Quasi-BICs due to symmetry mismatch in architected elastic plates

TL;DR

This paper demonstrates the existence of quasi-bound states in elastic plates caused by symmetry mismatch, combining theoretical modeling, simulations, and experiments to reveal new localized vibrational modes with potential resonator applications.

Contribution

It introduces the concept of quasi-BICs in elastic plates due to symmetry mismatch, supported by theoretical, numerical, and experimental validation.

Findings

Quasi-BICs are observed at the interface of engineered elastic lattices.

Symmetry mismatch between Bloch and defect modes causes mode confinement.

Experimental validation confirms the theoretical predictions.

Abstract

We report the existence of quasi-bound modes in the continuum (quasi-BICs) in architected elastic plates based on a square lattice. The structure consists of topologically trivial and nontrivial lattices, forming an interface and maintaining C2 symmetry. Carefully engineered interface gives rise to center quasi-BICs. We show how the mismatch in symmetry between the Bloch modes of the lattice and the defect modes confine them at the defect center, resulting in quasi-BICs. Our analysis begins with a square lattice-based spring-mass system. Finite element simulations on an architected plate comprising of slender curved and straight beams to achieve the desired stiffness variation predict quasi-BICs analogous to those in the discrete model. These predictions are validated with Laser Doppler vibrometry based experiments, confirming the presence of a quasi-BIC in the structure. The concept of quasi-BICs arising from modal symmetry mismatch paves the way for achieving localized modes in elastic structures, with potential applications as resonators.