4.7 Article

Ultrathin acoustic metamaterial as super absorber for broadband low-frequency underwater sound

Journal

SCIENTIFIC REPORTS
Volume 13, Issue 1, Pages -

Publisher

NATURE PORTFOLIO
DOI: 10.1038/s41598-023-34993-0

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In this research, an ultrathin acoustic metamaterial composed of space-coiled water channels with a rubber coating is proposed for underwater sound absorption. The proposed metamaterial achieves perfect sound absorption at 181 Hz with a deep subwavelength thickness. The introduction of a rubber coating leads to slow-sound propagation, which is crucial for achieving perfect low-frequency sound absorption.Parametric studies are conducted to investigate the effects of specific structural and material parameters on sound absorption. By tailoring key geometric parameters, an ultra-broadband underwater sound absorber is constructed, paving a new way for designing underwater acoustic metamaterials and controlling underwater acoustic waves.
In this work, an ultrathin acoustic metamaterial formed by space-coiled water channels with a rubber coating is proposed for underwater sound absorption. The proposed metamaterial achieves perfect sound absorption (a > 0.99) at 181 Hz, which has a deep subwavelength thickness ( A/162). The theoretical prediction is consistent with the numerical simulation, which demonstrate the broadband low-frequency sound absorption performance of the proposed super absorber. The introduction of rubber coating leads to a significant decrease of the effective sound speed in the water channel, resulting in the phenomenon of slow-sound propagation. From the perspective of numerical simulations and acoustic impedance analysis, it is proved that the rubber coating on the channel boundary causes slow-sound propagation with inherent dissipation, which is the key to meet the impedance matching condition and achieve perfect low-frequency sound absorption. Parametric studies are also carried out to investigate the effect of specific structural and material parameters on sound absorption. By tailoring key geometric parameters, an ultra-broadband underwater sound absorber is constructed, with a perfect absorption range of 365-900 Hz and a deep subwavelength thickness of 33 mm. This work paves a new way for designing underwater acoustic metamaterials and controlling underwater acoustic waves.

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