時間反轉陣列之聚焦解析度分析

Abstract

在水下通訊領域，近年來已應用時間反轉法於處理水下聲訊，時間反轉法為利用聲波時反回傳訊號的不變性，來補償水下環境變化而產生訊號的失真(distortion)。本篇論文主要目的為探討聚焦解析度（空間及時域解析度）與時間反轉陣列中拍發聲源數目及位置之關係。在低頻部分，吾人模擬一靜態水文波導環境，傳輸低頻聲訊由時間反轉陣列接收並拍發，在發射端接收聚焦訊號且進行分析。在高頻部分，由八支B＆K-8104水下麥克風組成時間反轉陣列，實驗地點於本系拖車水槽，證明時反法聲訊的聚焦性，應用虛像法模擬水槽環境做聲訊之比較，並且由交互相關性函數量化分析時反陣列元件位置與其聚焦結構的變化。其計算結果有助於國內未來建立時反陣列的最佳化，並達到應用於水下通訊之可適性。

Time-reversal processing is developed to enhance underwater acoustic communication in recent years. This technique has been introduced as an approach to compensate for distortion due to multiple path effect in propagation. In this thesis, the main objective is to analyze focal resolution (spatial and temporal resolution) and its relationship with element-number and the position of the time-reversal array. In the low-frequency part, simulation results of low-frequency signals received by the time-reversal array and retransmitted back to the source location are presented. In the high-frequency part, the time-reversal array is constructed with eight B&K-8104 hydrophones, and a NTU-ESOE water tank experiment is conducted to refocus signal. The experiment is also simulated using the image method to analyse the relation between the element position and the focal structure with cross-correlation function. The results of this research can help to provide the optimal design in building time-reversal array in the future.