Research On Key Technologies Of Long Distance Optical Fiber Sensing System For Vibration Detection With Broadband Frequency Bandwidth

Distributed fibre optic sensing systems have been used in many fields such as perimeter security,pipeline leakage monitoring,bridges and dams and residential buildings because of their high sensitivity to external signals,strong resistance to electromagnetic interference,good confidentiality of data transmission and wide sensing defence areas.In this paper,a wide-frequency domain long-range optical fibre sensing system is built based onΦ-OTDR technology.For extending the sensing distance of the system,optical fiber amplification and low-noise optical signal filtering techniques are used;based on wavelet packet decomposition algorithm for perturbation signal feature extraction and SVM training of perturbation signal features,multi-event and highly accurate pattern recognition of the system is achieved;for the frequency response range of the system,a new demodulation method is proposed,through the method of data reconstruction and doing Fourier transform,demodulation of the frequency information of the perturbed signal.Finally,ANSYS Workbench is used to simulate the pipeline gas leakage and compare the results with the actual pipeline gas leakage demodulation,analyse the relationship between the gas leakage signal,the pipeline pressure and the leakage aperture,and realise the pipeline gas leakage signal detection.The specific work content is as follows:(1)The research background and significance,characteristics and classification of distributed optical fiber sensors are introduced,and the current research status,working principle and performance index of Φ-OTDR sensing technology are explained,and the extension method of system monitoring distance and pattern recognition method are analyzed theoretically.(2)Based on the combination of optical fibre amplification and low-loss optical filters,the 45 km long-range monitoring and analysis of the SNR variation of the perturbed signals are achieved,and finally the influence of non-linear effects on the long-range testing performance of the fibre-optic sensing system is discussed.(3)The experimental system for pattern recognition was built,and the original feature information of the event signal was demodulated using wavelet decomposition,and the recognition of four different event types was achieved by model training based on support vector machines.(4)Frequency demodulation of wide-frequency domain long-range fibre-optic sensors and their application to real pipeline leaks are investigated.A distributed amplitude detector-based demodulation method for wide-frequency-domain fibre-optic sensing signals is proposed,and the system’s wide-frequency signal response capability from 2 Hz to 2.5 k Hz is verified.Simulations of pipeline gas leakage under different conditions are carried out with the aid of ANSYS Workbench software.A pipeline leakage imitation experiment was built to conduct sensing experiments and tests on pipeline gas leakage and to realise the system’s alarming of pipeline gas leakage events.