基于网络化局域共振基元的水下宽频强吸声材料研究

Excellent modern underwater acoustic absorbing materials which can achieve wide band strong acoustic absorption with structures of small size are urgently needed for their important applications in both military and commercial uses, such as sonar evasion by stealthy coating, underwater acoustic communication system. However, present materials usually exhibit poor acoustics-absorbing property under high hydrostatic pressure. This key issue hinders the development of deep-water noise-shielding materials. A network locally resonant underwater acoustic absorbing material is proposed which is based on a novel idea of introducing the local resonant units into a random network material structure. It possesses both high mechanical strength and strong underwater sound absorption property in a wide frequency band. The key scientific problem is further research on network locally resonant acoustic absorbing mechanisms and deep understanding of the quantitative design method for the optimal material performance and the response mechanism between locally resonant structure and pressure. Therefore, action mechanisms of resonant unit, network structure and component in network locally resonant acoustic materials will be investigated deeply by the finite element method and experimental study. The energy-dissipative mechanism under high hydrostatic pressure will be also discussed systematically. The research results will be meaningful in both tuning wide-band strong acoustic absorption under high hydrostatic pressure and control elastic wave in engineering application.

新型宽频水下吸声材料在规避声呐搜索消声覆盖层、水下声传输系统等方面有着迫切的国家需求。目前亟待解决的关键技术问题是提高材料在宽频范围内的吸声能力、保持材料在高静水压力下的强吸声特性以及加强复杂环境下材料的综合服役性能。在基础研究上的原理创新性探索和深入研究有利于关键技术问题的解决。我们提出基于局域共振吸声基元网络化的宽频水下吸声材料新构想，研究表明该材料能同时具备抗高静水压力和宽频强吸声特性。核心科学问题是建立起网络化局域共振吸声机制的合理力学分析模型，探索网络化局域共振结构对材料内弹性波传播与吸收的响应机制。本课题拟利用有限元分析方法并结合实验研究，深入探索局域共振单元、互穿网络结构以及材料物性参数之间的关系，并探讨压力环境下能量的耗散机制。本课题的研究将为解决材料高静水压力下宽频强吸声问题提供科学依据和新途径。

性能优异的水下吸声材料在噪声控制、声呐探测、潜艇声隐身及水声通讯等军民两用技术中一直有着迫切的应用需求。传统的水声材料通常是橡胶一类的高分子材料，受吸声机制所限，主要存在材料尺度大、低频性能差、吸声频带窄、不耐静水压力等问题，难以满足未来大潜深潜艇的隐身要求。因此，亟待解决低频范围内及复杂服役条件下（高静水压力）的吸声问题。局域共振声学超材料可以打破质量密度定律，以较小尺度实现对长波长声波的有效控制，为解决低频吸声问题提供了思路，但吸声频带过窄制约了它在水声中的应用。针对上述问题，本项目利用网络化局域共振基元间的强耦合作用，开展局域共振宽频带隙及宽频吸声机制研究，并将该机制拓展至新型水下宽频强吸声材料的研制研究中。利用有限元方法开展了声子玻璃的物理建模研究，依次建立了二维虚拟弹簧模型、二维泡沫金属网状模型及三维隐函数模型。并结合实验结果对局域共振吸声机制在声子玻璃中的表现形式进行了讨论，研究发现具有共振子强耦合作用的网络化局域共振是材料宽频强吸声的内因，其中局域共振作用是实现强吸声的关键，而互穿网络结构带来的强耦合效应是其呈现宽频的关键。在应用研究方面，通过性能优化使网络化局域共振材料在常压下500Hz-10000Hz内吸声系数大于0.8，在3MPa静水压力下1000Hz-10000Hz频率范围内吸声系数大于0.7，在4.5MPa静水压力下1000Hz-10000Hz频率范围内吸声系数大于0.6。测试结果表明网络化局域共振材料突破了传统水下吸声材料抗压能力与吸声性能不能兼顾的矛盾，可以满足大潜深的隐身需求。并对网络化局域共振材料进行拓展应用研究，重点考察了它在隔声、阻尼减振等方面的潜在应用。