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. © 2021 Acta Acustica.