A Novel Dispersion Compensation of Lamb Waves by Nonlinear Group Delay Estimation for Defect Imaging

The dispersive properties of Lamb waves result in lower accuracy in defect imaging. Some dispersion compensation methods are proposed to enhance imaging accuracy, which rely on known dispersive curves commonly unavailable in practice. In this article, a dispersion compensation method for Lamb waves is introduced to enhance the accuracy of defect imaging. This method utilizes nonlinear group delay estimation (NGDE) and operates when known dispersion curves are unavailable. By replacing the group velocity curve with time-frequency ridges, the problem of unknown dispersion curves is addressed. The traditional Carmona method for ridge extraction is optimized using NGDE to obtain more accurate ridges. Additionally, a method is proposed to calculate compensatory phases based on the group delay (GD) at the central frequency, resulting in nondispersive single-component signals. The ridge extraction and dispersion compensation simulation results demonstrate that the proposed method outperforms the matching pursuit (MP) and dispersion and multimode orthogonal MP (DMOMP) regarding signal-to-noise ratio (SNR) and relative error (RE). Subsequently, the method is also verified by application to defect imaging of delay-and-sum (DAS), weighted DAS (WDAS), and minimum variance distortionless response (MVDR), respectively, which can effectively improve imaging performance.