Underwater metamaterial absorber with impedance-matched composite

TL;DR

This paper presents a novel underwater acoustic metamaterial absorber using a tungsten-polyurethane composite that achieves broadband high absorption from 4 to 20 kHz by impedance matching and resonance engineering, with experimental validation.

Contribution

It introduces a new structured composite material for underwater sound absorption with broadband performance and subwavelength thickness, combining theoretical design and experimental realization.

Findings

Achieves high absorption from 4 to 20 kHz in water

Thickness is approximately 1/42 of wavelength at 4 kHz

Experimental results confirm broadband absorption performance

Abstract

By using a structured tungsten-polyurethane composite that is impedance-matched to water while simultaneously having a much slower longitudinal sound speed, we have theoretically designed, and experimentally realized, an underwater acoustic absorber exhibiting high absorption from 4 to 20 kHz, measured in a 5.6m times 3.6m water pool with the time-domain approach. The broadband functionality is achieved by optimally engineering the distribution of the Fabry-Perot resonances, based on an integration scheme, to attain impedance matching over a broad frequency range. The average thickness of the integrated absorber, 8.9 mm, is in the deep subwavelength regime (~{\lambda}/42 at 4 kHz) and close to the causal minimum thickness of 8.2 mm that is evaluated from the simulated absorption spectrum. The structured composite represents a new type of acoustic metamaterials that has high acoustic energy density and promises broad underwater applications.