Research On Fiber Bragg Grating Accelerometer In Microearthquake

With the in-depth study of geological and mineral exploration,microseismic monitoring technology has become an important means to identify and evaluate the macro damage and fracture degree of rock.The results are not only the key basis for the prevention of dangerous structures such as nuclear waste disposal and dams,but also the important support for the research of rock burst,mine water inrush and other mine dynamic disaster prediction technology.As a key device in the microseismic monitoring technology,the performance of accelerometer is very important whether it can effectively monitor the microseismic signals with large frequency coverage,weak energy and short duration.Fiber Bragg grating(FBG)acceleration sensor has the advantages of anti magnetism and anti explosion,high sensitivity and easy long-term monitoring.It has unique advantages in the measurement of medium and high frequency microseismic acceleration signal.However,scholars at home and abroad have done a lot of research on low-frequency sensors,and the research on medium and high-frequency sensors is still insufficient compared with the low-frequency field.Simultaneously,there are some problems in the existing medium and high-frequency FBG acceleration sensors,such as narrow measurement band,low sensitivity and poor anti-interference ability,which seriously affect the quality of monitoring results.In order to improve the performance index of medium and high frequency FBG acceleration sensor,the hinged FBG acceleration sensor is studied in this paper(1)This paper describes the characteristics of microseismic monitoring technology,summarizes the domestic and foreign optical fiber sensing technology and different types of FBG acceleration sensors,analyzes the vibration characteristics of FBG acceleration sensors,and summarizes the packaging methods of existing FBG acceleration sensors.(2)FBG acceleration sensors based on L-shaped bracket structure and symmetrical hinge structure are studied and designed.The theoretical formulas of resonant frequency and sensitivity of the two sensors are derived through mechanical analysis.The influence curve of structural parameters of the sensor on resonant frequency and sensitivity is obtained by using MATLAB to select the size parameters of the sensor,Finally,ANSYS finite element simulation is used to verify the theoretical model.(3)The vibration experimental system of FBG acceleration sensor is constructed,and the experimental performance of the two sensors is tested.The results show that the FBG accelerometer based on L-shaped bracket structure has a good flat response at 50-1000 Hz,with a sensitivity of 18 pm/g and a lateral disturbance of 8.87%.The FBG accelerometer based on symmetrical structure has a good flat response at 50-900 Hz,the sensitivity is about 18.92 pm/g,and the lateral disturbance is 9.05%.(4)In order to solve the problem of insufficient anti lateral interference ability of the hinge type accelerometer,a hinge type accelerometer based on double elastic plates is proposed.The mechanical model of the sensor is deduced and the modal simulation analysis is carried out by ANSYS.The sensor is developed and tested in the vibration experiment system.The results show that the hinged accelerometer based on elastic plate has a good flat response at 50-700 Hz,and its sensitivity is about 19.7 pm/g,and the lateral disturbance is 5.15%.