Author(s): Cheng Yong, Geng Linlin, Dong Jianzhu, Zhou Xiaoming
Wave controlling mediums are required to possess anisotropic stiffness and anisotropic inertial density simultaneously, which we denote by the dual anisotropy. In acoustics, the dual-anisotropic medium is referred to as the pentamode-inertial material—the general material model derived from transformation acoustics. In elasticity, the dual anisotropy is fundamental, and additionally needed are the Willis couplings between stress and velocity as well as momentum and strain. In this study, we have proposed the structured element models of dual-anisotropic solid metamaterials, which are expected to be used for acoustic and elastic wave controlling. The elementary cell consists in the stiff hexagonal lattice in which the soft two-bar inclusions are embedded. The anisotropic stiffness arises from the non-regular hexagon geometry, while the sharpened bar inclusion is to be designed by mimicking the sliding-boundary effect in fluid-solid composites in order to pursue the broadband anisotropic density. Almost non-dispersive dual-anisotropic properties have been acquired in the broad frequency range, as validated by both band-structure and effective-medium analyses. The dual-anisotropic materials can be used for elastic wave controlling in case of linear transformation where the Willis coupling is not requested. As an example, we have considered a carpet cloaking device, created by using the linear transformation. The parameters of this cloaking device are anisotropic in both stiffness and mass, and can be readily realized by the proposed metasolids. Full-wave simulations have been conducted to verify the cloaking performance. The proposed solid metamaterial, when its shear stiffness is diminished until neglected, would reduce to the pentamode-inertial material model. Application of this reduced model to acoustic control has also been explored. Our studies are expected to open a new route toward broadband acoustic and elastic wave controlling using dual-anisotropic solid metamaterials.
Name: Dr Yong Cheng