Simultaneous load and temperature measurement using Lophine-coated fiber Bragg gratings

This paper presents a single fiber Bragg grating (FBG) sensor that is capable of measuring the axial load and temperature simultaneously. The FBG sensor is coated with a block of recrystallized Lophine, which introduces the bandwidth modulation of the FBG reflectance spectrum. Thermal-mechanical testing of the Lophine-coated FBG sensor under different load and temperature combinations was carried out. It was discovered that the FBG bandwidth is linearly proportional to the applied load and temperature. By fitting the measured FBG bandwidths and central Bragg wavelengths as linear functions of the axial load and temperature, we demonstrated that the axial load and temperature can be inversely determined from the measured reflectance spectrum of a single Lophine-coated FBG sensor. The measurement errors for the axial load and the temperature were found to be ±4 gm and ±4 °C, respectively.