De-noising in ultrasonic detection of coarse-grained materials by wavelet transform soft-thresholding

To suppress the adverse effects of the structure noise and the electrical noise, the application of multiscale wavelet transform to ultrasonic detection of coarse-grained materials is discussed. According to the characteristics of the wavelet transform on the different scale of the structure noise, the electrical noise and the defect signal, we present an algorithm such that wavelet transform coefficients of noise are filtered by a changing threshold on the different scale and the detection signal is reconstructed with appropriate weight in order to enhance the signal-to-noise ratio. Experimental results show that this new method is effective, and the defect is detected easily.