Damage identification based on ridges and maxima lines of the wavelet transform

The paper analyses the transient vibration behaviour of structures using the continuous wavelet transform (CWT), which provides effective tools for detecting changes in the structure of the material. The advantage of the CWT over commonly used time-frequency methods like the Wigner–Ville and the Gabor transform is its ability to decompose signals simultaneously both in time (or space) and frequency (or scale) with adaptive windows. The essential information is contained in the maxima of the wavelet transform. From the ridges, the modal parameters of the decoupled modes can be extracted and the signal can be reconstructed. From the maxima lines, defects can be localized. This paper presents a new approach for the calculation of wavelet transform ridges and maxima lines, which is based on a direct integration of differential equations. The potential of the method is demonstrated by the analysis of the impact vibration response of different bars.