Application of STFT and HOS to analyse magnetostrictively generated pulse-echo signals of a steel pipe defect

A NDT technology based on the magnetostrictive effect is described in order to inspect steel pipes, and defect signals can be detected. This paper combines the short time Fourier transform (STFT) and the higher order spectra (HOS) analysis approaches to analyse magnetostrictively generated pulse-echo signals of a steel pipe defect. For different exciting mid-frequencies, the signals obtained are compared and analysed by using STFT and HOS methods. To compare the performance of STFT and HOS, the respective merits in the analysis of the pulse-echo signals are discussed. STFT method is appropriate for the estimation of the signal amplitude, and is easy in interpretation and implementation by using the fast Fourier transform. HOS has a potential to increase the time and frequency resolution, and can extract phase information from the different type of defect signals. The result shows that for application it is very necessary to perform more than one kind of STFT or HOS method to analyse the pulse-echo signals.