Digital Signal Analysis Method for Underwater Ultrasound

超音波傳遞過程能量集中、具有良好的方向性以及穿透力，以水作為介質的超音波傳導更能發揮其優越特性，一般而言，在水下超音波接收端系統中，訊號的檢測與分析必須是穩定且即時的，一個穩定系統可以防止誤判的情形發生，對於訊號能量的強弱判別不至於偏差過多；一個即時系統可以快速地偵測有效訊號，隨即作出反應，這意味著訊號分析方法需以精簡為要，且因為減少計算量更能降低接收裝置對電力的消耗。 本論文利用訊號產生器所發出的能量衰減訊號，模擬水下超音波訊號的實際衰減情形，透過具有類比數位轉換器的微控制器將聲波訊號轉為數位訊號，藉由數位濾波器、窗函數及離散傅立葉轉換等概念，設計出1MHz之超音波訊號在時域中的分析法以及在頻域中的分析法，有效檢測出訊號能量大小且具有良好動態範圍，同時符合低計算量的特性。In the underwater signal-receiving device, the detection and analysis of the ultrasonic signals is a real-time task and all the misjudgments must be prevented. Therefore we need to design a stable and real-time system, which means the time complexity of the analyzing method should be simplify; thus, the power consumption can be reduced. We simulate the underwater ultrasonic signals and its attenuation by SMBV signal-generating device, and receive digital signals from a microcontroller with a 14-bit analog-to-digital converter. The frequency-domain based and time-domain based signal analyzing method both managed to detect the energy of the 1MHz signal with high dynamic range, and the computing time is also well-controlled