USING PHASED ARRAY TECHNOLOGY AND EMBEDDED ULTRASONIC STRUCTURAL RADAR FOR ACTIVE STRUCTURAL HEALTH MONITORING AND NONDESTRUCTIVE EVALUATION

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1 Poeedings of IMECE 25: 25 ASME Inenaional Mehanial Engineeing Congess Novebe 5-3, Olando, Floida IMECE USING PHASED ARRAY TECHNOLOGY AND EMBEDDED ULTRASONIC STRUCTURAL RADAR FOR ACTIVE STRUCTURAL HEALTH MONITORING AND NONDESTRUCTIVE EVALUATION Lingyu Yu, PhD andidae Mehanial Engineeing Depaen, Univesiy of Souh Caolina Colubia, SC 2928, Vio Giugiuiu, Pofesso Mehanial Engineeing Depaen, Univesiy of Souh Caolina Colubia, SC 2928, ABSTRACT The ebedded ulasoni suual ada (EUSR was developed based on phased aay ehnology. I an ineogae lage suual aeas fo a single loaion using ulasoni guided Lab and Rayleigh waves geneaed by uned piezoelei wafe aive sensos (PWAS ha ae peanenly aahed o he suue. This pape bings ogehe seveal aspes of he ipleenaion and appliaion of EUSR o suual daage deeion: (a ipoving he nea field daage deeion; (b designing opiized phased-aay paens; ( designing a ini phased aay fo opa suues wih opliaed geoeies and uliple boundaies. Fisly, we dedued a genei foulaion fo phased aay dieional beafoing using he exa aveling waves foulaion wihou he liiing paallel-ays assupion used by ohe invesigaos. This algoih has been ipleened in he EUSR LabVIEW poga and is pefoane has been veified hough siulaion and expeienal ess. Seondly, we sudied he beafoing and lobe seeing haaeisis of a -D linea aay design. The influene of seveal geoey paaees was disussed in ode o ahieve he opial dieionaliy, inluding he nube of sensos in he phased aay, he spaing beween adjaen sensos, and he seeing dieion angles. Exensive siulaion sudies have shown ha he well-behaved dieional beafoing an be ahieved wih judiious aay design. Poof-of-onep expeiens fo esing hese esuls have also been se up and he peliinay esuls ae onfiing he effeiveness of ou appoah. Thidly, we invesigaed he possibiliy of applying he EUSR phased aay ehod o opa speiens and poposed he design of a ini phased aay. Laboaoy expeiens have been aied ou o pove he suessful ipleenaion of his onep. Finally, he pape ends up wih disussions and onlusions egading he beafoing, opiizaion and ipleenaion of he PWAS phased aays, as well as suggesions fo fuhe wok. INTRODUCTION Phased aays ae ade of uliple piezoelei eleens exied by pedeeined ie-delayed signals o geneae suual inefeene paens. By popely adjusing he ie delays, phased aay an phase see and fous he ulasoni beas a eain dieion. Soe of he advanages of phased aays ove onvenional ulasoni ansdues inlude high inspeion speed, flexible daa poessing apabiliy, ipoved esoluion, and he apabiliy of sanning wihou equiing ehanial oveen, i.e., dynai bea seeing and fousing []. The baksaeed ulasoni signals an be analyzed and hen apped ino an iage. Cuen ulasoni inspeion of hin wall suues (e.g., aiaf shells, soage anks, lage pipes, e. is a ie onsuing opeaion ha equies eiulous hough-hehikness C-sans ove lage aeas. One ehod o inease he effiieny of hin-wall suues inspeion is o uilize guided waves (e.g., Lab waves insead of he onvenional pessue waves [2, 3]. Guided waves popagae along he id-sufae of hin-wall plaes and shallow shells [4, 5]. They an avel a elaively lage disanes wih vey lile apliude loss and offe he advanage of lage-aea oveage wih a iniu of insalled sensos. Guided Lab waves have opened new oppouniies fo os-effeive deeion of daage in aiaf suues, and a lage nube of papes have eenly been published on his subje. The use of guided waves in onjunion wih phase-aay piniples has polifeaed widely in een yeas due o is obvious benefis. Howeve, an ipoan oadblok on he way owads he uilizaion of hese ehniques in aiaf suual healh onioing is ha he onvenional ulasoni ansdues used fo guided wave and phased-aay appliaions ae bulky and expensive, hus aking hei use in wide-aea suual healh onioing expensive and pobleai. Hene, a diffeen ype of sensos han he onvenional ulasoni ansdues is equied fo he SHM syses. Piezoelei wafe aive sensos (PWAS ae sall, non-inusive, inexpensive piezoelei wafes ha ae Copyigh 25 by ASME

2 peanenly affixed o he suue and an aively ineogae he suue. PWAS ae non-esonan devies wih wide band apabiliies. They an be wied ino senso aays and onneed o daa onenaos o wieless ouniaos [6]. As aive sensos, PWAS an be used as boh ansies and eepos of elasi waves. An ipoan haaeisi of PWAS is hei onidieionaliy. This akes PWAS bee suied fo lage aea inspeion using phased aay eleoni auoaed sanning (Convenional ulasoni ansdues fo guided-wave geneaion ae unidieional, and hene an only san by ehanially oaing he ansdue... GENERIC FORMULATION FOR BEAMFORMING Phased aay is a goup of sensos loaed a disin spaial loaions in whih he elaive phases of he espeive signals feeding he sensos ae vaied in suh a way ha he effeive popagaion paen of he aay is einfoed in a desied dieion and suppessed in undesied dieions [7]. Tha s o say, he phased aay as like a spaial file aenuaing all signals and saving hose popagaing fo eain dieions. Beafoing is he aay signal poessing algoihs ha fous he aay s signal apuing abiliy in a paiula dieion. Piezoelei-wafe aive sensos (PWAS ae sall, non-inusive, inexpensive piezoelei wafes ha ae peanenly affixed o he suue and an aively ineogae he suue [6]. They an be wied ino senso aays and seve as aive senso fo boh geneaion and eepion of elasi waves. We will dedue he geneal foula of PWAS phased aay based on he delay-and-su beafoing algoih wihou he liiing paallel-ays assupion... Delay-and-su Beafoing The idea of delay-and-su beafoing is: if a popagaing signal is pesen in an aay s apeue, he senso oupus, delayed by appopiae aouns and added ogehe, einfoe he signal wih espe o noise o waves popagaing in diffeen dieions. The delays ha einfoe he signal ae diely elaed o he lengh of ie i akes fo he signal o popagae beween sensos. Suppose hee is a efleo a he poin Pϕ (,. We will onside he wavefield geneaed a Pϕ (, by an aay of M sensos, loaed a { s }, =,, M-. The oigin of oodinae syse oinides wih he sensos phase ene whih is defined as he veo quaniy M s. Hene, he oigin is he poin whee s = M ( The wave eiing fo he h senso is y( = f(, whee is he veo fo he h senso o he efleo (Figue. ξ is he uni veo ha poins fo he oigin o he age poins Pϕ (, and ξ is he uni veo ha poins fo he h senso o he age poins Pϕ (,. The delay-and-su beafoing onsiss of wo seps: ( applying a delay Δ and a weighing fao w o he oupu of h senso; (2 suing up he oupu signals of M sensos. This poessing is defined as: M z ( = w y ( Δ = (2 w is he weighing fao, designing fo enhaning he beas shape and eduing sidelobe levels. The delay {Δ } ae adjused o fous he aay s bea on paiula popagaing dieion ξ. Ipoanly, he beafoing algoih vaies aoding o whehe he efleo is loaed nea o o fa fo he aay. O s ξ ξ h senso Pϕ (, Figue : he geoey sheais of he h senso and he efleo a Pϕ (, If he efleo is lose o he aay, i.e., wihin nea field (Figue 2a, he popagaing wavefon is uved (iula wavefon wih espe o he aay and he wave popagaing dieions ae dependen on he loaion of eah senso. When he efleo is fa away fo he aay, i.e., in he fa field o he aay (Figue 2b, he popagaion dieions of individual waves appoxiae paallel o eah ohe, ha s o say, ξ ξ, and he popagaing field wihin he aay onsiss of plane waves. ξ (a ξ ξ h senso (b ξ ξ h senso Figue 2: beafoing in nea- and fa- field o he aay: (a nea field; (b fa field [7] Conside a paiula dieion of wave popagaion ξ poining o he poin Pϕ (, fo he oigin (phase ene as shown in Figue. Fo fa-field siuaion, i will also be he popagaing dieions fo all he plane waves, egadless of he loaion of he sensos. Bu fo nea-field siuaion, he popagaion dieions vay fo senso o senso (Figue 2a. We need o 2 Copyigh 25 by ASME

3 define dieion veos fo eah seno, say, ξ As indiaed in Figue, we have: ξ = ξ =, = s s is he loaion of he h senso. fo h senso..2. Beafoing fo plane waves Assue a fa-field soue eiing a plane wave s( popagaing in he dieion ξ o he aay. The wavefon aiving a he aay is: f (, = s ( α (5 whee α = ξ / and is he wave popagaion speed. The h senso spaially sapled in his wave field yields: y( = s( α s (6 wih α = ξ /. By applying boh a weighing fao and a ie delay o i, we have: z( = w s( α s Δ (7 And hen su up he M sensos: M M z ( = z( = ws ( α s Δ = = (8 Fo equaion (8 we see, if we ake: Δ = α s (9 we will have: M z ( s ( w = = ( Hene, he beafoing signal is a onsan ies enhaneen of he oiginal signal. By applying pope ie delay (using foula in equaion (9, he aay s beafoing an be seeed o a eain dieion ξ, i.e.: M z (, = w f, Δ = ( (3 (4 (.3. PWAS phased aay beafoing foulaion Geneally, he wavefon a a poin x away he PWAS soue is: A i( ω k x f( x, = e x (2 Supposing we have an aay of M PWAS insalled a { s } sending ou signals in he dieion of { ξ } o Pϕ (, espeively, using equaion ( he synhei wavefon z (, a he poin Pϕ (, wih ie delay and weighing is: M z (, = w f(, Δ = s = The oigin is whee. Ohe vaiables ae defined as: = ξ = = (3 and = = s ξ = = = (4 s The wavenube of he wave popagaing in he dieion of ξ is defined as: ω k = ξ (5 whee ω is he wave s epoal fequeny. Using he noaions defined in equaion (3, (4 and (5, he wavefon fo he h senso aiving a he poin P (, an be wien as: A i( ω k f(, = e (6.3.. Fa-field beafoing using he paallel ay appoxiaion As disussed in., if a efleo is fa away fo he aay, he popagaion dieions of individual waves an be onsideed being paallel o eah ohe, i.e.,. ξ ξ. Hene, ω k ξ = k (7 and (8 Equaion (6 beoes: ξ ( s iω A f(, e ξ s iω A + = e ω A iω i ξ s = e e ω i ξ s f(, = f(, e (9 In equaion (9 he wavefon f (, is only dependen on he exponenial pa. The synhei waves of M sensos wih delaying and weighing heefoe is: M ξ s z (, = w f(, + +Δ = (2 If we adjus he ie delay Δ in suh a way ha ξ s Δ = (2 3 Copyigh 25 by ASME

4 z (, beoes: (, (, M z = f w = (22 When w =, he synhei signal is M ies einfoed f (,.3.2. Nea-field beafoing Wihin he field nea o he aay, he paallel ay appoxiaion is no valid. The exa aveling waves ae used fo he beafoing foulaion. ξ iω A f(, = e (23 iω f(, = f(, e / The synhei signal z (, is: M w z (, = f( + +Δ = / If we have Δ = w = / equaion (25 beoes: z (, = Mf(, We see, he wavefon a he poin Pϕ (, einfoing of he sending ou signal. (24 (25 (26 (27 (28 is sill M ies 2. PHASED ARRAY IMPLEMENTATION AND OPTIMIZATION, THE EMBEDDED ULTRASONIC STRUCTURAL RADAR USING LAMB WAVES Ebedded Ulasonis Suual Rada (EUSR is a new onep and ehodology fo in-siu nondesuive evaluaion (NDE of hin-wall suues. EUSR uilizes (a a PWAS aay ebedded ono he suue; and (b eleoni odules fo signal ansission/eepion, poessing, and inepeaion. The piniple of opeaion of he EUSR is deived fo wo geneal piniples: ( The piniple of guided Lab wave geneaion wih piezoelei wafe aive sensos (PWAS; (2 The piniples of onvenional phased-aay ada. I is assued ha eah aive senso in he aay as as an onidieional ansie/eeive D linea PWAS phased aay siulaion The EUSR ehodology was developed as an exension of soe pevious wok on he Lab wave popagaion NDE, based on he sudy of he Lab wave haaeisi [6]. Eah eleen in he PWAS aay plays he ole of boh ansie and eeive. The esponses of he suue o all he exiaion signals ae olleed. Adoped fo he beafoing poess. uenly used in phased-aay ada appliaions, he EUSR algoih applies an appopiae delay o eah signal in he daa se o ake he all fous on a eain dieion. When his dieion hanges wihin º o 8º ange, a viual sanning bea will fo and a lage aea of he suue an be ineogaed. Figue 3 is he sheais of a -D linea aay onsising of M PWAS, equally sepaaed by d. The span of he aay is D wih D (M-d. The oodinae oigin is defined o be he phased ene aoding o equaion (. The aay is disibued along he x-axis and eneed abou y-axis. The loaion of h veo is: M s = (( d, 2 (29 Pϕ (, y O d ξ s ξ, h senso D Figue 3: he sheais of an M-eleen -D linea PWAS phased aay. The oodinae oigin is loaed a he phased ene, i.e., he ene of he aay. Aoding o he Lab wave field foula shown as equaion (2, he synhei wavefon a he poin Pϕ (, is: d d exp j2 π / ( M d d λ DS(,,, M = λ M = (3 whee = s (3 Fo equaion (3 we see, he beafoing DS a a single angle is onolled by he aio of d/, he aio of d/λ, and he nube of sensos in he aay. Afe he die beafoing, we hen apply he ie delay and weighing o eah oponen in ode o see he bea o fo a eain dieion (. The delay-and-su beafoing is hen: d d exp j2 π / ( ( M δ d d λ DS(,,,, M = λ M = wih x (32 δ ( = ( (33 ξ = 4 Copyigh 25 by ASME

5 The siulaion esuls of oiginal beafoing (wihou delay and weighing and he dieional beafoing a = 45º is shown in Figue 4, wih M = 8, d/λ =.5, and d/ = /(M-*. The solid bea a 9º posiion is he oiginal beafoing and he dash bea a 45º posiion is he delay and weighed beafoing. Oiginal beafoing Beafoing a 9º o he sidelobes fo he ainlobe whih esuls in he obvious deeasing of he ainlobe and ineasing of sidelobes apliude. d / = /(M- 5 d / = /(M- 2 d / = /(M- Figue 4: he oiginal beafoing and dieional beafoing a 45º of an 8 PWAS linea phased aay wih d/λ=.5, d/=/(m Opiizaion of he PWAS aay We have found ou hough he equaion (32 ha he dieional beafoing a any angle depends on seveal paaees: ( he spaing beween adjaen sensos d; (2 he nube of sensos M; (3 seeing angle. Aong hese, he effe of spaing d is epesened by he wo aios d/λ and d/. Ou pevious wok on he Lab wave popagaion NDE [6] has found ou ha a he aio a/λ =.5 whee a is he widh of he PWAS, PWAS will geneae opial exiaion. Consideing he poin-wise assupion in he phased aay appliaion and he elaion d = a+δ a (Δ is he gap beween sensos, his elaion is epesened as a/λ =.5 in ou disussion. This aio sill follows he spaial sapling heoe ha d should be salle o equal o he half of wavelengh 2. λ is he wavelengh of he exiaion signal (equal o /f and hangeable by fequeny uning Raio of d/ The aio of d/ is elaed o he definiion whehe a poin is loaed in he fa o nea field o he phased aay. The fa field an be onsideed as he aea whih disane o he phase ene is uh lage han he size of he aay, i.e., he span D of he aay. Convenionally, he aea an be eaed as a fa field if D/ > 5. The nea field an be anywhee below his aio wih he lowe lii, vey lose o he aay field is defined as D/ = onsideing he exisene of sidelobes. Fo ou poin-wise soue, hee is D (M-d. Hene he aio of D/ an be ansfoed o d/ using: d/ = D/(M- Figue 5 shows he beafoing siulaion of an 8-PWAS aay a vey lose (d/ = /(M- field, nea field (d/ = /(M- 2, and fa field (d/ = /(M- 5 o he aay. Fo he siulaion esul we see, he dieionaliy is bes in he fa field wih sall sidelobes. When geing lose o he aay, he sidelobes inease in nubes and apliudes. A he vey lose aea o he aea (whee D/ =, a lage aoun of enegy leaks 2 In ode o avoid spaial aliasing, he aio of d/λ should be salle of equal o.5 [7]. Figue 5: he beafoing of an 8 PWAS linea phased aay (wihou delay a diffeen d/ aio wih d/λ=.5. The solid line is he beafoing fo fa field (d/=/(m- 5; dash line is fo nea field (d/=/(m- 2 and do line fo vey nea field (d/=/(m- o he aay Nube of sensos, M In ode o ahieve bee dieionaliy, fine ainlobe and salle sidelobes ae desied. Figue 6 shows he opaison esuls of he beafoing using 8 and 6 PWAS espeively wih d/=/(m- 5 (fa field. I shows ha wih 6 sensos, we have a fine dieional lobe and salle sidelobes. Moe sensos will bing bee dieionaliy and fewe disubanes fo he sidelobes. M = 8 45º M = 6 Figue 6: he beafoing of 8 PWAS aay and 6 PWAS aay a 45º, espeively wih d/=/(m Seeing angle Seeing angle is anohe fao ha affes he beafoing. The beafoing a º, 3º, 6º, 9º, 2º, 5º using 8 PWAS is shown in Figue 7. Fisly, he beafoing ae syei abou 9º. Seondly, wihin º~9º ange, he beafoing loses is dieionaliy a sall angles suh as º and 3º in he plo. Howeve fo º o 3º, he dieionaliy sas geing bee. Lasly, when ineases, he dieionaliy is ipoved wih sidelobes being suppessed (opaing 3º wih 6º and 9º. 5 Copyigh 25 by ASME

6 Copaed o he beafoing of 8 PWAS, he beafoing of 6 PWAS (Figue 8 shows bee dieionaliy no only a lage angles suh as 6º and 9º (hinne dieional ainlobes a oesponding bu also a he lowe angle 3º. A 3º, he beafoing of 6 PWAS aay sill keeps he dieionaliy. Beafoing a 5º Beafoing a 2º Beafoing a 9º Beafoing a 6º Beafoing a 3º Beafoing a º Figue 7: he beafoing of 8 PWAS aay a º, 3º, 6º, 9º, 2º, 5º wih d/=/(m- 5. Beafoing a 5º Beafoing a 2º Beafoing a 9º Beafoing a 6º Beafoing a 3º Beafoing a º Figue 8: he beafoing of 6 PWAS aay a º, 3º, 6º, 9º, 2º, 5º wih d/=/(m- 5 The beafoing of 8 PWAS aay wih d/ = /(M- a diffeen angles ae shown in Figue 9. Again, we see he beafoing ges bee a lage. Howeve, he esuls in Figue shows, a eain, he aio of d/ will no affe he ainlobe, i.e., he dieionaliy. Ye, he sidelobes sengh is affeed. I deeases wih salle d/. Bu he diffeene beween nea field (d/ = /(M- 2 and fa field (d/ = /(M- 5 o d/ = /(M- ae alos negligible. In suay, a well-behaved dieional beafoing an be ahieved wih judiious aay design aoding o ou siulaion es. In ode o have good dieionaliy a lage angula ange, a lage aoun of sensos and/o salle d/ aio ae desied. Howeve, we anno inease he nube of sensos indefiniely due o he wiing onens. 8º Beafoing wih d/ = /(M- 6º Figue 9: he beafoing of 8 PWAS aay a 2º, 4º, 6º, 8º wih d/ = /(M- 4º 2º Beafoing wih d/ = /(M- Beafoing wih d/ = /(M- 5 Beafoing wih d/ = /(M- 2 Beafoing wih d/ = /(M- Beafoing a 4º Figue : he beafoing of 8 PWAS aay a 2º wih d/ = /(M-, /(M- 2, /(M- 5, and /(M Sofwae ipleenaion: he Ebedded Ulasoni Suual Rada (EUSR sofwae Pulse-eho ehod is used in he ebedded ulasoni suual ada syse. A age is assued a P(,. The ansiing-eeiving beafoing is sweeping he ange in ineasing angles and eeiving an eho when =. The eho will be eeived on all sensos and applied wih eain ie delay fo synhonizaion. Lab waves an exis in a nube of dispesive odes. Howeve, hough soohed one-bus exiaion and fequeny uning, i is possible o onfine he exiaion o a paiula Lab wave ode, of aie fequeny f, wave speed, and wave lengh λ=/ f. Hene, he soohed one-bus signal geneaed by one PWAS is of he fo: st( = s (os2 π f (34 whee s ( is a sho-duaion soohing window ha is applied o he aie signal of fequeny f beween and p (Figue. The piniple of delay-and-su beafoing is hen applied o he PWAS-geneaed guided waves, assuing a unifo linea aay of M PWAS spaing a d, wih eah PWAS aing as a poinwise oni-dieional ansie and eeive. The oal signal eeived a poin P(, will be he aplified signal pesened in equaion (28. Tha s o say, hee is an M ies inease in he signal sengh wih espe o a siple senso. The eeiving signal beafoing an be geneaed by eaing he poin P as an oni-dieional soue a (, and he delay will be applied he he signals eeived a he h senso in he aay. The synhonized eeiving signal a all sensos hen ae ahieved: 2 AM M 2 sr( = st( = (35 In geneal, he age loaion is unknown, i.e. is unknown. The oodinaes used in he ada syse is he pola oodinaes. The oase esiaion of is ipleened by using he sweeping ehod. Tha s o say, EUSR will san hough º o 8º by ineening by º fo eah sep, unil he axiu eeived enegy is obained. ax{e R ( } is he axiu eeived enegy by he definiion: 6 Copyigh 25 by ASME

7 + p = R 2 E ( s (, d R p (36 Figue is an exaple of he ansied signal and eeived signal pai apued in ou expeien. By apping he ie of fligh ino disane spae, we an ahieve he iage of a sanned speien. st( z( = sr( + v( p p τ: ie of fligh Tansission pulse Reepion eho Figue : he ansied signal and he eeived signal The laboaoy expeien seup is shown in Figue 2. The speiens ae 22- long, - hik squae aluinu plaes wih an 8-eleen 7- x 7- PWAS aay a he ene. The daage is siulaed by hough-plae aks 4 long and.5 wide. Figue 3 shows he apping iage of a speien wih wo aks a 67º and 7º in fon of he PWAS aay espeively. (a d = 7, 7x7 M squae PWAS 57 (22.45 in 22- sq., - hik 224 T3 (22.45-in sq.,.4-in hik 6 (24. in p + (a 3 Figue 3: EUSR expeien on a speien having wo offside aks a 67º and 7º: (a speien sheai; (b EUSR apped iage and/o sall d/ value ae desied. Ineasing nube of sensos is no doub he easie way o ahieve obvious ipoveen. Howeve, his will esul in he oplexiy of he wiing and lage size of phased aay, espeially when he phased aay is applied o speiens wih opa and/o oplex geoey whee spae is liied. Hene, we poposed a design of using ini-aay onsising of sale-down PWAS. The diension of he peviously used egula PWAS, eihe squae o ound, is 7-. We hen sale he down o 5- only. By his eans, he oplee size of he aay shinks by a leas (7- M - 5- M. If M = 8, his will be 6-. The ini- PWAS aay akes ou phased aay fuhe suiable fo he inspeion of sall suues wih oplex geoey heefoe. 3.. Fequeny uning of he ini-aay: he swee iple poin One onen in he ini-pwas aay is, he aio of d/λ (o d/λ has o eain onsan,.5. Wih salle spaing d (o salle diension a he wavelengh λ of he exiaion signal needs o be deeased as well. Salle wavelengh also eans an exiaion wih highe fequeny is desied. In ode o avoid Lab wave dispesion in highe fequeny ange aused by opliaed wave ode oposiion [8], a pope exiaion fequeny is neessay fo he funion of phased aay [9]. Figue 4 shows he goup veloiy of Lab waves in he Aluinu-224-T3 speien of 3- hikness. (b 8 PWAS aay TDS2 digial osillosope DAQ PC S HP332 signal geneao The swee iple poin: (663 khz, 35 /s Auoswih uni Vg, /s A A Speien unde inspeion (b Figue 2: EUSR expeien using an 8 eleen PWAS aay: (a speien layou; (b expeien seup 3. MINI-ARRAY DESIGNING AND IMPLEMENTATION In he opiizaion disussion, we onluded ha o have bee behaved beafoing of he PWAS phased aay, oe sensos Fequeny, khz Figue 4: Lab wave goup veloiy of Aluinu-224-T3 of 3- hikness (Boai and Giugiuiu 25 7 Copyigh 25 by ASME

8 Wihin he illusaed fequeny ange of ~8 khz, hee ae 3 odes of Lab wave exising, S, A and A. Fo os fequenies, he 3 odes avel a a diffeen speed, whih is no waned fo good iaging. Howeve, fo he plo we see, aound he fequeny 663 khz, hee is a swee poin whee he 3 odes ee eah ohe, i.e., have he sae goup veloiy (35 /s. By using his fequeny as he exiaion fequeny fo ou ini-aay, we an opially keep he wave pake fo sepaaing Expeiene esing An Aluinu-224-T3 speien (5-x46-, 3- hik wih a hough hole of 6- is insalled wih egula 8 PWAS aay and ini aay wih sall PWAS on eah side (Figue 5. The hole is 8- away fo he aays. 5- Aay Regula aay 7- squae Hole Mini aay 5- squae Figue 5: expeienaion fo opaing he deeionabiliy of egula PWAS (7- sq. and ini-pwas (5- aay. Consideing he laeal and bounday efleion, daping aeial is applied along he bounday o absob he efleions so ha he ehoes olleed by he aay ae solely due o he hole defe. Figue 6 is he iages of phased aay inspeion using he egula PWAS and ini PWAS espeively. The iage of ini aay (Figue 6b indiaes hee is a defe a 8 pependiula o he aay whih oely shows he eal siuaion while he iage of he egula aay has eain deviaion (i indiaes he defe is loaed away. Also, We noie he ini aay has a elaively salle blind aea opaed o he egula aay, i.e., he ini aay an hek he aea uh lose o he aay. These esuls onfi he idea of using a saled down phased aay... (a Figue 6: iages of he inspeion using egula PWAS (7- sq. and ini-pwas (5- aay: (a EUSR iage using 7- PWAS; (b EUSR iage using 5- PWAS 4. CONCLUSIONS In his pape, genei foulaion fo phased aay dieional beafoing was obained by using he exa aveling wave s foulaion wihou he liiing paallel-ays assupion. Then he beafoing and lobe seeing of -D linea PWAS Lab (b wave phased aay was eseahed wih exensive siulaion onening he affes of seveal paaees inluding: ( nube of sensos; (2 spaing beween sensos; (3 seeing angles. Lage nube of sensos, salle spaing (o salle aay size, o paiula seeing angle an lead o opial beafoing. Bu he opiizaion on he ohe hand is liied by he insallaion suh as wiing onens o available spae. Siulaion esuls show ha a well behaved dieional PWAS phased aay an be ahieved wih judiious aay design. Fuheoe, a ini-pwas aay was poposed fo he daage deeion of opa suues wih opliaed geoey. Fequeny uning beoes a seious issue fo his aay and we sugges using a swee iple poin in he Lab-wave ode plo. Ou peliinay expeien on a sall plae wih hole defe shows ipoved deeion wih he ini PWAS aay. Wih he genei phased aay foulaion, we envision o popose oe aay design fo oe poweful phased aay daage deeion. Fuhe heoeial eseah on he opiizaion is also aying on. Copliaed speiens will be eployed o veify he appliaion of he ini PWAS aay. ACKNOWLEDGMENTS Suppo fo he Ai Foe Reseah Lab hough UTC Cona #3-S47-33-C of F3365--D-58 is hankfully aknowledged. REFERENCES Wooh, S.C. and Shi (999, Y., Opiu Bea Seeing of Linea Phased Aays, Jounal of Wave Moion, 2 J.L Rose, "Reen Advanes in Guided Wave NDE," 995 IEEE Ulasonis Syposiu Poeedings, (Pisaaway, NJ: IEEE, 995, pp J.L. Rose, A Baseline and Vision of Ulasoni Guided Wave Inspeion Poenial, ASME J. Pessue Vessel Tehnology: Speial Issue on Nondesuive Chaaeizaion of Suual Maeials, 24 (3 (Augus 22, pp I.A. Vikoov, Rayleigh and Lab Waves (New Yok: Plenu Pess, J.L. Rose, Ulasoni Waves in Solid Media (Cabidge, U.K.: Cabidge Univesiy Pess, Giugiuiu, V., Bao, J. (24, Ebedded-Ulasonis Suual Rada fo In-Siu Suual Healh Monioing of Thin-Wall Suues, Suual Healh Monioing an Inenaional Jounal, Vol. 3, NO. 2, pp Johnson, D.H. and Dudgeon, D.E. (993, Aay signal poessing: Coneps and Tehniques, PTR Penie-Hall In., Uppe Saddle Rive, NJ Gaff, K.F. (975, Wave Moion in Elasi Solids, Oxfod Univesiy Pess 9 Boai, G., Giugiuiu, V. (25, Siulaion of he Lab Wave Ineaion beween Piezoelei Wafe Aive Sensos and Hos Suue, SPIE's 2 h Inenaional Syposiu on Sa Suues and Maeials and h Inenaional Syposiu on NDE fo Healh, Monioing and Diagnosis, Sensos and Sa Suues Tehnologies fo Civil, Mehanial, and Aeospae Syses Confeene, San Diego, CA, 7- Mah, 25, pape # Copyigh 25 by ASME