薄微穿孔板吸音機制之物理洞察

The physical Insight of the absorption mechanism on thin mirco-perforated panel

蔡哲玄(Che-Hsuan Tsai)

指導教授 ： 陳國在

國立臺灣大學/工學院/工程科學及海洋工程學研究所/碩士(2009年)

https://doi.org/10.6342/NTU.2009.03097

摘要

微穿孔板吸聲體的穿孔可視為許多赫姆茲共振器相互並聯，其理論的重要點在於，假設板上各孔的特性互不影響，且入射的聲波幾乎不擾動板材。本論文旨在探討薄微穿孔板振動對於吸音率之影響。
在實驗方面，首先改變微穿孔板之穿孔孔徑、板厚、背後空氣層厚度，以雙麥克風阻抗管法進行實驗，求得各試材的聲阻抗率及吸音率，並進一步分析各尺寸參數吸音效能的優劣，並將吸音率之實驗結果與理論計算互相比較。
其次以橫向剪切干涉術，取得干涉條紋圖，使用Matlab模擬出板材振動模態，以克拉里尼圖形驗證振動模態。最後，分析薄微穿孔板吸音率以及板共振模態的關聯性。
實驗結果顯示，在吸音率量測方面，板厚、穿孔孔徑固定時，空氣層越厚，吸收頻率越往低頻移動，而其赫姆茲共振頻率亦越小；孔徑、空氣層固定時，改變板厚對於吸音率之影響不明顯；板厚、空氣層固定時，穿孔率越小，其整體吸音率會明顯提高。在光學量測方面，當板共振模態為圓對稱(circular symmetric)時，吸音率才會有高峰出現。

關鍵字

微穿孔板

並列摘要

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.
In 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.
Secondly,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.
In 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.

並列關鍵字

MPA

參考文獻

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