Acoustic helical dichroism enhanced by chiral quasi-bound states in the continuum

TL;DR

This paper demonstrates how chiral quasi-bound states in the continuum within acoustic meta-cavities can significantly enhance acoustic helical dichroism, enabling stronger chiral sound-matter interactions for sensing and manipulation.

Contribution

It introduces a novel approach using QBICs in chiral meta-cavities to amplify acoustic helical dichroism, overcoming limitations of traditional resonators.

Findings

Chiral meta-cavities support QBICs with high Q-factors and 3D chirality.

Achiral meta-cavities do not enhance acoustic HD.

Chiral meta-cavities show pronounced HD enhancement with vortex states.

Abstract

Acoustic helical dichroism (HD) arises from the interaction between vortex beams carrying orbital angular momentum (OAM) and chiral media, yet such chiral sound-matter interactions are typically weak. Here, we employ quasi-bound states in the continuum (QBICs) in acoustic meta-cavities composed of coupled Helmholtz resonators to enhance acoustic HD. We design both achiral and chiral meta-cavities that support QBICs in the form of vortex states with high Q-factors. Using full-wave numerical simulations, we show that the QBICs in the achiral meta-cavities cannot enhance acoustic HD due to the absence of a chiral wavefront. In contrast, the chiral meta-cavity exhibits a pronounced HD enhancement through the QBICs with a 3D helical wavefront, which can be excited by incident waves either with or without OAM. Our work identifies two essential requirements for enhancing acoustic HD effect via QBICs: a high Q-factor of the states and 3D chirality of the state fields, which usually compromise each other in conventional acoustic resonators. The findings open new avenues for achieving strong chiral sound-matter interactions, with potential applications in acoustic chiral sensing and acoustic OAM manipulation.