Sensing with Geometry-Dependent Magnetostriction Via an Embedded Fiber Bragg Grating

Abstract

Fiber optic current sensors (FOCSs) have unique advantages in electromagnetic interference immunity and direct current measurements. Here, magnetostrictive composites and their interactions with embedded ber Bragg gratings (FBG) were explored to form novel FOCSs with predictable and temperature-independent sensitivity. Magnetostrictive, particularly Terfenol-D/epoxy, composites maintain the mangetostrictive expansion under an external magnetic eld while gaining exibility in engineering. In contrast to ordinary strain gauges, an embedded FBG can provide an optical signal inferring simultaneously a strain and its gradient inside a composite. In principle, the sensing of strain gradient is thermally independent. Creating appropriate geometries for magnetostrictive composites enables the conversion of a uniform external magnetic eld into an internal one with a certain eld gradient that enacts a strain distribution inside the composite transferred to the FBG. Hence, the strain gradient sensing with the FBG can be exploited for temperature independent measurement of the external magnetic eld. Such a strain gradient will alter the spectral properties of the FBG, such as the power and bandwidth of the returned optical signal. The experimental results from two separate sensors have conrmed the trend that is predicted by the theory and simulations. They will substantiate the claim of sensitivity tuning solely with geometry. These FOCSs will provide reliable reading for wide operating temperatures if the underlying materials allow.