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Characterization of dispersion curves in plate-like structures is possible with guided Lamb waves. In this research, experimental development of dispersion curves relies on the spectrogram, which suffers from the Heisenberg Uncertainty Principle. Reassignment is capable of localizing ill-defined dispersion curves. Unfortunately, reassignment also introduces spurious components, which reduce reassignment performance. This research develops an algorithm that provides both localization of dispersion curves and elimination of spurious components. To achieve this, an alternative formulation of reassignment called differential reassignment is superimposed with nonlinear anisotropic diffusion. The combined algorithm is then applied to reassign experimentally measured spectrograms, leading to a significant increase in clarity. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

This research applies wavelet and short time Fourier transform (STFT) techniques to enhance the interpretation of experimentally measured transient ultrasonic waveforms. Specifically, this work applies these advanced signal-processing methodologies to two applications: (1.) detection of cracks in plate specimens; and (2.) the interpretation of acoustic emission (AE) signals. The first case examines experimentally measured (with laser ultrasonics) guided waves in both uncracked and cracked plates. This study investigates the sensitivity, accuracy, and robustness of both the wavelet transform and STFT to determine crack size and location. The second case examines AE signals that emanate from a fatigue crack. This work shows that wavelets enable the quantitative characterization of AE signals, enhancing the ability to determine both source type and location. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]