Thermal And Mechanic Sensing And Experimental Study Based On Optical Fiber Grating And Optical Fiber Fabry-Perot For Low Temperature Environment

With the development of science and technology,the level of space technology development in the deep space has become a manifestation of a country's comprehensive strength.In the course of application,aerospace vehicles not only have to withstand extreme external environments such as strong magnetic fields and ultralow temperatures.Therefore,the development of sensors and sensing systems with good temperature tolerance and anti-electromagnetic interference is also a common concern of technicians in the field.The optical fiber measuring instrument has the characteristics of anti-electromagnetic interference,small volume,light weight and high precision.At the same time,the optical fiber sensor has good tolerance to low temperature,which makes it suitable to apply to the extreme environment of aerospace.Low temperature is one of the extreme environments that spacecraft must face when operating,Temperature monitoring of the core part of the spacecraft at low temperatures and liquid level monitoring of the cryogenic liquid fuel of the rocket engine are prerequisites for the normal operation of the spacecraft.Aiming at the demand of thermal and mechanic parameters sensing in low temperature environment,this paper studies thermal and mechanic sensor and sensing system with the low temperature tolerance based on optical fiber grating and optical fiber Fabry-Perot sensing technology,the work mainly includes the following aspects:1.The fiber Bragg grating temperature sensing mechanism is theoretically analyzed.For better use in low temperature environment,the fabrication process is studied,and the fiber Bragg grating sensor with low temperature tolerance and high stability is developed.The temperature response of the sensor without adhesive was verified by experiments in the vacuum environment of-260 °C to 0 °C and in atmospheric pressure of 10 °C to 150 °C.and the stability of the sensing system was analyzed.2.The temperature and pressure sensitivity characteristics of the differential pressure optical fiber Fabry-Perot sensor are theoretically analyzed.The temperature characteristic of the fiber Fabry in the temperature range of-260 ° C to-100 ° C in the vacuum low temperature environment is experimentally studied and compared with the fiber Bragg grating sensor.Experiment results show that the optical fiber Fabry-Perot sensor has good linearity of temperature response at low temperature,which is better than fiber grating.3.The low temperature liquid level measurement is carried out by using the optical fiber Fabry-Perot sensor.The influence of the residual gas in the Faber cavity on the liquid level measurement is analyzed,and the low temperature liquid level experiment is carried out under the low temperature liquid nitrogen environment.The experimental results show that the optical fiber Fabry-Perot sensor has a good linear relationship with the liquid nitrogen level,and the measurement error is less than ±5 mm.Experiments on static and dynamic changes of liquid level in liquid hydrogen have been carried out,which proves the feasibility of the sensor in various low temperature liquid level measurement.