Spatial filtering of sound beams by sonic crystals

We propose and numerically demonstrate the feasibility of spatial filtering, i.e. a selective removal of the high spatial frequency components, of narrow acoustic beams during their propagation along a two-dimensional sonic crystal. The filtering effect occurs due to two different mechanisms, depending on the particular form of the dispersion surfaces of the propagation modes in sonic crystal. Reflection or deflection of undesired spatial frequency components occurs for these two mechanisms. It is shown that, as a consequence of spatial filtering, the angular spectrum of the beams is narrowed, and the noisy beams are efficiently cleaned.