Enhancing thermal reliability of fiber-optic sensors for bio-inspired applications at ultra-high temperatures

The rapid growth of bio-(inspired) sensors has led to an improvement in modern healthcare and human-robot systems in recent years. Higher levels of reliability and better flexibility, essential features of these sensors, are very much required in many application fields (e. g. applications at ultra-high temperatures). Fiber-optic sensors, and fiber Bragg grating (FBG) sensors in particular, are being widely studied as suitable sensors for improved structural health monitoring (SHM) due to their many merits. To enhance the thermal reliability of FBG sensors, thermal sensitivity, generally expressed as alpha(f) + xi(f) and considered a constant, should be investigated more precisely. For this purpose, the governing equation of FBG sensors is modified using differential derivatives between the wavelength shift and the temperature change in this study. Through a thermal test ranging from RT to 900 degrees C, the thermal sensitivity of FBG sensors is successfully examined and this guarantees thermal reliability of FBG sensors at ultra-high temperatures. In detail, f has a non-linear dependence on temperature and varies from 6 : 0 x 10(-6)degrees C-1 (20 degrees C) to 10.6 x 10(-6) degrees C 1 (650 degrees C). Also, FBGs should be carefully used for applications at ultra-high temperatures due to signal disappearance near 900 degrees C.