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Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
Comparison between the raw Lamb wave signal and the extracted S0 mode (a); and the short-time Fourier transform (STFT) spectrogram of the raw Lamb wave signal (b).