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

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

**Andrey V. Lebedev
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Alexander I. Khilko
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*Hydroacoustic Div., Inst. Appl. Phys., Russian Acad. Sci., 46 Ulyanov str.,
Nizhny Novgorod 603600, Russia
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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.]