|
碩士論文公告區 |
||
| 年度： | 91 | |
| 姓名： | 黄俊諺(Jiun-Yan Huang) | |
| 論文題目(中)： | 運用小波轉換改善超音波法檢測混凝土訊號判讀 | |
| 論文題目(英)： | Improving the Signal Detection of Ultrasonic Pulse Velocity Method Based on Wavelet Transform | |
| 摘要(中)： | ||
| 傳統的訊號分析是建立在傅立葉轉換的基礎之上，但由於傅立葉轉換無法表達訊號的時頻局部性質，因此有了小波轉換的發展，小波轉換相較於傅立葉轉換最大的不同，便是小波轉換是一種時間窗與頻率窗都可改變的時頻局部化分析方法，即在低頻部分具有較高的頻率分辨率和較低的時間分辨率，而在高頻部分具有較高的時間分辨率和較低的頻率分辨率。 以超音波檢測混凝土，會因為混凝土本身非均質材料的特性及不同邊界所造成複雜的波傳路徑影響，而使得超音波訊號出現難以解讀之訊號波形，本文利用小波轉換將超音波訊號進行時頻分析，發現小波轉換在提取特徵訊號及展示其時間成分具有良好的效果。 |
||
| 摘要(英)： | ||
| Fourier transform is frequently used in analyzing the frequency content of a transient signal. The drawback of Fourier transform is that the time-domain characteristic cannot be shown simultaneously. Wavelet transform is one of the time-frequency dual transforms that provide the transient frequency content of a signal. The length of both time window and frequency window can be varied in wavelet transform. As a result, the time resolution is better in high frequency band while the frequency resolution is better in low frequency band. This makes wavelet transform a very attractive tool for analyzing the ultrasonic wave through concrete. Current study focuses on the time dependence of spectral characteristics of ultrasonic waves propagating in concrete. Wavelet transform is applied to simulated signals as well as real signals. Sources of excitation are compared and features of corresponding wavelet transforms are identified. The peaks of signals obtained from heated concrete appear to be delayed in time and the associated scales shift to lower frequencies. | ||
| 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-0823103-084320 | |