Dual Mechanism Distributed Optical Fiber Sensing Based On The Combination Of Brillouin And Rayleigh Scattering

Distributed Brillouin optical fiber sensing has the advantages of long measurement distance and large amount of sensing points with the measurement range up to the endurance limit of optical fiber,which has broad application prospects in the field of structural health monitoring.However,the measurement resolution of this technology is low,which limits its application in certain fields.Although Rayleigh sensing can distinguish small detail changes,it has the defect of cumulative measurement error,which makes it unsuitable for sensing with a large measurement range.For this reason,a dualmechanism distributed optical fiber sensing scheme based on Brillouin and Rayleigh scattering is proposed in this paper.The Brillouin and Rayleigh sensing in a single optical fiber are combined to complement each other,which can break through the technical bottleneck of the existing single sensing mechanism and achieve distributed strain sensing with both high resolution and large measurement range.The main research work is as follows:Firstly,the basic principles of Brillouin optical time-domain analysis technology and phase-sensitive optical time-domain reflection technology are analyzed,and their sensing mechanisms are deduced and simulated,respectively.By constructing a dual-mechanism sensing model combining Brillouin and Rayleigh scattering,the physical mechanism under the combined action of the two sensing is explored.Secondly,a dual-mechanism sensing experimental device is designed and built.The same set of frequency-scanning optical pulses are used to extract Brillouin and Rayleigh sensing signals simultaneously on a single test fiber,which can complete the determination of Brillouin and Rayleigh strain coefficients.In addition,two sets of periodic vibration sensing experiments with different amplitudes are carried out.The Rayleigh sensing is used to achieve a high-resolution relative strain measurement,and the absolute strain reference provided by the Brillouin sensing is combined to achieve a high-resolution absolute vibration sensing of 3.4 n?.Finally,through numerical simulation and experimental verification,the cumulative error effect of the Rayleigh sensing in the large strain measurement process is studied,and the reason for the error is analyzed preliminarily.Large-range dual-mechanism dynamic sensing experiments with small detail changes under different motion states are carried out.Among them,the strain detail changes applied in the experiments are embodied as 80 Hz sawtooth vibration signals with amplitudes of 1.5 ??and 750 n?,respectively.The adaptive noise cancellation technology is introducted to correct the cumulative error of the Rayleigh sensing by using an absolute measurement reference provided by the Brillouin sensing,which can achieve the integration of dual mechanism sensing.The strain measurement range of the adaptive fusion results depends on Brillouin sensing,and the strain resolution relies on Rayleigh sensing.Thus,on the ?-level benchmark,the dual-mechanism dynamic strain sensing with a dynamic measurement range of 311.9 ?? and a resolution of 4.8 n? is realized,which has the advantages of both Brillouin and Rayleigh sensing.