The physical Insight of the absorption mechanism on thin mirco-perforated panel
Date Issued
2009
Date
2009
Author(s)
Tsai, Che-Hsuan
Abstract
The absorption performances of a mirco-perforated panel can be regarded as the behavior produced by a lot of parallel Helmholtz resonators.The most important point in this theory is to assume the aperture in the mirco-perforated panel is independent to each other,and the incident waves almost can’t cause the panel to vibrate.Meanwhile,the mainly idea of this theory is to discuss how the vibration of thin circular mirco-perforated panel affect the absorption coefficients involved.n the experiment to be involved,we firstly change the diameter of the aperture of panel,thickness and perforation and the thickness of air layer behind the panel. Therefore,it is to use the Two-Microphone method to get the acoustic impedance formula of the tested structures.And then the influence on the sound absorption coefficients by all parameters involved is analyzed by comparing the results between theory and experiment. econdly,we get interference stripe by using lateral shearing interferometer,and then use Matlab program to get phase map.We use Chladni Patterns to verify the mode shape in the mirco-perforated panel.Finally,we analyze the correlation between the absorption coefficients and the mode shape in the thin circular mirco-perforated panel.n this experiment,the results of absorption coefficient show that the thicker the air layer,the lower the Helmholtz resonant frequency is.In addition,the peak of absorption coefficient moves to lower frequency.When both the aperture of the panel and the air layer are fixed,the effect to the absorption coefficient is not obvious by changing the thickness of the panel.The lower perforation is,the higher the sound absorption coefficient when the thickness of the panel and the air layer are fixed.Regarding to the optical measurement,the absorption coefficient will reach the peak only when the mode shape of the thin mirco-perforated panel is in circular symmetry.
Subjects
MPA
Type
thesis
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