Interaction of Sound with Sound in Water in the Presence of a Solid Surface

Abstract

Recent experiments involving the scattering of sound by sound have produced negative results for the case of noncollinear beams. When two perpendicularly intersecting finite-amplitude sources (frequencies of 7 and 5 MHz, pressure ampltiudes of 4.5 and 1.8 atm, respectively, at the center of the interaction region) were allowed to interact in water, no scattering at the sum and difference frequencies was observed although pressure levels of 0.07 dyn/cm2 could be measured with a 10 dB S/N ratio. However, scattering has been observed for the same case when solid objects, such as rigid cylinders, are placed in the interaction region. It appears that diffraction of the primary beams by the solid object produces an array of collinear beams, which generate the sum and difference frequencies. Measurements of the interaction at the sum frequency are presented for the case of rigid cylinders (radii 14 and 164 in) in the interaction region. Furthermore, a simple theory is proposed which yields results in good agreement with the experimental data. [This research was supported in part by the Office of Naval Research.]