Abstract
Distributed acoustic sensing based on phase-sensitive optical time-domain reflectometry (Φ-OTDR) has been widely used in many fields. Phase demodulation of the Φ-OTDR signal is essential for undistorted acoustic measurement. Digital coherent detection is a universal method to implement phase demodulation, but it may cause severe computational burden. In this paper, analog I/Q demodulation is introduced into the Φ-OTDR based DAS system to solve this problem, which can directly obtain the I and Q components of the beat signal without any digital processing, meaning that the computational cost can be sharply reduced. Besides, the sampling frequency of the data acquisition card can theoretically be lower than the beat frequency as the spectrum aliasing would not affect the demodulation results, thus further reducing the data volume of the system. Experimental results show that the proposed DAS system can demodulate the phase signal with good linearity and wide frequency response range. It can also adequately recover the sound signal sensed by the optical fiber, indicating that it can be a promising solution for computational-cost-sensitive distributed acoustic sensing applications.
Highlights
Distributed acoustic sensing (DAS)—a technique that can monitor the dynamic perturbations along an optical fiber—has been widely used in many fields such as perimeter security [1,2], structure health monitoring [3], and pipeline monitoring [4,5,6,7,8]
We can clearly see that the piezoelectric ceramic (PZT) vibration signal are respectively located at 2069 m and 2201 m, which means that the proposed DAS system is and the sound signal are respectively located at 2069 m and 2201 m, which means that the proposed capable of detecting multiple acoustic events simultaneously
The spatial average kurtosis (SAK) value of PZT vibration and the DAS system is capable of detecting multiple acoustic events simultaneously
Summary
Distributed acoustic sensing (DAS)—a technique that can monitor the dynamic perturbations along an optical fiber—has been widely used in many fields such as perimeter security [1,2], structure health monitoring [3], and pipeline monitoring [4,5,6,7,8]. Phase-sensitive optical time-domain reflectometry (Φ-OTDR) is the most commonly used scheme for DAS systems It injects coherent light pulses into an optical fiber, detects the Rayleigh backscattering (RBS) lightwave from the sensing fiber by a photodetector. The components can be sampled by a low-speed to the beat signal, meaning that we do not need to perform Hilbert transform in the digital domain data acquisition card (DAQ). Differential betweenarea, two points locatethe at the twosignals sides ofthroughout the perturbation area, the computational cost of the proposedthe system is low enough to achieve rather than to demodulate the phase signals throughout fiber. The acoustic-modulated RBS lightwave from the sensing fiber is superposed with the local reference light at a 50:50 OC, and detected by a balanced photodetector (BPD).
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