Ultrasonic guided-waves characterization with Warped Frequency Transforms

In this work a new time-frequency procedure for the extraction of multimodal and dispersive guided waves (GWs) from a recorded time-waveform is presented. The proposed ldquoWarped Frequency Transformrdquo (WFT) is based on a time-frequency domain tiling chosen to match the spectro-temporal structure of the different propagating guided waves by selecting an appropriate warping map which generates non-linearly frequency modulated atoms. The WFT transformation is fast, invertible, covariant to group velocity-delay shifts and, in force of the more flexible tiling, presents enhanced modes extraction capabilities. An application to Lamb Waves propagating in an isotropic plate is presented to show the potential of the proposed procedure.