




版權(quán)說明:本文檔由用戶提供并上傳,收益歸屬內(nèi)容提供方,若內(nèi)容存在侵權(quán),請進(jìn)行舉報(bào)或認(rèn)領(lǐng)
文檔簡介
ModernSensors
Lecture11X.WuAReviewofLecture10Twotypesofcommonlyusedacousticsensors:Bimorphceramic---likebimetalthermistor/piezoelectricCrystal:ADP,sodium-potassiumtartrate
tetrahydrate----piezoelectricLimitationstoacousticsensingBeamspreadAttenuationduetofrictionwithairandwatermoleculesTargetreflectioncross-sectionPiezoelectricityMaterialconstitutiveequationBasicIntent:ChemicalSensorsOverviewbasicconceptsforsensingofchemicalquantities.Thisisobviouslyanextremelybroadtechnicalarea,sothisoverviewwillbeincomplete,butisintendedtocoverthebasicissuesandsomeapplications.HumanNoseThehumannasalsensingapparatuscontainsaremarkablyflexibleandsensitivedetectioncapability.Youarecapableofdetectinganddistinguishingthousandsofdifferentsmellswithalmostinstantaneousrecognition.Odordetectionismadeverycomplicatedbecauseofthelackofactualuniquenessinthechemicalbasisofmostsmells.Thereisno"garlicmolecule"thatisdistinctfromthe"enchiladamolecule";yetyoucaneasilydistinguishthesesmells.HumanNose(cont.)Allbiologicalodordetectionsystemsarebasedonafairlysmallnumberofdistinguishablesensors.Thesmellrecognitionsystemisbasedonpattern-matchingoftheresponseofthedifferentchemicalsensorsinthenosetovariousodors.Garlicandenchiladasproduceaslightlydifferentcollectiveresponseintheentiresetofsensorsinyournose,andyourbrainhasstoredanextensivecollectionofthesepatternswhichareusedforcomparisons.
Psychologistshavefoundthattheseodorpatternscanbeamongthestrongestofmemories,andsmellsareoftenusedtoaidinthereconstructionofmemories.ChemicalSensingSystemChemicalsensingsystemdesignersneedtodrawlessonsfromthesebiologicalsystems.Animportantlessonisthatamulti-functionalsystemwillprobablyneedtouseasmallsetofdistinctsensorsandapattern-matchingalgorithmtoidentifyodorsaccurately.AresponsivematrixPattern-MatchingalgorithmIdentifyOdorsDetectorsofParticularMoleculesIfachemicalsensingapplicationrequiresdetectionofaparticularmolecule,severaltechniquesareavailable.Thesetechniquesarebasedontheuniquepropertiesofparticularmolecules.Onesetofpropertiesisassociatedwiththevibrationalandrotationalmodesofmolecules.Theexactenergiesofthesemodesisgenerallyuniquetoaparticularmolecule,andmaybeusedforidentificationpurposes.Mostvibrationsandrotationsare"opticallyactive",meaningthattheymaybeexcitedbyabsorptionofaphoton,ormayrelaxbyemissionofaphoton.Thesephotonabsorptionsaregenerallymostlikelytooccurintheinfrared,soinfraredspectroscopyisagenerallyusefulwaytoidentifymolecules.
Forexample,COdetectionCO:Averysimplemolecule(2ballsandaspring),capableofoscillatingatasinglefrequencyrotationsabout2axes(bothperpendiculartothelineconnectingtheatoms).Inquantummechanics,avibrationisrepresentedasasinglefrequencyQuantummechanicsincludes"SelectionRules"whichstronglyfavorrelaxationasinglestepofh/2atatime.Thisfeatureshowsupintheinfraredspectrumasasingleabsorption.COdetection(cont.)InthespectrumoftheabsorptionofCO,weseeapairofabsorptionpeaks.ThispeaksplittingisduetothefactthatCarbonexistsinisotopeswhichhaveatomicmassof12or13.TheadditionalmassoftheC13reducesthevibrationalenergysimplybecauseitlowerstheresonantfrequency:2150-2180wave-numberOr~4.5m(midinfrared)CommercialCODetectorsThebio-mimeticgelsensor:designedtomimicthebody'sresponsetocarbonmonoxidebycontinuallyabsorbinggas.
Metaloxidesensorsaremoreaccurateandarethecommontypeofsensoremployedinhomemodels.Thistypeofsensorusessolidstatetin-dioxidecircuits,whichclearquicklyandcontinuallymonitortheairforpresenceofcarbonmonoxide.
InstantDetectionandResponse(IDR)electrochemicalsensingtechnology,whichisclaimedtobethemosteffectivedetectionmethod.Optical?
On-chipOpticalDetectionMicro-ringresonator:nPressureRotationalenergy:NH3Inadditiontovibrations,moleculesalsocanhaverotationalenergy.InthespectrumofNH3(ammonia),therotationalspectrumcontributesaseriesofclosely-spacedlinescenteredaboutthevibrationalpeaks.Theseexcitationsinvolvetheabsorptionofaphotonandthechangeofboththevibrationalandrotationalenergy.Method1:InfraredSpectroscopyEachmoleculehasadistinctinfraredspectrum.Infraredspectrometersmaybeusedtomeasuretheabsorptionspectrumofagassample,andtolookforfeatureswhichindicatethepresenceofparticulargasconstituents.Inthisinstrument,lightfromasourcepassesthroughasample-filledchamber,thenthroughachopperwheel,afilterselector,andisfocusedontoadetector.Thefilterselectorconsistsofapairoffilterswithverynarrowinfraredtransmissionbands.Oneofthefilter'stransmissionbandiscenteredonthemolecularabsorption,andtheotheriscenteredjustoffthepeakoftheabsorptionbandofinterest.Byalternatingbetweenthesetwofilters,adifferencesignalmaybedetectedonlywhenthemoleculeofinterestispresent.Thisapproachcanbeoptimizedonlyforasinglemoleculeatatime,butisveryreliableforsuchsingle-moleculeapplications.AnexampleofsuchanapplicationwouldbeaCOdetectorforaautomotiveexhaustinspection/monitoringsystem.DifferentiatemoleculesbytheirmassesMassSpectroscopyBesidesthevibrationsandrotations,moleculesmayalsoberecognizedbytheirmass(ormassspectra...).Therefore,massspectrometersarealsousedtodetectanddistinguishmolecules.AdiagramofamagneticmassspectrometerisshownhereMassSpectrometerInthisdevice,
Oneimportantdrawbacktosuchaninstrumentisthatthemoleculesmusttraveltheirentirepathwithoutscatteringfromothermolecules.Inairatatmosphericconditions,theaveragedistancebetweencollisionsis1micron.Sincetypicalmassspectrometersneed10-100cmoftrajectory,thepressuremustbe6-9ordersofmagnitudelowerthanatmosphericpressure.Therefore,massspectrometersgenerallyrequirevacuumpumps.MoleculesIonizedAcceleratedinE-fieldDeflectedinMagneticfieldByLorentzforceAseriesofdetectorsCollect/countparticularmoleculesChromatography:aclassicOperationasampleisaddedtoapressurizedcarriergas,andforcedtodiffusethrougha"column",whichisessentiallyaverylongnarrowtube.Thecomponentsofthesamplediffuseatdifferentratesthroughthecolumn,andthedetectorattheendrecordsasignal-vs.-timetracewhichcontainspeaksthatmaybeidentifiedasbelongingtoaspecificsample.ChemSensorsv.s.BiosensorsThetermbiosensorreferstoanysensorthatusesanactivebiological(orsometimesbiologicallyderived)
componentinthetransductionprocess.Thismaybeasensorycelltakenfromalivingorganism,andmountedonanelectrode.Alternatively,antibodiesmaybeused,whichwilllockontothematerialofinterest,andholditinanappropriatepositionforsensing.Afurtheroptionistouseanenzymethatcatalysesareactionthatcanbedetectedbysuitablemeans.Sincethereisconsiderableinterestinmonitoringbloodglucoselevels(toprovideclosedloopcontrolofbloodglucose,bymeansofanartificialpancreas,fordiabetics),bloodglucosesensorshavereceivedmuchattention.Oneoftheseisbasedontheglucoseoxidaseenzyme;sothissensorwillbeoutlined.Biosensors:bloodglucosesensorsAlotofresearchhasgoneintothesesensors;biosensorsandbloodglucosesensorsinparticular.Whilstprogresshasbeenmade,therearestillalotofproblemstobesolved.Onebigprobleminthisareaisthatthesensorperformancedriftsordegradesovertime,ofteninunpredictableways.Sothedevicehastobecalibratedregularly,orjustbeforeuse.Clearlyabloodglucosesensorthatonlygivesreliablereadingsoveraperiodofahundreddayscannotbeusedinanimplantedartificialpancreas.Thus,whiletherearemanypotentialusesforchemicalsensors,theiruseisoftencomplicatedbycalibrationrequirements.ISFETsensorsISFETssensetheconcentrationofaparticularioninasolution.generallybasedontheenhancementmodeMOSFETstructure.IntheISFET,thegatemetalisreplacedwithanionselectivemembranethedeviceisimmersedinasolution.Ionsinthesolutioninteractwiththeionselectivemembrane.Whenthereisahighconcentrationofpositiveionsinthesolution,alotofthemwillaccumulateonthegate,wideningthechannelbetweenthesourceanddrain.+VProblem:lowyieldforanadhesivemembraneChemFET/integratedISFETGlucoseoxidasebasedsensorTheenzymeisimmobilisedonaplatinumelectrode,andcoveredwithathinpolyurethanemembranetoprotecttheenzymelayer,andreducethedependenceofthesensoronbloodoxygenlevels.GlucoseoxidaseGluconicacidEnzymeconversionEnzymeInteractsw/OxygenionsWater+O2MeasurableResistanceProblem:SlowResponseb/cnomoleculemovementFiberopticchemicalsensors(FOCS)Operatebytransportinglightwhich,eitherbywavelengthorintensity,providesinformationaboutanalytesintheenvironmentsurroundingthesensor.Theenvironmentisusuallyairorwater.FOCScanbecategorizedasintrinsicorextrinsic.ExtrinsicFOCSsimplyuseanopticalfiberasameanstotransportlight.Anexampleisthelaserinducedfluorescence(LIF)conepenetrometer.TrinsicFOCSusethefiberdirectlyasthedetector.Aportionoftheopticalfibercladdingisremovedandreplacedwithachemicallyselectivelayer.Thesensoristhenplaceddirectlyintothemediatobeanalyzed.Interactionoftheanalytewiththechemicallyselectivelayercreatesachangeinabsorbance,reflectance,fluorescence,orlightpolarization.Theopticalchangeisthendetectedbymeasuringthechangeinlightcharacteristiccarriedbytheopticalfiber.FOCS(cont.)TypicalUses
PrimarilybeendevelopedtomeasurevolatilepetroleumconstituentssuchasBTEXandchlorinatedVOCs(volatileorganiccompounds)suchasTCE,PCE,andcarbontetrachlorideinwater,air,orsoilgas.ThesensorshavebeendevelopedtobeplaceddownmonitoringwellstoprovideinsitumeasurementsofVOCconcentrationsingroundwater.FOCStypicallymeasuretotalVOCconcentrationsandarenotcapableofdistinguishingindividualvolatileorganicchemicals.Withappropriatechemicallyselectivelayers,FOCSarecapableofmeasuringSVOCs(semiVOC)aswell.FOCS(cont.)ManyofcommercialFOCSarecoating-basedsensors.Aportionofthecladdingisreplacedbyaproprietarycoating,whichselectivelyandreversiblyadsorbstheorganictargetanalytes.Thecoatingadsorbsorganicswhilerepellingwater.Theinteractionbetweentheorganictargetanalytesandthecoatingchangestherefractiveindexofthecoating.hydrophobic/organophilicchemicalcoating.Thechangeintheindexdecreases
theamountoflightgeneratedbyanLEDtransmittingtothedetector.Theresultantlossoflightismeasuredinproportiontotheconcentrationoforganicspresentinthesample.FOCS:PerformanceDetectionLimitsTypicaldetectionlimitsarearound1ppmforVOCsinwater.Lowerdetectionlimitsarepossiblewithpre-concentrationoftheanalyte.CalibrationCalibrationconsistsofmeasuringtheresponseofthedetectortoacalibrationstandard.Calibrationstandardsshouldconsistofaseriesofknownanalyteconcentrationsinarepresentativesamplematrix.Detectorresponseisplottedagainstanalyteconcentrationtogenerateacalibrationcurve.Aswithmostmoderninstrumentation,calibrationanddataacquisitioniscontrolledandrecordedwithamicroprocessorSamplePreparationFOCSaretypicallyusedforinsitumeasurementsprecludingsamplepreparation.FOCS:advantagesAdvantages
ThedesignofintrinsicFOCSprovidesinsituand
realtimemonitoring.FOCSaresmallinsizeduetosmallfiberopticdiameters.Opticalfibersareflexiblewithinlimitsallowinggreateraccesstodifficultlocations.Transmissionoverlongdistancesallowmonitoringindeepwellsandprovideameasureofsafetyformonitoringofhazardousatmospheres.Multielementanalysisispossibleusingvariousfibersandasinglecentralunit.FOCS:LimitationsManyFOCSarenotcompoundspecificandwillreacttomanyVOCsandwillproduceareadingonlyfortheconcentrationoftotalVOCs.Thedetectionlimitscanbehighcomparedwithconventionalanalyticalmethodssuchasgaschromatography.mainlyusedtodetectgrosscontamination.Somesensorsaretemperatureandtimedependent.Becausesensorresponseisbasedondiffusion,themeasuredconcentrationmayvarywithtimethattheFOCSisincontactwiththetargetanalyte.Therefore,itiscriticalthatequilibriumbeachievedbeforeameasurementistaken.Slowresponse:MostFOCSreachequilibriumin5to10minuteswhichisindicatedbyasteadystatesignal.Thenumberofreversiblereactions,thatisadsorptionandsubsequentdesorption,islimited,soprobesmayhavetoberegeneratedafterextend
溫馨提示
- 1. 本站所有資源如無特殊說明,都需要本地電腦安裝OFFICE2007和PDF閱讀器。圖紙軟件為CAD,CAXA,PROE,UG,SolidWorks等.壓縮文件請下載最新的WinRAR軟件解壓。
- 2. 本站的文檔不包含任何第三方提供的附件圖紙等,如果需要附件,請聯(lián)系上傳者。文件的所有權(quán)益歸上傳用戶所有。
- 3. 本站RAR壓縮包中若帶圖紙,網(wǎng)頁內(nèi)容里面會有圖紙預(yù)覽,若沒有圖紙預(yù)覽就沒有圖紙。
- 4. 未經(jīng)權(quán)益所有人同意不得將文件中的內(nèi)容挪作商業(yè)或盈利用途。
- 5. 人人文庫網(wǎng)僅提供信息存儲空間,僅對用戶上傳內(nèi)容的表現(xiàn)方式做保護(hù)處理,對用戶上傳分享的文檔內(nèi)容本身不做任何修改或編輯,并不能對任何下載內(nèi)容負(fù)責(zé)。
- 6. 下載文件中如有侵權(quán)或不適當(dāng)內(nèi)容,請與我們聯(lián)系,我們立即糾正。
- 7. 本站不保證下載資源的準(zhǔn)確性、安全性和完整性, 同時(shí)也不承擔(dān)用戶因使用這些下載資源對自己和他人造成任何形式的傷害或損失。
最新文檔
- 大學(xué)英語自我介紹高級(5篇)
- 2025-2025學(xué)年度學(xué)生課外活動計(jì)劃
- 三年級下學(xué)期網(wǎng)絡(luò)安全教育活動計(jì)劃
- 計(jì)算機(jī)科學(xué)與技術(shù)的未來發(fā)展方向范文
- 濕地植物栽培成活率的保護(hù)性措施
- 登高作業(yè)的應(yīng)急救援和防護(hù)措施
- 兒童藥物管理與安全使用計(jì)劃
- 實(shí)驗(yàn)室低值易耗品采購和管理流程
- 企業(yè)員工健康服務(wù)流程
- 2025年新課標(biāo)教材小學(xué)語文教學(xué)情況調(diào)研報(bào)告范文
- 護(hù)士N1晉級N2述職報(bào)告
- 中國糖尿病防治指南(2024版)解讀
- 食堂食材配送采購?fù)稑?biāo)方案(技術(shù)標(biāo))
- 山東省汶上縣市級名校2025屆中考生物全真模擬試卷含解析
- 2025年度智能硬件產(chǎn)品全國區(qū)域獨(dú)家代理合同3篇
- 辦公室安全知識培訓(xùn)課件
- 2025年四川省成都市青白江區(qū)招聘50人歷年高頻重點(diǎn)提升(共500題)附帶答案詳解
- 2025年浙江嘉興市眾業(yè)供電服務(wù)限公司招聘38人高頻重點(diǎn)提升(共500題)附帶答案詳解
- 【課件】第12課+理想與典范-古希臘與古羅馬美術(shù)+課件高中美術(shù)人教版(2019)美術(shù)鑒賞
- 建筑行業(yè)安全隱患舉報(bào)獎(jiǎng)勵(lì)機(jī)制
- 公司事故隱患內(nèi)部報(bào)告獎(jiǎng)勵(lì)機(jī)制
評論
0/150
提交評論