The electromagnetic acoustic detection features small echo signal and
low signal-to-noise ratio. In order to effectively extract the implicit defect feature in
unstable signal, the diagnosis method of ensemble empirical mode decomposition(
EEMD) based on lifting wavelet packet is proposed. Firstly, the influence of high
frequency noise on EEMD is removed by using lifting wavelet packet transform
algorithm with improved threshold function and selecting optimal threshold; then,
the de-noised signal is decomposed with EEMD, the echo signal is analyzed in time
and frequency domains. The results show that the method of EEMD based on lifting
wavelet packet can remove the noise of the echo signal effectively and extract the
malfunction feature in the low SN R signal. This method provides reliable basis for
defect diagnosis.