BIOEN 316 Ultrasound & FET practice questions »Drawacartoonofanultrasoundtransducerorprobe,withlabelsfortheimportantcomponents
andabriefdescriptionofthepurposeofeachone.
»DeterminethethicknessofapiezoelectriccrystalmadeofLeadzirconatetitanate(PZT)thatwill
produceultrasonicwavesoffrequency2MHz.(Ultra)soundtravelsthroughPZTatabout4000m/s.
»DeterminethefrequencyshiftΔfobservedwhenapairof2MHztransducer(onesending,one
receiving)isusedtomeasurethevelocityoffluidthatismovingthroughasmalltubeat15cm/sec.
Assumethatthetransducerpairisaimed30°fromparallelwiththeflow.
»TheobservedreflectedDopplersignalgenerallyhasanenormouspeakatthetransducer’s
resonancefrequencyf0,andaverysmallpeakattheDopplerfrequencyf0+Δf.Explainwhywe
mightexpectonelargepeakandonesmallpeakinoursmall‐tubevelocitymeasurement.
»Althoughsomeelectronicdevicessuchasoscilloscopescansamplebriefsegmentsofsignalsat
100MHzormore,andsomesophisticatedhigh‐performance(read“expensive”)systemscan
handlecontinuousMHzrangesampling,thisfrequencyisoftennotpracticalinsimplercircuitsfor
long‐termsignalsampling.Inthesesituationswecannotsamplethe~2MHzsignalandisolatethe
desiredΔfwithdigitalIIRfilters.Howcouldyouprocessthecontinuous‐timesignaltoenableyou
tosampleitatarelativelylowfrequency?Afterdoingso,youcanpassthesignalthroughadigital
high‐passfilterwithatransitionregion(cutofffrequency)thatseparatesthehigh‐amplitudemain
peakfromthesmallerpeakatΔf?Statewhatyouareactuallydoinginthetimedomainandwhatis
happeningmathematicallyinthefrequencydomain.Includeafigurethatillustratesyour
procedure.
»Itislogicaltoassumethatthe2‐MHztransducer,whichcontainsthekeypartsthatyouincluded
inquestion1,isoptimizedforcontinuous‐waveultrasound.Whatistheprimarythingthatyou
wouldchangeaboutthetransducerifyouweretoconvertittoanimagingtransducerwherepulses,
notcontinuouswaves,areproduced?Explainwhythischangemakesita“low‐quality”transducer.
»Schmitttriggers.Supposethatwewishtoconvertasmoothpulsesignalintoasquarewaveto
useasaclocksignalforadigitalcounter.Thepulsesignalismodeledasthesumofthree
sinusoids:
vp(t)=sin(2πt)+0.75sin(4πt)+0.1sin(120πt)
a)Whataretheperiodandfundamentalfrequencyofthissignal?
b)Proposeacircuit,includingcomponentvalues,thatwillproduceonecycleofasquarewaveper
fundamentalperiodofthesignal.
pulse signal, volts
2
1
0
-1
-2
0
Print date: 6/3/2014 0.5
1
1.5
time, seconds
2
2.5
3
BIOEN 316 Ultrasound & FET practice questions »Brieflyexplainwhysomeelectrodesareconsidered“reversible”whilesomeareconsidered
“irreversible.”Provideanexampleofeachtypeofelectrodeandanapplicationinwhicheachtype
mightbeused.
»Comparethefunctioningofion‐selectivefield‐effecttransistors(oranotherFET‐basedsensor)
toasensorthatcontainselectrodes.Stateanappropriateapplicationforeachone.
Print date: 6/3/2014