A Simple Passive Arc-Shape Temperature-Independent Load Sensor Using a Pair of Fiber Bragg Gratings

Abstract

In this paper, a novel arc-shape FBG (Fiber Bragg Grating) load sensor is developed with a pair of FBGs embedded symmetrically in an elastic bending beam. The FBG pair is produced with peak wavelength separation of about 0.4 nm. The FBG with shorter wavelength is located above the neutral layer and another with longer wavelength below the neutral layer. As a result, the two peak wavelengths of the FBG pair move apart with lateral force applied but move together in the same direction when surrounding temperature varies, both in a linear manner. A very low temperature-dependency of only 0.04 pm/ C across the temperature range from 35 C to 82 C has been achieved, which makes it suitable for dynamic lateral force measurement even when the environmental temperature varies. Due to the fact that the sensor module consists of only the grating fiber with two FBGs and some elastic material, which are purely passive components, hence, the temperature effect of this sensor can be self-compensated without a need of any active temperature controller or other temperature-isolation mechanism, thus in principle, this sensor module is passively temperature-independent.

Proof-of-concept study of bolt connection status monitoring using fiber Bragg grating curvature sensor

“…Nevertheless, the temperature also leads to a wavelength shift of the FBG. Therefore, in applications, the temperature effect on the measurement can be compensated by using an additional FBG to monitor the temperature [52] or by directly using a temperature-independent curvature sensor [53].…”

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

“…FBG is sensitive to both temperature and strain, which makes it complicated to measure each variable independently. When FBG is used for temperature measurement, it is necessary to use packaging and other methods to deal with the influence of strain on wavelength drift [1]. In order to ensure the uniformity and accuracy of the sensor values, the newly developed sensor must be calibrated and tested before it can be applied.…”