Characterization of Lamb Waves in Absorbing Plates

摘要

This research uses a combination of laser ultrasonics, signal processing and analytical modeling techniques to examine the propagation of transient Lamb waves in absorbing plates — in particular an isotropic plate with a lossless fluid on one side. The motivation is to develop a non-contact, point source-receiver technique capable of measuring attenuation of Lamb waves in lossy situations in general. The theoretical model enables an understanding of loss mechanisms and enables prediction of attenuation. The laser ultrasonic techniques enable broadband, point source-receiver idealization. The proposed signal processing technique, the short-time Fourier transform, resolves a signal into the time-frequency domain and enables Lamb mode separation and calculation of energy distribution at specific frequency-velocity points on the dispersion curves. The experimental procedure uses a stress-free plate as a reference for system variation and other loss mechanisms. Then, a plate with fluid on one side is tested to validate the signal processing algorithm. There is satisfactory agreement between the attenuation measured and predicted in the frequency range of interest.