毕业论文外文文献翻译测控技术与仪器聚合物传感器集成到无线数据采集系统中以适合监测环境和生理的发展过程.docx

毕业论文外文文献翻译测控技术与仪器聚合物传感器集成到无线数据采集系统中以适合监测环境和生理的发展过程.docx

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毕业论文外文文献翻译测控技术与仪器聚合物传感器集成到无线数据采集系统中以适合监测环境和生理的发展过程

DEVELOPMENTOFPOLYMER-BASEDSENSORS

FORINTEGRATIONINTOAWIRELESS

DATAACQUISITION

SYSTEMSUITABLEFORMONITORINGENVIRONMENTALANDPHYSIOLOGICALPROCESSES

BiomolecularEngineeringVolume23,Issue5,October2006,Pages253-257

ABSTRACT

Inthiswork,thepressuresensingpropertiesofpolyethylene（PE）andpolyvinylidenefluoride（PVDF）polymerfilmswereevaluatedbyintegratingthemwithawireless

dataacquisition

system.Eachdevicewasconnectedtoanintegratedinterfacecircuit,whichincludesacapacitancetofrequencyconverter（C/F）andaninternalvoltageregulatortosuppresssupplyvoltagefluctuationsonthetransponderside.Thesystemwastestedunderhydrostaticpressuresrangingfrom0to17kPa.ResultsshowPEtobethemoresensitivetopressurechanges,indicatingthatitisusefulfortheaccuratemeasurementofpressureoverasmallrange.OntheotherhandPVDFdevicescouldbeusedformeasurementoverawiderrangeandshouldbeconsideredduetothelowhysteresisandgoodrepeatabilitydisplayedduringtesting.Itisthoughtthatthisarrangementcouldformthebasisofacost-effectivewirelessmonitoringsystemfortheevaluationofenvironmentalorphysiologicalprocesses.

Keywords:

pressure;thickfilm;polymers;

sensor

;wireless

1.Introduction

Inmanyprofessionsandindustries,theabilitytomakemeasurementsindifficulttoreachordangerousenvironmentswithoutriskingthehealthofanindividualisnowanecessity.Awayofwirelesslytransmitting

datafromthesensor,

whichisatthepointofinterest,toaremotereceiverisrequired.Usingthisapproach,

sensors

canbeimplantedinadifficulttoreachorharshenvironmentandleftthereforaperiodoftime.

Sensors

designedtomeasureanynumberofparametersincludingpressure,conductivityandpHcouldbeused（Barrie,1992,Astaras,2002andFlickandOrglmeister,2000）.

Data

transferistypicallyachievedusingradiofrequenciestosendinformationtoareceiver,whichisremotefromtheareaofinterest.

Apartfromindustrialandenvironmentalapplications,these

acquisition

systemscouldrevolutionisethehealthcaresysteminanumberofareas.Theycouldfindapplicationsinthetreatmentofpatientswhichhaveexperiencedextremetraumasbymonitoringcriticalparameterssuchasintra-cranialpressure（FlickandOrglmeister,2000B.B.FlickandR.Orglmeister,Aportablemicrosystem-basedtelemetricpressureandtemperaturemeasurementunit,IEEET.Bio-Med.Eng.47（2000）,pp.12–16.FullTextviaCrossRef|ViewRecordinScopus|CitedByinScopus（15）FlickandOrglmeister,2000）.However,inamoreroutinesettingtheycouldalsobeusedtomakelongtermmeasurementsofbiologicalfluidpressureforclinicalstudiesinseveralareas,suchascardiology,pulmonologyandgastroenterology（Yangetal.,2003）.Inthefuture,itmayevenbepossibletomonitorpatientswhiletheyresideintheirhomeorcontinuetowork（Budinger,2003）.

Withtheseapplicationsinmind,awireless

dataacquisition

system,includingacapacitancetofrequencyconverter（C/F）andaninternalvoltageregulatortoprovideastableoperationhasbeendeveloped.Thecircuitrywasdevelopedtominimisepowerconsumption,aspowerwillnotberandomlyavailableinthetestenvironment.Thesystemwasdevelopedspecificallyforthemeasurementofpressure.Twocapacitivestructureswereformedusingpolyethylene（PE）andpolyvinylidenefluoride（PVDF）forthesensinglayer.Thesematerialswerechosenfortheirbiocompatibleandmechanicalproperties.Capacitivestructuresarepreferredastheyleadtolowerpowerconsumptionandhighersensitivitythantheirpiezoelectriccounterparts（Puers,1993）.

PVDFisalow-densitysemi-crystallinematerial,consistingoflongrepeatingchainsof

CF2

CH2

molecules.Thecrystallineregionconsistsofanumberofpolymorphs,ofwhichtheα-andβ-phasearemostcommon.Theβ-phaseispiezoelectricandhasmanyadvantagesincludingitsmechanicalstrength,widedynamicrange,flexibilityandeaseoffabrication（PayneandChen,1990）.PoledPVDFfilmshavebeenemployedinthedevelopmentofdevices,whichcanbeusedinawiderangeofapplications,forexample,providingrobotswithtactile

sensors

andthemeasurementofexplosiveforces（Payneetal.,1990andBauer,1999）.

Inamedicalcontext,poledPVDFfilmshavebeenpopularinthedevelopmentofplantarpressure-measurementsystems,wheretheirflexibilityandtheeasewithwhichelectrodepatternscanbeattachedhasbeenaparticularadvantage（LeeandSung,1999）.MicromachineddevicesusingPVDFasaflexibleelementinthesystemhavealsobeendevelopedforuseinanendoscopicgrasperbecauseofitshighforcesensitivity,largedynamicrangeandgoodlinearity（Dargahietal.,1998）.

Polyethyleneisacosteffectiveandversatilesemi-crystallinepolymerconsistingofrepeating

CH2

CH2

units.Themostcommonformsarelow-densitypolyethylene（LDPE）andhigh-densitypolyethylene（HDPE）,wherethedensityisrelatedtothedegreeofchainbranching.Itisamaterialwhichisusefulinpressure-sensingapplicationsandhasbeenpopularforuseinthedevelopmentofflexibleelectronics（Harsanyi,1995andDomenechetal.,2005）.PEisparticularlypopularinthefabricationofpolymer/carbon-blackcompositesforpressuremeasurement（Zhengetal.,1999andXuetal.,2005）.Furthermore,polyethyleneterephtalate（PET）hasbeenidentifiedasanelectretmaterialwithpossibledynamicpressuresensingapplications（Paajanenetal.,2000）.

Inthiswork,bothPEandPVDFfilmswereformedintoasandwichcapacitor,whichwasthensubjectedtochanginghydrostaticpressures.Thefilmsdeformedunderpressureandtheresultingchangeincapacitancewastransmittedwirelesslythroughtheliquidtoanexternalreceiver,whichconvertsthesignaltoacorrespondingvoltage.

2.Experimentalprocedure

Thesensinglayerswereintheformoffilmswiththicknessofapproximately100 μm.ThePVDFfilmhasadominantβ-phaseandwaspurchasedfromPrecisionAcousticsLtd.TheLDPEfilmwassuppliedfromGoodfellowCambridgeLtd.TheYoung'smodulusofeachmaterialisanindicationofhowlikelythematerialistodeformunderappliedpressureandisquotedtobe8.3 GPaand0.1–0.3 GPaforPVDFandPE,respectively.

Toformthecapacitors,DuPont4929silverpastewasdepositedusingaDEKRS1202automaticscreen-printertoformelectrodesmeasuring15 mm × 10 mm.The

sensor

structureisshowninFig.1.ThisapproachwasusedasdifficultiesindepositingotherelectrodematerialsonPVDFhavebeenrecorded（PayneandChen,1990）.Afterdeposition,theelectrodesweredriedinairandcuredat100 °Cfor30 min.Theelectricalpropertiesofeachdeviceweremeasured,from1 Hzto1 MHz,usingaSolatronS11260ImpedanceGain/PhaseAnalyser.

Fig.1.StructureofthePVDFandPEcapacitor.

Toevaluatetheperformanceofeachmaterialunderpressure,capacitorswereindividuallyconnectedtotheinterfaceandtransmittercircuit.The

sensor

wasprotectedusingathin,flexiblewaterproofmembrane.Thecircuitwascontainedinaweatherproofhousing.Thiswasarigidstructureofdimensions54 × 59 mm2andwasnecessarytoprotecttheelectronicsfromtheliquidenvironment.Toconnectthe

sensor

totheinterfaceanopeningwasdrilledintothehousingandtheconnectionsweremadewaterproof.

Thechangeincapacitancewithincreasingdepthinaliquidenvironmentwasthenrecorded.Thepressureinthiscaserangedfrom0to17 kPa.Thechangeincapacitancewasconvertedtoafrequency,whichwaswirelesslytransmittedtoanexternalreceiver.Thetransmitterandreceiverarebatterypowered.Acomparisonofthepowerrequirements,thiscircuit（markedwithanasterisk）iscomparedtootherstandardinterfacecircuitsisshowninTable1.AblockdiagramofthetransmitterandreceiversystemcanbeseeninFig.2.

Table1.Powerconsumptionfor

sensor

interfacecircuits

Interface

Currentconsumption

Supplyvoltage（V）（minimum）

UniversalcapacitivereadoutIC–MS3310

2.9–6.0 mA

5

ACbridge

2–10 mA

None

Andersonloop

1–3 mA

3

C-F-V（usingF-Vconverter）LM2907

5–8 mA

3

C-F-V（usingF-Vconverter）TC9400

1.5–6 mA

10

C-F-V（usingPLL）*

<500 μA

2.3

Fig.2.Blockdiagramoftheinterface,transmitterandreceiversystemusedtomakemeasurementsunderhydrostaticpressure.

Themainelementofthe

sensor

interfacecircuitisanintegratedcapacitancetofrequencyconverter,whichisusedtolinkthe

sensor

tothetelemetrysubsystem.AnexternalvoltageregulatorisusedtoimprovethestabilityoftheoutputfrequencyandRFtransmission.ACMOSdualtimer（TLC556）wasselectedtoimplementtheC/Fconversioninastablemode.TheoutputfrequencyisgiveninEq.

（1）.

（1）

wherefoutistheoutputfrequency,Cxisthe

sensor

capacitance,R1andR2arethetimerfrequencyset-upresistors.Afrequencyshift-keying（FSK）transmitterof160 kbpshasbeenselectedtosendthesignalcomingfromtheCMOSoscillator.Atthereceiverside,thereceivedtonesareconvertedtovoltagelevelsusingphaselockedloop（PLL）unit.ThisICisamicro-powerdevicesinceittypicallydraws20 μA.Therelationshipbetweenthefrequency（f）andthevoltage（V）hasbeenmeasuredtobe

f=V×13.1 kHz/V

（2）

Thevalueof13.1 kHz/Vwasfoundbymeasuringtheslopeofthechangeinfrequencywithvoltageforthevoltage-controlledoscillatorasshowninFig.3.ItshouldbenotedthatwhilethePLLunitreducespowersupply,itcreatesanon-linearoutputsignal.Thereforethe

sensor

responsewillappeartobenon-linear.

Fig.3.MeasuredF/Vcharacteristics