在非破壞檢測技術中，平板蘭姆波具有長距離傳遞且不易衰減的特性，可進行大範圍的檢測，然而多模態及頻散現象，往往造成檢測上缺陷訊號辨識的難度。時間反轉法是一項自聚焦技術，能補償蘭姆波造成的頻散現象，會在有效地形成空間上和時間上的聚焦。本研究以有限元素法，模擬鋁板上蘭姆波波傳行為，選擇4組頻厚積和2種激振方式，激振單模態或多模態的蘭姆波，探討模態特性和頻散現象，對於時間反轉法聚焦效果的影響，結果顯示選擇頻厚積值為2 MHz-mm，在平行於平板方向激振，能產生數目較多且較頻散的模態，具有最佳的聚焦效果。將時間反轉法應用在蘭姆波缺陷檢測上，缺陷型態為圓孔和縱向凹槽，結果顯示能大幅提高圓孔缺陷的回波訊號振幅，最大可提高1.69倍。在檢測長度為5 mm，寬度為1 mm，深度為1 mm的縱向凹槽缺陷方面，採用時間反轉法，並未能有效的提升此類型缺陷的檢知能力。

In one of the non-destructive testing techniques, Lamb waves, because of its ability to propagate a long distance and being hard to attenuate, can detect a wide range of area. However, due to its multimodal and dispersive characteristics, identifying the signals of defects during the test is often difficult. Time reversal method, a self-focusing technique, can offset the dispersion of Lamb waves and effectively focus on the spatial and temporal domain. This study applies the finite element method to stimulate the propagation of Lamb waves on an aluminum plate, selecting four sets of frequency-thickness products and two excitation types to excite the single-mode or multimode Lamb waves. This study aims to discuss the effects of modal and dispersion on the focus of the time reversal methods. The results show that 2 MHz-mm and in-plane excitation can produce numerous, more dispersive modals with the best focus effect. If we applied the time reversal method to testing the defects of Lamb waves, and the defects are circular and longitudinal notches, then, according to the results, the reflection signal amplitude of the circular defects can be highly increased. According to the test results of small-sized notches, the time reversal method cannot effectively improve the detecting ability of this defect.

中文摘要 ...........................................................................i
英文摘要 ..........................................................................ii
目錄..................................................................................iii
表目錄 .............................................................................vi
圖目錄 ............................................................................vii
第一章、緒論 ..................................................................1
1.1 研究動機與目的........................................................1
1.2 文獻回顧 ...................................................................2
1.3 本文架構 ...................................................................7
第二章、基本理論 ..........................................................8
2.1 平板型蘭姆波........................................................... 8
2.1.1平板蘭姆波波傳之特徵方程式..............................8
2.1.2頻散曲線圖............................................................14
2.1.3波形結構................................................................16
2.2 時間反轉法..............................................................17
2.3應用時間反轉法於蘭姆波.......................................18
2.4 有限元素法..............................................................19
2.5二維傅立葉轉換法...................................................20
第三章、研究方法.........................................................28
3.1蘭姆波波傳有限元素模型.......................................28
3.1.1有限元素法模型建立...........................................28
3.1.2網格劃分...............................................................29
3.1.3輸入訊號與施加負載...........................................29
3.1.4求解與後處理分析...............................................30
3.2應用時間反轉法於蘭姆波之有限元素模型..........31
3.2.1有限元素法模型建立...........................................31
3.2.2 應用時間反轉法於蘭姆波..................................31
3.2.3 輸入訊號與施加負載..........................................32
3.2.4求解與後處理分析...............................................32
3.3 蘭姆波檢測缺陷之有限元素模型........................ 33
3.3.1有限元素法模型建立...........................................33
3.3.2 網格劃分..............................................................33
3.3.3輸入訊號與施加負載...........................................33
3.3.4求解與後處理分析...............................................34
第四章、結果與討論....................................................45
4.1蘭姆波波傳模擬結果和討論..................................45
4.2應用時間反轉法於蘭姆波波傳模擬結果與討論..46
4.3應用時間反轉法於蘭姆波缺陷檢測結果和討論..47
第五章、結論與建議....................................................63
5.1 結論 ........................................................................63
5.2 建議與未來展望.....................................................64
參考文獻........................................................................65

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