- 學位論文
水下阻抗管之設計與吸音材量測
Design of Underwater Impedance Tube for the Measurement of Material Acoustic Characteristics
摘要
本文旨在設計及製作一個專門用來量測水下吸音材的量測系統，藉此可以量測不同材料的聲學參數，例如反射係數、正向入射吸收係數、以及特殊音響阻抗比等。其免除了以往如迴響室等龐大硬體工程的建造，在價錢上較為低廉，機動性也較高。 首先，根據ASTM設計規範為阻抗管之設計準則，進而配合波導管平面波傳理論設計出不同管徑的阻抗管各一組。其次，為了測試阻抗管的可用性，利用轉換函數法針對所需之實驗配置經由不斷的測試來證明如此的設計是否可行。再者由於管壁的剛性與否，將會影響到波導管的波傳模態，所以我們加以配合彈性波導管理論，進而求出其模態頻散曲線以及質點位移分佈圖，進一步的比較剛性與彈性波導管之差異。這些被量測到的特性可用於基本研究和發展吸音材，並可供學術界相關研究作參考。
關鍵字
阻抗管並列摘要
The thesis mainly discusses the design and fabrication of underwater impedance tube for the measurement of material acoustic characteristic. This test method can be applied to measure sound reflection coefficient, normal incidence sound absorption coefficient and specific acoustic impedance ratio of materials. Firstly, the impedance tubes of different sizes are made according to ASTM standards and the theory of plane wave propagation. Then the theory of a transfer function method of measuring normal incident in-duct acoustic properties is presented. However, the elastic moduli and density of the tube wall and the fluid are often of similar magnitudes, and the rigid wall approximation is invalid. As a result, for example, the plane-wave mode characteristic of the rigid wall waveguide degenerates to a mode with phase velocity somewhat slower than the intrinsic sound velocity. So we study the two (ET0 and ET1) low-frequency axisymmetric propagation modes in the liquid-filled elastic tube waveguide and it is be shown for numerical calculations of modal dispersion curves and particle displacements. The properties measured with this test method are useful in basic research and product development of sound absorptive materials.