### ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

## 2aSA2. Variable phase coupling coefficient for leaky waves from resonance
scattering theory and physical aspects of background contributions.

**Philip L. Marston
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*Dept. of Phys., Washington State Univ., Pullman, WA 99164-2814
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Approximations are examined for the coupling coefficient G[sub l] for the
launching and detachment of leaky waves having application to situations where
thin shell theory is not applicable. The approach is based on a comparison of
ray and resonance scattering theory (RST) formulations which includes effects
on the phase of G[sub l] of higher-order Debye approximations of Hankel
functions and derivatives [P. L. Marston, Wave Motion (accepted for
publication)]. The comparison includes a frequency dependent transition
(between soft and rigid limits) for the RST background factor in the product
expansion of the S function. The transition is formulated such as to not affect
|G[sub l]|. The high frequency phase of G[sub l] for limiting background cases
previously examined [P. L. Marston and K. L. Williams, J. Acoust. Soc. Am.
Suppl. 1 83, S94 (1988)] S94 (1988)] is recovered. A variable phase term
depending on the background transition function corresponds to a term given by
the convolution formulation of variable curvature scattering [P. L. Marston,
34--41 (1995)] when applied to thin circular cylindrical shells. Other
correlations with shell theory are evident. Diffractive and inertial aspects of
the background contribution are also examined. [Work supported by the Office of
Naval Research.]