Porous materials for sound absorption

An underwater metamaterial for broadband acoustic absorption at low frequency

Optimization of low frequency sound absorption by cell size control and multiscale poroacoustics modeling

Microstructure-based experimental and numerical investigations on the sound absorption property of open-cell metallic foams manufactured by a template replication technique

Low-density nanofibrous aerogels enable various applications but are often hindered by their fragile bendability and poor tensile strength. Herein, we report a strategy to design nanofibrous aerogels with robust bendability and superelastic property, which has been achieved by fabricating bamboo lashing-like structures through a freeze-drying method. The obtained reinforced nanofibrous aerogels (RNFAs) can maintain their structural integrity after 100 bending-recovery cycles at a bending angle of about 100°. Particularly, the RNFAs can completely revive from large deformation with a fast recovery speed (∼834 mm s-1). Significantly, the internal hierarchical porous structures and hydrophobicity of the materials provide them with ultralight properties (density <11 mg cm-3), efficient sound absorption capability (noise reduction coefficient of 0.41) and good moisture resistance; thus, they are promising options in cabins, vehicles, and the regulation of indoor reverberation.

Ultralight, superelastic and bendable lashing-structured nanofibrous aerogels for effective sound absorption.

Influence of hole shape on sound absorption of underwater anechoic layers

A simplistic unit cell model for sound absorption of cellular foams with fully/semi-open cells

A combined theoretical and numerical study is carried out to quantify the influence of material properties (e.g., real part and loss factor of Young’s modulus, material density) and geometrical parameters (e.g., layer thickness, height of hole) on the sound absorption performance of an underwater rubber layer containing periodically distributed axial holes. A theoretical model is developed based on the method of transfer matrix as well as the concept of equivalent layering of holes with variable cross section. Numerical simulations with the method of finite elements are subsequently carried out to validate the theoretical model, with good agreement achieved. Physical mechanisms underlying the enhanced acoustic performance of the anechoic layer as a result of introducing the periodic holes are explored in terms of the generated transverse waves and the high-order mode of vibration. The results presented are helpful for designing high-performance underwater acoustic layers with periodically distributed cavities by tailoring relevant material properties and geometrical parameters.

Underwater Acoustic Absorption of Composite Anechoic Layers With Inner Holes

Modified theory of a microperforated panel with roughened perforations

Circular pores with sub-millimeter diameters have been widely used to construct micro-perforated panels (MPPs), the acoustical performance of which can be predicted well using the Maa theory (Maa D-Y, J Acoust Soc Am, 104 (1998) 2861) We present a tunable MPP absorber with periodically arranged cylindrical pores, with their cross-sectional shapes systematically altered around the circle while maintaining their cross-sectional areas unchanged Numerical analyses based on the viscous-thermal coupled acoustical equations are utilized to investigate the tunable acoustic performance of the proposed absorbers and to reveal the underlying physical mechanisms We demonstrate that pore morphology significantly affects the sound absorbption of MPPs by modifying the velocity field (and hence viscous dissipation) in the pores Pore shapes featured as meso-scale circular pores accompanied with micro-scale bulges along the boundaries can lead to perfect sound absorption at relatively low frequencies This work not only enriches the classical Maa theory on MPPs having circular perforations, but it also opens a new avenue for designing subwavelength acoustic metamaterials of superior sound absorption in target frequency ranges

Xuewei Liu

Papers

Influence of hole shape on sound absorption of underwater anechoic layers

A simplistic unit cell model for sound absorption of cellular foams with fully/semi-open cells

Underwater Acoustic Absorption of Composite Anechoic Layers With Inner Holes

Modified theory of a microperforated panel with roughened perforations

Tunable acoustic absorbers with periodical micro-perforations having varying pore shapes