An automatic optimal excitation frequency tracking method based on digital tracking filters for sandwiched piezoelectric transducers used in broken rail detection

Based on digital tracking filters and wireless communication technology, an automatic optimal excitation frequency tracking method for sandwiched piezoelectric ultrasonic transducers (SPUTs) is proposed. The proposed frequency tracking method uses a variable-step frequency search strategy and the optimal excitation frequency is determined by analyzing the receiving signals in time and frequency domains. Then the field test is carried out by the pitch-catch setup under different test distances: 50 m, 100 m, and 150 m. It is proved that compared with SPUTs excited at series resonance frequency, the FFT (Fast Fourier Transformation) amplitude, power spectrum density and Peak-to-Peak value are greatly improved and the maximum time-frequency energy becomes more concentrated when SPUTs are actuated at the optimal excitation frequency. Specially, the FFT amplitude, power spectrum density and Peak-to-Peak value can achieve the largest increase by 104.42%, 31.54%, 71.36%, respectively when the test distance is equal to 50 m. It can be concluded that the proposed frequency tracking method can efficiently track the optimal excitation frequency and be easy to achieve integration and automation. (C) 2018 Elsevier Ltd. All rights reserved.