Research Of Fiber Bragg Grating Acceleration Sensor Based On Flexible Hinge

The main research content of this thesis is medium and high frequency fiber grating acceleration sensing technology.The research goal is FBG accelerometer based on symmetrical flexible hinge,a model of acceleration sensor based on flexible hinge is established,and solving the problem of low frequency range and low sensitivity of existing FBG accelerometer.FBG accelerometer as a passive device,compared with the electrical sensor,can resist electromagnetic interference.It can transport information from far away and also can work in harsh environments.However application of FBG accelerometer is limited.The reason is that most of the existing mature fiber grating acceleration sensors are based on cantilever and metal diaphragm structure,whose way of encapsulation is complex,and can't fulfil the requirement of medium and high frequency measurement.The flexible hinge acts as an elastic element for transferring movement,and has many advantages such as no friction,no wear,easy processing,small size,high sensitivity.For the above advantages of flexible hinge and FBG,by applying flexible hinge to FBG accelerometer,the performance of the sensor can be improved,but the measured sensitivity of existing FBG accelerometer based on flexible hinge is still not high.In this paper,a novel model of FBG accelerometer based on symmetrical flexible hinge is proposed through systematically studying the dynamic characteristics of FBG and flexible hinges,and the structural parameters are optimized through the theoretical formula.Verified by laboratory and third-party measurement,FBG accelerometer of medium frequency and high frequency are gotten,measurable frequency ranges are 10-1000 Hz and 10-1500 Hz,sensitivity is46 pm/g and 23 pm/g,linearity can reach more than 0.999,and sensors have a good characteristic of the resisting transverse interference.The main work of this paper:(1)Based on the theory of optical fiber sensing and model and acceleration sensor,different structure and different encapsulating method of sensors are systematically analyzed.FBG accelerometer model based on symmetrical flexible hinge of two-point encapsulated is proposed.(2)Themechanical model of FBG accelerometer based on symmetrical flexible hinge is established.The theoretical formula of the sensitivity and resonant frequency of the sensor is deduced.The effects of the structural parameters on the sensitivity and resonance frequency is discussed.Through the finite element analysis,the modal analysis and harmony analysis of the sensor is done,and the validity of the theoretical formula is verified.(3)Encapsulating model of FBG accelerometer based on symmetrical flexible hinge is built.And the calibration experiments were carried out.The experimental contents include the experiment of sensitivity calibration of the sensor,the experiment of the amplitude-frequency response,the experiment of the transverse interference and the experiment of temperature coefficient calibration.(4)The FBG accelerometer is used for detection of the bearing and compared with the piezoelectric acceleration sensor.The experimental results show that the sensor can effectively identify the typical fault characteristic signal of the bearing and can meet the need of the actual and high frequency vibration test.