0 P I E A S2015MS Word 2010 Table of Contents1List of figuresList of Tables2CHAPTER 2Overview of Ultrasonics and UltrasonicTransducers2.1. UltrasonicsUltrasonics isthenamegiventothestudyandapplicationof soundwaveshavingfrequencies higher than the human audible range (i.e. > 20 kH! though this frequencyactually varies with age"# $he history of ultrasonic technology is not very old but thephenomenon itself was there in nature# %ertain animals have used ultrasound to probeplaces where light is unavailable over a time scale of millions of years& echo locatingbats and intelligent forms of underwater life (e.g.! whales and dolphins" are among themost adept for target identification and range finding# Humans cannot hear ultrasound!but theyusedthis inancient times bytamingwolves! withtheir keenultrasoundhearing! for aiding in the hunt# $oday! they are doing this by developing technology todetect! generate and process ultrasound searching in different media# Ultrasound can beused to solve the e'isting problems in diverse areas as engineering! physics! chemistry!medicine! microscopy! underwater detection! ranging! navigation! etc# (mong these! to a)great e'tent! ultrasonics techniques havealreadyfoundtheir e'istenceine'tensiveapplications in the fields of sonar! biomedicine and non*destructive testing (+,$"#Prior to World War II, sonar, the technique of sending sound waves through water andobserving the returning echoes to characterize submerged objects, inspired earlyultrasound investigators to explore ways to apply the concept to medical diagnosis. In!"! and !#$, %o&olov studied the use of ultrasonic waves in detecting metal objectsand invented the image tube. 'ulhauser, in !#, obtained a patent for using ultrasonicwaves, using two transducers to detect flaws in solids. (irestone in !)* and %imons in!)$ developed pulsed ultrasonic testing using a pulse+echo technique. ,n biomedicineside, Pohlman investigated the therapeutic uses of ultrasonics in !#! and from !)-extensive study of ultrasonic medical imaging started in .nited %tates and /apan. In allof these fields, further developments are continuously in progress with theadvancements towards better piezoelectric materials.(lmost all of the applications are based on two unique features of ultrasonic waves -1.&. Ultrasonicwavestravel slowly! about 10/timesslower thanelectromagneticwaves# $his provides a way to display information in time! create variable delay!etc.". Ultrasonicwavescaneasilypenetrateopaquematerials! whereasmanyothertypes of radiation such as visible light cannot# 0ince ultrasonic wave sources areine'pensive! sensitive! and reliable! this provides a highly desirable way to probeand image the interior of opaque ob1ects#2ither or both of these characteristics occur in most ultrasonic applications# $his thesisaddresses the ma1or constituent of the field of ultrasonics named pieoelectricity# 32.2. Pieoelectricit!4ieoelectricityis thepropertyof materials possessingthepieoelectriceffect# $hedirect pieoelectric effect is the production of electrical polariation in a material by theapplication of mechanical stress# 0uch materials are known as pieoelectric materialsand they also display the converse pieoelectric effect of mechanical deformation uponapplication of electrical charge# $hese effects are shown in 5ig# (2#1"#History ofpieoelectricity can be found in literature -2.# $herefore! while the overall crystal remains electrically neutral! the difference in chargecentre displacements results in an electric polariation within the crystal# $his electric/"igure #2.1$ (a" 6 (b" 7oltage generated when pressure is applied(c" 6 (d" %hange in shape when voltage is applied4ieoelectric8aterial9attery0witch %losed4ieoelectric8aterial9attery0witch :pend" 7oltage %onnected c" (t rest4ieoelectric 8aterial7oltmeter4ieoelectric 8aterial7oltmeter 4ressurea" (t rest b" Under 4ressurepolariation due to mechanical input is perceived as pieoelectricity# $he pieoelectricand converse pieoelectric processes are illustrated in 5ig# (2#1"#$he electric and mechanical behaviour of any pieoelectric material can be described intensorform-).bythelinearsimultaneousequations(theconstitutivelawin0train*%harge form"&0 1 d 20 d 1 s %1t0# ## # + =+ =(2#1"where% is the mechanical strain vector; & is the electric charge density vector;T is the mechanical stress vector;E is the electric field vector;/0?s! pieoelectric crystals made fromquartcrystals and magnetostrictive materials were primarily used# Pieocera)ic*Pol!)er Co)+osites4ieoelectric ceramics are nowsometimes replaced by another type of materialcomprising the active ceramic and passive polymer! called pieocomposites! forbroadbanddevicesforunderwatersonarandmost ofbiomedical applicationsduetocertain advantages#aspect ratio (height to kerf width" of the ceramic pillars are the most importantparameters from a fabrication and applications point of view#@"igure #2.,$ ( schematic diagram of 1*) connectivity pieocomposite 4olymer 8atri'HeightAerf Bidth%eramic 4illar4illar Bidth"igure #2.11$ Cmpedance magnitude of transducers with single layer with matching layer and with backing in water11010010000 5 10 15 20Frequency (MHz)Electrical Impedance ()Single layerWith Matching ayerWith Matching ! "ac#ing"igure #2.1-$ .mpedance magnitude of transducers with single layer! and with matching layer for an air*backed transducer0$111010010000 5 10 15 20Frequency (MHz)Electrical Impedance ()Single ayerWith Matching ayer"igure #2.12$ %omparison of output pressure from transducers with single layer! with matching layer! and with backing in water* in time domain%&%'%202'&(0 1 2 ) ' 5*ime (S)+utput ,re--ure (.,a)Single ayerWith MatchingMatching ! /ac#ingDbacking# Eater on! the loading media were chosen to be water on the front face and air atthe back# ( set of data comprising electrical impedance and pressure output in time andfrequencydomaintostudytheeffect of backingandmatchingis demonstratedin5igures (2#10"! (2#11"! (2#12"! and (2#1)"! respectively# T/e Relevant LiteratureBithmore novelty! Hossack-10. and(ngelsen et al. -11. have described howto use backing and matching layers forbroadbandor multiple*frequencybandultrasonic transducers# Hossack and(uld proposed active matching layer ofactive material -12.! 9oloforoshinvented a novel integrated matchinglayer ofacompositematerial forhighperformance -1).# $oda proposed amatching layer design concept fornarrow band continuous waves -13.# Cnthe literature! Hunt et al. have discussedquarter*wave matching layers of thetransducers for pulse*echo medicalimaging -1/.# Billaten has formulateda complete set of equations for one*dimensional modelling from firstprinciples for stacked transducers forreciprocal systems -1=.# He hasperformed this modelling structure withvarious matching layer combinations#>"igure #2.2'$ ), plots for first five harmonics of the output pressure from an air*coupled transducer; (a" fundamental! (b" second! (c" third! (d" fourth! and (e" fifth harmonic020406080100020406080100024681012141618010 2030 40 5060 70 8090 1000501005101520253035400204060801000204060801005101520253035400204060801000204060801005101520253035400102030405060708090100020406080100050100150200250300350e$a$b$c$ d$Table 10 Co)+arison of 1arious (odels on Training and Test &ata for all 2"sG.ModelA.ModelCode G.ModelA.ModelCodeTraining Data Test DataWF 1RMSE0.1621 0.1335 0.0869 0.2215 0.1365 0.0966MAE 0.1256 0.1143 0.0575 0.1708 0.1100 0.06!SDE 0.1621 0.0988 0.0868 0.1860 0.1144 0.0950WF"RMSE0.1743 0.1048 0.0975 0.1792 0.1206 0.1157MAE 0.1309 0.0797 0.06"! 0.1352 0.0879 0.07!9SDE 0.1743 0.1074 0.0957 0.1738 0.1195 0.115"WF!RMSE0.1672 0.1100 0.1071 0.1888 0.1388 0.1!50MAE 0.1242 0.0835 0.069 0.1405 0.0972 0.087SDE 0.1672 0.1070 0.1071 0.1821 0.1378 0.1!"9WF

RMSE0.1618 0.1074 0.1061 0.1963 0.1174 0.11"MAE 0.1251 0.0835 0.0681 0.1516 0.0867 0.0780SDE 0.1618 0.1074 0.1061 0.1703 0.1153 0.1118WF 5RMSE0.1603 0.1355 0.11!5 0.2124 0.1236 0.1"0!MAE 0.1154 0.0997 0.0715 0.1616 0.0872 0.0770SDE 0.1603 0.1189 0.11!5 0.10"0 0.1125 0.11902.3. References-1. ,# %heeke! .ltrasonic Instruments and 2evices! (cademic 4ress! %(! U0(! C09+ 0*12/*)1>/1*@! pp# 3@1*/=2! 1>>>#-2. 8 $rainer! 3elvin and piezoelectricity! 2uropean Fr# of 4hysics# 23! pp# /)/*/32! 200)#-). H# (llik and $#F#@0#-3. (# 9allato! Piezoelectricity4 ,ld effect, new thrusts! C222 $rans# Ultrason# 5erroelec# 5req# %ont# 32 (/"! pp# >1=*>2=! 1>>/#-/. +# 0etter! Piezoelectric materials in 2evices! 245E 0wiss 5ed# Cns# :f $ech#! C09+ 2*>@00)3=*0*)! 8ay 2002#-=. A#8# Eakin! 1hin film resonators and filters! C222 0ymp# 4roc#! pp#D>/*>0=! 1>>>#-@. F# Arautkramer and H# Arautkramer! .ltrasonic 1esting of 'aterials! 3th 2dition! 0pringer*7erlag! C09+ )*/30*/12)1 6 0*)D@*/12)1*3! 1>>0#-D. 4#. 9# >>#-11. F# Hossack! 2'tended bandwidth ultrasonic transducer! United 0tates 4atent! /!>/@!D/1! 0ep# 1>>>#-12. roceedings! pp# =11*=13! 1>>1#12