Improvement in underwater acoustic absorption performance of open-celled SiC foam

Abstract

Abstract Open-celled silicon carbide (SiC) foam has been proven of a promising underwater acoustic absorption material. However, further improvement of its sound absorption capacity especially at low frequency is restricted by the acoustic impedance mismatch between the foam material and the water surrounding it. How to tailor the existing SiC foam in order to achieve an optimized impedance match is a key issue. In this work, the underwater acoustic absorption performance of open-celled SiC foam is studied by both analytical and experimental methods. First, based on Zwikker–Kosten’s theory, the modified Johnson–Allard (J–A) model is proposed to analytically predict the absorption performance of liquid-saturated SiC foam. Then three approaches including (i) backing the test samples by a 30-mm-thick air cavity, (ii) enclosing a certain amount of water and (iii) filling the samples with silicon oil are proposed to improve the underwater sound absorption performance of SiC foam. The underwater acoustic absorbency of the silicon oil filled SiC foam is significantly improved, especially in the low frequency band. A sound absorption coefficient near unity is achieved by this manner over a significant portion of the investigated frequency range, eg. 750–4000 Hz. The foam partially filled with water also shows enhanced sound absorbency at low frequency, but the foams backed by air gap and saturated fully by water display degraded sound absorption capacity.