本論文之目的，在於研究主動式聲納對水下目標物之瑞利表面回波信號特性分析。在散射回波信號中，鏡面反射波及稜角波提供目標物之形狀訊息；共振散射、表面波信號則提供目標物之材料特性之訊息。在表面波部分，以瑞利波回波信號最強，因此，對目標辨識提供了最佳之訊息。

本研究係根據實心圓球與實心圓柱之瑞利表面回波之理論結果及物理特性，並藉由目標物之縮尺實驗，量測瑞利表面回波信號，以模擬實際水下目標物偵測、辨識之應用。因此，在實驗架設部分，吾人以超音波反射回波之方式，進行目標物之縮尺實驗，並選取適當ka值之量測範圍。且針對不同之k值及a值進行多組實驗量測，探討不同入射波頻率對瑞利波之影響。進而對不同目標物之形狀、尺寸、材質進行量測，觀察瑞利表面回波與ka值之相對關係。此外，亦在不同角度量測瑞利表面回波之能量散射分佈情形。最後進行各種實驗結果之歸納工作，找出瑞利表面回波之最佳量測條件。由其實驗結果顯示，瑞利表面回波確實對目標物之材料特性辨識提供極佳之解析訊號。

This thesis studies the target identified by analyzed scattering signal which is from active sonar impinged under water. In general, the specular reflected waves and corner waves provide the information of target profile in scattering signal. The resonance scattering waves and surface waves submit the material properties of target by analysis signal. The Rayleigh wave is a candidate for target identified in surface wave analysis.

Since then, the theorem focuses on Rayleigh wave propagation on solid sphere and cylinder in this thesis. To analyze the problem of scattering wave, if the normal mode methed is applied to solve it, the character of reflected surface wave can not appear on the solution. So the Sommerfeld-Watson transform(SWT) method is used to solve it. This method can convege the infinite partial-wave series rapidly and the physical property of acoustic wave can be elucidated easily.

In experiment, the reduced scale experiment is setup for Rayleigh wave measurement using ultrasonic wave. For Rayleigh wave discussion, the individual profile, sizes and material of target is applied respectively in this experiment. The beam pattern is also measured in the Rayleigh wave filed. The result appears the target identified by analytical Rayleigh wave obviously.

目錄……………………………………………………………………………...I
表目錄…………………………………………………………………………IV
圖目錄…………………………………………………………………………..V
中文摘要……………………………………………………………………….X
英文摘要……………………………………………………………………....XI
第一章 緒論…………………………………………………………………..1
1.1 前言………………………………………………………………1
1.1.1 何謂聲波…………………..………………….………….1
1.1.2 為何在水下要使用聲波……..…………………..………1
1.1.3 瑞利表面波…..………………………………..…………2
1.2 研究動機與目的…………………………………………………3
1.3 文獻回顧…………………………………………………………4
第二章 理論簡介……………………………………………………………..7
2.1 簡介………………………………………………………………7
2.2 目標物之散射信號………………………………………………8
2.2.1 目標物之表面彈性環繞波……………………………..10
2.2.2 目標物之內部穿透傳遞波……………………………..16
第三章 實驗架構與量測……………………………………………………24
3.1 文獻參考………………………………………………………..24
3.2 水中圓球之散射實驗…………………………………………..26
3.2.1 實驗儀器設備及散射目標物…………………………..26
3.2.2 圓球散射實驗之架構…………………………………..33
3.3 水中圓柱之散射實驗…………………………………………..35
3.3.1 實驗儀器設備及散射目標物…………………………..35
3.3.2 圓柱散射實驗之架構…………………………………..40
3.4 目標物散射回波信號之量測方法………………………………42
3.4.1 實驗步驟…………………………………………………42
3.4.2 信號處理…………………………………………………43
3.5 量測結果…………………………………………………………44
第四章 實驗結果與討論……………………………………………………..46
4.1 理論計算值………………………………………………………46
4.2 圓球散射實驗之量測結果………………………………………53
4.3 圓柱散射實驗之量測結果………………………………………57
4.4 瑞利表面回波之散射花樣…………..………………………….94
第五章 結論與建議…………………………………………………………..98
5.1 結論………………………………………………………………98
5.2 建議……………………………………………………………..100
參考文獻……………………………………………………………………..102
附錄A 散射回波之背景壓力………………………………………...……105
附錄B 吸音材料之特性……………………….…………………...……...106
附錄C 波的種類及型式…………………………………………………...107

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