結合三參數校正法的充水阻抗管的發展與應用

DEVELOPMENT AND APPLICATIONS OF A WATER-FILLED IMPEDANCE TUBE BY EMPLOYING THE THREE-PARAMETERS-CALIBRATION METHOD

本研究主要是依據ASTM E1050-98（2006）設計規範，發展出直立式充水阻抗管，用來量測材料於水中的聲學阻抗。此外，本研究引進三參數校正方法，由兩個不同位置的水聽器所測得的聲波電壓訊號比值，或稱為轉移函數，直接求出材料的聲波反射係數。本研究先利用所發展的系統量測聲波在水與空氣界面的反射係數。試驗結果顯示與以往常使用的轉移函數法或交換麥克風法相較，本研究所發展的系統量測所得到的不同頻率聲波在自由液面的反射係數的振幅與相位，與理論值更為吻合，且實驗結果具可重複性。在確立試驗結果的準確性與可重複性之後，本研究量測水中聲波在不同材料試片表面的反射係數，以測試所發展的系統在量測材料於水中聲學阻抗特性的實用性；測試材料包括鋼板、矽膠及PU膠。測試結果顯示本研究發展的充水阻抗管結合三參數校正法，可簡易並準確地測得在不同聲波頻率下材料表面的反射係數與聲學阻抗。

"Based on the standard test method provided by ASTM E1050-98 (2006), this work develops a vertical water-filled impedance tube for measuring the underwater acoustic impedance of materials. The three-parameters-calibration method was employed to determine the complex reflection coefficients from the voltage ratio of the sound signals measured by hydrophones at two different locations. This voltage ratio is also referred to as transfer function. Firstly, the developed system was used to measure the complex reflection at the interface between the water and the free surface. Experimental results reveal that the measured reflection coefficients were closer to the theoretical values compared with those obtained using the transfer function method or the sensor-switching technique. The repeatability of the experimental data was also assured. After having verified the accuracy and repeatability of the experimental results, the developed system was used to measure the acoustic reflection coefficient of various material to test the capability of the developed system for measuring the reflection coefficient of material in the underwater environment. The tested material includes steel, silicon rubber, and PU (polyurethane) rubber. The tests demonstrate that the acoustic reflection coefficients and impedance of material can be easily and accurately measured by the proposed impedance tube combined with the three-parameters-calibration method."