### ASA 127th Meeting M.I.T. 1994 June 6-10

## 3aPA7. Contactless characterization of antisymmetric edge wave dispersion
along truncated wedge using electromagnetic acoustic transducer.

**Jacques R. Chamuel
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*Sonoquest Advanced Ultrason. Res., P.O. Box 81153, Wellesley Hills, MA
02181-0001
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Accurate laboratory measurements are compared with approximate theoretical
calculations on the dispersion of antisymmetric flexural edge waves propagating
along the apex of a truncated 6061 aluminum wedge with an apex angle
(Theta)=26.7(degrees). The wedge waves are detected with a specially designed
electromagnetic acoustic transducer in the frequency range 30--500 kHz. Phase
velocity dispersion plots are obtained from gated sinusoidal signals and
wavelength measurements averaged over 10--20 wavelengths. The general
characteristics of the experimental phase velocity dispersion data closely
matched the approximate theoretical parabolic model by McKenna et al. [IEEE
Trans. Sonics Ultrason. SU-21(3), 178--186 (1974)] derived for small apex
angle. The measured dispersion curve was duplicated using a truncated wedge tip
width 57 (mu)m in the parabolic approximation calculations while the actual
measured tip width was 62 (mu)m Antisymmetric flexural wedge waves obtained
from a sharp apex (3 (mu)m) are practically nondispersive as expected in the
same frequency range. Previously reported laser ultrasonic dispersion
measurements obtained by Jia et al. [Appl. Phys. Lett. 61, 2970--2972 (1992)
and IEEE Ultrason. Symp. Proc. 1993, paper B4] revealed unexplained measured
dispersion behavior of antisymmetric wedge flexural waves based on a phase
analysis method. Contactless electromagnetic acoustic direction of
antisymmetric wedge waves provided dispersion results in agreement with
theoretical calculations. [Work supported by ONR.]