低频大宽带声学超结构的多阶共振高效吸声机理

Multi-Order Resonance and High-Efficiency Sound Absorption Mechanism of Low-Frequency Large-Band Acoustic Metamaterials

针对传统吸声材料效率低、频带窄的不足,设计了一种多阶共振超表面。多阶共振超表面通过在共振腔内部插入一个或多个带有小孔的分隔板来构造,使其保持原吸声峰和结构尺寸不变情况下,在较宽频带内获得多个近乎完美的吸声峰,明显增加了吸声频带宽度。通过吸声系数和相对声阻抗率对迷宫二阶共振超表面的高效吸声特性进行分析,并研究了孔径变化对二阶共振超表面吸声特性的影响规律;采用声电类比法推导出多阶共振超表面的等效声阻抗,并将二阶共振超表面等效成二自由度质量弹簧系统,通过系统固有频率和固有振型分量对多阶共振吸声机理进行深入分析。考虑到亥姆霍兹共振腔内空气的热黏性,在对多阶共振超表面的理论计算进行推导时,引入了等效密度和可压缩性的理论。通过对多单元耦合参数的精确平衡,设计了9个单元组成的低频宽带亚波长超表面吸收器,该超表面厚度为8 cm,在310~1560 Hz的频带范围内具有连续优异的吸声特性,平均吸声系数高达90%以上。这项研究可为实现低频大宽带吸收提供一个新的思路,并在工程降噪中有潜在的应用前景。

Aiming at the shortcomings of low efficiency and narrow frequency band of traditional sound-absorbing materials,a multi-order resonance metasurface is designed.The multi-level resonant metasurface is constructed by inserting one or more partition plates with small holes inside the resonant cavity,so that while maintaining the original sound absorption peak and the same structure size,it can obtain multiple nearly perfect sound absorption peak to obviously widen the sound absorption bandwidth.The efficient absorption characteristics of the maze second-order resonance metasurface are analyzed by the sound absorption coefficient and the relative acoustic impedance ratio,and the effect of the aperture change on the sound absorption characteristics of the second-order resonance metasurface is investigated.The equivalent acoustic impedance of the first-order resonance metasurface,and the second-order resonance metasurface is equivalent to a two-degree-of-freedom mass spring system,and the in-depth analysis of the multi-order resonance sound absorption mechanism is performed via the system natural frequency and natural mode components.Taking thermal air viscosity in Helmholtz resonant cavity into account,the theory of equivalent density and compressibility is introduced during deducing the theoretical calculation of the multi-order resonance metasurface.Following accurate balancing the coupling parameters of multiple elements,a low-frequency broadband sub-wavelength super-surface absorber is designed,which is composed of nine units and has a thickness of 8 cm.This absorber is endowed with continuous and excellent sound absorption characteristics within the frequency band of 310-1560 Hz,an average sound absorption coefficient reaches higher than 90%.This research provides a new idea for the realization of low-frequency large-bandwidth absorption,and has potential application prospects in engineering noise reduction.