ASA 126th Meeting Denver 1993 October 4-8

5aPA15. Measurements of focused, finite amplitude sound beams reflected from curved targets.

Michalakis A. Averkiou Inder Raj S. Makin Mark F. Hamilton

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

The reflection of focused, finite amplitude sound beams from curved targets in water was investigated experimentally and theoretically. Measurements of small signal diffraction effects were used to characterize the effective radius (1.9 cm) and focal length (15 cm) of the source, the center frequency of which is 2.25 MHz. Detailed comparisons are made between measurements of harmonic generation in the incident focused beam and numerical results from a computer code that solves the KZK equation in the frequency domain [Naze Tj(slashed oh)tta et al., J. Acoust. Soc. Am. 89, 1017--1027 (1991)]. Reflection from both convex and concave target surfaces is considered. The targets are made of nickel with different radii of curvature down to a minimum of 5 cm. Measurements of the reflected beam were obtained with a membrane hydrophone that was placed between the source and the target. Theoretical predictions for harmonic generation in the reflected field were obtained by modifying the computer code to account for the phase shifts introduced by interaction of the incident beam with the target. Theory and experiment are in good agreement for both the incident and reflected beams. [Work supported by the Packard Foundation and the Office of Naval Research.]