Modal Decomposition of Double-Mode Lamb Waves

Abstract

This research proposes a technique to decompose a transient, multi‐mode, Lamb wave, time‐domain signal into its individual Lamb wave modes. The technique is derived for a plane‐strain Lamb wave signal consisting of two Lamb wave modes (double‐mode Lamb wave signal). The proposed technique assumes knowledge of the propagation dispersion characteristics of Lamb waves, i.e. relationships between frequency and the real part of wavenumber of existing modes. These relationships can be obtained by other signal processing techniques such as the two‐dimensional Fourier transform or the short‐time Fourier transform. The proposed technique is verified for simulated signals to demonstrate the method’s accuracy in an almost‐ideal situation. The simulation uses eigen‐expansion method for calculation of the total response as a combination of responses due to all existing Lamb modes. The comparison between the decomposed and simulated signals demonstrates the validity of the proposed technique.