Acoustic metamaterial absorbers based on confined sonic crystals

TL;DR

This paper develops a theoretical and experimental framework for acoustic metamaterial absorbers using confined sonic crystals, demonstrating enhanced absorption through increased viscous losses and tailored effective properties.

Contribution

It introduces a no-unknown-coefficient formulation for structured sonic crystal lattices and experimentally validates the improved absorption performance of confined sonic crystals.

Findings

Higher filling fractions enhance loss factors.

Confined structures increase viscous losses and reduce bulk modulus.

Experimental results confirm improved impedance matching and absorption.

Abstract

Theoretical, numerical and experimental results examining thermoviscous losses in sonic crystals are presented in this work, enabling the fabrication and characterization of an acoustic metamaterial absorber with complex-valued anisotropic inertia. The formulations developed can be written with no unknown or empirical coefficients, due to the structured lattice of the sonic crystals and organized layering scheme, and it is shown that higher filling fraction arrangements can be used to provide a large enhancement in the loss factor. To accurately describe these structures in a realizable experimental configuration, confining structures are needed which modify the effective properties, due to the thermal and viscous boundary layer effects within the sonic crystal lattice. Theoretical formulations are presented which describe the effects of these confined sonic crystals, both individually and as part of an acoustic metamaterial structure, and is demonstrated experimentally in an acoustic impedance tube. It is observed that confined sonic crystals demonstrate an increase in the viscous losses and a reduction in the effective bulk modulus, enabling better acoustic absorber performance through improved impedance matching and enhanced absorption.