8]. single,continuousmatchinglayerwas designed to testthepropertiesofthematchinglayerwithth ecomposite,and validateth eeffectivecompositeparametersusedin th esimpleID model.twas expected thatgoodtransducercharacteristicswouldbeobtained,includingsmooth bandshaperesponse an dth erequiredbandwidthusingamatchinglayer of4.24MRayl.hiswas demonstratedin an earlyprototypemodule.

Figure48 .hotographofa3 x12PZTpreform usedin theprototypearrays.Experience hasshownthata continuousmatchinglayer willlimit thedirectivitypattern below th etheoreticalvalue,30in thiscase.Asexpected,verylowacceptance was observedon thearraymodulewithcontinuousmatching layer.herefore,adicedmatchinglayerdesignwas generated tosolvethisissuebasedonexperiencewithmedicalarrays. icingth ematchinglayer,however,increasedthecomplexity of th edesignsubstantially,sinceakerffillingmaterialhad to befoundthatnotonlykeepstheelements decoupledto obtainthedesiredacceptanceangle,butsurvivein ahighpressureenvironment.naddition,themodesexcitedin thematchinglayerareconsiderably morecomplexsincelateralmodesinthedicedmatchinglayerwillstrongly coupletothepreferred mode. singsimplecoupledmodetheory,which was showntohavegoodcorrelationtothelowestordersymmetricLambwave[9],an effective velocityan dimpedancewas generatedto use inthedesignsimulationtools.hematchinglayerstructurewasthoroughlysimulatedusingthePZFlex FEM toolan dcomparedto experimental results[10].Withintherangeofmatching layeraspectratiosconsidered,th eFEM simulationshowedthattheeffectivevelocityofth elayer was identicalto theasymptotic valueobtainedfrom coupledmodean d Lambwavetheoryoverthelargerangeofaspectratios.his was asomewhatsurprisingresultan dwarrantsfurtherstudy.hematchinglayerusedwas1.8m m thickan dwas dicedcompletely throughtoth ecomposite on a3mm pitchcorresponding tothemajor elementpitch,asca nbeseenin Figure49 .


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42

Figure49 .Schematicofth efinalarraygeometrywithoutelevationapodizationshowingthe12electrodedelements.Havinggeneratedth ebasiccompositean dmatchinglayer design,theremainingke yissueswerethebackingmaterial,compositefiller,an dkerffiller materials.incethisarrayoperatedin receivemodeonlywithlongtimedelaysbetweentransmitan dreceive,almostan ymechanicallyrigidbackingwouldsuffice. simplelowacoustic impedancemix ofSD80polyurethane an dmicroballoonswasused.hekerffiller was an entirely differentstory. ifficultiesin measuringgoodpropertiesoflossypolymersprecludedusingasimulationapproach to thisproblem;onsequently,manysamplemoduleswereconstructedwithvariouslossycompositefilleran dkerf filler materialsin atotallyempiricalapproach.hesearedescribed in thenextsection.ArrayConstruction andTestResults:Several7elementarraymodules(Figure50)werebuiltand testedusingarelativelystiffShoreD80polyurethane compositefillermaterial.Severalsurprisingresultswereobtainedfrom thesesamples.Whileth ecompositebyitselfshowedonlyveryminorlateralan dstopband resonances nearth edesign passband,applyingthematchinglayercausedmanydeleteriousresonancesto increaseinstrength an dsignificantlyreducetheusablebandwidth.nbothth econtinuousan ddicedmatchinglayer cases,astrongresonanceat3 50kHzprovidedunacceptable passbandripple.naddition,thematchinglayerresonancewas foundto beconsiderablylowerin frequencythanpredicted bytheID modelusingeffectivevelocitiesan dimpedances.hisphenomenonca nmosteasilybeseeninFigure51 ,whichshowsth eelectricalimpedanceofon eelementin a dicedmatchinglayerarraymodule.umerousan dregularly spacedresonancesareshown,in additionto coupledceramican dmatchinglayerresonances. lso,asexpected,theacceptanceanglewas below 20fo rthecontinuousmatchinglayercase.nfortunately,theacceptanceanglefo rthedicedmatchinglayercaseshowedlittleimprovement.


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43

Figure50.hotograph of one7elementarraymodule.ft: IZ I B : eKR A MA X 20.00 K 2AG BA X 90.00 d a PHASE 44755.2SBi15.5392 K B AHIM a . B ee aBHI N-90.00 oAMAX-2.00000E+04 100.000Hz 000.000Hz

Figure51 . Air loaded electricalimpedancemagnitudeof one testarrayelementshowingelectronicalharmonics.Aftersomeconsideration,itwas agreedthattheseresonanceswereth eresult oflateralmodeharmonicsin th eoverallarraymodulestructure,mostofwhichresulted from resonances in th e12 pillar,elevationdirection.his becameevidentasth earray manufacturingprocesseswas steadily improved;theresonanceswereclearlyregularlyspacedharmonicsofalowfrequencyfundamental,whichcorresponded roughlyto th eelevationdimension.hesemodeswerealsoseenon aFEM generatedimpedancecurve.Itwas concludedthatalossiercompositefillermaterialwouldneedto beemployedin ordertodampou ttheseresonances.onsequently,aseriesof sampleswereconstructedusingsofterpolyurethane fillers,includingShoreD70 ,ShoreD75 ,an dShoreD65 ,aswellassomemicroballoon/urethanemixtures. Table12summarizes theconstructionofthesecoupons.


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44Table12.Summaryofth e7elementtestcoupons.

Coupon Filler MatchingLayer Encapsulation1 ShoreD80 none ye s2 ShoreD80 ShoreD80 yes 3 ShoreD80 epoxy yes 4 ShoreD80 epoxy no5 ShoreD80 partiallydicedepoxy no6 ShoreD80 diced epoxy no7 ShoreD80 dicedepoxy no 8 voided(20%)ShoreD80 diced epoxy no 9 ShoreD80 none no 10 ShoreD75 dicedepoxy no 1 1 ShoreD65 diced epoxy no 12 voided(20%)ShoreD75 diced epoxy no 13 voided(20%)ShoreD65 diced epoxy no 14 ShoreD65(3x22) diced epoxy no

final ShoreD65(3x22) diced epoxy no Themicroballoons had verylittleeffecton dampening theseresonances;softerfillershelped considerably,butno ttotheextent needed.Manufacturingconcernsprecludedusingevensoftermaterialsthanth egummyShoreD65 urethane. tthispoint,theremaining avenueleftwas toincreaseth enumberofpillarsin theelevationdirection,stillleavingonly12 electroded an delectricallyactive.hisloweredthefundamentalelevational acousticresonancean dallowedagreaterdampinglengthtocomeintoplayfo rth eharmfulelevationalharmonics.twas easyfrom amanufacturingstandpointto generate22pillarsin elevation(seeFigure47);onsequently,afinalmodulewas builtin thisconfigurationusingth eShoreD65 fillermaterial.heair-loaded electricalimpedanceof on eelement ofthismodule(#14)isshownin Figure52 .hesecurvesshow littleevidence ofdeleteriouselevationalharmonicsan dpromisedacceptablearrayperformance parameters.ft: IZ I B: KR A MAX IS.00 K OAG B HAX 98.BB dtg PHASE 29671.800z10.2259 Kf t-38.0759 JAIN 0.888 a START00.000HtBHIN98.80 it% STOP 1 80880.080Hz Figure52. Air-loadedelectricalimpedance ofarraymodule# 1 4showinglittleevidenceofelectricalharmonics.Two-wayimpulsean dfrequencyresponsecharacteristicsweregeneratedfo rthisarraymodulewith sealedai rkerfs(Figure53). Thebandwidthisalessthanth eoriginal


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45 specification(320-425 kHz),butisstillimpressive fo raresonantsonararray.Thetwo-way acceptanceangleis32whichispracticallythetheoreticallimit.

1

ULXJUtM 1

-i\K.A f t .wyii

- - 1 -i 1 1

^ -n^^V^ 1 X n / 3 - z E ^-h ^ ? -iifK' E ^v "$^-a-rl|Tr 3 f|sL" :n h - JKi l ^ JEEEEEEEEE i zEESM lI.1USUU3MMMM]UIJ)Miii. 7 1 7 1M t.U U f. 1

Figure53 . im ean dfrequencyresponseofelementofmodule# 1 4withair-filledkerfs.However,sealedair gapsareunacceptable fo rasonararraydu eto th ehighpressureunderseaenvironment.his arraymodule(#14)was kerf-filledwithastandardsonarencapsulanturethanean dretested.hebandwidthimprovedto 275-485kHzFigure54),butth eacceptance anglefellto only22(Figure55).hi sconfiguration was usedin building th efirsttw ofull100 elementcurvedarrays,whilefurthermoduleswerebuiltto testadditionalkerf fillermaterials.osubstantialimprovementin theacceptanceanglewas notedusingavarietyof soft,lossymaterials.learlytheneedfo raccuratematerialparameters fo rlossypolymersisneededaswellin orderto simulatethisimportantparameterin FEM calculations.Thefinalprototype(S/N003)was thereforebuiltwiththesamekerffillerastheprevioustwo.


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46

*i*

IM5II1UUU> UJlM li)aiUJliU} LT IT )UMS M)

Figure54. Timean dfrequencyresponseof anelementofmodule# 1 4withencapsulant- filledkerfs.

ii-

t

\/ \/--u -It

^lOm-

Figure55.roadbandroundtripangularresponseofan elementofmodule# 1 4withfilledkerfs.Aftertestingthefinalarraytestcoupon,tw o100elementprototypearraywerefabricated(Figure46).Figure57showstheprocessflowfo rarrayfabrication.Ceramicpreformsweremolded,burnedout,an dsinteredin22x45 pin couponswith standardM SIinjectionmoldingtechniques.ThesewerefilledwithSD65polyurethaneand thenlappedtofinalthickness(Figure57).Theouter10elementswerecoveredwithanonconductiveurethane an dthencoated witha conductivesilverepoxywhichservedasth eelectrode.Thenonconductiveurethanepreventedtheouterelementsfrom beingelectricallyaddressed.A


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47filledepoxymatchinglayerwas caston eachcouponan dthendicedthroughtothecompositetoseparateboththematchinglayeran dtheindividualarrayelements(Figure58).Aseriesofarraymoduleswerebondedtogethertoform thefull100 elementarray,wireswereattached,an dthearraycurvedtothedesiredshape.A circuitboardwhichfansou tfromastandardconnectortothearrayelementswas bondedto th etopan dbottomofthecurvedcomposite(Figure59).Thecircuitboardsactedasboth and electricalconnection an dacavityfor castingthevoidedurethanebacking.Wiresweresolderedtoth ecircuitboard,an dtheentirearraywas castin urethane.Theurethaneactedasbothan encapsulantan dakerffiller.

FabricateComposi te

1 ApplyandDiceMatchingLayer Assemble Composi te AttachWires

Encapsulate

Figure56. Theprocessflowfo rfabricatingthe100 elementreceivearrays.Twofullcurvedarrayprototypeswereconstructedbythemethodshownin Figure57with 100activeelementsan dsealedfo r undersea use.Thefirstunit(S/N 001)was builtfo rUSRD,butwas nevershippedbecauseoffacilityclosings.Thesecondprototype(S/N002)was shippedto UDI-Fugrofo rcalibratedarrayreceivesensitivityan ddirectivity tests,an dincorporationintotheirdemonstrationimagingsystem.his particulararraywas slightlyoffradiuson eachend,whichledto phaseerrorsin th ebeamformingprocessawayfrom th emiddlehalf ofthearray. thirdarray(S/N 003)was constructed whichcorrectedthisproblem,an dwas alsoelevation apodizedto reducesidelobes. 16x3apodizationconfigurationasshownin Figure60 was chosen.his was achieved byelectrodingth emiddle3x10pillarsin elevation an dextendingtheelectrodepattern1 x3additionalpillarson bothends.imulationofthispatternshowedthatthesidelobesshouldbereducedfrom -1 2to -2 0dBwhilemaintaining the15beamwidth(at500kHz).Thisarrayhad no tbeensystem testedasofthisreportdate.


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48

Figure57.hotograph ofon earraymoduleafterlappingtofinalthickness.

Figure58.hotograph of an arraymodulewithdicedmatchinglayer.

Figure59.hotographofa partiallyassembled curvedarrayshowingtheintegralcircuitboard.


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4 9

DSDnunDIDHsuHUHDDDDDDDDDDDDDDDDDDDDDDDDDIDDIDDSD

DDDDDDDDDHDDDDDassDDDDDDDDDDDDDDDDDD111DIDDDDDUD

coveredwithnonconductivepolyurethaneon back Helectroded Dno telectroded

Figure60 .chematicrepresentationoftw oarrayelementsshowingtheapodizationpattern.Capacitance an dimpedancemeasurements weremeasured fo reachelementofeveryarraybeforeshipping.Figure61showsatypicalimpedanceplotan dTable13summarizesthecapacitance results.

Table13 .Elementcapacitanceresultsfo r th ethreeprototypearrays.AverageCapacitance

S/N001 104.89.6(9.1%)S/N002 102.87.2(6.9%)S/N003 114.3+10(8.7%)

In addition to th ecapacitancean dimpedance measurements,UDIullycharacterizedarrayS/N 002.ThesesresultsaresummarizedinTable14.


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50Table4.Arraytestresultsfo rS/N 002.

M ax ReceiverSensitivity -193dBrelV/|iPa-3dBBandwidth 208-453 kHz(74%)Beamwidth,250kH z 31Beamwidth,3 75 kH z 30.5 Beamwidth,500kHz 24

COUPONL 7/2/97A : IZ l: 0 o MKPA MAX0.00 Kfi MACB MAX 60.00eg i'rA MIN 1.000 KfiB/OIV 20.00ec*MKR 362 500HZ MAC

; : J 3T'bO.COOH i - oeg

1 i4i3 rN N '\^/ -N; t 7^-V--^.> - ~J H^T 1rV r& \ J \5 v^ " * ^ ^ _ ^ d2-

START 1 00000.000HzSTOP 600000.000Hz2.64KnPHASE-33. 1Figure61 .ypicalimpedanceplotof on earrayelement.

Thesensitivityofthisarraywas comparable tonarrowbandarrayscurrentlyin use,butits74 % bandwidthwillallowfo rseveralbroadbandimagingmodesto beemployed.heelementbeamwidthwasacceptable for mostofth epassband,fallingoffto24 at 500 kHz.Thesecondarraywithimprovedmechanicalphaseuniformityshouldproveusefulin demonstrating broadbandimagingmodalities.OtherApplicationsDemonstrationsCAVESSensors Basedon technicaldiscussions amongMSI,NRL,and NU WC(M .Moffett),an effortwas undertaken to develop velocitysensorsfo rpotentialus ein th eprogram.hemotivationwas to exploitMSI'slow costinjection moldingtechnologyto manufacture thesensorsfo r thisapplication.Traditionally,hydrophones(pressuresensors)havebeenusedtodetect underwateracousticwaves. ydrophoneshavemaximumsensitivity whenmountedon arigidbackingsurface.owever,velocity sensorsaremoreeffectiveacousticwavedetectorsfo rmountingon thecompressible,pressure-releasematerialnow beingusedto coatthehullsof Navyvessels.


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51 Velocitysensorsshouldhavethefollowingcharacteristics: highsensitivitytomotionsnormaltothemountingsurfacelowtransversemotionsensitivitylow pressure(hydrophone)sensitivity lo wprofile(thickness)area-averagedoutputlow electronicnoisefloor(lessthanse astate0ambientacousticnoise)densityequalto thepressurereleasematerials(=1.3g/cc)stabletotypicalsubmarinehydrostaticpressureslowcostMostofth eaboverequirementsweredemonstratedin thiseffort. nalyticalan dmodelingsupportwas provided byNRL(R.Corsaro).Several100x100 x18m m (4x4x0.7inch)panelswereproduced.ac hcontained 16net-shapemoldedmonolithicPZTaccelerometer elements(Figures62an d63)an dalownoisepre-amplifier(Figure64 )inaneutrally-buoyantan dwaterproofpackage(Figure65).helo wnoisepre-ampwas designedan dfabricatedbyNRL.

Figure62. Net-shapemoldedPZT monolithicaccelerometerelementsusedin thefirstgenerationCAVESpanels.


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5 2

Niplate (topandbottosurfacesonly)

1mm

Figure63 . DrawingofmonolithicPZTaccelerometer elements usedin th efirstgenerationpanels.

Figure64. Low-noisepre-amplifierdesigned an dfabricated byNRLan dusedon boardth efirstgenerationaccelerometer panels.hepre-ampdimensionsare10.7x32.7x6.3 mm.


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53

Figure65 . Firstgenerationaccelerometer panelsassembledbyM SIan dtestedatNU WC -USRD.hepanelmeasured100 x100 x18mm an dcontained16PZT monolithicaccelerometer elementsfo r areaaveraging.Each accelerometerpanelcontainedmultiplenet-shapeformedmonolithicPZT-5H accelerometer elementsdistributedthroughoutthepanelin order to obtainan area-averagedresponse.hemeasured sensitivityof eachaccelerometer elemen twas approximately 50mV/g,in closeagreementwithprediction.Animportantfeatureof themonolithicaccelerometerdevicewas thatthemassan dsensorelementswereformedtogether from th esamematerialan din th esamemanufacturingprocess.eparateconstruction of themasswas eliminated,aswas theprocessofbondingth emassto th esensor.eliabilitywas improvedsincethebonduncertaintywas not an issuein thismonolithic design.Anaccelerometerarray,consistingof16monolithicPZTelementsbondedto aGRP(glass reinforced polymer)boardan dusedfo rth efirstgenerationpanels,isshownin Figure66 .Theelectricalsignalsfrom themultiple elementswerecombinedan dfedintoan on -boardpre-amplifierwhichdrivesalength ofcoaxialcable.or th efirstgeneration panels,acustom designed,lownoisepre-ampwas fabricatedbyNRL(Figure64).K ey specificationsfo rthepre-amparelistedin Table15.

Table15 .re-ampSpecifications.Gain 12dBat1 .5kHzSupplyvoltage 18V D CBandwidth(1dB ) 0.4-6.0kH zNoise 1 1nV/Hz 1"at1.5kHz .6 fA/Hz 1"Dimensions 10.7x32.7x6.3m m (0.42x.2 9x0.25inches)


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54

M SIdesignedan dimplementedalow profile,lowdensitypackagefo rtheaccelerometerpanels.igid,lowdensity(0.4g/cc)syntacticfoam was machined withchambersfo rthePZTelementsan don-boardpre-ampan drecessesfo rtheGRPboardaswellasth etopand bottom steelplates.hemachinedsyntacticfoam configurationisshownin Figure67 .heGRPboardan dsteelplatesarebondedto th efoam corewithhigh strengthepoxy.igure68showsapartially assembledpanel.heassembledpackagewas thenwaterproofedwithpolyurethane (Figure65).Thefirstgenerationpanelsshowedgoodaccelerationsensitivitywhentestedin ai ron ashakertable.heinitialin-water evaluation of thesefirstpanelsatth eNavalUnderseaWarfareCenter - UnderwaterSoundReferenceDetachment(NUWC-USRD)indicatedasignificantpressuresensitivitythatisbelieved to bedu eto abasestraintransmittedtothePZT elementfrom thecircuitboardontowhichitismounted.hisproblem was furtheranalyzed an dsolvedunderthene wSmartPanelsprogram (ONR/DARPA contract N00014-97-C-0236).

Figure66. Photograph of16elementPZTaccelerometerarray,withtheindividualelementssolderedtoaGRPboard.


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55 SteelPlateRecess2places21/2"x3" .....V. . GRPBoardRecess21/8"x21 /8 '

r

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7/16"dia.-16places AccelerometerCavi t iy0.313"x1.375"Pre-ampCavi ty

3.625" x3.625"

MOJO So. 0.030'J 1-0.035" Figure67 . Configuration and dimensionsofth erigidsyntacticfoam coreusedfo rthefirstgenerationaccelerometerpanels.

Figure68 . Partiallyassembled firstgenerationaccelerometer panel,showingpre-machinedsyntacticfoam corewiththe16PZTaccelerometerelementsin place.


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56

HydrophoneArraysThehydrophonearraydesignin Track4was basedon previousworktodevelop1-3 compositearraysfo rsubmarineminedetection applications NU WC contractN66604-96-C-E978).heoverallarraydimensionswere7.608"x3.998"x0.300"with0.705"x0.953"individualelements.hecompositematerialutilizedPZT-5Hceramicina"soft"(shoreA60)polyurethanematrix.heceramiccomponentcomprised15%ofthecompositevolume.tiff,lightweightcopper cladGRPcoverplateswerebondedtothecompositesurfacesto maketheelectricalconnectionsto theceramicelements.hecoverplatesweresubsequentlymechanicallysectionedto definetheindividualelementsin th earray(Figure69).

Figure69 .hotographoftopsectionedcompositeusedto maketh e40 elementarrays.Thepiezoelectricconstant(d 33 ),capacitance,dielectricloss,an dpressuresensitivity ofeach elementin th efinishedarraywas measured.heseareshownin Figures70an d71 and tabulatedin Tables16an d17.hirtyfeetof insulatedelectricalcable(typeRG174)was attachedto on esideof eachelement,an da uniform groundplanewas madebyelectricallyconnectingth eothersideofeachelementtogether.wogroundwireswererunfrom thegroundplanefor redundancy.Onearray(#103-1)was encapsulatedinawaterproof polyurethane jacket.heotherarray(#103-2)was mountedontoasoundabsorbingbackingmaterial(Syntech SAD M-1)withaholepattern thatallowedth ewiringtopassthroughit.hearrayan dbackingstructurewerethenencapsulated in polyurethane waterproofing.igure72 isaphotographofth efinishedarray(#103-2).ThefinishedarraysweredeliveredtoNUWC,Newport,RIan dsubsequentlyshipped to Northrop-Grumman OceanSystems,Annapolis,M Dfo rtesting.


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57Table16.haracteristicsofArray#103 -1 .

Row RowRowRowRowRowRowRowRowRow 10d33(+) 550 600 540 540 565 565 540 590 590 575Cap.(pF) 399 380 384 407 392 406 415 389 400 399 ColumnLoss 0.031 0.034 0 .031 0.036 0.04 0.043 0.06 0.065 0 .041 0.044 1 dBv (corr.) -188.6 -188.4 -188.8 -188.5 -188 .1 -188.9 -188.9 -188.8 -188.6 -188.0d3 3(+ ) 565 590 585 540 545 530 555 550 550 575Cap.(pF) 389 424 399 392 420 439 407 408 400 409 ColumnLoss 0 .031 0.037 0.045 0.03 0.037 0.024 0 .031 0.024 0.034 0.026 2dB v (corr.) -188.0 -188.5 -188.5 -188.2 -188.6 -188.6 -188.3 -189 .1 -188.6 -187.9d33(+ ) 630 555 555 540 540 520 550 525 555 585Cap.(pF) 384 406 424 409 431 445 399 418 421 422 ColumnLoss 0.024 0.032 0.038 0.026 0.034 0.025 0.017 0.025 0.022 0.030 3dB v (corr.) -188.6 -188.8 -189.1 -188.6 -188.6 -188.6 -188.5 -188.6 -188.7 -188.5d3 3(+ ) 625 560 575 565 590 580 560 570 580 650Cap.(pF) 383 388 394 398 397 407 414 409 417 420 ColumnLoss 0 .041 0.028 0.029 0.024 0.034 0.035 0.03 0.033 0.034 0.030 4dB v (corr.) -188.9 -188.8 -189.2 -188.9 -188.8 -188.9 -188.8 -189 .1 -188.6 -188.4

-191.0

-190.0

-189.0

C O 188.0

m -187.0

Ave :188 . 6dB Dev . :.3 dB Var.:+ /-0. 7 dB

-186.0

-185.0

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8 1 0 11121 3141 5 1 61 7 181 9 202 12223 24252627 28293031 3233 34353637383940

Figure70 . raphshowingthepressuresensitivity ofarray#103 -1 .lementtoelementuniformity isbetterthanldB.

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