Design Of Mode-identification System For Ultrasonic Guided Waves Based On 2D-FFT

Ultrasonic guided wave has the characteristic of long-distance transmission, and is fit for wide range detection, especially suitable for all kinds of pipeline inspection and rail flaw detection.Due to wave dispersion and multi modes of ultrasonic guided wave, the modal identification is the foundation of all kinds of detection task and array transducer is needed to extract the modal characteristic signal. Aiming at the modal analysis of ultrasonic guided wave and phase velocity measurement, ultrasonic guided wave mode recognition system is built in this paper.Comparing different methods to recognize modes of guided wave in time domain and frequency domain roundly, the spatial and temporal frequency estimation method based on 2D-FFT is used to identify the guided wave modes. Data matrix with the time-space information processed by 2D-FFT can be transferred to the relationship of guided wave frequency and wave number. With the specific frequency, different wave number can be extracted to calculate phase velocity values of different modes as the formula of wave number and phase velocity. In this way, different modes can be identified under the same frequency by comparing the theoretical value.This paper studies the guided-wave mode-recognition algorithm based on 2D-FFT, proposing the overall scheme of the modal identification system and the selection parameters of linear-array probe. In view of the array probe’s signal acquisition, this paper mainly introduces the system based on FPGA and ARM. Through the design of hardware and software optimization, the 32-channel synchronization and high-speed data acquisition is finished, and the data can be transmitted to pc machine for display and saving. Experiments are carried out to verify the system by comparing the phase velocity values from semi-analytical finite element method (fem).It is proved that the system can realize different modes under the same frequency of guided wave in iron plate and aluminum plate.This paper completes all the work about design, manufacture, debugging of ultrasonic guided wave mode recognition system based on 2D-FFT. And the experiments prove that the system has good capability to identify guided wave mode identification. The system can be widely applied in seamless rail flaw detection, longitudinal stress testing and other fields.