Research on combined denoising based on Wavelet packet transform for EMAE signal

Electromagnetically induced acoustic emission (EMAE) technique is a new nondestructive testing (NDT). It does nondestructive detection with the effect of dynamic electromagnetic loading to generate a stress field stimulating stress waves from the defects. When EMAE is used to detect crack in the metal sheets, the EMAE signal is easy to be disturbed by various sources of noises, and the detectability of defect signals is greatly lowered. Concerning the characteristics of EMAE signal and main noises, a new method composed of Wavelet packet threshold denoising combined with decomposing and recomposing is presented. In order to promote the effect of denoising, it adopts a improved threshold function to denoise. The experimental results show that the denoising method is valid, it can obtain the main characteristic of the original signal and has superior features over the conventional methods and it is applicable in engineering.