Existing solid composite structures composed of several viscoelastic materials and metals mainly exploit diverse resonances, damping, and scattering to realize underwater acoustic wave functionalities. However, low-frequency broadband underwater sound absorption and insulation are still hard to capture with an acoustic coating possessing subwavelength thickness and lightweight nature simultaneously. This paper reports the systematic simulated and experimental validations of a porous-solid underwater metaconverter, consisting of a rubber layer and a topology-optimized elastic metasurface to exhibit broadband functionalities of sound absorption and insulation caused by the strong reflective and transmitted longitudinal-to-transverse wave conversion, while sustaining broadband impedance matching. Various results confirm the predicted capabilities of underwater broadband high-efficiency sound absorption (>80%) or insulation (20 dB) within the range of 2–10 kHz for a large- and limited-size sample, providing an estimate of the energy-converting effect and phenomenon. The present study provides possibilities for elastic wave energy dissipation, harvesting, and underwater acoustic stealth via metasurfaces.

中文翻译：

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用于宽带水下吸声和隔音的多孔固体元转换器

现有的由多种粘弹性材料和金属组成的固体复合结构主要利用不同的共振、阻尼和散射来实现水下声波功能。然而，同时具有亚波长厚度和轻质特性的声学涂层仍然难以捕获低频宽带水下吸声和隔音。本文报告了多孔固体水下元转换器的系统模拟和实验验证，该元转换器由橡胶层和拓扑优化的弹性超表面组成，以展示由强反射和传输的纵向到横向引起的吸音和隔音的宽带功能波转换，同时维持宽带阻抗匹配。各种结果证实了大型和有限尺寸样本在 2–10 kHz 范围内的水下宽带高效吸声 (>80%) 或绝缘 (20 dB) 的预测能力，提供了能量的估计-转换效果和现象。本研究为通过超表面进行弹性波能量耗散、收集和水声隐身提供了可能性。