Lamb Waves Time-reversal Method using Frequency Tuning Technique for Structural Health Monitoring

Lamb wave time reversal method is a new and tempting baseline-free damage detection technique for structural health monitoring. With this method, certain types of damage can be detected without baseline data. However, the application of this method to thin-wall structures is complicated by the existence of at least two Lamb wave modes at any given frequency, and by the dispersion nature of the Lamb wave modes existing in thin-wall structures. The theory of Lamb wave time reversal has not yet been fully studied. This paper addresses this problem by developing a theoretical model for the analysis of Lamb wave time reversal in thin-wall structures based on the exact solutions of the Rayleigh-Lamb wave equation. The theoretical model first used to predict the existence of single-mode Lamb waves. Then the time reversal behavior of singlemode and two-mode Lamb waves is studied numerically. The advantages of single-mode tuning in the application of time reversal damage detection are highlighted. The validity of the proposed theoretical model is verified through experimental studies. In addition, a similarity metric for judging time invariance of Lamb wave time reversal is presented. It is shown that, under certain condition, the use of PWAS-tuned single-mode Lamb waves can greatly improve the effectiveness of the time-reversal damage detection procedure.