Abstract
The asymmetric dual Mach–Zehnder interferometer (ADMZI) based vibration sensor effectively extends the sensing distance, however, the asymmetry seriously deteriorates the positioning accuracy. In this paper, an adaptive tunable Q-factor wavelet transform (TQWT) based long-distance asymmetric sensing system is proposed and experimentally demonstrated for the positioning of wide-frequency-range knocking vibration signals. The TQWT can extract the time-frequency features of the non-stationary signals by performing multi-scale decomposition. Firstly, the positioning method adaptively determines the decomposition levels by analyzing the power spectrum of the vibration signals, which not only effectively suppresses the effect of low-frequency noise, but also accurately extracts the main time-frequency variation characteristics of the vibration signals with various bandwidths. Then, the time delay between the time-frequency characteristics is obtained using a cross-correlation algorithm, and the vibration position is demodulated. Experimental results show that the method can accurately locate vibration signals with bandwidths of 10–80 kHz at a sensing length of 125 km. For high-frequency, strong vibration signals, the standard deviation of the positioning is around 35.1 m. For low-frequency, weak signals, the proposed method can still achieve effective positioning compared with the traditional approaches with a standard deviation of approximately 238.1 m. The proposed scheme can significantly improve the applicability of the asymmetric interferometer based vibration sensing system.
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