Research On Optical Fiber Accelerometer For Bridge Vibration

Optical fiber sensing measurement technology with strong electromagnetic interference resistance, high measuring accuracy, great stability, good ability of remote sensing signal transmission and easy to reuse into network advantages, has become an important development direction in the field of engineering structural health monitoring. According to the actual needs o f bridge vibration monitoring, this article proposed a 45° F-P cavity based on optical fiber accelerometer design. Through the mechanism analysis, the structure optimization design, sensing medium optimization, encapsulation technology and performance test research, developed a FP-45 optical fiber accelerometer. The accelerometer meets the requirements of bridge vibration monitoring. In this article, the main research work and innovations are as follows:Firstly, throng analysing the bridge vibration characteristics acceleration signal perception pathway and optical fiber F-P accelerometer sensing principle, this article proposes a 45° F-P cavity optical fiber acceleration sensor design scheme. This design scheme on the basis of the existing optical fiber F-P accelerometer structure design, using 45° mirror F-P cavity, effective to solve the existing contradiction on fiber-optic accelerometer between resonance frequency and sensitivity, without any increase in mass quality under the premise of improve the sensitivity of the sensor.Secondly, based on the structure optimization design of the sensor’s sensitive unit(cantilever beam, foundation, quality block, fine-tuning bolt) and sensing unit(45° F-P cavity, built- in mirror steel tube, the photosensitive road), the sensor of the structure size of each component is determined. The sensor shape size is 120 mm×80 mm×45 mm. The accelerometer has the advantage of compact structure, light weight and easy installation.Thirdly, through the optical fiber sensing medium of F-P accelerometer(including optical fiber, reflective film and G- lens self- focusing lens, etc.) of the optimization test, determine the optimal optical fiber core diameter, the size of the reflective film and F-P cavity structure. When using the 9/125 μm optical fiber and the same core classics of G- lens and 2×1 coupler, a silver film with 1.5 mm diameter, 90% reflectivity and all the built- in membrane structure can significantly increase the beam intensity in beam coupled into t he fiber, and obtain the best F-P cavity interference fringe contrast, improve the stability of the optical fiber F-P accelerometer.Lastly, on the basis of the film paste of sensor technology, packaging technology and the overall structure of G- lens lens packaging technology research, determined the encapsulation technology of the sensor, made FP-45 optical fiber accelerometer, and carried on the performance evaluation test. Experimental results show that the sensor in measuring range, sensitivity, frequency range, frequency response and reliability indicators meet the design requirements, apply to the long-term monitoring of bridge structure vibration...