选择性滤波声学超材料平板结构研究

The acoustic metamaterial has recently attracted much attention of researchers because of its unusual behavior not readily observed in natural materials. Better understanding of the acoustic metamaterial, in relation to the multi-discipline issues such as in physics, mechanics and materials science, is of great importance for theoretical investigation and engineering applications. Based upon the concept of vibration absorbers, this proposal will study how to design and analyze an acoustic metamaterial structure with many film-mass unit cells. To establish a nonlinear dynamic model for an acoustic metamaterial plane, the damping behavior of the rubber film will be described by a fractional constitutive model, and the nonlinear stiffness will be expressed by the polynomial function of deformation. According to the numerical calculations by using finite element method and the testing results, the vibration properties and band-gap effect will be examined. By identification of the optical mode in vibration, the operation frequency can be determined. To design a single-layer metamaterial-based plane, a correlation will be established between the vibration properties and the dimension of the unit cell, as well as the space between two cells. As for multi-layer plane consisting of various types of single-layers, its band-gap behavior and filter characteristics will be studied by considering such factors as constraint and distribution of integrated film-mass subsystems. Further more, an approach will be presented to develop a multi-layer metamaterial plane. Our studies will demonstrate the effect of the viscoelasticity of rubber film, pre-stress and boundary constraint on the filter properties of the acoustic metamaterial plane, which provides a base for the structural design and application of metamaterial-based broadband selective filter.

声学超材料由于表现出自然界材料不易出现的特异行为而受到国内外广泛关注。它的研究涉及物理、力学、材料等多学科难点问题，对其中科学问题的研究具有重要的理论意义和应用价值。本申请基于振动吸收器原理，研究以橡胶薄膜、集中质量为子结构胞元的声学超材料设计与分析等问题。采用分数阶本构描述薄膜材料阻尼特性、多项式函数表征材料非线性刚度，建立结构动力学分析模型，利用有限元技术并结合试验研究超材料平板结构的振动特性及带隙效应。通过对结构振动光学模式的识别，确定超材料平板工作频率。建立薄膜子结构胞元尺寸及胞元间距与超材料平板振动特性关联关系，对不同类型单层平板组合的多层平板，考虑约束条件及子群分布等因素，研究带隙行为及滤波特性，在此基础上提出多层平板结构设计方法。本研究将揭示薄膜材料粘弹性、预应力、边界约束等因素对声学超材料平板滤波性能的影响规律，为宽频带选择性滤波声学超材料结构设计与应用提供依据。

薄膜型声学超材料由于轻薄的特点，在低频滤波领域具有很高的应用价值，然而其频率带隙窄的特点限制了它的应用。为实现宽频带选择性滤波，本项目从单层结构和多层结构组合两方面研究实现宽频带滤波。在薄膜声学超材料研究中，薄膜材料一般采用的是线弹性模型，因此结构带隙频率与激励频率无关。当考虑材料的粘弹性行为后，我们发现带隙频率是与外部激励频率相关的，而且随着材料阻尼的增加，负等效质量的变化增大，但在一定条件下，阻尼对等效质量几乎没影响。根据这一结论，有可能通过材料阻尼设计开发出可变频率禁带的超材料，从而扩大噪声控制应用范围。在单层结构设计上，提出了具有自相似结构的薄膜声学超材料平板结构，利用有限元技术并结合试验研究了超材料平板结构的振动特性及带隙效应，通过分析多层自相似结构声学超材料板的传递特性，建立了板间距、组合数等参数的多层结构设计方法。研究表明，通过自相似质量环的控制可实现波的选择性过滤。研究结果可应用于噪声控制领域。为拓展声学超材料结构应用范围，在多层声学材料板结构研究基础上，提出了多层声、热复合隐身功能超材料概念，开展了多层结构的热性能设计，通过不同材料性能组合可实现热隐身，降低了热隐身衣开发难度，为声、热多功能隐身材料的开发提供了依据。可以预计，复合隐身超材料在国防领域有极大应用价值。