- 學位論文
格雷互補對於超音波量測之應用
The Application of Golay Complementary Pairs in Ultrasound Measurements
摘要
格雷互補序列對擁有良好的自相關特性，可以取代短脈衝及相關函數近似脈衝的單一序列(例如虛擬隨機序列)，提升超音波訊號在接收端偵測的準確度。由於一個格雷互補對包含兩個序列，這兩個序列的傳送方式(交錯、先後傳送)會影響到接收準確度。但使用虛擬隨機序列或格雷互補對取代短脈衝的共同問題是總發射訊號時間(Total Transmission Duration, TTD)增長，造成近距離無法偵測，使盲域(blind zone)增大。因此，接收準確度的提升及盲域的減小是格雷互補對應用於超音波的關鍵問題。兩者之間有著取捨關係。 本論文探討格雷互補對用於超音波使用不同傳送方式發射訊號，對於接收辨別準確度及盲域大小的影響。我們提出使用正交同時傳送成對的格雷互補序列，比起交錯或先後傳送準確度更高且盲域大幅減小。另一部份探討超音波傳送訊號因反射在盲域內，接收訊號遭到部分截斷損失(truncation)時，各種傳送方法及不同格雷互補對於接收辨別準確度的影響。研究結果顯示，使用恰當的傳送方式可以大幅減少盲域，使格雷互補對的特性充分發揮，進而改善接收準確度性能；使用恰當的接收方式可以提升盲域內訊號的接收品質。不同格雷互補對的選擇則影響較小。
並列摘要
Golay complementary sequence pairs have nice correlation properties and can replace short pulses or pseudo random sequences to enhance ultrasonic signal reception accuracy. A Golay complementary pair includes two sequences, and the method to transmit these two sequences will affect the reception accuracy. A common problem when using pseudo random sequences or Golay complementary pairs to replace short pulses is that the Total Transmission Duration (TTD) will increased, which leads to a larger blind zone. As a result, there is a tradeoff between reception accuracy enhancement and blind zone reduction for the application of Golay complementary pairs in ultrasound systems. In this thesis, we discuss and compare different transmission methods of Golay complementary pairs in ultrasound systems. We propose to orthogonally transmit a pair of Golay complementary sequences simultaneously. This method provides higher accuracy and smaller blind zone compare to existing methods such as interleaving or concatenation. In addition, we also discuss the situation when the ultrasonic received signals are partially truncated when the reflection interface is in the blind zone. Our results show that appropriate transmission and reception methods can not only reduce the blind zone, but also improve the accuracy of reception. The selection of different Golay complementary pairs has less effect in signal quality compare to the transmission and reception methods.