Optimal scale wavelet transform for the identification of weak ultrasonic signals

Various noise suppression techniques based on wavelet transform (WT) are widely used in non-destructive testing and evaluation (NDT&E). A weak ultrasonic signals identification method by using the optimal scale wavelet transform is proposed in this paper. The selection of the optimal scale is realized by maximizing the negentropy of the discrete wavelet transform (DWT) coefficients. The central frequency and bandwidth of the optimal scale wavelet matched that of the ultrasonic signal very well. Numerical and experimental results have been presented to evaluate the effectiveness of the optimal scale wavelet transform on ultrasonic flaw detection. This technique is a simpler and effective technique for processing heavy noised ultrasonic signals, and is greatly time-saving comparing with other typical wavelets transform.