基于微穿孔板和卷曲背腔复合结构的低频宽带吸声体

Low-frequency broadband absorbers based on coupling micro-perforated panel and space-curling chamber

通过引入卷曲腔的概念并结合微穿孔板所设计的吸声结构具有深亚波长厚度、低频宽带吸声和高效吸声的特性.通过理论分析、数值模拟和实验,揭示了卷曲吸声结构工作的物理机制.首先在理论上分析单个吸声体的吸声性能并进行了数值和实验验证,两个吸声单体的共振频率分别为282和429 Hz.进一步,基于模耦合理论将低/高频吸声单体联合起来,设计出一个厚度只有100 mm(~λ/12,λ为相对低频吸声单体共振频率对应的波长),在较宽频带(232~533 Hz)内吸声系数大于0.5,在262~469 Hz内吸声系数大于0.8的宽频高效吸声结构.理论、仿真与实验结果符合较好.与传统的大体积吸声结构相比,本研究提出的轻薄高效吸声体具有结构简单和容易制造等特点,在低频噪声控制工程中有潜在的应用前景.

Conventional acoustic absorbers, which are made of porous and fibrous materials, usually have a structural thickness comparable to the working wavelength, which inevitably hinders their applications in low frequency range. A microperforated panel with a backward cavity has high efficient absorption in low frequency region, yet still processes a bulky size comparable to the resonant wavelength.In the past two decades, metamaterials and metasurfaces, which possess the functionalities cannot be achieved by the natural materials, such as deep-subwavelength thickness, negative mass density or bulk modulus, negative refraction, etc.,have got continuous attention and hence rapidly developed. Using the compact structures, such as membrane-type acoustic metamaterials, curling-up space structures, Helmholtz resonators with embedded apertures, to realize perfect absorption in low frequency has broadened the horizon of the acoustic absorption and provided a novel way for noise control. However,because of the dispersive nature of resonance, the aforementioned perfect absorbers cannot achieve broadband high absorption, which unavoidably confines their application. It is known that a micro-perforated panel features a broadband characteristic, while curling-up space structures have the capacity in absorbing the low frequency waves. Therefore, we come up with the idea of utilizing the micro-perforated panel and curling-up chamber to realize the high absorption in low and broad frequency region.In this work, we propose a hybrid absorber. By introducing the concept of curling chambers and coupling them to microperforated panels, the proposed acoustic absorber possesses remarkable properties such as deep-subwavelength thickness,broad absorption band and high absorption efficiency. Theoretical analyses, numerical simulations and experiments are carried out to reveal the underlying physical mechanism of the acoustic absorbers, whose results showed excellent agreements with each other.First, we theoretically analyze the absorption performance of each component consisting of a micro-perforated panel and a curling chamber. Then, we conduct the numerical validation and operate the experiment to verify the theoretical model.Through numerical optimizations, we finally design the two components achieving perfect absorption at lower(282 Hz)and higher(429 Hz) frequencies, respectively. Using the coupled mode theory, we present an absorber coupling the lowand high-frequency components. The hybrid absorber possesses the ability that the absorption coefficient is larger than 0.5 in the frequency range from 232 to 533 Hz, and larger than 0.8 from 262 to 469 Hz, while its structural thickness is only 10 cm(λ/12, λ is the working wavelength corresponding to the lower resonant frequency). To understand the underlying physical mechanism, we use the commercial software COMSOL MULTIPHYSICS to show the interaction(i.e., coupling)between the two components. As shown by the simulated results, at the resonant frequency of each component(282 or 429 Hz), when planar wave impinges normally on the whole absorber surface, only the corresponding component has sound energy exchange with the outside. However, at the frequency between the two resonant frequencies, both of them switch sound energy with the outside, which demonstrates the coupling effect. In this way, the hybrid absorber can realize the broadband high absorption in low frequency range. Compared to traditional bulky structures, the proposed absorber possesses the ability such as easy to fabrication, deep subwavelength and broadband high absorption, and hence may be widely used in noise control engineering.