Study On Sensing Characteristic Of Fiber Bragg Grating At Cryogenic Temperature

In cryogenic fields such as aerospace, larger superconducting magnet, natural gas storage and transportation, many materials and components in this extremely complicated environment encounter cryogenic temperature, high magnetic field, high pressure, vacuum and so on. In order to prevent catastrophic accidents due to lack of prediction and monitoring, parameters such as temperature, stress and strain of these materials and components should be monitored in real-time. Fiber Bragg Grating (FBG) sensors, which have the characteristics of high sensitivity, immunity to electromagnetism interference, high reliability, low cost, small bulk, multiplexing capabilities and so on, are ideal sensors for the measurement.According to strain monitoring requirements in practical large cryogenic engineering, and the paper is supported by the Key Program of National Fund (50935005). The cryogenic temperature characteristics, cryogenic strain characteristics and cryogenic packaging process of FBG are studied. The main content and research results are:1. A novel device is designed to conducting the cryogenic temperature measurement experiments of FBG and thermometer. The cryogenic temperature characteristics of FBG are studied by experiments. The wavelengths of FBG are measured and the temperature sensitivities of FBG are obtained in the temperature range from room temperature to cryogenic nitrogen temperature.2. One FBG sensor bonded onto a polymer substrate is designed. The strain sensing characteristics and cryogenic chirp phenomena of FBG sensor are studied by experiments. The FBG sensor has good strain sensing performance. The chirp phenomena of FBG at liquid nitrogen temperature can be eliminated by proper packaging process and sticking process.3. Cryogenic strain characteristics of FBG sensor are investigated with the tensile experiments employed at liquid nitrogen temperature. The valid elastic-optic constant of FBG is measured, which is about 0.99. A real-time strain sensing in fatigue tests of magnet material at liquid nitrogen temperature using FBG sensor is conducted.