Strongly frequency-dependent negative refraction of a two-dimensional sonic crystal wedge

Negative refraction of a two-dimensional sonic crystal prism has been numerically demonstrated by finite-difference time-domain (FDTD) simulations. It is shown that both positive refraction and negative refraction can be predominant corresponding to different frequencies in the second band. The equifrequency surfaces and some expansion coefficients have also been calculated by the plane-wave expansion method to help understand the FDTD results. These frequency-dependent properties of negative refraction are attributed to the coupling between higher-order Bragg waves inside the sonic crystals and the waves in the homogeneous medium.