A Theoretical Study on the Characteristics of Acoustical Matericals
Date Issued
2004
Date
2004
Author(s)
I-hang, TSENG
DOI
zh-TW
Abstract
The objective of this research was to discuss the absorption coefficient and transmission loss of porous materials lined with partitions. In the thesis, we used Biot’s theory to derive the equations of waves propagating in a fluid-saturated porous material and combined with the transfer matrix of porous materials introduced by Allard to evaluate the pressure and speed of any given point on the material. If we furthermore put the boundary conditions between various materials into a matrix, we will then be able to evaluate the absorption coefficient and transmission loss of multi-layers of materials.
At first, we introduced the wave propagation of porous materials and find that there could be two compression waves and one shear wave existing in porous materials. We then applied the transfer matrix introduced by Allard to evaluate the absorption coefficient and the transmission loss of the materials and also compared the results to the previous lectures, including experiments and theoretical analysis, to verify the accuracy of the present method.
Then the absorption coefficient and transmission loss of materials in air and in water was discussed respectively. For the sound absorption investigation, glass wool and PU foam on air and rubber in water were studied. It can be found that the sound absorption coefficient improved obviously when porous materials are put in layer with high density one in front of the sound source. For sound insulation in air, we focus on the sandwich structures that are formed by steels lined with porous material. The purpose is to create a light weight and high efficient insulation material. In the absorption of sound in the water, we simulated the conditions of submarines in naval environments in order to absorb the sounds of the sonar system of enemy ships. In the sound insulation in the water, we simulated sono-tones of submarines to lay efforts on lowering the loss of transmission.
Finally, the parameters, such as density, thickness of porous media, thickness of steel of each material in air and porosity, pore size, thickness of porous materials, thickness of steel and incident angles in water were investigated and also the influence on the sound absorption and insulation were discussed.
Subjects
組合結構
多孔材料
吸音
隔音
Biot theoretical
absorption coefficient
acoustical matericals
SDGs
Type
thesis
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