| Vibration signal measurement sensors are widely used in the fields of structural health monitoring,oil and gas exploration,civil engineering monitoring and microseismic fracture detection,and with the expansion of application fields,vibration sensors also put forward diversified requirements.Along with the maturity of fiber Bragg grating sensing technology,vibration signal detection technology based on fiber Bragg grating（FBG）has gradually attracted the attention of researchers.Because fiber sensor has many advantages,such as small size,anti-electromagnetic interference,corrosion resistance,remote measurement and so on,it provides a new technical scheme for vibration detection sensor.In this paper,the vibration sensing system is studied by using FBG as sensing element.The main contents of the paper are as follows:This paper studies the development background and present situation of microseismic monitoring technology,introduces the common vibration sensor types,and analyzes the basic principle of several traditional fiber optic vibration sensors.Therefore,the working principle of FBG vibration sensor and the method of vibration signal measurement are put forward.The research status of fiber Bragg grating vibration sensing structure is deeply investigated,and the strain and temperature sensing mechanism of fiber Bragg grating is studied.The demodulation method of FBG based on long period fiber grating（LPFG）is presented,the basic working principle and main writing methods of long period fiber grating are introduced,and several grating formation mechanisms of writing fiber grating are discussed.The experimental device of CO2laser writing grating was set up,and the factors affecting the performance of grating transmission spectrum were analyzed by simulation and experiment.In order to realize the high precision demodulation of the central wavelength of Bragg fiber Bragg grating by writing the long-period fiber grating,In this paper,the writing method of LPFG（long-period fiber gratings）was studied and compared,and the CO2laser was successfully used to fabricate long-period fiber gratings with a peak loss amplitude of 25dB.Using the long-period fiber Bragg grating as a demodulation device,an experimental system was built to test its stress and temperature response characteristics.The cantilever beam type metal strain gauge was used as a sensing system,and the FBG was pasted on its surface as a sensitive element to test its dynamic response characteristics.The experimental results show that the edge filter demodulation method based on long-period fiber Bragg grating is not only easy to manufacture,but also has a good linear dynamic range,and can achieve high demodulation precision in the demodulation of FBG reflection wavelength.A novel fiber Bragg grating（FBG）acceleration sensor with the double-hinge structure is designed and analyzed.The influence of the structural parameters on the sensor characteristics is determined theoretically and the structural parameters are optimized by the finite element method.By adopting the optimal structural parameters,the double hinge structure is prepared with 304 stainless steel and the FBG which is pasted on the surface of the two hinges is used to measure the acceleration sensing characteristics.The experimental results reveal the vibration frequency measurement range of the sensor is 50～600 Hz,the acceleration sensitivity at 600 Hz is 300 m V/g,and the resolution is 1 mg/Hz1/2.At the same time,by optimizing the hinge structure parameters and the demodulation scheme,the operating frequency range and sensitivity can be improved to achieve the purpose of wide dynamic response range and high sensitivity. |
