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

Sonoquest Advanced Ultrason. Res., P.O. Box 81153, Wellesley Hills, MA 02181-0001

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.]