Existence of broad acoustic bandgaps in three-component composite

Experimental and theoretical studies of acoustic transmission through a two-dimensional three-component composite composed of a square array of coated cylinders embedded in an epoxy resin are presented in this paper. The coated cylinders consist of steel inner core and rubber coating, which has much smaller wave velocity and mass density than the matrix and inner material. We observed a broad bandgap in the measured power spectrum along the GammaX propagation direction where only the noise level is measured. The two-component counterparts composed of a square array of steel cylinders embedded in an epoxy resin without rubber coating are also studied to investigate the influence of the soft coating on the properties of bandgaps. The transmission spectrum along the GammaM direction is also presented in the paper. The finite-element method has been employed to calculate the transmitted power spectrum, which is in good agreement with the experimental results. The calculated displacement configurations at the frequency inside and out of the bandgaps illustrate the generation mechanism of the gaps.