An acoustic bending waveguide designed by graded sonic crystals

The acoustic bending waveguide can be designed by engineering the index distribution in a bending structure. We employ a two-dimensional graded sonic crystal (GSC) to realize a graded index medium. The refractive indices of a graded index medium can be discretized and the discrete refractive indices are approximated by using GSCs. The effective refractive indices of the sonic crystals are obtained by using the plane wave expansion method. Simulations and transmission spectra of the bending waveguides with the continuous index variation and the GSC approximation are calculated by using the finite-element-method. The results show that the acoustic bending waveguide based on the GSC can be achieved in the low frequency limit and its operating frequency is broadband.