Fiber Bragg Grating Demodulation System And Method Of Data Processing Theories And Experimental Research

With the development of optical sensor technology, fiber Bragg grating (FBG) sensor has the advantages of resistance to electromagnetic interference, corrosion resistance, excellent insulation, wide measuring range, easy for multiplexing, solving problems that other sensors can't solve, etc, these sensors as one of the faster-developing technology are widely applied in the field of civil engineering, aerospace, petrochemicals, electric power, medical treatment, shipbuilding industry, and so on. In this dissertation, theoretical and experimental studies on FBG sensing demodulation system and data processing method were carried out, which specifically includes:Embark on the transmission of FBG, the detailed theoretical analysis was carried out based on the axial strain characteristic, temperature characteristic and cross-sensitivity characteristic, and the corresponding mathematical model were derived. According to the distribution of transverse force, the dissertation discussed the spectra changing state under transverse uniform force and inhomogeneous force respectively, distills feature information volume which reflects external signals, and studies the relation between the feature information volume and sensing volume. Based on the characteristic twisted HiBi fiber and coupled mold theory of FBG, the coupled equation of twisted HiBi fiber grating was proposed, the relation between spectra response and twist angle was analyzed and proved by transfer matrix method.The FBG wavelength demodulation method with M-Z interferometer constituted of 2×2 and 3×3 couplers is studied, the interrelation system sensing model is established and the correlative theoretical analysis was carried on. The optical path and electro circuit related with demodulation system is designed. On the basis of traditional phase-unwrapping technique combined with the particular condition, a fast phase-unwrapping method is proposed. Several typical state characteristics of vibration demodulation system are analyzed and studied using the proposed demodulation scheme and phase-unwrapping method. The FBG wavelength demodulation method with M-Z interferometer constituted of 2×2 and 3×3 couplers was combined with tunable F-P filter technique and frequency continuous wave (FMCW) technique respectively, and the corresponding distributed FBG vibration sensing network is designed.Based on the basic principle of GA and FBG theory, considering the characteristics of FBG's reflected spectrum under the difference condition, the application method of GA in FBG sensing system was systemic analyzed and studied. The relevant mathematical model of sensing system was established, and the objective function and individual fitness evaluation policy interrelated with GA were also established. The improvement and correction measurement to GA were analyzed, and the effects of each parameter on GA were analyzed. The wavelength demodulation can been realized using GA in FBG axial strain sensing system, and the stress measuring using GA in FBG sensing system under transverse force through spectra optimizing.The experimental system of characteristic analysis on FBG, vibration and GA's application study was constructed, and the corresponding hardware electro circuit and software of the date acquisition, processing and analysis were designed. Using the designed system, we respectively on the experimentally study on the characteristic of FBG under transverse force and torsion, the free vibration demodulation of signal FBG based on 2×2 and 3×3 couplers, the vibration of FBG based on 2×2 and 3×3 couplers and F-P filter technique, the vibration of FBG based on 2×2 and 3×3 couplers and FMCW technique, the demodulation of FBG under axial strain using GA, and the spectra analysis of FBG under transverse uniform force using GA.