Study on FBG Coupling Effects and Absolute Temperature Compensation Technique Based on Long-term Monitoring Data

While optical FBG applied in long-term structural health monitoring (SHM) as strain gauge, temperature influence should be taken into account due to the fact that FBG shows strain and temperature coupling effects and the wavelength change induced by 1 degree centigrade almost equals 10 times that from 1 micro strain, so the valid and reliable temperature compensation technique is in great need for optical FBG to be applied in long-term practical field applications. By now, it is still a question whether FBG is proper for long-term SHM or not because of shortage of long-term monitoring data to illuminate the coupling effects and how to carry out reasonable temperature compensation. In this paper, based on the theoretic analysis of coupling errors, OFBG' strain and temperature cross-sensing properties, the strain sensing properties of FBG in different temperatures and the temperature sensing properties in different strain states, have been studied using experimental data. And the coupling effects caused by both strain and temperature have also been analyzed. Moreover, an absolute temperature compensation technique of the OFBG strain gauge has been brought forward to avoid the crossing coupling effect, and the reliability of this method have been validated through the long-term monitoring data. The test results show that it is valid and reliable for the OFBG to be used as sensing element for long-term SHM.