Broadening the Bandgaps of Sonic Crystals by Varying Shapes, Sizes and Orientations of the Scatterers

Abstract

Sonic Crystals are noise barriers wherein the incident sound waves are scattered multiple times by the periodically arranged scatterers placed inside a host fluid. Used as sound attenuators, sonic crystals attenuate sound over frequency bands known as bandgaps. Broadening and lowering the bandgaps is the primary objective of this work. Effect of changing the shape, size and orientations of the scatterers on the band characteristics have been reported here. Different shapes of the scatterers are found to affect the band characteristics of the sonic crystals. Adding local resonance to the scatterers introduce a new attenuation mechanism due to local acoustic resonances. A new type of double circle split-ring resonator is also proposed which use acoustic resonance to produce additional bandgaps. Size and orientation of the scatterers are also found to affect the bandwidth and center frequency of the bandgaps. The band diagram, transmission loss, eigenmodes are computed using finite element method. COMSOL Multiphysics, a commercially available finite element software has been used to implement FEM and model the two-dimensional unit cells and the sonic crystal arrays. Due to the large difference in impedance of the steel scatterer embedded in air, the scatterers are assumed to be sound hard (sound rigid) which imposes a condition where normal component of acceleration is zero.