ASA 130th Meeting - St. Louis, MO - 1995 Nov 27 .. Dec 01

4aPA12. Effects of frequency-dependent absorption on the propagation and attenuation of high-intensity acoustic waves containing shocks.

Vera A. Khokhlova

Oleg A. Sapozhnikov

Dept. of Acoust., Phys. Faculty, Moscow State Univ., Moscow 119899, Russia

Michalakis A. Averkiou

Lawrence A. Crum

Univ. of Washington, Seattle, WA 98105

Shock waves used in extracorporeal lithotripsy and ultrasonic surgery are greatly influenced by thermoviscous losses in the tissue. The influence of the frequency dependence of the absorption coefficient on nonlinear wave distortion and energy attenuation has not been investigated in detail up to now. For absorption frequency dependence other than quadratic, the corresponding nonlinear evolution equation is often complicated and thus frequency domain methods are more effective. The presence of the shock, however, makes this analysis time consuming due to the large number of spectral components needed in the numerical calculation. To avoid this complexity, a semianalytical method that enables calculations with relatively few harmonic components is used. Propagation in media with various power law absorption is considered. It is shown that energy attenuation of an initially sinusoidal wave in a medium with linear power law absorption is quite similar with that in a medium with quadratic power law absorption, even though the waveforms are quite different. The effect of selective absorption of a certain harmonic component is also investigated. It is shown that second harmonic selective absorption does not prevent shock formation, but results in much less energy attenuation over large distances. [Work supported by NIH, FIRCA, and RFFI.]

All posters will be on display from 8:00 a.m. to 12:00 noon. To allow contributors an opportunity to see other posters, contributors of odd-numbered papers will be at their posters from 8:00 a.m. to 10:00 a.m. and contributors of even-numbered papers will be at their posters from 10:00 a.m. to 12:00 noon. To allow for extended viewing time, posters will remain on display until 8:00 a.m. on Friday morning.