Investigation of the Underwater Absorption and Reflection Characteristics by Using a Double-Layer Composite Metamaterial

Abstract

It is well-known that the acoustic stealth of an underwater vehicle composed of a non-watertight structure has been facing severe challenges. The origins of this effect are associated with the fact that the coupling between the water and the mechanical structure is not negligible because both sides are in the water. Along these lines, the idea of forward absorption and backward reflection was proposed in this work to address this issue. More specifically, a composite underwater acoustic metamaterial (AM) was designed based on different layers, namely a sound absorption layer and a sound insulation layer from the outside to the inside. The sound absorption layer was made of a soft rubber matrix with embedded steel scatterers (ESs) to enrich the coupled resonance effects, while the sound insulation layer was composed of hard rubber with a built-in cavity to improve the impedance mismatching between the AM and the water. The impact of the number and thickness of the embedded ESs on the acoustic performance of the AM was also thoroughly investigated via a finite element method (FEM). A fast non-dominated genetic algorithm (NAGA-II) with elite strategy was used to optimize the position and the size of the ESs. The optimization results revealed the high absorption at the forward incidence and the high reflection at the backward incidence. Thus, our work provides a novel and effective approach for improving the acoustic stealth of underwater vehicles composed of non-watertight structures.

Review of Underwater Anechoic Coating Technology Under Hydrostatic Pressure

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An Optically Transparent Metamaterial Absorber with Tunable Absorption Bandwidth and Low Infrared Emissivity

“…Water can form a singlemedium absorbing structure, or combine with other absorbing materials to form multi-layer absorbing structures. In addition, water-based MMAs can easily achieve tunable absorption by changing the shape, ion concentration, and temperature of water [36][37][38]. Compared to other tunable absorbers, water-based tunable absorbers exhibit superior angle and polarization stability [39,40].…”

Broadband Waterborne Multiphase Pentamode Metastructure with Simultaneous Wavefront Manipulation and Energy Absorption Capabilities

“…Inspired by this mechanism and introducing the viscoelasticity of the substrate, strong low-frequency waterborne absorption is realized by Wen et al with a sub-wavelength sample [ 4 ], but the inferiority of this is that the effective frequency bandwidth is very narrow. A lot of studies have been conducted to expand the effective frequency bandwidth by introducing multi-resonators [ 5 , 6 , 7 , 8 , 9 ], metal spiral and inter-connecting structures [ 10 , 11 , 12 ], air cavities and combinations of them [ 13 , 14 , 15 , 16 , 17 ]. For example, Wang et al proposed a broadband waterborne absorbing metamaterial with gradient cavity array strengthened by a carbon fiber framework [ 15 ].…”