An Approach for Sub-Second Imaging of Concealed Objects Using Terahertz (THz) Radar

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1、JInfraredMilliTerahzWaves(2009)30:1297–1307DOI10.1007/s10762-009-9515-5AnApproachforSub-SecondImagingofConcealedObjectsUsingTerahertz(THz)RadarK.B.Cooper&R.J.Dengler&N.Llombart&T.Bryllert&G.Chattopadhyay&I.Mehdi&P.H.SiegelReceived:2April2009/Accepted:7May2009/Publishedonline:22May2009#U.S.Gov

2、ernment2009AbstractHigh-resolution,long-rangedetectionofperson-borneconcealedweaponshasrecentlybeendemonstratedusingaterahertzimagingradar.However,theradar’simageacquisitiontimemustbegreatlyshortened,fromminutestolessthanonesecond,beforethesystemcanbeeffectivelydeployedinareal-lifethreatenvir

3、onment.Hereweanalyzethemajorsystemmodificationsnecessaryforincreasingthespeedofaterahertzimagingradarbyuptotwoordersofmagnitude.KeywordsTHzradar.Imagingradar1IntroductionThemosttechnologicallymaturemillimeter-andsubmillimeter-waveimagersforconcealedweaponsdetectionrelyonpassivedetectionofradi

4、ation,wheretheimagecontrastofhiddenobjectsarisesfromacombinationofemissivityandreflectivitydiversity,aswellasthelocalconditionsofthermalbackgroundradiation.Comparedtoactiveimagingsystems,passiveimagershavetheadvantagesofasimplerandlower-costhardwarearchitecture,andtheycandetectcontrabandoften

5、withgoodfidelity,freeofspeckleorinterferenceeffects.However,unlikeimagersthatactivelyilluminateatarget,passivesystemsmustconfrontafundamentaltradeoffbetweendetectionsensitivityandimagingspeed.Thistradeoffarisesbecausethepassivelydetectedpowercontrastofascenehasanupperboundthatisfixedbythetemp

6、eraturedifferencebetweenaperson’sbodyandthelocalthermalenvironment.Thiscontrastworsensatthesubmillimeterwavelengthsneededforhigh-resolutionimagery,wheretheradiometricskytemperatureapproaches300K.Forexample,state-of-the-artroom-temperaturebolometers,whichattainanoiseequivalentpower(NEP)ofafewp

7、W/1/2Hzinthesubmillimeter-waveregime,candetectthermaltemperaturedifferencesof~1Kwithasignal-to-noise(SNR)ofunityina1Hzbandwidth[1].BecausetheSNRofpassivedetectionscalesasthesquarerootoftheintegrationtimetint,theapproximaterequiredtimeK.B.Coop