Dispersive Wave Analysis using the Chirplet Transform

Abstract

Time-frequency representations (TFR) are a widely used tool to analyze signals of guided waves such as Lamb waves. As a consequence of the uncertainty principle, however, the resolution in time and frequency is limited for all existing TFR methods. Due to the multi-modal and dispersive character of Lamb waves, displacement or energy related quantities can only be allocated to individual modes when they are separated in the time-frequency plane.

The chirplet transform has been introduced as a generalization of both the wavelet and Short-time Fourier transform. It offers additional degrees of freedom to adjust time-frequency atoms which can be exploited in a model-based approach to match the group delay of individual modes.

The objective of the current thesis is to apply the algorithm proposed by Kuttig to a series of candidate nondestructive evaluation problems. The accuracy and robustness of the CT based procedure is examined for each of these example problems and is benchmarked against analytical solutions (if available) and to the conventional STFT.