Some results on the scattering of guided elastic SH waves from material and geometric waveguide discontinuities

The scattering of guided elastic SH waves from step discontinuities in the material properties and/or geometry of otherwise uniform Bat layer waveguides is analytically/numerically analyzed. Analytical results for the case of a step discontinuity in material properties in a layer of uniform thickness an presented for comparison with later numerical results, The case of a sudden change in thickness of the waveguide, possibly in conjunction with a change in material properties, is solved numerically. The solution is based on an expansion of the wave fields on either side of the discontinuity in terms of the normal modes permissible in the analogous infinite layer and subsequent determination of the modal expansion coefficients. A ''non-coupling'' condition is proposed and proven which explains why particular modes are not generated in the scattering process. A ''perfect-coupling'' condition is also introduced, and the exact transmission amplitude of any mode satisfying the condition is given explicitly. (C) 1996 Acoustical Society of America.