ASA 125th Meeting Ottawa 1993 May

4pPA1. An experimental investigation of the nonlinear interaction of noncollinear sound beams.

Ronald A. Roy

Appl. Phys. Lab., Univ. of Washington, Seattle, WA 98105

Junru Wu

Univ. of Vermont, Burlington, VT 05405

The nonlinear interaction between two pulsed, Gaussian ultrasonic beams propagating through degassed and filtered water was studied. One beam had a center frequency of 3.5 MHz and a peak pressure amplitude (in the interaction region) of 450 kPa. The other possessed a center frequency and peak pressure amplitude given by 3.0 MHz and 320 kPa, respectively. With the axes of the beams intersecting perpendicularly in the near-field, no sum-frequency scattered pressure amplitude greater than 0.03 Pa was detected outside the interaction region. The insertion of a brass sphere into the center of the interaction region resulted in the generation of two partially collinear scattered beams, and a sum-frequency scattered signal level of 0.9 Pa was subsequently detected at a 45(plus or minus)0.5(degrees) scattering angle. Experiments with collinear beams generated using a single projector driven by two electrically summed tone bursts (center frequencies=3.0 and 3.5 MHz) indicate the production of sum and difference frequencies in quantitative agreement with Westervelt's theory for the parametric end-fire array [J. Acoust. Soc. Am. 32, 934A (1960)]. [Work supported by APL IR Funds.]