Application of the short time Fourier transform to interpret ultrasonic signals

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.