Mechanisms of Acoustic Surface Wave Generation by Rigid Cyllinder Arrays

The propagation of an acoustic impulse over a surface constructed from regularly spaced rigid cylinders on a rigid plane has been simulated using multiple scattering theory. The simulations show that the surface causes a complex signal comprising a main pulse and a tail. The tail has a rich frequency spectrum with peaks that can, in general, be interpreted using Bragg diffraction theory. However, this interpretation is not valid for the lowest frequency peak. The spacing between the rigid pipes generates an “organ-pipe” type resonance. Above a height corresponding to three times the cylinder diameter these resonances combine to form a signal, demonstrating the characteristics of a surface wave. Results of experimental measurements confirm this interpretation