As China accelerates the implementation of the marine power strategy, the demand for advanced underwater sound-absorbing materials has become increasingly urgent. Unlike air absorption, the high hydrostatic pressure and complex marine environment impose more stringent requirements regarding underwater sound-absorbing materials. The essence of the sound absorption problem is how to efficiently transform elastic energy into heat or other forms of energy. This paper reviews the traditional underwater sound absorbing materials based on both the intramolecular friction and the energy dissipation mechanisms. The main problem of traditional underwater sound-absorbing material is attributable to its poor sound absorption performance under low frequency and high hydrostatic pressure. On the one hand, this is because the underwater sound-absorbing material is of limited thickness. Besides, due to the limitation of the mass density law, it cannot effectively absorb the low-frequency sound waves from the water. On the other hand, elastic material, such as polymer, becomes"hard"under high hydrostatic pressure, thus the conversion efficiency of acoustic elastic energy is greatly reduced. With the development of local resonance theory and the concept of metamaterials, a series of new underwater sound absorbing materials have been produced, which provide new ways to solve the problems encountered in developing underwater sound absorbing materials. The local resonance theory states that a small-scale structure can control the spread of long sound waves. Therefore, it can solve the problem of sound absorption at low-frequencies. This paper focuses on the theory of local resonance, the development of new sonar wood and phonon glass, and other novel underwater sound- absorbing materials. Based on the local resonance theory, the phonon glass material can im-prove the compression performance by introducing the porous metal skeleton structure, and solve the problem of poor sound absorption performance under high hydrostatic pressure. At the end of this paper, the future development of underwater sound-absorbing materials is explored.%随着我国加速实施海洋强国战略,对先进水下吸声材料的需求日益迫切.与空气吸声不同,水下的高静水压力和复杂的海洋环境对水下吸声材料提出了更为苛刻的要求.吸声问题的本质是如何将弹性能高效地转化为热能或其他形式能量.本文综述了主要以聚合物分于内摩擦机制及界面耗能机制为基础的传统水下吸声材料.传统水下吸声材料面临的主要是其在低频及高静水压力下吸声性能差的问题.这是因为:一方面受质量密度定律的限制,有限厚度的水下吸声材料无法有效吸收水中传来的低频声波;另一方面,在高静水压力下,弹性材料如高分于聚合物会变"硬",从而大大降低了声波弹性能的转换效率.随着局域共振理论及超材料概念的提出,发展出了一系列新型水下吸声材料,为解决水下吸声材料遇到的难题提供了新思路.局域共振理论的特点是可以用小尺度结构控制长波声波的传播,从而可以解决低频吸声问题.本文重点综述了局域共振理论,以及由此发展出的声于木堆、声于玻璃等新型水下吸声材料.声于玻璃材料在局域共振理论基础上,通过引入多孔金属骨架结构提高了材料的抗压性能,从而解决了高静水压力下材料吸声性能变差的问题.本文最后对水下吸声材料未来发展方向进行了展望.
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