Research On Fiber Grating Cross-sensitivity And Network Construction

Fiber grating sensors with high sensitivity, anti-electromagnetic interference, easily being multiplexed for distributed sensing and so on, have become a significant research field. With the rapid development of fiber grating sensors and network technology, fiber grating sensor networks are developed towards high-capacity, long distance, high-precision, large-scale distributed sensing, which have been widely applied for boundary security, health monitor of bridge, temperature sensor of power system. This dissertation is focused on solving cross-sensitivity between temperature and strain of fiber grating and constructing sensor network technology. The main works are achieved as the following.Firstly, Sensing principle, multiplexing technology and demodulation technique of fiber Bragg grating are investigated in this dissertation. Progress of fiber grating sensor are briefly introduced. The basic principles of fiber Bragg grating sensor are also given.Secondly, temperature and strain cross-sensitivity problem of fiber grating is studied. A kind of demodulation scheme is proposed based on genetic algorithm. A fast demodulation model of genetic algorithm is established. According to the mathematical analysis, the genetic algorithm fitness function and target equation are determined. With the proposed scheme, we discuss the demodulation results for the different center wavelengths and peak reflections of the two FBGs. Numerical results demonstrate that the proposed demodulation scheme based on genetic algorithm can effectively demodulate the change of the temperature and strain separately without the requirement of two same fiber grating in the method of the traditional reference fiber grating, and make the construction of fiber sensing system easier at the same time.Finally, sensor network based on fiber gratings with weak reflection are investigated. First, the effect parameters such as grating length and the modulation depth of refractive index on the properties of FBG are discussed. Then the effect of Rayleigh scattering and multipath effect on the multiplexing capacity of fiber grating sensor network are investigated, and thus the formula between fiber grating reflectivity and multiplexing capacity are deduced. On the basis of the above result, we propose a circular sensor network by using weak reflection fiber grating array. Theoretical simulations demonstrate the validity and reliability of the proposed sensor network scheme.