On scattering effects due to the proximity and relative position of two bubbles in a sound field

Abstract

Recently the authors published results from a theoretical and experimental investigation on scattering of sound from two bubbles symmetrically arranged about the combined beam axis of a set of transducers [J. Acoust. Soc. Am. 107, 3006–3017 (2000)]. In this presentation the investigation is extended to two additional geometries, with the two bubble array placed at angles of 0° and 45° from the combined beam axis. For each angle, the half interbubble distance d is varied such that the dimensionless variable kd ranges from 0.2–5 (for the 0° case) and 0.2–10 (for the 45° case), where k is the acoustic wave number. Modeling is accomplished by using a closed-form solution derived from the multiple scattering series, with the bubble scattering function expressed in terms of spherical harmonics. Experimental data are obtained by symmetrically arranging two bubbles, each of radius a≊425 μm, on a fine nylon thread, with the bubbles insonified by tone bursts with a center frequency of 120 kHz. The data closely agree with the simulations, and it is verified that, regardless of the geometry, for kd≤1 the response of the two bubble array drastically departs from the one due to single scattering. This departure is attributed to multiple scattering and is manifested as a reduction in backscattered radiation.