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Lamb Waves Mode Decomposition Using the Cross-wigner-ville Distribution

A.B. ZOUBI, V.J. MATHEWS, J.B. HARLEY, D.O. ADAMS

Abstract


Guided Lamb waves have been widely studied for characterizing damage in structures. Lamb waves are characterized by their multimodal and dispersive propagation, which often complicate analysis. As a result, separating the mode components arriving at each acoustic emission sensor is a critical part of many guided wave Structural Health Monitoring (SHM) systems. This paper considers an active SHM system in which the monitored structure is excited with a linear chirp signal using piezoelectric actuators. The measured signals are analyzed to decompose the individual Lamb wave modes. The method employs the cross-Wigner-Ville Distribution (xWVD) between the excitation signal and the received sensor signal and assumes that overlapped modes in the time domain may be separable in the timefrequency domain to reconstruct the modes separately. The mode decomposition method uses a ridge extraction algorithm to identify the location of the individual modes in the time-frequency distribution and separate them using a rectangular window. Once the individual modes are separated in the time-frequency domain, the inverse xWVD is used to reconstruct the modes in the time domain. The method’s effectiveness to separate and reconstruct the first two fundamental Lamb wave modes (zeroth symmetric and zeroth anti-symmetric) is demonstrated in the paper through numerical simulations and experimental results on an aluminum plate.

doi: 10.12783/SHM2015/237


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