Abstract

A Theoretical Approach to Nonlinear Propagation of Ultrasound Beams Using Higher-Order Parabolic Approximation

T.Kamakura, K.Aoki (Department of Electronics, University of Electro-Communications, Tokyo, Japan); T.Ishiwata (Oki Electric Industry Co., Ltd., Tokyo, Japan.)

e-mail: kamakura@ee.uec.ac.jp

This report is concerned with a new theoretical approach for analyzing intensive sound beams emitted from a planar and a strongly focused aperture source. In particular, the analysis is restricted to sound fields near the source, where an ordinary parabolic equation fails to be applicable. Using the wide-angle parabolic approximation based on a four-term Taylor expansion, a beam model equation is derived in a straightforward manner. Except the region near the source, the first three harmonic pressures along and across the beam axis are predicted to be almost the same amplitudes as those by the Khokhlov-Zabolotskaya-Kuznetsov (KZK) equation. Some numerical and experimental examples demonstrate that the model equation proposed is fully applicable to the theoretical analysis of focused beams from a concaved source with a half-aperture angle of about 30 degrees.

Section : 1