ASA 128th Meeting - Austin, Texas - 1994 Nov 28 .. Dec 02

5aPA12. Transmitted beam distortion and rotation due to mode conversion between acoustic and shear waves at liquid--solid interfaces.

B. J. Landsberger

M. F. Hamilton

Yu. A. Il

Dept. of Mech. Eng., Univ. of Texas at Austin, Austin, TX 78712-1063

An experiment was performed with a pulsed sound beam incident on a 6-cm-thick aluminum block immersed in water. Tone bursts were radiated at 1 MHz by a circular source of radius 1.2 cm, which was positioned 10 cm away from one side of the block. Transmitted acoustic beam patterns were measured in the water beyond the opposite side. Attention was devoted to angles of incidence in the neighborhood of the critical angle for compression waves in the block (~13.5(degrees)). The use of pulses, and the strong refraction of the compression wave in the block, enabled isolation of effects associated with the shear wave. Distortion in the form of multiple beam splitting, and up to 4(degrees) increase in the effective propagation direction of the transmitted beam (relative to the angle of the incident sound beam), were observed. Computations based on standard Fourier-transform techniques, but excluding contributions due to the compression wave in the block, yield good quantitative agreement with experiment. For the conditions in this experiment, calculations indicate that the distortion and rotation of the transmitted sound beam are due mainly to the mode conversion at the second interface. [Work supported by AASERT and ONR.]