Thickness Effects in Overlay Guides for Elastic Surface Waves

The analysis here is concerned with waveguides for elastic surface waves where the guiding structure consists of an overlay of rectangular cross section on the surface of an infi- nite substrate. When the overlay is thin with respect to the wavelength various perturbation techniques can be used to determine the dispersion curves of such guides. By using an approach which treats the overlay and the region under the overlay in a manner similar to the polynomial variational ap- proaches which have been used for propagation modes of rods and plates, the analysis here allows an investigation of the effects of overlay thickness on the dispersion curves and on the displacement distributions in the overlay and in the sub- strate. The infinite series introduced into the displacement distribution can be truncated at different orders depending on the accuracy desired and on the tolerable computational complexity. Two different orders of truncation are discussed and numerical results for several different modes are presented showing both the dispersion and displacement behaviour for a gold overlay on a fused quartz substrate.