Ultrasonic Lamb waves multimodal separation through independent component analysis in the time-frequency domain

To facilitate Lamb waves signal analysis and mode characterization,a multimodal Lamb waves identification method combining Short-Time Fourier Transform(STFT) and Independent Component Analysis(ICA) was proposed.Temporal signals were first projected into the time-frequency domain using STFT.Since different modes were relatively independent in the time-frequency domain,ICA was then introduced to realize the multimodal separation.The group velocity curve of each mode was extracted according to its time-frequency energy ridge.Thus,the plate thickness can be further estimated.The proposed method was applied to the Finite-Difference Time-Domain(FDTD) simulation and the steel plate experiment,with A0,S0 and A1 mode being separated.The average error of group velocity estimation in simulation and experiment was about 1.5% and 2.0%,with that of plate thickness estimation being 0.3% and 2.0%approximately.The simulation results show that,as the Signal-to-Noise Ratio(SNR) is not less than 0 dB,the timefrequency independent component analysis method can be used for Lamb waves multimodal separation,group velocity curves extraction and plate thickness estimation.