Abstract
This work proposes an EMD-based STFT flight time extraction method to recognize the different modes of overlapped Lamb wave detecting signals (OLWDS) in aluminum plate due to its dispersion and multi-modes property. Firstly, empirical mode decomposition (EMD) is performed on the OLWDS and several intrinsic mode functions (IMFs) are obtained, which turn out to be capable of clearly separating the OLWDS of different modes. Secondly, the flight time is extracted from one of the IMFs by implementing short-time Fourier transform (STFT) on the selected IMF, and extracting the energy density distribution based on the center frequency component of Lamb waves. The experimental platform for different modes of OLWDS recognition in aluminum plate is established. The results show that this method can extract more accurate flight time values compared with the Hilbert-Huang transform (HHT) method and can accurately recognize the overlapped Lamb waves of different modes.