Comparison of Lamb wave focusing performance using wave dispersion-compensated actuation and plano-concave lenses

Abstract

Lamb waves are often used for damage detection in structures. Hot-spot monitoring via wave focusing is considered in this study, which can be achieved by using a plano-concave aspherical lens. Once attached to the plate, the lens modifies the effective plate thickness, and therefore changes the Lamb wave characteristics, such as wavenumber and phase velocity, providing a convenient way of controlling Lamb waves. Another possibility for focusing Lamb waves is to use multiple actuators and design dispersion pre-compensated excitation signals with an embedded time delay. These two approaches can be combined together. We conducted numerical simulations using the time-domain spectral element method based on the 3D elasticity theory and demonstrated that the A0 mode of Lamb waves could be focused on the desired focal point. We compared the efficacies of the plano-concave lens approach, the dispersion pre-compensated focusing approach, and a combination of both approaches, emphasizing the advantages and disadvantages of each method.