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碩士論文公告區 |
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| 年度： | 92 | |
| 姓名： | 紀郁芳(Yu-Fang Chi) | |
| 論文題目(中)： | 超音波脈波訊號之小波分析 | |
| 論文題目(英)： | Wavelet Analysis of Ultransonic Signals Through Concrete | |
| 摘要(中)： | ||
| 大多數的應力波訊號均含有大量的暫態頻域成分，且易受到傳遞路徑中介質的不同影響。為了研究混凝土中應力波訊號在局部時間範圍的頻域特徵，本研究應用小波轉換，因小波轉換可在訊號的高頻部分採用小時間窗，在低頻部分則採用大時間窗進行分析，可以有效彌補傅立葉轉換的不足之處。 本研究以砂漿製作 圓柱試體，與分別埋入人為缺陷，其幾何形狀分為球形與圓盤狀。應力波的激發是以一個週期的正弦波訊號，由超音波探頭導入試體，再由接收探頭將捕獲的應力波轉變為電訊號，以便取得完整試體與人為缺陷之超音波訊號，再以複數小波轉換擷取超音波訊號之特徵，結果發現，人為缺陷距發送探頭越遠，造成訊號特徵的持續發生時間越長，特徵訊號並出現頻寬變大的趨勢，可用於簡化超音波訊號通過混凝土的複雜資訊。進一步將前述方式應用於受高溫延時作用後的混凝土試體，得知隨著延燒時間的增加，而使主要訊號特徵往低頻移動，並可由圖像上清楚的辨識其持續發生的時間。 |
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| 摘要(英)： | ||
| Elastic waves traveling in solid media usually contain a lot of time-variant spectral components. The objective of the current study is to analyze the local spectral characteristics in the elastic wave signal propagating through concrete. Wavelet theory is used since it is capable of analyzing the local spectral content of signals based on size-variable window functions. Standard cylindrical specimens were fabricated with cement mortar. Artificial defects were embedded inside the specimen with different geometry. The piezoelectric transducer is excited using a single-cycle tone-burst signal at 54kHz. The through-transmission ultrasonic signal was then digitized and subjected to the wavelet analysis. The wavelet coefficient plots showed that the bandwidth and the lasting period of the signal characteristics both increased as the distance between the artificial defect and the transmitting transducer increased. Further application of the wavelet analysis to concrete specimens was carried out to quantify the effects induced by simulated fire exposure. There was an increasing tendency for the signal characteristics to shift to low frequencies as the exposure time increased. The lasting periods of the characteristic frequency band of the ultrasonic signals were readily determined from the wavelet coefficient plots. | ||
| 檔案： | 沒有相關檔案 | |
| 相關連結： | http://ethesys.lib.cyut.edu.tw/ETD-db/ETD-search-c/view_etd?URN=etd-0826104-073845 | |