Bridge Multi-parameter Of The Fiber Bragg Grating Sensor Technology And Systems-based Research

In recent years, the applications of fiber Bragg grating (FBG) has been attracted great attention in the field of optical sensing and communication. FBG sensor has the advantages of resistance to electromagnetic interference, big signal bandwidth, high sensitivity, easy multiplexing, light weight, compact conformation, easy for fiber connection, realizing wavelength absolute coding, linking many sensors into sensing network using various multiplexing technology, realizing multi-point monitoring to achieve its properties through embedding in the internal structure of materials, or adhibiting on the surface mount, etc. These sensors have extensive prospect in the security monitoring area of the special occasions, such as the large buildings and oil wells. In this paper, the theoretical and experimental studies on multi-parameters sensing technology and system using FBG were carried on, which specifically includes:The establishment of FBG's temperature sensing model and strain sensing model were introduced based on coupled mold theory. The effect of correlation parameter on the reflected spectrum was analyzed. Because of the coupling problem, the principle and technique for the temperature compensation of FBG sensors were given when using as strain sensor. The best annealing parameters were given by theoretical analysis and experiments.Considering the need of long-term monitoring for civil engineering, several practical FBG sensors were developed and their sensing characteristics were investigated experimentally. Such as FBG strain sensor, FBG temperature sensor and FBG accelerometer. The research indicated that the sensitivity and stability of practical FBG sensors can satisfy the needs for civil engineering long-term monitoring.Study on the characteristic of FBG demodulation system is one of the most important parts of the subject study. On the basis of analyzing several familiar demodulation techniques of distributed FBG system, a wavelength scanning demodulation system based on continuous wave tunable frequency is designed. At the same time, tunable narrow-band light source, which is composed of wide-band light source and tunable optical filter, is adopted to demodulate multiplex signals. This method not only supply wider tunable range but also afford higher signal to noise ratio. A mixture multiplexing method that combines optical frequency domain reflectometry (OFDR) and wavelength division multiplexing (WDM) is proposed to address FBG sensing array. The proposed system scheme is testified to have faster demodulation and higher stability by analyzing theoretically and researching experimentally.Based on above research, multi-parameters monitoring system based on FBG has been designed. The software of data acquisition, signal processing and analysis system have been established. The practical FBG sensors have been successfully used in monitoring during construction stage and service time. The experimental results indicate that FBG sensors can monitor the temperature and strain effectively for a long time, as well as have higher stability. So, it's a practical structure monitoring sensor. The FBG strain sensor can monitor the strain and vehicle flux of important position accurately. FBG sensors can not only supply precision data for bridge's static and dynamic testing but also supply gist for bridge's working state assessment and health diagnosis. The FBG bridge monitoring system shows the outstanding stability and endurance throughout the whole process of bridge's construction, accomplishment and service time in two years. It can satisfy the needs for long term monitoring of armored concrete structural bridge, as well as provide continuous and accurate information.