### ASA 128th Meeting - Austin, Texas - 1994 Nov 28 .. Dec 02

## 5aPA5. Acoustic scattering from a rigid sphere coated with multiple layers
of absorbing materials: Eigenfunction expansion method.

**B. S. Sridhara
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*Ind. Studies Dept., Middle Tenn. State Univ., Murfreesboro, TN 37132
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**Sadasiva M. Rao
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*Auburn Univ., Auburn, AL 36849
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Far-field scattered properties for a rigid sphere coated with several
layers of absorbing materials have been obtained using the eigenfunction
expansion method. The sphere coated with m number of acoustic layers and placed
in air, in a lossless situation, was considered. Compatibility conditions of
sound pressures and sound velocities were applied at layer interfaces. The
resulting (2m+1) complex linear algebraic equations involving material
properties, and the spherical Bessel, Newman, and Hankel functions, were
written in the matrix form. Computer codes were developed and the equations
were solved for the coefficients which, along with other variables and
parameters, were used to compute the scattered field properties. The
formulation was verified by computing the far-field scattered parameter and
comparing it with the available standard results. Far-field scattered
properties were computed for a rigid sphere coated with a total of 12 different
layers. In each case, the magnitude of the far-field scatter parameter was
computed and plotted as a function of the angle in the range from 0(degrees) to
180(degrees). It was observed that the scatter parameter was sensitive to the
change in the angle and the variation was relatively large in the range from
100(degrees) to 160(degrees) in the case of certain layers.