Polarization State Conversion Achieved by Chiral Mechanical Metamaterial

Abstract

Chiral metamaterials have paved the way for progress in wave propagation and polarization control. In particular, chiral elastic metamaterials attracted considerable scientific attention due to their distinctive properties such as acoustical activity and auxeticity. Such characteristics arise from additional degrees of freedom for tuning the embedded micro- and macro-rotations. Herein, we use 3D chiral mechanical metamaterials to realize the polarization state conversion functionnality. A structural design of a 3D chiral metamaterial capable to induce up to 90° rotation in the plane of polarization is presented. This feature enables a straightforward switch between the three polarization states existing within a solid material, namely, longitudinal state, shear horizontal state, and shear vertical state. Efficient conversion from longitudinal movement to transverse movement is demonstrated. A discrete mass-spring model is proposed for these 3D chiral structures that describes the conversion behaviors based on the corresponding elastic coefficients. The engineered chiral metamaterial polarization converter is a promising device for efficient momentum conservation conversions. This allows converting longitudinal waves into shear waves while preserving the initial stimulating wave characteristics.