Dispersion Compensation and Mode Separation of Lamb Waves Using Two-component Signals of Laser Interferometer

Due to the problems of dispersion and multi-modes overlap for ultrasonic Lamb wave propagation, it is difficult to use it in many fields, such as long-range inspection. After ultrasonic Lamb waves are generated by a broadband ultrasonic pulse, these problems make the wave packets to spread out and various modes overlap in both time and space domain as they propagate through a plate or pipe. It is a very challenging to separate individual modes using traditional signal processing techniques. A two-component signal processing technique is presented in this paper to separate individual Lamb wave mode and then compensate its dispersion, according to the characteristics of Lamb wave structures and dispersion curves. This technique is carried out based on the inplane and out-of-plane displacements detection by laser interferometer. The numerical synthetic Lamb wave signals for both component generated by Gaussian sources are first calculated, and then the proposed algorithm is processed and verified using these numerical simulation signals including both A0 and S0 modes for various frequency-thickness products. The compensation of mode conversion Lamb wave occurring when one single mode interacts with a notch in the plate is discussed. In using the finite element simulation method, transmission tests are illustrated to prove the accuracy of algorithm and its ability of localization for defect.