時間反轉法應用於平板裂縫偵測

Application of Time Reversal Method to Detect the Crack of Solid Plate

現代聲學中的時間反轉法（Time Reversal Method, TRM）概念已經應用在結構健康檢測的研究中，近年來時間反轉法理論已經發展到可經由表面波的傳遞來檢測結構是否有裂縫的產生。本研究將利用表面臨經由結構裂縫所引發之散射波（Scattered Wave），經時間反轉法處理後推算出裂縫位置。本研究首先運用ANSYS有限元素分析軟體，以模擬的方式進行理論上的驗證。利用平面彎曲波經過結構裂縫處所產生的散射效應，藉由振動學理論計算出散射訊號後，再結合時間反轉法計算出裂縫位置。其次以實驗來驗證時間反轉法理論應用於平板裂縫偵測的可行性。此外在有限元素數值分析計算中，本研究也探討了訊雜比（Signal to Noise Ratio, SNR）的大小對於時間反轉法的還原影響，以及陣列效應對於訊號重建的效果。 Through the success of acoustic development, the concept of the time reversal method is currently being applied in structural health monitoring by the transmission of surface waves. The transmission of surface waves is used to detect the structural cracks in many fields. In this study, the scattered signal of the surface waves due to crack of a structure is utilized to pinpoint the crack location through the time reversal method. In the present investigation, the finite element analysis is applied to simulate the surface wave propagation and to verify the effectiveness of using the time reversal method for locating a crack on a plate. The flexural waves in the plate will produce scattered waves when they propagate through the crack of a plate. The scattered waves may be used to calculate the cracks' location by applying the time reversal theory and the vibration theory together. Experiments have been conducted and prove the feasibility of using the time reversal method to detect crack locations. The signal to noise ratio effect and the array effect in sending and receiving signals are also studied to prove the method's credibility.