Longitudinal-Twist Wave Converter based on Chiral Metamaterials

TL;DR

This study explores how chiral metamaterials can convert longitudinal waves into twist motion, demonstrating broad frequency range conversion with potential applications in mechanical wave control.

Contribution

It introduces a novel chiral tetragonal-beam metamaterial design and analyzes its longitudinal-twist conversion capabilities using finite element and analytical methods.

Findings

Longitudinal waves are partially converted into twist over a broad frequency range.

Chirality significantly influences the efficiency of L-T conversion.

Quasi-total conversion occurs at specific frequencies.

Abstract

Advances in material architectures have enabled endowing materials with exotic attributes not commonly available in the conventional realm of mechanical engineering. Twisting, a mechanism whereby metamaterials are used to transform static axial load into twist motion, is of particular interest to this study. Herein, computations based on the finite element method, corroborated by an analytical approach derived from applying Lagrange's equations to a monoatomic spring-mass system, are employed to explore the longitudinal-twist (L-T) conversion exhibited by a chiral tetragonal-beam metamaterial. Firstly, we perform an eigenvalue analysis taking into account the polarization states to highlight the potential contribution of the longitudinal mode in the L-T conversion. We contrast the twisting behavior of the chiral cell with that of other homogeneous medium, octagonal-tube, and non-chiral cells. Moreover, we demonstrate the influence of the cell's chirality on the L-T conversion using both time-domain and frequency-domain studies. The findings indicate that at least a portion of the longitudinally propagating wave is transformed into twist throughout a broad frequency range and even quasi-totally converted at distinct frequencies.