Denoising Method Of Ultrasonic Lamb Wave Signal

In recent years, with the large area plank is widely used in industry, nondestructive testing for the defects of plank becomes more and more important. Ultrasound lamb waves is widely used in nondestructive testing due to it’s a good many merits:flexible and diversified forms of testing,ability of high power to detect, the function of long distance, simple apparatus to detect.But the disturbed noises and envirnmental acoustics during the process of collecting Ultrasound lamb waves makes the lamb wave become complex,and directly influences the reliability and accuracy of nondestructive testing,finally hinder the further development of the ultrasound lamb waves application.So,we need to adopt appropriate and effective signal processing method for lamb waves to deal with the noise signal. This paper in ultrasonic lamb wave denoising aspects of the main work to do the following:1、Based on analysis of wavelet transform and adaptive threshold denoising method, we propose orthogonal wavele transform based on adaptive threshold denoising method to process single mode and multi-modal lamb wave signal. First, we use the orthogonal wavelet transform to the remove the the signal’s correlation, and then eliminates noise from the signal by using adaptive threshold method, finally, reconstruct the signal by using wave reconstruction algorithm. The results of simulation indicate that the method can more efficient to remove the noise of the lamb wave signal.2、Because of Empirical Mode Decomposition(EMD) method and wavelet threshold denoising method have advantages and disadvantages, so we combine the Mode Decomposition(EMD) method and wavelet threshold denoising method to deal with the single model and multi-modal ultrasonic lamb waves signal. The results of simulation indicate that this method can eliminate noise of the single model and multi-modal ultrasonic lamb waves signal effectively.3、In fact, the multi-mode ultrasound lamb waves is superposition of muli-type signal, which can cause the superposition of noise. So we combine the Empirical mode decomposition (EMD) method and Wavelet Packet denoising method to deal with the measured multi-mode Lamb wave signal. The results of simulation indicate that this method can eliminate noise of multi-mode lamb waves and keep detail information of signal well.