Refraction effects in the generation of helical surface waves on a cylindrical obstacle

We investigate the scattering of compressional waves from an infinite, circular-cylindrical obstacle, and the excitation during the scattering process of surface waves that propagate along helical paths over the cylinder surface. For the case of a rigid or soft obstacle, the surface waves are external, and are obtained via the use of a Watson transformation. For the case of a penetrable cylinder, additional internal, resonant surface waves are generated for which the phase and group velocity dispersion curves can be obtained from the Resonance Scattering Theory. We perform a detailed study of certain refraction effects which take place upon the generation of the surface waves by the incident plane wave.