Fiber-Optic Current Sensor Based on FBG and Terfenol-D with Magnetic Flux Concentration for Enhanced Sensitivity and Linearity

This paper presents the design, fabrication, and characterization of two compact fiber-optic current sensors (FOCS) based on fiber Bragg gratings (FBG) and the magnetostrictive alloy Terfenol-D. Finite-element-method (FEM) simulations assisted key optimizations in the geometry of similar FOCS proposed previously, allowing the implementation of magnetic flux density concentration techniques that resulted in sensors using very small amounts of Terfenol-D. Two prototypes of FOCS with the same geometry and size were manufactured for performance comparison purposes, one using a 2.21-g solid, bulk bar of Terfenol-D onto which a sensing FBG was bonded, and the other using magnetostrictive polymer composite (MPC) with oriented magnetic domains using only 0.42 g of Terfenol-D powder and epoxy resin with a sensing FBG embedded within the composite block. Both FOCS were characterized with currents of up to 800 Arms, and presented linearity errors smaller than 1% of full-scale range (FSR). The prototypes presented greater sensitivities taking into account that only less than 6% of Terfenol-D was employed in comparison to previous FBG-based FOCS. Transient-responses of the FOCS prototypes were also measured showing that the proposed sensors might be applied not only to current metering, but also to fault detection in high-voltage lines. Temperature compensation methods were also proposed and discussed for the developed FOCS.