A new theoretical approach to the analysis of nonlinear sound beams using the oblate spheroidal coordinate system

In this article, the authors propose a new model equation which describes w ell progressive sound beams from a planar piston source with a circular ape rture. The theory is based on the oblate spheroidal coordinate system and i s easily extended to the analysis of nonlinear propagation of finite amplit ude sound beams. The resultant beam equation facilitates numerical calculat ions in the far held. An experiment is performed in water using a 5-MHz pla nar ultrasonic transducer with a 9-mm radius aperture, and the results are compared with the theoretical prediction for sound pressure amplitudes of t he fundamental and second harmonics. They are in excellent agreement with e ach other along and across the beam axis. (C) 1999 Acoustical Society of Am erica. [S0001-4966(99)01106-6].