Noise reduction for ultrasonic Lamb wave signals by empirical mode decomposition and wavelet transform

Ultrasonic Lamb waves have been widely used in the nondestructive testing and evaluation of materials – in particular, plate-like structures. The received ultrasonic Lamb wave signals are often noisy. An effective noise reduction technology is highly important to accurately assess the conditions of the plate-like structures. In this paper, a noise reduction method for Lamb wave signals based on the empirical mode decomposition method and adaptive threshold wavelet transform is presented. We demonstrate the advantages of the proposed method first by employing computer-simulated signals, after which we employ more realistic signals. Simulated and experimental data obtained from a steel plate are used to evaluate the performance of the proposed method qualitatively and quantitatively. The results show that the proposed method effectively reduces noise for ultrasonic Lamb wave signals.