A prior knowledge of group velocities of Lamb wave modes is a key for analysis of time signals in guidedwavebased structural health monitoring. The identification of multiple wave modes may be complicated due todependency of group velocity on frequency (dispersion). These dependencies for infinite plate of constant thicknesscan be calculated by a numerical solution of analytic equation. Two alternative approaches to determine groupvelocities of zero-order Lamb wave modes in aluminum plate were used in this work: Two-dimensional FastFourier Transform (2D-FFT) and methods of time-frequency processing. 2D-FFT requires a high number of timesignals in equidistant points, therefore it was applied on data from finite element analysis of wave propagation inthe plate. Group velocities for chosen frequencies were also determined using wavelet transform (WT) of signalsas differencies of times of arrival measured by a pair of piezoelectric transducers. The results from 2D-FFT andwavelet transform were compared to the analytic solution.
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