transducer performance

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ME-492 Non-Destructive TestingLaboratory Report

Tran s du c er Per fo rm a nc eL ab o rato r y No .5

Written by: Eric S. Krage, Mitch Miller, & RyanHahn Class Section 01Instructor: Dr. J ikai Du Date Performed: 11/14/2012

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Table of ContentsList of Figures, Tables and Experimental Apparatus 2Introduction 3Theory 5Experimental Procedure .Experimental Results and Analysis 7Conclusion 8References and Appendix 11

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L is t o f F ig uresFigure 1: Steel bloc with holes 10.71, 17.53, and 23.89mm from left to right respectively 3Figure 2: Wire across two plates to determine focal zone 4

Figure 3: Wire and Plate with holes setup as scanned VFigure 4: Unfocused transducer in water 5Figure 5: Focused Transducer "Spherical Dish" in water 5

List of TablesTable 1 Ratio of two signals 8Apparatus

Unfocused Transducer f =1 MHz, D = 1.125" \Immersion Tank VFocused Transducer f = 20 MHz, D=1.5" /Focused Transducer f = 10 MHz, D = 3.0"

Digital calipers

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IntroductionThe purpose of this laboratory procedure isto learn and,easure acoustic fields of !pcused andunfocused transducers. We will measure near field distance. focalleng.t~ focal zQ-ne,and b~diameter. Also, we will measure the focal length variation due to acoustic velocity of the testmaterial andwater isexamined. The immersion tank ith focused and unfocused transducerswill be used aswell asthe ultrasound reflectors.

Test Samples

Figure 1:Steel bloc with holes 10.71,17.53, and 23.89mm from left to right respectiv y

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Figure 2: Wire across two plates to determine focal zone

Figure 3: Wire and Plate with holes setup as scanned

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Theoretical Information , o ~/, ~_JtJ..)..Yv .

Near Field Transduce!((J2 ~-rThe ear fiel ransducer is adevice that converts energy in ultrasonic waves above thenormal range 0 -uman audibility. This piezoelectric transdl~cer which converts electricalenergy into ultrasonic waves ischanged by changing the srze f the transducer and the ACvoltage applied. This produces very high frequency oscillation and producing high frequencywaves.We define the point at which the waves are focused to be the focal zone and can becalculated using the equation to area and shape of the transducer and the velocity of thepropagation media. The following figures, Figure 4 and 5show the unfocused and focusedultrasonic t ansducers respectively. Aswe examine the difference between the two we noticthe ca zone larger for the unfocused transducer indicated by the red rings in the cent ofthe image. L-t-aJ ?i".~ .

\ v........ SoundDl"C5$\Itelf\w~r(41oQ-izO"10mrn)10

j 0" /,'0 ................................................. .L60 00 100 120

ZiI"'n140 160 IS O 200 I Sc1B

Figure 4: Unfocused transducer inwater10~ .__ ..._.- ,...~ ..- SQtlM prcuore IIIw.rel {"MHz,D 1Omtn)I

.150 120 1 4 < , 100 100

Figure 5: FocusedTransducer "Spherical Dish" inwater

D2 D2 it fN=-=4l 4 - *'-1-==_-1The length of the focal zone i efined by~~2tarting and ending points that are 6d8 from thefocal point to be calculated us the follo,.ing.Fz=N * ' F a ; * ' ( . . 2 ) " "I o f f-r t=' CuSV ~


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p/ED [-6dB] =0.2568'" D * - IfFinally we need to calculate the variations in the focal length that are due to the acousticvelocity of the test material. The change in the focal length can be predicted using the followingequation.. (,C t-m )/P=F-MP*'- C~.Experimental ParametersUnfocused Transducer (f = lMHz, 0 = 1.125")The ultrasonic (-Scan system water immersion system was used. The transducer parameterswere synchronized with the system software. The transducer was moved toward the aluminumplate until the front surface reflection was clearly seen. Then we adjust the angle manipulatorusing the two threaded knobs on the transducer to maximize the rface reflection in otherwords make the incident waves normal to the surface of the terial. The near field distancewas measure to be approximately 180mm. The measurements were taken using the systemsoftware controlled stepper motors that allowed the transducer to scan over the materi~~~eing _ e e devaluaty.d. 1. t~y" c r y , , ? \ ~

/ I:U l~ 1 .1 e.2-V'Focused Transducer (f =20MHz, D =0.25" F=1.5") - b " ~1 ~ q.The next step was to replace the unfocused transducer with the focused one by unscrewing itfrom the stand in the immersion tank. The transducer was moved toward the aluminum plateuntil the front surface reflection could be clearly observed. The angle manipulator was againused to maximize the signal making the incident waves normal to the material surface. Thetransducer was then moved to ultrasound reflector and the height and the x, y tositlon wasadjusted to further maximize the reflection which resulted in a compie rectified response. Inorder to ensure the transducer parameter the focallen th was.measure in. the time it takes ) ~ ~for the signal to reach the ultrasound reflector and return back to the transducer. The time c i d 7 - . z cl?fdifference was m a~ to be 51us. . g.the time difference the measured focal length was A f p(c~calculated.

C '" .tJ .tF'Xp8"m~'"' ~ w 2 37 .5 "Th is va Iu e is nea rly match ing w ith th e ma n ufa c tu rer specification s of 1 .5 " , and e.. Ieng ththe gain value of the system was adjusted so the signal amplitude was 80% high on themonitor. To find the focal zone of the transducer it was moved in the Zdirection over thesample and the distance was calculated/he amplitude of the signal en it as at 40% of

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maximum on each side. Fz= Z l - Z 2 = 34.96mm. The beamdiameter was measured bymovingthe transducer in the Xdirection along the sample to calculate the beam diameter suchthatBD= Xl - X2 = 0.9m. Note there will be asymmetries inthe displacements due to the wavegenerating ana ; , ~ ~filter to ip the high frequency. To eliminate this asymmetry aband passfilter could be usedto f / l C t 4 ')cJ...J IJeW)onl'i_allo anarrow fre uenc band to begenerated. t rFocused Transducer (f =10MHz/ 0 =0.50/1 F =3.0/1)The focal zone and the beam diameter of the 10MHz transducer was found using the sameprocedure and can be found inthe appendix of this report. The lOMHz transducer was usedtoseethe variation in the aluminum plate with the holes in it Figure 1.The NDTAutomatioimmersion tank systemwas set up to scanthe entire part. The observation was dosuccessfully and the three holes were viewed on the monitor at their relative depths.R es u l ts A n a ly s isUnfocused Transducer (f =1MHz/ 0 =1.125/1) ~'i 14::) t ;ll-/tt,/M:o .,The theoretical calculation of the near field distance of the transducer . ~ted~2mm. As previously noted the theoretical calculation can be seen intheappendix. Note that the error between the values is rather large. The possible error ismainlydue to human error like improper reading of wave signals.Also, some of the error may be dueto the vibrations of the transducer motion systemthat iscaused due to the speed of movementof the transducer inthe immersion tank. ~ frqt(.G / ~ /'Focused Transducer (f = 20M Hz, 0 = 0.25# F = 1.5#) -r~ I < i< - { CfoIblcUt-. ~ .. ftn .. - .

c/7'-f: (/-7 t U 2 , . . . e ; J J -eP~"'7?~ -"?The theoretical calculations of the focal zone and beamdiameter shown inthe appendix are ~ C'l fl~o1'discussed.The error in the values is lessthan that of the unfocused transducer but still show ~"S:Oand above average experimental error of 5%which isexpected. This error seems to have come .romasmall signal set up problem. Dueto the small oscilloscope error the transducers weremoved almost twice asfar as nee . Other possible error could be in the alignmen 0 etram ucer with the sample surface causin an aberration inour suspected beam. Third andfifth order spherical aberrations of the transducer surface itself can give rise to an error. Theseaberrations U5.e-cLOJ -uniform focal zone and beamdiameter through the sample m~~~d /causingsignal distortions. __~ ~J. J ~ /l.d.-_ ~ ~ ~ ~

ttA40 (rft~/ r''->'TV YFocused Transducer (f =10MHz/ 0 =0.50/1 F =3.0/1)The 10MHz focused transducer values can be found inthe appendix. The error was betterwithin the experimental error which allows us to saythat we have improved our testing

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techniques through this experiment and have exhausted some of the changes needed. Theremaining error is most likely human error tJ-e to the lack of time to complete the experimentin the allotted time.The NDT Automation immersion tank system was setup to automatically scan the entirealuminum sample that has the three holes contained within. The signal generated by theimmersion system represented the holes respective depth when refe~ Lab#1.QuestionsThe phenomena discovered in this lab was that sound waves passing through materials act verysimilar to the way light acts as it changes media. Like light, sound waves reflect, bounce off theboundary, and refract, change angles because of a speed difference in one medium versus theother.The amplitude ratio oftwo signals corresponding to certain decibels is given in Table 1.

Table 1 Ratio of two signalsdB =20 loglO(AR) Vatio Ratio dB

1.4142 0.707 -y'2 0.5 -64 0.25 -12100 0.01 -40

ConclusionsIn conclusion the experiment was successful in understanding and utilizing the capabilities ofthe focused and unfocused transducer. The design parameters were practiced in an immersiontank on a thread of wire and aluminum samples. The NDT Automation system capabilities werealso practiced to evaluate the scanning procedure to automatically evaluate the samples.CalculationsUnfocused Transducer 1MHz,D = 1.125" Diameter of Unfocused TransducerF = 1MHz Frequency of Unfocused Transducer

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Cwater=1.5 mm/us Velocity of sound in waterj)'J."JNfield= =136.09mm

4i< C, er-----..c:Theoretical Near Field Distance

. . ,,,J oN! . \ JP~ IVi~~ Experimental Near Field LowNL=127.5mm ~ t r " ' l j

ENH=150mm Experimental Near Field HighNf' 1 .- B~'L%difference =te (l j =.3%

NJi.~fdPercent Difference in Near Field

%difference Ern r N [cf31 ri =9.3%ENE

Percent Difference Near FieldFocused Transducer 20 MHz 1 0 5 " Focal Length,D=0.25" Diameter of Focused Transducerf =20 MHz Frequency of Focused Transducer

Focal Length of Focused TransducerCwater=1.5 mm/us Velocity of sound in water

})Z"l /Nfield= =34.41mm ,4" CW(lt~r Theoretical Near Field Distance

FzoneN fi81d (~ )z * ' ( . 2 PL ) = 18.92 Theoretical Focal ZoneNPiefd 1+0.5,,-.,-- /jYFieldBDT =0.2568 * D ; ." - - P : - - =0.461nm Theoretical Beam DiameterN fi~ ld .BDexperimental0.58mm+0.5 =1.08~ Experimental Beam DiameterFZ,exp=8.1mm+9.2mm =17.3mm /

( B D )difference = 1- _1'._' .=57.2%BDexp -Experimental Focal ZoneDifference Between Beam Diameters

( FZT)%difference = 1 - --' - =8.6% /FZ,eNr; ./ Percent Difference Focal Zones

Focused Transducer 10 MHz 3.0" Focal Length,D=0.50" Diameter of Focused Transducer

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f= 10 MHz Frequency of Focused TransducerF L =3.0" Focal Length of Focused TransducerCwater=1.5 mm/us Velocity of sound in water

IJ"~fNfield = =68.82mm'hC \ " a c e r Theoretical Near Field Distance

Fzone=Nfi/31d '" ( - - - - . ! L ) 2 ' " ( 2 FL ). = ~ Theoretical Focal ZoneNPield 1. 0.5*-,.,--"FreidBDT =0.2568'" Dl :; < ~ =.92m1],1

''Vfi&'ld L Theoretical Beam Diameter

BDexp=0.46mm+0.72 =1.18mm/FZ,exp13.71mm+26.14mm =39.85mm

Experimental Beam DiameterExperimental Focal Zone

%difference =( 1 - BD .T . ): =21.6%BDexp Difference Between Beam Diameters( P Z T ) . /%difference = : 1- --' - =5.1%FZ ,f! Jf'P Percent Difference Focal Zones

Change in focal length using 10 MHz transducerFw =3.0" Focal Length in WaterCm=6 mm/us Sound Velocity in Test MaterialCw=1.5 mm/us Sound Velocity in WaterMP =15.8 mm Thickness of plate

Distance from top of block to focus energy on thebottom of aluminum block.

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ReferencesRose, J oseph L. Ultrasonic Waves in Solid Media. Cambridge [ u.a.: Cambridge Univ. 2004]

Appendix.Question 3

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