An improved technique for modal decomposition of a double-mode Lamb wave signal

This study develops a technique to decompose a multi-mode, transient Lamb wave signal into individual Lamb mode signals. The previously-proposed technique (presented at the SPIE NDE conference 2005) showed an encouraging efficiency for numerically-simulated signals, but suffered when evaluating real experimental signals due to its high sensitivity to noises and experimental errors. The improved technique starts with the same assumption of known Lamb wave propagation characteristics (known propagation dispersion curves). However, a highly-strict signal model governing the development of the previously-proposed technique is relaxed to tolerate unavoidable presence noises and errors, and the problem is re-formulated. For actual experimental signals, some additional signal processing techniques are introduced in signal pre-conditioning. The entire implementation of the improved technique is first tested with simulated signals, and then applied to actual experimental signals. The final results with real experimental are presented and discussed.