On the use of aerogel as a soft acoustic metamaterial for airborne sound

TL;DR

This paper explores the use of silica aerogel in soft acoustic metamaterials to achieve exotic properties like negative density and broadband slow sound, supported by theoretical analysis and experimental validation.

Contribution

It introduces a novel application of silica aerogel in compact soft acoustic metamaterials, demonstrating a wide range of effective properties including negative density and broadband slow sound.

Findings

Experimental validation of effective density and sound speed.

Achievement of negative density and near-zero density properties.

Good agreement between theoretical models and experimental data.

Abstract

Soft acoustic metamaterials utilizing mesoporous structures have recently been proposed as a novel means for tuning the overall effective properties of the metamaterial and providing better coupling to the surrounding air. In this work, the use of silica aerogel is examined theoretically and experimentally as part of a compact soft acoustic metamaterial structure, which enables a wide range of exotic effective macroscopic properties to be demonstrated, including negative density, density-near-zero and non-resonant broadband slow sound propagation. Experimental data is obtained on the effective density and sound speed using an air-filled acoustic impedance tube for flexural metamaterial elements, which have previously only been investigated indirectly due to the large contrast in acoustic impedance compared to that of air. Experimental results are presented for silica aerogel arranged in parallel with either 1 or 2 acoustic ports, and are in very good agreement with the theoretical model.