Distributed Fibre Sensing System for Vibration Detection
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Solution Overview
Problem
Traditional distributed fibre vibration sensing systems face limitations in high-frequency vibration sensing due to the contradiction between vibration frequency response bandwidth and sensing distance, and they struggle with spatial resolution and detection range, often resulting in low signal-to-noise ratios and inaccurate positioning.
Innovation Solution
A distributed fibre sensing system that generates optical frequency comb signals and employs a phase demodulation algorithm to eliminate interference and polarization fading, combined with frequency-division multiplexing and swept-frequency optical pulses to expand vibration frequency response bandwidth and improve spatial resolution and detection distance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the transmission time interval of probe pulses is increased to achieve larger vibration response bandwidth, then the vibration frequency response bandwidth is improved, but the maximum detection distance decreases because the round trip time of light in the sensing fibre must be less than the transmission time interval
Solution Approach 1:
The patent divides the frequency spectrum into multiple non-overlapping frequency bands and uses separate digital band-pass filters for each band. This segmentation allows the system to process different frequency components independently, effectively expanding the overall vibration frequency response bandwidth without requiring a single long pulse interval that would limit detection distance.
Solution Approach 2:
The patent changes the parameter of pulse transmission by using swept-frequency optical probe pulses with continuously varying frequencies instead of single-frequency pulses. This parameter change allows multiple frequency bands to be swept through during each pulse transmission, effectively multiplying the vibration frequency response bandwidth while maintaining the same pulse transmission interval and detection distance.
2Measurement precision
If the duration of optical probe pulse is shortened to achieve high spatial resolution, then the spatial resolution is improved, but the power of optical probe pulse decreases resulting in limited detection range
Solution Approach 1:
The patent uses periodic swept-frequency optical probe pulses that sweep through multiple frequency bands in sequence. This periodic action allows the system to accumulate signal energy over multiple frequency sweeps while maintaining short pulse duration for high spatial resolution. The EDD algorithm processes these periodic signals to extract vibration information, effectively overcoming the power limitation.
Solution Approach 2:
The patent employs a composite signal processing approach combining swept-frequency modulation with EDD algorithm. This composite method integrates the advantages of frequency sweeping (energy accumulation) with short pulse duration (high spatial resolution), achieving both high spatial resolution and adequate detection range through the synergistic combination of multiple technical means.
3Ease of operation
If intensity-based demodulation is used for simplicity, then the demodulation algorithm is simple, but the signal-to-noise ratio is low and phase demodulation errors occur due to interference fading and polarization fading
Solution Approach 1:
The patent replaces the traditional intensity-based demodulation method with an EDD algorithm that operates on the phase information of optical signals. This substitution eliminates the problems of interference fading and polarization fading that plague intensity-based methods, significantly improving signal-to-noise ratio and measurement precision while maintaining computational efficiency through the use of digital signal processing techniques.
Solution Approach 2:
The patent introduces an intermediary reference signal in the EDD algorithm that serves as a mediator to extract vibration information from the swept-frequency optical probe pulses. This reference signal acts as a stable reference that eliminates the need for direct intensity measurement, thereby avoiding interference and polarization fading effects while maintaining algorithmic simplicity through coherent detection principles.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system achieves high spatial resolution and long detection distance, enhances signal-to-noise ratio, and accurately detects and positions vibration points, overcoming the limitations of traditional systems by eliminating weak reflection points and phase demodulation errors.
Implementation Method 1
electro-optic modulation and acousto-optic modulation are performed on local light, so that optical pulses can be obtained
Implementation Method 2
electro-optic modulation and acousto-optic modulation are performed on local light, so that optical pulses can be obtained
Implementation Method 3
coupling and frequency beating are performed on obtained Rayleigh backscattered optical signals
Implementation Method 4
coupling and frequency beating are performed on obtained Rayleigh backscattered optical signals and the local light
Implementation Method 5
obtained optical signals are subjected to photoelectric conversion and demodulation
Data Source
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AI summary
A distributed fibre sensing system and a vibration detection and positioning method therefor are disclosed. The system comprises: a signal generating module, a light source module, an optical frequency comb generating module, a frequency sweeping and pulse generating module, an optical circulator, a sensing fibre, an interference module, a photoelectric conversion module and a detection and position module. The method comprises: generating a plurality of digital band-pass filters with different frequency bands without any overlapping by a positioning unit in the detection and position module, and performing digital filtering on original data segments from a plurality of swept-frequency optical probe pulses, thereby obtaining a plurality of reflectivity curves of the sensing fibre; performing a fading elimination processing on the reflectivity curves, thereby obtaining a plurality of averaged reflectivity curves of non-interference fading and polarization fading; performing a phase processing on the averaged reflectivity curves, thereby obtaining phase variance curves; and determining a vibration point according to variances in the phase variance curves, and finally obtaining a position and a vibration waveform of the vibration point. The present invention has a high positioning accuracy, a large range of vibration frequency response and a high signal-to-noise ratio of vibration waveform.