| Fiber grating is a spatial phase grating formed in the fiber core based on the photosensitivity of fiber material.As a wavelength modulation passive device,fiber grating has the advantages of anti-electromagnetic interference,high temperature and high pressure resistance,corrosion resistance,multi-parameter measurement and easy networking and multiplexing,therefore it has attracted extensive research and attention in the field of optical sensing.Generally,it is necessary to detect vibration in the fields of oil and gas resource exploration and development,structural health monitoring,aerospace and transportation.However,the traditional sensors for measuring vibration acceleration have shortcomings such as poor anti-electromagnetic interference ability,poor stability and difficulty in realizing distributed measurement.Applying fiber grating sensing technology to the above fields to measure vibration acceleration has vital research significance and practical value.In this paper,the research of FBG(Fiber Bragg Grating)accelerometers with medium and high resonant frequencies is carried out in view of the development goals of small and compact FBG accelerometers with wide frequency band and high sensitivity,which is based on the analysis of the research status of FBG accelerometers and the sensing principle of fiber grating.The main contents are as follows:(1)The research and development status of FBG accelerometers are studied,and the coupled mode theory of fiber grating and the sensing principle of strain and temperature of FBG are analyzed.The mechanical model of the accelerometer is established,and its amplitude-frequency and phase-frequency characteristics are analyzed.On this basis,the working principle of the FBG accelerometer is studied.The main performance parameters of the FBG accelerometer and the issues that need to be paid attention to in the sensor package are analyzed,which provides guidance for the subsequent design and research of FBG accelerometers.(2)A single-hinge FBG accelerometer is studied.The working principle of the sensor is theoretically analyzed,and then the influence of the main structural parameters of the sensor on the resonance frequency and sensitivity is analyzed.The numerical simulation analysis of the sensor is carried out by using finite element software,and the performance of static bending,dynamic sensing and temperature effect of the sensor is experimentally studied.The results show that the sensor has a good linear response to static bending;the sensor has a good response to acceleration with a flat region of50～950 Hz for the amplitude-frequency response,and the sensitivity is about 10 pm/g;in the temperature range of 30～100~oC,the sensor has a good response to temperature with low sensitivity;the sensor is small and compact,but the ability to resist transverse interference is poor.(3)A symmetrical double-hinge based FBG accelerometer is proposed and researched to improve the sensing performance of the single-hinge based FBG accelerometer.The working principle of the sensor is theoretically analyzed,the packaging fabrication method and process of the sensor are clarified,and the acceleration sensing performance of the sensor is experimentally studied.The results show that the amplitude-frequency response of the sensor is relatively flat in the range of 50～600 Hz,and the FBG wavelength drift has a good linear relationship with the acceleration;due to the design of the symmetrical sensitization structure,the sensitivity of the sensor is about 41pm/g with good repeatability compared with the single-hinge based FBG accelerometer;the cross-sensitivity of the sensor is less than 5.5%of that in the main vibration direction,and the anti-transverse interference performance of the sensor has been effectively improved.(4)Based on the symmetrical double-hinge structure and dual FBG differential motion,a dual grating temperature compensation FBG accelerometer is proposed,designed and studied,which can solve the strain-temperature cross-sensitivity problem in hinged FBG accelerometers.The working principle of the sensor is theoretically analyzed,the vibration mode of the sensor is studied and analyzed by the finite element software,and the acceleration sensing performance of the sensor is experimentally studied.The research shows that the sensor has a good flat zone in the range of 50～800Hz,and has a good response to acceleration,the average sensitivity is about 48 pm/g with good repeatability;the temperature compensation can be achieved within the range of 27～88~oC,which verified the validity of the sensor design.(5)A Y-beam based FBG accelerometer is investigated.The working principle of the sensor and the influence of structural parameters on the resonant frequency and sensitivity of the sensor are theoretically analyzed,and the acceleration sensing performance of the sensor is experimentally studied.The results show that in the range of 50～400 Hz,the sensor has a good flat zone of amplitude-frequency response,and has a good linear response to acceleration with the sensitivity of 57.4 pm/g;in the range of25～85~oC,the temperature response of the sensor is stable with a lower sensitivity of10.4 pm/~oC.The sensor is compact with higher sensitivity,and has the feature that the sensitivity can be adjusted by replacing the mass block while the main structure is unchanged.After progressive research on improvement,the performance of the designed and researched FBG accelerometers has been enhanced,laying a foundation for practical application. |
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