Degenerate bound states in the continuum in square and triangular open acoustic resonators

TL;DR

This paper investigates degenerate bound states in the continuum in square and triangular open acoustic resonators, revealing their high Q-factors and sensitivity to perturbations, which could impact acoustic device design.

Contribution

It introduces the concept of degenerate Friedrich-Wintgen BICs in symmetric acoustic resonators, highlighting their robustness and potential for practical applications.

Findings

Degenerate BICs maintain high Q-factors over a wide size range.

Triangular resonators' BICs are highly sensitive to small perturbations.

Degenerate BICs can be efficiently switched with minimal perturbations.

Abstract

We consider square and equilateral triangular open acoustic resonators with the $C_{4v}$ and $C_{3v}$ symmetries, respectively. There is an unique property of square and triangular resonators of accidental number four-fold degeneracy of eigenstates that gives rise to two-fold degenerate Friedrich-Wintgen (FW) BICs. Compared to usual FW BICs the degenerate FW BICs maintain high $Q$-factor in wide range of the size of resonators. That removes the fabrication difficulties of proper choice of resonator. The presence of degenerate BICs in triangular resonators is extremely sensitive to switch output flows by small perturbations with $100\%$ efficiency.