微穿孔板复合板型声学超材料的低频吸声

针对单层微穿孔板的低频吸声问题提出了微穿孔板复合板型声学超材料结构。将板型声学超材料置入微穿孔板结构的背腔内部实现结构复合。实验结果表明:在相同背腔厚度下,复合结构的吸声性能整体优于单层微穿孔板结构,其中复合结构的吸声曲线从396~892 Hz均大于0.6,在453 Hz处吸声系数达到0.972。利用有限元方法对复合结构进行了仿真,仿真计算的吸声曲线与实验吸声曲线的趋势基本相同,同时发现低频吸声主要由板型声学超材料与声波相互作用贡献。板型声学超材料的吸声峰值的对应频率处,其等效动态质量密度从正变负。在复合结构内部的微穿孔板和板型声学超材料存在相互耦合作用,使得复合结构的第一峰值发生微小偏移。增加板型声学超材料的质量块重量可以使第一吸声峰值向低频移动;保持总背腔厚度不变,增加板型声学超材料的子腔厚度,也可以使第一吸声峰向低频移动。      

微穿孔板复合对二次余数扩散结构扩散性能影响研究

扩散吸声结构(Diffsorber)能应用于室内外声品质的改善,具有很好的研究意义和应用前景。微穿孔复合QRD结构能显著提高低频吸声性能,但复合对扩散性能的影响未见报道。本论文对QRD结构及其与厚度为0.6mm,穿孔率为1%,2%,3%的微穿孔板复合结构的扩散性能进行测试,得出了相应的反射声能极坐标图和扩散系数。研究结果表明,微穿孔复合QRD结构在中低频特别在结构自身共振频率范围内具有良好的扩散性能,扩散系数在0.8到0.95之间,随着频率增加,复合结构的扩散性能有下降的趋势,同时由于微穿孔板的吸声性能,复合后结构的空间反射声能普遍降低5dB左右。     

水下微穿孔吸声体结构设计与试验研究

根据马大猷院士的微穿孔板(MPP)理论,提出在可设计的夹芯复合隐身结构的空腔中附加微穿孔板层的水下微穿孔吸声体。基于微穿孔板的精确计算理论及水下声隐身结构的特点,考虑空腔深度、穿孔板厚度、穿孔直径及穿孔率等对微穿孔板吸声性能的影响,对水下微穿孔吸声体进行了结构设计。利用脉冲声管法对水下微穿孔吸声体试样的吸声系数进行了测量,结果表明:水下微穿孔吸声体有效地拓宽了低频吸声频带,其微穿孔板结构参数的影响规律也与理论分析一致;对于多种吸声机理并存的水下微穿孔吸声体的空腔个数、形状及谐振特性等也是影响吸声性能的重要因素,在实际的工程应用中必须结合所关心的频带对水下微穿孔吸声体进行匹配优化设计。      

机械阻抗与声阻抗结合提高微穿孔板低频吸声性能

提出了在微穿孔板后部引入机械阻抗形成组合结构来解决微穿孔板低频吸声性能差的问题。由机械阻抗板两侧质点速度相同得出机械阻抗单元的传递矩阵,采用传递矩阵法将其与空腔、微穿孔板单元串接,建立组合结构理论计算模型;通过分析品质因子获得带宽与机械阻抗板质量成反比;试验得出组合结构在400 Hz附近有系数为0.8以上的吸声峰值,试验结果与理论计算吻合。在传统微穿孔板共振吸声机制的基础上加入机械共振,能够实现在不增加结构厚度的前提下提高低频吸声性能;降低机械阻抗板质量并且适当控制边界阻尼系数可以实现吸声频带的拓宽。      

内置谐振器的轻薄宽频吸声器结构设计与分析*

微穿孔板吸声器的吸声频带相较于亥姆霍兹谐振器更宽,但其低频吸声的实现需要较大的空气背腔,这对结构尺寸有限制的场合存在一定局限性。本文设计了一种轻薄吸声降噪结构(内置亥姆霍兹谐振器的微穿孔板吸声器,简称MPPHR),将微穿孔板吸声器与亥姆霍兹谐振器进行了结合,提升吸声器的低频吸声性能的同时兼具了微穿孔板宽带吸声的优点。首先基于微穿孔板和亥姆霍兹谐振器理论建立了等效电路模型并计算了结构的声阻抗。然后通过有限元对MPPHR的吸声特性进行了参数研究。最后验证了MPPHR的声阻抗模型和有限元仿真的准确性。研究结果表明：MPPHR结构拥有更宽吸声频带,厚度仅为30mm的MPPHR的半吸收频带可达1294Hz,相较于同等厚度下的微穿孔板吸声器宽近500Hz。此外,MPPHR拥有更好的低频吸声效率。     

微穿孔板结构的设计

微穿孔板结构是无需多孔性材料的宽带共振吸收系统,这是过去为使吸声结构不受使用条件而研制的。在本文中,对穿孔板及穿孔板结构的特性做了进一步的分析,求得给定简单共振系统的吸声特性直接了当计算其结构参数的方法,简化了设计工作。对双层微穿孔板结构,证明其高频率特性基本与简单共振结构相同,次级共振结构的作用主要是使有效空腔在低频加大,因而展宽低频响应,这也使设计化简。文中还讨论了根据结构求出吸声特性的方法。     

三层微穿孔板的优化设计及特性分析

根据马大猷的微穿孔板理论,计算了三层微穿孔板的吸声系数.应用遗传算法对其结构参数进行了优化,并对其吸声特性进行了分析研究,与优化后的双层微穿孔板结构进行比较,结果表明:经过遗传算法优化后的三层微穿孔板在频域上能够获得更加饱满的吸声系数曲线,接近传统吸声材料的吸声性能.并且通过实验验证了优化设计的结果.     

二次余数扩散结构复合穿孔板扩散吸声研究

声学结构研究一直以来都是学术领域的研究热点。扩散吸声结构(Diffsorber)由于兼具扩散和吸声性能而具有很好的研究意义。本研究将具有良好扩散性能的二次余数扩散(Quedratic:residue diffusers,QRD)结构和具有良好共振吸声性能的穿孔板结构进行组合,依据标准AES-4id-2001对二次余数扩散结构及其与厚度为1 mm,穿孔率分别为3%,5%,8%的穿孔板复合后结构的扩散性能进行了实验研究,得到了相应的反射声能极坐标图和扩散系数。结果表明,复合结构在100 Hz至800 Hz的频率范围内仍具有良好的扩散性能;复合结构反射声能在穿孔板共振频率范围内有明显的下降(平均超过2 dB)。本研究可为扩散吸声结构的设计与研制提供依据。      

微穿孔介电弹性体薄膜的吸声性能试验分析*

针对普通薄膜型降噪结构的吸声性能较差和吸声带宽较窄的问题,本文设计了一种微穿孔的介电弹性体薄膜吸声结构。该结构由穿孔的介电弹性体薄膜与背腔组合而成,目的是拓宽介电弹性体薄膜低频率段的吸声带宽。针对微穿孔的介电弹性体薄膜吸声结构,从试验角度分析穿孔薄膜初始厚度、穿孔孔径及穿孔间距对结构吸声性能的影响。分析结果可知：通过适当增加薄膜的初始厚度,薄膜的整体吸声性能得到有效提升,最大可将319Hz吸声频带的吸声系数从0.2提升至0.7;减小薄膜的穿孔孔径能够有效拓宽穿孔薄膜的吸声频带,可使吸声系数0.4以上的吸声带宽由304Hz拓宽至432Hz;适当控制穿孔间距能够达到更好的吸声效果。     

基于微孔板与折曲通道的亚波长宽带吸声结构设计

本文设计了一种由微穿孔板与折曲通道组成的亚波长宽带复合吸声结构,对该复合吸声器低频宽带吸声机理进行了详细分析,建立了该复合吸声结构的理论吸声解析模型与有限元数值分析模型,完成了吸声理论解和数值解的相互验证.该吸声结构在整体厚度为60 mm时,理论上实现了在200—500 Hz频段内平均吸声系数达0.8的低频高效吸声.同时在整体厚度为90 mm时,理论上实现了180—350 Hz频段内多处峰值达0.95的准完美吸声.该复合吸声结构在低频噪声控制工程中具有一定的应用前景.     

Sound absorption of microperforated panel mounted with helmholtz resonators

Microperforated panel (MPP) absorbers have been widely used in noise reduction and are regarded as a promising alternative to the traditional porous materials. However, the absorption bandwidth of a single-layer MPP is insufficient to compete with the porous materials. In order to improve the sound absorption ability of the single-layer MPP, MPP mounted with Helmholtz resonators (MPPHR) is introduced. Based on the MPP, Helmholtz resonators theory and electro-acoustical equivalent circuit principle, sound absorption properties of MPPHR are studied. Simulation and experimental results show that MPPHR have two peak frequencies and one anti-resonant frequency. The low-frequency peak is dependent on the Helmholtz resonators, while the high frequency peak is close to the peak of the single-layer MPP. The low-frequency sound absorption peaks move to low frequency with the neck length and the volume of Helmholtz resonators increasing. The high-frequency sound absorption peaks move to high frequency with the volume of Helmholtz resonators cavity increasing. Multiple Helmholtz resonator parallel MPP structure can provide more sound absorption than single MPPHR at low frequency range due to the introduction of more additional sound absorption peaks.     

Enhancement of low-frequency sound absorption of microperforated panels by adding a mechanical impedance

In order to solve the bad low frequency sound absorption of the Micro-Perforated panel(MPP)absorber,mechanical impedance was introduced in the back of the MPP absorber to form a composite structure.According to the same particle vibration velocity on both sides of a plate,the mechanical impedance plate transfer matrix could be obtained.The units of the mechanical impedance,cavity and MPP were connected in series with the use of the transfer matrix method,thus creating the composite structure’s theoretical calculation model.The quality factor affecting absorption bandwidth was analyzed.Bandwidth is inversely proportional to the mechanical impedance plate mass.During the experiments,when at close to 400 Hz,the composite structure reached an absorption peak with a coefficient of above 0.8.Experimental results concurred with theoretical calculations.Mechanical resonance is added based on the traditional MPP resonance sound absorption mechanism.Through this,the performance of low frequency sound absorption can be improved without increasing the thickness of the structure.The frequency band can be broadened by reducing the mechanical impedance plate mass and controlling its boundary-damping coefficient.     

Sound absorption performance of gradiently slit-perforated double-porosity materials

A gradiently slit-perforated double-porosity material is proposed by introducing macro-scale periodic gradient slit-perforations into traditional porous materials with singleporosity.This material is one kind of multiscale material since it includes two scales of matrix micro-pore size and slit-perforation size.A theoretical model is developed for the sound absorption of the gradiently slit-perforated double-porosity material.In the model,the material is divided into lots of thin layers and each layer is approximated to be straight slit-perforated material.The equivalent density and dynamic compressibility of each thin layer are given by using the low or high permeability contrast double-porosity theory.Then the sound pressure and particle velocity relations between adjacent thin layers are obtained by employing the transfer matrix method.Finally,the surface acoustic impedance and the sound absorption of the gradiently slit-perforated porous material can be calculated.A finite element model is further established to validate the accuracy of the theoretical model.In the considered frequency range of 100-3000 Hz,the simulation results agree well with theoretical results.The influence of multiscale structural parameters on the sound absorption performance of the porous materials is analyzed theoretically and numerically.It is proved that the multiscale structure design can significantly improve the sound absorption performance of porous materials.Compared to the slit-perforation gradient,the slit-perforation width plays a more significant influence on sound absorption.The sound absorption enhancement mechanism of the multiscale structure design is revealed by the analysis of the sound pressure and energy dissipation distributions in the material.This work provides a multiscale structural design method for improving the sound absorption performance of traditional porous materials at broadband frequency.     

梯度穿缝型双孔隙率多孔材料的吸声性能

在传统单一孔隙率多孔材料中引入宏观尺度的周期性梯度穿缝结构设计,构造出梯度穿缝型双孔隙率多孔材料,其包含多孔材料基体微孔尺度与穿缝尺度两个尺度。采用分层等效的理论建模方法,将复杂梯度渐变问题变为多层均匀等效层叠加问题。针对不同特征尺寸的多孔材料薄层,分别采用低、高两种渗透率对比度双孔隙率理论,给出了其等效密度和动态压缩系数,再应用传递矩阵方法得到了相邻薄层之间的声压和质点速度传递关系并求得其表面声阻抗,从而建立了梯度穿缝型双孔隙率多孔材料的吸声理论模型。发展了多尺度材料声学有限元数值模型,在所考虑的100~3000 Hz频段范围内数值模拟结果完全吻合理论模型结果。理论与模拟分析了多尺度结构参数对双孔隙率多孔材料吸声性能的影响,结果表明引入多尺度梯度结构设计能够显著提高单一孔隙率多孔材料的吸声性能,且穿缝尺度比穿缝梯度影响更为显著;精细数值模拟获得的声压和能量密度分布云图揭示了多尺度结构设计的吸声增强机制。该工作可用于指导双孔隙率多孔材料的多尺度结构设计,从而提高多孔材料的中低频吸声性能。      

Experimental study on sound absorption performance of microperforated panel with membrane cell

Microperforated panel (MPP) absorbers have been widely used in noise reduction and are regarded as a promising alternative to the traditional porous materials. However, the absorption bandwidth of a single-layer MPP is insufficient to compete with the porous materials. In order to improve the sound absorption ability of the single-layer MPP, a composite MPP sound absorber with membrane cells (MPPM) is introduced. Sound absorption properties of the MPPM are studied by the impedance tube experiment. Results show that the membranes have a significant influence on the sound impedance. The sound absorption performance of MPPM gradually increases with the increase of the membrane area. The single-layer MPP with some small area membrane cells may have the same effect and single large area membranes. By adjusting the size of the membrane cells, one can implement a sound absorber with a wider absorption bandwidth and higher absorption peaks than the single-layer MPP.     

含三聚氰胺多孔材料分层复合介质吸声特性*

三聚氰胺泡沫材料是一种具有高开孔率的多孔材料,具备优良的吸音、防火隔热及环保性能,可以作为吸声材料与弹性板、空腔介质形成复合结构,在建筑、航空、交通工具等工程领域有广泛的应用。该文基于Biot理论和分层介质在交界面处的不同边界条件,建立非均匀复合介质背衬刚性壁面结构的理论声学模型,详细分析了多孔材料布局对复合结构吸声特性的影响。该文理论模型计算的结果与阻抗实验得到的垂直入射吸声系数基本一致,验证了理论模型的正确性。结果表明:在多孔材料前面增加空气层可以改善高频吸声特性;在多孔材料后面增加空气层可以改善复合结构低频吸声特性。通过合理配置多孔材料,可以在应用需求频段上达到满意的吸声效果。     

四边简支含多孔材料双层板隔声特性

有限大含多孔材料和空气层复合板结构隔声特性的研究尚不充分。该文旨在研究四边简支边界条件下复合板结构隔声特性。首先基于流体饱和多孔弹性介质的声传播理论计算了声波在多孔介质中的传播波数；继而采用四边简支边界条件下板结构的模态函数，利用模态叠加法和伽辽金法推导了复合板结构隔声系数理论模型，并数值求解复合板隔声量。将理论模型得到的四边简支复合板隔声量与实验结果对比，验证了理论模型的正确性。最后，详细讨论了边界条件、板结构尺寸和多孔材料厚度等主要参数对隔声特性的影响。结果表明：四边简支复合结构隔声特性曲线上“谷值”出现得较少，并且简支复合板隔声特性的第一个“吻合频率”比固支支撑复合板更靠近低频，当频率超过3000 Hz以后，简支和固支边界条件复合板结构隔声特性趋于一致。