Maximum electro-momentum coupling in piezoelectric metamaterial scatterers

Abstract

Engineered piezoelectric metamaterials can possess electro-momentum coupling between the macroscopic momentum and electric stimuli. This indicates the applicability of such metamaterials for wave scattering with an extra design degree of freedom, in the same way as Willis materials. To fully utilize this novel bianisotropy, we derive for the first-time theoretical bounds on electro-momentum coupling in wave scattering via energy conservation. As this coupling acts on both elastodynamics and electromagnetics, the polarizability tensor is generalized to fill their link in the bounds. Our derived bounds are verified via analytical scattering solutions. Results show that the bianisotropic scattering can be of the same order as the non-bianisotropic terms via the aid of electro-momentum coupling even for small Willis coupling. We further reveal the possibility of using electro-momentum coupling for tunable cloaking. This sheds light on the promising potential of piezoelectric metamaterials for tunable scattering devices whose bianisotropy can be modulated by external electric stimuli.