Acoustic measurement of the flow resistivity of a rigid porous material via low frequency transmitted waves—Frequency approach

2020 ◽  
Vol 148 (4) ◽  
pp. 2457-2457
Author(s):  
Mustapha Sadouki ◽  
Nassima Ait Kaid ◽  
Hanane Hassine
Keyword(s):  
Porous Material ◽  
Low Frequency ◽  
Acoustic Measurement ◽  
Transmitted Waves ◽  
Flow Resistivity

Low-frequency sound absorption of a tunable multilayer composite structure

2021 ◽  
pp. 107754632110082
Author(s):  
Hanbo Shao ◽  
Jincheng He ◽  
Jiang Zhu ◽  
Guoping Chen ◽  
Huan He
Keyword(s):  
Porous Material ◽  
Absorption Coefficient ◽  
Composite Structure ◽  
Low Frequency ◽  
Acoustic Absorption ◽  
Multilayer Composite ◽  
Absorption Frequency ◽  
Acoustic Absorption Coefficient ◽  
Simulation And Experiment ◽  
Single Material

Our work investigates a tunable multilayer composite structure for applications in the area of low-frequency absorption. This acoustic device is comprised of three layers, Helmholtz cavity layer, microperforated panel layer, and the porous material layer. For the simulation and experiment in our research, the absorber can fulfill a twofold requirement: the acoustic absorption coefficient can reach near 0.8 in very low frequency (400 Hz) and the range of frequency is very wide (400–3000 Hz). In all its absorption frequency, the average of the acoustic absorption coefficient is over 0.9. Besides, the absorption coefficient can be tunable by the scalable cavity. The multilayer composite structure in our article solved the disadvantages in single material. For example, small absorption coefficient in low frequency in traditional material such as microperforated panel and porous material and narrow reduction frequency range in acoustic metamaterial such as Helmholtz cavity. The design of the composite structure in our article can have more wide application than single material. It can also give us a novel idea to produce new acoustic devices.

Wind Noise Reduction for Outdoor Measurement Microphones With Windscreens

2008 ◽  
Author(s):  
Z. C. Zheng ◽  
Ying Xu
Keyword(s):  
Noise Reduction ◽  
High Frequency ◽  
Low Frequency ◽  
High Flow ◽  
Low Flow ◽  
Computational Techniques ◽  
Wind Noise ◽  
Flow Resistivity ◽  
Materials Used ◽  
Wind Noise Reduction

In this study, effects of windscreen material property on wind noise reduction are investigated at different frequencies of incoming wind turbulence. The properties of porous materials used for the windscreen are represented by flow resistivity. Computational techniques are developed to study the detailed flow around the windscreen as well as flow inside the windscreen that uses a porous material as the medium. The coupled simulation shows that for low-frequency turbulence, the windscreens with low flow resistivity are more effective in noise reduction. Contrarily, for high-frequency turbulence, the windscreens with high flow resistivity are more effective.

scholarly journals Acoustic measurement of a 3D printed micro-perforated panel combined with a porous material

Measurement ◽  
2017 ◽  
Vol 104 ◽  
pp. 233-236 ◽  
Author(s):  
Zhengqing Liu ◽  
Jiaxing Zhan ◽  
Mohammad Fard ◽  
John Laurence Davy
Keyword(s):  
Porous Material ◽  
Acoustic Measurement ◽  
3D Printed

scholarly journals Inverse Measurement of the Thickness and Flow Resistivity of Porous Materials via Reflected Low Frequency Waves-Frequency Approach

2021 ◽  
Author(s):  
Mustapha Sadouki
Keyword(s):  
Reflection Coefficient ◽  
Direct Problem ◽  
Fluid Model ◽  
Low Frequency ◽  
Low Frequencies ◽  
Reflected Waves ◽  
Two Samples ◽  
Flow Resistivity ◽  
Theoretical Reflection ◽  
Low Frequency Waves

A direct and inverse method is proposed for measuring the thickness and flow resistivity of a rigid air-saturated porous material using acoustic reflected waves at low frequency. The equivalent fluid model is considered. The interactions between the structure and the fluid are taken by the dynamic tortuosity of the medium introduced by Johnson et al. and the dynamic compressibility of the air introduced by Allard. A simplified expression of the reflection coefficient is obtained at very low frequencies domain (Darcy’s regime). This expression depends only on the thickness and flow resistivity of the porous medium. The simulated reflected signal of the direct problem is obtained by the product of the experimental incident signal and the theoretical reflection coefficient. The inverse problem is solved numerically by minimizing between simulated and experimental reflected signals. The tests are carried out using two samples of polyurethane plastic foam with different thicknesses and resistivity. The inverted values of thickness and flow resistivity are compared with those obtained by conventional methods giving good results.

scholarly journals High-Temperature and Low-Frequency Acoustic Energy Absorption by a Novel Porous Metamaterial Structure

2021 ◽  
Author(s):  
Qihang Liu ◽  
Xuewei Liu ◽  
Chuanzeng Zhang ◽  
Fengxian Xin
Keyword(s):  
High Temperature ◽  
Theoretical Model ◽  
Porous Material ◽  
Energy Absorption ◽  
Low Frequency ◽  
Acoustic Energy ◽  
Frequency Range ◽  
Metamaterial Structure ◽  
Equivalent Inclusion ◽  
Absorption Performance

AbstractIn this paper, we propose a novel porous metamaterial structure with an improved acoustic energy absorption performance at high-temperature and in the low-frequency range. In the proposed novel porous metamaterial structure, a porous material matrix containing periodically perforated cylindrical holes arranged in a triangular lattice pattern is applied, and additional interlayers of another porous material are introduced around these perforations. The theoretical model is established by adopting the double porosity theory for the interlayer and the cylindrical hole which form an equivalent inclusion and then applying the homogenization method to the porous metamaterial structure formed by the equivalent inclusion and the porous matrix. The temperature-dependent air and material parameters are considered in the extended theoretical model, which is validated by the finite element results obtained by COMSOL Multiphysics. The acoustic or sound energy absorption performance can be improved remarkably at very low frequencies and high temperature. Furthermore, the underlying acoustic energy absorption mechanism inside the unit-cell is investigated by analyzing the distribution of the time-averaged acoustic power dissipation density and the energy dissipation ratio of each constituent porous material. The results reveal that regardless of the temperature, the acoustic energy is mostly dissipated in the porous material with a lower airflow resistivity, while the acoustic energy dissipated in the porous material with a higher airflow resistivity also becomes considerable in the high-frequency range. The novel porous metamaterial structure proposed in this paper can be efficiently utilized to improve the acoustic energy absorption performance at high temperature.

scholarly journals A Case Study of Low Frequency Noise Assessed Using DIN 45680 Criteria

2002 ◽  
Vol 21 (4) ◽  
pp. 181-198 ◽  
Author(s):  
Ian Rushforth ◽  
Andy Moorhouse ◽  
Peter Styles
Keyword(s):  
Measurement Techniques ◽  
Low Frequency ◽  
National Standard ◽  
Acoustic Measurement ◽  
Frequency Noise ◽  
Industrial Site ◽  
Low Frequency Noise ◽  
Industrial Estate ◽  
Resultant Data

This paper describes a case study in which low frequency noise was suspected of causing disturbance in a semi-rural location close to an industrial estate. Previous attempts using conventional acoustic measurement techniques to resolve the case, or even prove the existence of a real acoustic problem, had proved unsuccessful. In the present study, the authors applied a novel integrated acoustic/microseismic measurement system, and assessed the resultant data using criteria from the German national standard DIN 45680. Using this approach, the authors successfully resolved the low frequency noise problem and, after a test involving a sequential shutdown at a suspect industrial site, established the precise cause of the disturbance. The paper thus supports the criteria in DIN 45680 as a predictor of annoyance due to low frequency noise and as an aid in resolving such problems. It also illustrates the flexibility of the combined acoustic/microseismic technique and the advantages of the method over conventional techniques.

Measuring flow resistivity of porous material via acoustic reflected waves

2005 ◽  
Vol 98 (8) ◽  
pp. 084901 ◽  
Author(s):  
N. Sebaa ◽  
Z. E. A. Fellah ◽  
M. Fellah ◽  
W. Lauriks ◽  
C. Depollier
Keyword(s):  
Porous Material ◽  
Reflected Waves ◽  
Flow Resistivity

Broadening perfect sound absorption by composite absorber filled with porous material at low frequency

2020 ◽  
pp. 107754632098021
Author(s):  
Baozhu Cheng ◽  
Nansha Gao ◽  
Yunke Huang ◽  
Hong Hou
Keyword(s):  
Porous Material ◽  
Sound Absorption ◽  
Low Frequency ◽  
Material Structure ◽  
Frequency Noise ◽  
Complex Frequency ◽  
Acoustic Model ◽  
Efficient Design ◽  
Absorption Frequency ◽  
Plane Method

To enhance the low-frequency broadband sound absorption, we propose an absorber filled with porous material and establish a relative acoustic model. Based on the critical coupling condition, a Helmholtz absorber was designed to achieve perfect sound absorption at 172 Hz by the complex frequency plane method. Considering the weak adjustability and acoustic impedance of the Helmholtz absorber, we devised four absorber filled with porous material units that can achieve perfect sound absorption at discrete frequencies between 400 and 488 Hz with a thickness of only 51 mm. A composite absorber filled with porous material was designed by arranging four absorber filled with porous material units in a coplanar manner. The broadband perfect sound absorption of the composite absorber filled with porous material was subsequently verified by simulation and experiment. The thickness of the composite absorber filled with porous material is only 1/18 of the wavelength corresponding to the perfect absorption frequency, and it shows excellent subwavelength characteristics. The theoretical acoustic model of the composite absorber filled with porous material and the complex frequency plane method can achieve a more efficient design of broadband perfect sound absorbers. The composite absorber filled with porous material not only realizes low-frequency broadband perfect sound absorption but is also lightweight and easy to fabricate. This demonstrates the composite absorber filled with porous material structure has great potential for application in low to mid frequency noise control.

Measuring permeability of porous materials at low frequency range via acoustic transmitted waves

2007 ◽  
Vol 78 (11) ◽  
pp. 114902 ◽  
Author(s):  
Z. E. A Fellah ◽  
M. Fellah ◽  
F. G. Mitri ◽  
N. Sebaa ◽  
C. Depollier ◽  
...  
Keyword(s):  
Porous Materials ◽  
Low Frequency ◽  
Frequency Range ◽  
Transmitted Waves
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