Study And Design Of A Three-axis Fiber Bragg Grating Accelerometer Based On Pull-push Mechanism

A new kind of seismic wave detection method has emerged recently using fiber optic sensors. The advantages of fiber optic sensors are high sensitivity, immunity to electromagnetic interference, excellent insulating ability, etc. Therefore, fiber optic sensing is a powerful technology with wide spread in applications in the area of earthquake prediction, seismic exploration for oil and gas and security. Fiber Bragg grating (FBG) sensors are one of the most exciting developments in the field of optical fiber sensors in recent years.The thesis presents an overview of FBG sensor technology regarding many aspects including sensing principles, properties and interrogation. A three-axis fiber Bragg grating (FBG) accelerometer which has uniform sensitivities to three axes was developed for seismic application. This paper presents the design, simulation and calibration of the three-axis accelerometer. A series of experiments were performed to measure harmonic vibration and shock vibration.Firstly, a single-axis FBG accelerometer with intensity modulation-direct detection interrogation system was put forward and designed in the paper. Experiments with different excitation frequencies were implemented, which demonstrate its good mechanical structure and fabrication technology. Accordingly, a novel three-axis FBG accelerometer based on the single axis FBG accelerometer was proposed and a series of periodic vibration tests were finished to prove its performance at different excitation frequencies.Then, finite element analysis (FEA) was used to predict the strain distribution on the FBG and the frequency response of the sensor. The simulation was performed utilizing commercial software ANSYS. The results based on FEA model were compared with datum obtained in the vibration experiment. The precise knowledge of the acceleration was measured by PZT accelerometer which provided high sensitivity. The full described dynamic sensitivity of three-axis accelerometers represented by3-by-3matrix was given. The results indicate the accelerometer has a sensitivity of 0.068V/G in a measured full scale±2.5m/s2. The cross axis sensitivity was measured as-75.5dB,-75.5dB and-78.2dB, respectively.Finally, our work is reviewed and the remaining problems are pointed out.