Ultrasonic Lamb waves have been widely used for non-destructive evaluation and testing. However, the inversion from the measured guided signals to the material properties is still a challenging task in terms of multimodal dispersive signal processing and parameter estimation.

Here, we present a robust strategy including the high-resolution extraction of the multimodal dispersion curves and model-based elastic property estimation. First, the estimation of signal parameters via rotation invariant technique (ESPRIT) is employed to extract the dispersion curves of the Lamb waves in the plates. Then, the particle swarm optimization algorithm is used to retrieve the optimal model parameters by maximizing the objective function built from the dispersion equations. The elastic properties (i.e., two independent constants for the isotropic plate and four constants for the transversely isotropic plate) can thus be determined. The proposed model-based inversion strategy offers several advantages: (1) the high-resolution estimation of dispersion curves allows the objective function built for the parameter inversion without a peak-finding process. (2) The ESPRIT based dispersion curves extraction strategy offers a sharp objective function in the parameter space. (3) The inverse problem for ultrasonic waveguide characterization is solved using the PSO optimizer which can be implemented with ease and few parameters need to be tuned.

The relevant research was published inUltrasonicson August 2021, with the title of “High-resolution Lamb waves dispersion curves estimation and elastic property inversion”. Qi Chen is the first author, and Young Researcher Kailiang Xu and Professor Dean Ta are the corresponding authors. This work was supported by the National Natural Science Foundation of China, Program of Shanghai Academic Research Leader, Shanghai Rising Star Program and Shanghai Natural Science Foundation.(Qi Chen, Kailiang Xu*, and Dean Ta*, Ultrasonics, 115, 106427,2021)