Reduced order derivation of the two-dimensional band structure of a mixed-mode resonator array

TL;DR

This paper investigates the 2D band structure of a mixed-mode metamaterial resonator array, introducing a reduced order analytical method that approximates the band structure efficiently and aligns well with numerical results.

Contribution

It presents a novel reduced order analytical approach for approximating the band structure of complex metamaterials with minimal computational effort.

Findings

The metamaterial exhibits mixed P and SV wave branches with a unique propagation angle.

The reduced order model accurately predicts low-branch band structures.

Avoided level crossings indicate exceptional points in the complex domain.

Abstract

In this paper, the 2D band structure of a mixed-mode metamaterial resonator array for in-plane waves is investigated. The band structure in the interior and on the boundary of the irreducible Brillouin zone as well as 1D dispersion diagrams for different propagation angles are calculated numerically and presented. Additionally, a reduced order analytical method is established to compare and approximate the band structure. The studied metamaterial, with a T-shaped cantilever beam as resonator in its square array repeating unit cells, exhibits branches with mixed P and SV waves except at exactly one angle of propagation. This paper also reports on the occurrence of avoided level crossings, which are related to the existence of exceptional points in the complex domain. A reduced order analytical approach is used that can generate partial (low branches) band structure with relatively little computational effort. The reduced order model agrees well with the numerical results for these low branches and can provide support in mode identification and band sorting. With proper adjustments in parameters, this analytical method will be applicable for other metamaterials that have similar unit cell structure.