Two-dimensional Helmholtz resonator arrays. Part I. Matched asymptotic expansions for thick- and thin-walled resonators

TL;DR

This paper introduces a new multipole method combined with matched asymptotic expansions to accurately compute the band structures of 2D Helmholtz resonator arrays, capturing complex features like anisotropy across various parameters.

Contribution

It develops a novel asymptotic multipole formulation that extends existing models to accurately describe the first band and band gaps for thick- and thin-walled resonators.

Findings

Accurate representation of the first band over broad frequency ranges.

Identification of how wall thickness affects band gap width and frequency.

Capture of low-frequency anisotropy across different filling fractions.

Abstract

We present a novel multipole formulation for computing the band structures of two-dimensional arrays of cylindrical Helmholtz resonators. This formulation is derived by combining existing multipole methods for arrays of ideal cylinders with the method of matched asymptotic expansions. We construct asymptotically close representations for the dispersion equations of the first band surface, correcting and extending an established lowest-order (isotropic) result in the literature for thin-walled resonator arrays. The descriptions we obtain for the first band are accurate over a relatively broad frequency and Bloch vector range and not simply in the long-wavelength and low-frequency regime, as is the case in many classical treatments. Crucially, we are able to capture features of the first band, such as low-frequency anisotropy, over a broad range of filling fractions, wall thicknesses, and aperture angles. In addition to describing the first band we use our formulation to compute the first band gap for both thick- and thin-walled resonators, and find that thicker resonator walls correspond to both a narrowing of the first band gap and an increase in the central band gap frequency.