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1、5ElementsandcontrolsystemsThroughoutthisbook,wehavebeendiscussingtheuniqueabilitiesofsmartmaterialstoactlocallyanddiscretelyinrealtime.Wenowknowhowtheyfunction.Buthowdowedecidewhenwewantthesematerialstoactandforwhatpurpose?Furthermore,wheredowefindthenecessaryinformationfor
2、guidingtheresponse?Fundamentaltotheunderlyingtechnologicalinfrastructureofoursocietyareinnumerabledevicesformeasuringtheextentorquantityofsomething,orforsensingchangesinthestateofanobjectorenvironment(asimplethermometerpressuregageprovidesanexamplehere).Therearealsomanydevi
3、ces(transducers)forchangingenergyfromoneformtoanother,e.g.,chemicalenergyintoelectricalenergy.Aclassicgeneratorconvertsmechanicalenergyintoelectricalenergy.Likewise,therearemanyactuationdevicesinusewhereinenergyistransformedintoaphysicalorchemicalaction.Electricalenergymigh
4、tbeusedtopoweradrillorrotateafan.Smartmaterialscanassumemanyformsandservemanyofthedifferentrolesdescribed.ManyofthemorebasicactionsandbehaviorsofsmartmaterialsthatweredescribedinChapter4canbedirectlytranslatedintorolesassensors,transducers,oractuationdevices.Indeed,manysmar
5、tmaterialsofeithertheproperty-changingclassortheenergy-exchangingclassinherentlyprovidevarioussensoryfunctions.Itshouldbeevidentthatthebehaviorsdescribedareoftenidenticalwithwhatmoreclassicallydefinedsensors,transducersandactuatorsaccomplish;butthattheydosointegrallywithint
6、hematerialitself.Apropertychangeinamaterialthatoccursinresponsetoanexternalstimuluscannormallybeuseddirectlyasasensorforthatsamestimulus.Weknow,forexample,thatasimplethermochromicmaterialchangesitscolordirectlyinresponsetoatemperaturechange.Achangeinthecolorofamaterial,ther
7、efore,isamarkerofthechangeintemperatureofthesurroundingenvironment.Aswaspreviouslynoted,thesesamethermochromicmaterialschangecolorsatspecifictemperaturelevels.Thus,colorscanbecalibratedwithtemperaturelevelstoprovideatemperaturemeasurementdevice.Sincethesematerialscanalsobed
8、esignedtochangecolorsatspecifictemperaturelevels,itisquiteeasytoproducevisuallyeva
