Variational mode decomposition linked wavelet method for EMAT denoise with large lift-off effect

Abstract

Electromagnetic acoustic transducer (EMAT) is an emerging non-destructive testing technique which is widely used in the industry. EMAT has advantages of a non-coupling agent with the capability of big lift-off detection. However, EMAT has an issue of low efficiency in conversion and it is susceptible to noise. This paper proposes a modified variational mode decomposition (VMD) linked wavelet method for EMAT denoising. It enables to suppress both high-frequency narrowband noise and normal noise in EMAT signals with a large lift-off detection condition. In particular, a new ultrasonic echo signal model with a large lift-off influence is proposed for interpretation of denoising mechanism. To investigate the efficacy and the robustness of the proposed method, experimental studies have been carried out for different test samples. A comparative analysis has been undertaken to confirm that the proposed method not only removes the noise but also preserves the information of defect. The Matlab demo code can be linked: http://faculty.uestc.edu.cn/gaobin/zh_CN/lwcg/153392/list/index.htm.