Abstract
The excitability of zero group velocity (ZGV) Lamb waves using a pulsed laser source is investigated experimentally and through numerical simulation. Experimentally, a laser based ultrasonic technique is used to find the optical spot size on the sample surface that allows an optimal coupling of the optical energy into the ZGV mode. Numerical simulations, using the time domain finite differences technique, are carried out to model the thermoelastic generation process by laser irradiation and the propagation of the generated acoustic waves. The experimental results are in good agreement with the numerical predictions. The experimentally and numerically obtained responses of the plate are investigated by a short-time Fourier transform. The responses show that the source diameter does not affect the fundamental behavior of the temporal decay of the ZGV mode.
Highlights
At zero group velocity (ZGV) points within the dispersion relations of plates, the slope of the dispersion curve and, the group velocity of the wave mode, becomes zero.[1]
This paper considered the excitability of ZGV Lamb waves by laser-ultrasound
The excitability of the ZGV modes was determined through the Fourier transform of the calculated and measured signals
Summary
At zero group velocity (ZGV) points within the dispersion relations of plates, the slope of the dispersion curve and, the group velocity of the wave mode, becomes zero.[1] Their curiosity originates from the fact that in physical acoustics the energy propagation is associated with the group velocity.[2] At ZGV points, energy cannot be carried away from a given excitation source, leading to a strong and detectable resonance of the plate. The practical relevance of the results, in terms of spot size selection for a given application, is reviewed
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