ASA 130th Meeting - St. Louis, MO - 1995 Nov 27 .. Dec 01

2pUW12. Total scattering cross section of two acoustically coupling balls.

Andrey V. Lebedev

Alexander I. Khilko

Hydroacoustic Div., Inst. Appl. Phys., Russian Acad. Sci., 46 Ulyanov str., Nizhny Novgorod 603600, Russia

The problem of a plane acoustic wave scattering at two acoustically coupled balls is considered. The solution is obtained via the theorem of addition for spherical functions. Asymptotic cases of extremely low and high frequency are analyzed. It is shown that in a general case in a low-frequency region total scattering cross section is two times more than for uncoupled balls. In the case of acoustically soft balls the coupling leads to decrease this value due to mutual damping of vibrations via near fields. It was found that in this case there is the optimal ratio of balls radii when the total scattering cross section reaches maximum. In the high-frequency region one can see clearly manifested spatial scales that are conditioned by geometrical sizes of the coupling system. It leads to character oscillations in the frequency dependence of scattering cross section. Maximal influence of the coupling effects in the high-frequency region is manifested when one of the balls is in shadow of the other. In this case, dominant oscillations are defined by condition kd=(pi)n (``d'' is the distance between the balls' centers) and caused by perturbations of the scattering pattern by the shading ball. [Work sponsored by ISF.]