Acoustic Bound States in the Continuum in Coupled Helmholtz Resonators

TL;DR

This paper demonstrates the creation and control of acoustic bound states in the continuum using simple coupled Helmholtz resonators, enabling easy tuning of metastructures for advanced wave manipulation.

Contribution

It introduces a straightforward system of coupled Helmholtz resonators for realizing and tuning bound states in the continuum, with experimental validation.

Findings

Quasi-bound states in the continuum can be excited in simple resonator systems.

Tuning intrinsic losses affects spectral properties and can induce exceptional points.

Experimental and numerical results confirm the feasibility of easy-tunable acoustic metastructures.

Abstract

Resonant states underlie a variety of metastructures that exhibit remarkable capabilities for effective control of acoustic waves at subwavelength scales. The development of metamaterials relies on the rigorous mode engineering providing the implementation of the desired properties. At the same time, the application of metamaterials is still limited as their building blocks are frequently characterized by complicated geometry and can't be tuned easily. In this work, we consider a simple system of coupled Helmholtz resonators and study their properties associated with the tuning of coupling strength and symmetry breaking. We numerically and experimentally demonstrate the excitation of quasi-bound state in the continuum in the resonators placed in a free space and in a rectangular cavity. It is also shown that tuning the intrinsic losses via introducing porous inserts can lead to spectral splitting or merging of quasi-\textit{bound states in the continuum} and occurrence of \textit{exceptional points}. The obtained results will open new opportunities for the development of simple and easy-tunable metastructures based on Helmholtz resonances.