Low temperature characteristics of FBG with free arc shape for low temperature monitoring

Abstract

It is important to monitor the iced condition for operating wind turbine blades. However, most sensors are difficult to be used in this quite cold and lightweight environment. Although the fiber bragg grating (FBG) is a good candidate for the case. With the change of the temperature, the thermal expansion coefficient and thermo-optical coeffecient of FBG material will affect the accuracy of characteristics of FBG sensor. Aiming at the application of fiber optic sensor in low temperature environment and ultrathin requirement, the low temperature characteristics of FBG sensor with free arc shape package has been studied. The low temperature calibration experiments of two packaged FBG samples are tested from -35°C ~20°C in a constant temperature freezer with alcohol tank. The effects of low temperature characteristics of two FBGs packaged with free straight and arc shape tubes are compared. The results show that arc shape can effectively reduce the repeatability error and improve its accuracy due to providing possible low temperature contracting of the optical fibers. Flat arc shape makes it possible to package ultrathin FBG temperature sensor.

Strain transfer characteristics of fiber Bragg gratings at ultra-low temperature

“…Latka I explored the temperature characteristics of FBG on substrates with different CTE, demonstrating that these special substrates are usable for temperature measurements well below 50K 1 ; Guo ZS investigated the characteristics of strain and temperature of FBG in the temperature range of 123-273 K. Experiments showed that the relationship between wavelength change and temperature can be expressed by a third-order polynomial, and the wavelength is linearly related to the strain, so it is believed that the FBG can realize high-precision strain measurements at low temperatures 2 ; Guo T used FBG connected to an F-P interferometer to realize a large strain measurement of 1.5^10 7 με at low temperatures ranging from 20°C to 70°C 3 ; Yang T researched the strain transfer characteristics of multilayer fiber optic sensor structures at low temperatures, and experiments showed that different temperature loads or lead to different strain transfer errors 4 ; Zhang Z used an FBG strain sensor encapsulated by a double fixture tube and a stainless steel tube for monitoring the structural safety of bridge cranes at low temperatures 5 ; Lu Huanlang investigated the sensing characteristics of encapsulated FBG at low temperatures using a free-arc shape, and experimental results showed that the electric arc shape could improve the precision of fiber shrinkage 6 .…”