Acoustic bi-anisotropy in asymmetric acoustic metamaterials

We report the experimental realization of acoustic bi-anisotropy by asymmetric acoustic metamaterials (AAMs). Asymmetric phases of reflection coefficients are achieved in different-bilayer AAM with different resonant properties on either side, and asymmetric amplitudes of reflection coefficients are achieved by introducing material loss. The existence of acoustic bi-anisotropy means that the effective parameters on either side are asymmetric. A modified direct method is presented to obtain unified effective parameters, and the calculated unified effective parameters meet the requirements of passive metamaterials. This work explores acoustic bi-anisotropy in asymmetric structures, and provides new avenues to tailor reflection waves.