Considerations on Linear Phased Array transducers with Circular Crystals ECNDT Prague 2014

Transcription

1 Considerations on Linear Phased Array transducers with Circular Crystals ECNDT Prague 2014 Dr. Y. Oberdörfer, Dr. T. Bruch Imagination at work.

2 Agenda 1. Motivation 2. Considerations on non-uniform element shapes 3. Favorable applications 4. Summary 2

3 Motivation Most prevalent linear arrays crystal shape has uniform elements Rectangular crystals allow electronic scanning with constant apertures 1 2 n active aperture 3

4 Motivation Rectangular crystals allow flexible forming of apertures 1 2 n active aperture 4

5 Motivation However normally compression wave probe designs have circular crystal Sound beam formation / rotational symmetry Isobar presentation of sound field (free-field) calculated for a rectangular oscillator with b/a = 0,6. left: z = 0,8 a²/λ right: z = 3,2 a²/ λ 1) 1) Krautkrämer J, Krautkrämer H., Werkstoffprüfung mit Ultraschall, Springer Verlag Berlin Heidelberg New York London Paris Tokyo, 5. völlig überarbeitete Auflage, 1986

6 Motivation Since couple of applications require steering capability more than scanning linear phased array probe with circular crystal diameter D pitch = const. active aperture 6

7 Motivation Ease of use Ergonomically beneficial Wear resistance instead of delay lines Acoustically comparable to conventional probes 7

8 Considerations on non-uniform element shapes Different element areas might influence electrical and acoustical behavior Area ratio is function of element count, not of diameter or pitch Area ratio of elements normalized to largest element area 8

9 Considerations on non-uniform element shapes Crystal / element has capacitive portion that is a function of area,, Equivalent electrical circuit of piezoelectric crystal 2) 2) W. P. Mason, Piezoelectric Crystals and Their Application to Ultrasonics, D. Van Nostrand Company, Toronto, New York, London,

10 Considerations on non-uniform element shapes Does the varying element capacity influence excitation/sensitivity? Qualitative comparison of area ratio and single element sensitivity 24 mm, 4 MHz, 16 elements ( conv. B4S-(E) ), back wall (K1, 25 mm) 10

11 Considerations on non-uniform element shapes Qualitative comparison of area ratio and single element sensitivity Single element sensitivity not obviously function of capacity 11

12 Considerations on non-uniform element shapes Is single element sens. characteristics mainly an acoust. properties? CIVA 3) simulation: no influence of electronics, purely acoustical 3) CIVA is distributed in Europe by EXTENDE, Massy, France 12

13 Considerations on non-uniform element shapes comparison of simulated and empirical single element data, 24 mm, 4 MHz, 16 elements, back wall (K1, 25 mm), averaged data Single element sensitivity seems to be an acoustical property 13

14 Considerations on non-uniform element shapes Contribution of out-most elements? CIVA simulation 2*N), switching off outmost elements 10 mm Switched-off elements on both sides 14

15 Considerations on non-uniform element shapes Calculating eccentricity from orthogonal beam profile show the deformation even more clearly # of inactive elem. on either side Half profile db, x-direction /[mm] Half profile db, z-direction /[mm] eccentricity 0 9,9 9,9 0,0 1 10,4 10,0 2,9 2 11,3 9,9 5,5 3 13,0 9,8 8,6 Also out-most elements contribute significantly to sound field formation 15

16 Favorable applications - DGS Rotationally symmetric sound-fields natural fit to DGS Rotational symmetry also while steering mm, 4 MHz, 16 elements, steel (5920 m/s) Sound pressure distribution perpendicular to acoustical axis 16

17 Favorable applications - DGS DGS curve for each steering angle has to be gaincompensated DGS possible with just one reference echo, e.g. flat back wall at 0 17

18 Favorable applications - DGS Gain compensation curve for 10 mm, 16 elements, 2 and 4 MHz 18

19 Favorable applications - DGS DGS with phased array probes comparable to conventional probes 3 mm FBH curve at 0 immersion technique, steel-rod 10 mm, 16 elements, 2 MHz 19

20 Favorable applications - DGS DGS with phased array probes comparable to conventional probes 3 mm FBH curve at 5 immersion technique, steel-rod 10 mm, 16 elements, 2 MHz 20

21 Favorable applications - DGS DGS with phased array probes comparable to conventional probes 3 mm FBH curve at 10 immersion technique, steel-rod 10 mm, 16 elements, 2 MHz 21

22 Favorable applications - DGS 22

23 Favorable applications threaded bolts Inspection of bolts for corrosion or defects Circular shape of probes perfect fit for shape of bolts 180 turn for 360 inspection 23

24 Favorable applications - inspection of castings Differentiation between isolated and clustered pores Differentiation not easily possible with conventional probes Rough surface benefit of having protection membranes, no delay lines necessary 24

25 Favorable applications - inspection of castings isolated pores clustered pores 25

26 Summary Motivation of using linear phased array probes with circular crystal Electrical and acoustical characteristics of non-uniform elements DGS capability over steering range Shape factor beneficial for inspection of bolts Protection membrane instead of delay lines to avoid wear Inspection range not limited by delay lines 26

27 Summary More information on probes and applications 27

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