Acoustic wave transmission through a bull's eye structure

We study experimentally and theoretically acoustic transmission through a bull's eye structure, consisting of a central hole with concentric grooves imprinted on both sides of a thin brass plate. At wavelength slightly larger than the groove periodicity, a transmission peak was observed for normally incident acoustic wave, with excellent collimation ( only +/- 2 degrees divergence ) at far field. This phenomenon is a manifestation of the two- dimensional circular version of structure- factor induced resonant transmission. Theoretical predictions based on this mechanism are in good agreement with the experiments. (C) 2008 American Institute of Physics.