Wave propagation in a 2D sonic crystal with a Helmholtz resonant defect

In this paper, we study the wave propagation of a 2D local resonant sonic crystal consisting of polymethyl methacrylate cylinders in air background. The Helmholtz resonator is placed at the point defect to be a local resonant defect. Band structures are calculated by using the finite element method with a periodic boundary condition. Band structures of the sonic crystal with a circular and Helmholtz resonant (HR) defect are discussed and compared. The frequencies of the defect band depend strongly on the geometric size of the defect. The transmission spectra are measured experimentally. The experimental results are in good agreement with the analytical band structures. The defect mode characteristics of the sonic crystal with a HR defect can be used in the implementation of new acoustic devices.