A theoretical investigation of STW propagation at abrupt or distributed changes in surface loading

Two ways of calculating the STW propagation characteristics for waves along a surface with varying mass loading are presented. One method is best suited for abrupt transitions and is based on conventional eigenmode expansion. In the other the boundary conditions at the surface are expressed as an eigenvalue problem. This method allows arbitrary mass loading profiles to be analyzed. A set of scaling rules is given which allows field distributions and losses obtained for one geometry and surface loading to be used also for scaled structures. The scaling applies in a parabolic approximation of the shear wave slowness curve. Different types of mass transitions are studied, as abrupt, stepped, or graded transitions. For abrupt transitions in the parabolic approximation the losses are, as expected, found to be as given by a simple mode overlap integral, brit with some ringing in amplitude and phase at the surface downstream from the transition. Graded or in other ways distributed transitions may have much reduced losses and ringing