Zero group velocity Lamb waves for non-destructive testing of plate structures: a review of principles, applications, and prospects

This review presents the current status of zero group velocity (ZGV) Lamb waves for localised high-resolution inspection of plate structures. ZGV modes are dispersion-defined resonances that confine elastic energy near the excitation point and occur at frequencies where group velocity is zero while phase velocity remains finite. The review summarises the physical basis, common excitation and detection methods and the signal-processing procedures used to extract ZGV resonance frequencies. It surveys applications of non-destructive testing (NDT) in thickness measurement, delamination and adhesion assessment, corrosion and coating inspection and thin-film characterisation, and it discusses key advantages and limitations. The review concludes by outlining emerging directions in hybrid physics – data inversion and digital-twin integration aimed at automated field deployment of ZGV-based structural health monitoring.