The quest for low-frequency and broadband underwater sound absorption materials with lightweight and pressure-resistant properties is constantly pursued in engineering applications. However, existing underwater absorbers are restricted by conventional design concepts and struggle to strike a balance among these requirements. Notably, the acoustic performance of these absorbers tends to deteriorate substantially with an increase in hydrostatic pressure. To address this gap, this work proposes a sandwich metasurface configuration and systematically conducts topology optimization to achieve the limiting absorption performance within specific lightweight and pressure-resistant constraints. The sandwich metasurface consists of two layers of rubber and an intervening porous structure, with the rubber layers serving as energy-dissipating components and the porous structure acting as the core for performing wave manipulation and pressure resistance. Subsequent numerical simulations and experimental tests confirm that the optimized metasurface can achieve excellent pressure-resistant capability and superior acoustic performance: the average absorption coefficient exceeds 0.9 from 1 kHz to 10 kHz and the variation in the average absorption coefficient is only 2.2 % even under a hydrostatic pressure of 3 MPa. A semi-analytical method is proposed to reveal that the key to highly efficient sound absorption lies in the strong transmodal conversions manipulated by the optimized porous structure. The formation of transverse modes greatly enhances the rubber’s ability to dissipate elastic waves. This work provides a novel theoretical tool for systematically constructing lightweight and pressure-resistant absorbers in underwater engineering applications.

中文翻译：

---

通过拓扑优化实现用于水下吸声的轻质耐压夹层超表面


在工程应用中，人们一直在追求具有轻质和耐压特性的低频和宽带水下吸声材料。然而，现有的水下减震器受到传统设计理念的限制，难以在这些要求之间取得平衡。值得注意的是，这些吸收材料的声学性能往往会随着静水压力的增加而大幅恶化。为了解决这一差距，这项工作提出了一种三明治超表面构型，并系统地进行拓扑优化，以实现特定轻量化和耐压约束下的极限吸收性能。夹层超表面由两层橡胶和一个中间的多孔结构组成，橡胶层用作能量耗散成分，多孔结构用作执行波操纵和耐压的核心。随后的数值模拟和实验测试证实，优化的超表面可以实现优异的耐压能力和卓越的声学性能：从 1 kHz 到 10 kHz 的平均吸收系数超过 0.9，即使在 3 MPa 的静水压力下，平均吸收系数的变化也仅为 2.2 %。提出了一种半解析方法来揭示高效吸声的关键在于优化的多孔结构操纵的强跨模态转换。横向模式的形成大大增强了橡胶消散弹性波的能力。该工作为水下工程应用中系统构建轻质耐压减震器提供了一种新颖的理论工具。