Chiral Triclinic Metamaterial Crystals Supporting Isotropic Acoustical Activity and Isotropic Chiral Phonons

TL;DR

This paper introduces a simpler, more fabricable chiral triclinic metamaterial crystal that exhibits broadband isotropic acoustical activity with larger effects than complex quasicrystals, despite increased fabrication sensitivity.

Contribution

It proposes and analyzes a novel chiral triclinic metamaterial design with enhanced isotropic acoustical activity compared to prior complex quasicrystal architectures.

Findings

The triclinic design shows larger acoustical effects.

It maintains broadband isotropic acoustical activity.

The structure is less complex and more fabricable.

Abstract

Recent work predicted the existence of isotropic chiral phonon dispersion relations of the lowest bands connected to isotropic acoustical activity in cubic crystalline approximants of 3D chiral icosahedral metamaterial quasicrystals. While these architectures are fairly broadband and presumably robust against fabrication tolerances due to orientation averaging, they are extremely complex, very hard to manufacture experimentally, and they show effects which are about an order of magnitude smaller compared to those of ordinary highly anisotropic chiral cubic metamaterial crystals. Here, we propose and analyze a chiral triclinic metamaterial crystal exhibiting broadband isotropic acoustical activity. These 3D truss lattices are much less complex and exhibit substantially larger effects than the 3D quasicrystals at the price of being somewhat more susceptible to fabrication tolerances. This susceptibility originates from the fact that we have tailored the lowest two transverse phonon bands to exhibit an "accidental" degeneracy in momentum space.