Research On Fiber Bragg Grating Acceleration Sensor Based On Chirp Effect

The measurement of low frequency vibration signals plays an important role in the fields of earthquake warning,health monitoring of large buildings,military anti-submarine and geological exploration.When seismic signals are used as excitation sources,picking up seismic low-frequency vibration signals with fiber grating acceleration sensors is an important means for damage identification and evaluation of buildings.And after the earthquake is often accompanied by physical field coupling thermal,mechanical,magnetic,and so on more complex environment and extreme temperature environment of traditional wavelength demodulation of fiber Bragg grating acceleration sensors are highly susceptible to temperature changes,leading to vibration signal distortion measurement,in view of the fiber grating in the low frequency vibration signal measured on temperature and strain of sensitive issues at the same time,to carry out the address FBG acceleration sensor is sensitive to temperature and strain of the cross,advancing the FBG sensing technology of seismic low frequency vibration acceleration signal of high performance detection is of great significance.Therefore,this paper developed a temperatures-insensitive fiber Bragg grating acceleration sensor by using the chirped effect of fiber Bragg grating under the action of non-uniform stress field.The main contents include:(1)Through theoretical analysis of fiber grating sensing principle and formation mechanism of chirp effect,the response characteristics of power and bandwidth of FBG reflection spectrum under non-uniform stress were studied,and the theoretical model of FBG acceleration sensor was established.Matlab software is used to simulate the reflection spectrum of grating under the action of non-uniform field.On this basis,the non-uniform strain field test system of FBG is built.According to the numerical simulation and test results,the mechanism and influence characteristics of the chirp phenomenon of FBG are obtained.(2)This paper introduces a right-angle beam temperature sensitive FBG acceleration sensor based on strain chirp effect.MATLAB software is used to optimize the structural parameters of the sensor,and ANSYS finite element software is used to simulate and analyze the structural strain and modal characteristics of the sensor.According to the structure optimization parameters and simulation values of the rectangular beam sensor under non-uniform strain field,the real object is made.(3)in view of the rectangular beam chirp FBG acceleration sensor results and the simulation effect is not ideal,in order to better use of chirp effect and improve the performance of the sensor on the basis of the rectangular cantilever improvement is carried out for the cantilever beam structure,designed the sinusoid curvature beam FBG acceleration sensor,using MATLAB software to the sensor structure parameters optimization,using the finite element software ANSYS to strain sensor's structure and modal characteristic simulation analysis.Under the action of gradient strain field,the structural parameters of curved beam sensor are optimized and numerically simulated,and the real object is made.(4)An experimental test system of fiber Bragg grating acceleration sensor based on chirp effect was built for experimental verification.By comparing and analyzing the amplitude-frequency response characteristics,linear response characteristics and temperature stability of the two sensors,the performance parameters of the sensor were obtained by combining the simulation results.The results show that compared with the rectangular beam sensor,the sinusoidal beam sensor is more likely to produce chirp effect and is insensitive to temperature change.The sensitivity of the beam was about 317 pm/g,which is significantly higher than that of the rectangular beam,which is about 256 pm/g.The natural frequency is 56 Hz,which realizes the high performance detection of low frequency vibration signal.