Asymmetric lateral beaming of sound in a bianisotropic phononic crystal

Abstract

Willis materials or bianisotropic acoustic materials that couples pressure to particle velocity provide rich physics for sound manipulation. It has recently been shown that tailored Willis acoustic scatterers with resonance effects can display significant cross-coupling between the monopole and dipole responses. In this talk, we show that the multiple scattering in a bianisotropic phononic crystal composed of Willis acoustic scatterers also leads to interesting coupling behavior. The asymmetric structure in our design is non-resonant in the frequency range of interest. However, the nonlocal effect due to the multiple scattering among the scatterers leads to coupling between quadrupole and dipole responses. The phononic crystal is tuned to match the second-order Bragg scattering with two leaky guided modes. We show that a normally incident wave can be steered to propagate along the positive and negative directions perpendicular to the incident direction with different amounts of energy. Simulation and experimental results will be discussed.