Thermal Characteristics of FBG Sensors at Cryogenic Temperatures for Structural Health Monitoring

초록

Fiber Bragg grating (FBG) sensors have been applied to many researches on structural health monitoring (SHM) due to many advantages over other fiber optic sensors. Moreover, FBG sensors have a large permissible range of temperature, namely from cryogenic to ultra-high temperature. Generally, many previous researches conducted using FBG sensors were based on the assumption that the coefficient of thermal expansion (CTE) and the thermo-optic coefficient (TOC) of FBG sensors are constants. However, they should be considered variables for higher accuracy when FBG sensors are applied to circumstances with temperature changes. In this paper, CTE and TOC of FBG sensors were precisely investigated from ambient room temperature (20 oC) to cryogenic temperature (-160 oC). For this purpose, a new non-linear relationship between the wavelength shift and temperature change was proposed. From the test results, it was showed that the sum of CTE and TOC had a non-linear dependency on temperature and varied from 5.9 ？e10-6/ oC (20 oC) to 1.6？e10-6/ oC (-160 oC).