Abstract: The reassignment method is a widespread approach in processing nonstationary signals for obtaining high aggregation and less overlapping components in time-frequency representations. Unfortunately, by using this traditional method, there exist some problems such as unavoidable overlapping components and low signal-to-noise ratio values. A novel time-frequency reassignment method based on nonparametric snakes is proposed for guided wave mode identification of steel strands. According to research results, it is clarified the proposed reassignment method based on nonparametric snakes can obtain high resolution time-frequency representations with significantly higher aggregation and improved signal-to-noise ratio compared with the short-time Fourier transform and traditional reassignment method. Furthermore, compared with group velocity dispersion curves in one of helical wires of the steel strand, the spectrogram provided by the proposed method can give the information of main ultrasonic guided wave modes and describe the trend of group velocity changes of these modes more accurately. Therefore, the proposed time-frequency reassignment method can provide a valuable basis for improving ultrasonic guided wave identification in different waveguides.

Key words: Nonparametric snakes, Reassignment, Steel strand, Time-frequency analysis, Ultrasonic guided waves