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.

A flare system in oil platform is a combustion stack used to burn off excess gases that cannot be processed and gases that have to be eliminated in emergency shutdown to avoid the risk of explosion. Gas flow measurement in flares is still considered challenging because the measurement has to attend many specific demands, quite different from any other flow measurement application. For these types of measurements many sensor technologies are available, however they are all very expensive, and only a few ones can attend all demands. The objective of this paper is to present a flow rate sensor based on Fiber Bragg Grating (FBG), cross-correlation and heatwave travel time techniques. The system was developed with inexpensive components and is little-intrusive, capable of attaining the rangeability of the flare demand and independent of gas composition, pressure and temperature.

In this letter, we performed finite element method (FEM) simulations, fabrication, and experimental characterization of two prototypes of fiber-optic current sensors (FOCS) based on fiber Bragg grating (FBG) and Terfenol-D for monitoring current in high-voltage transmission lines. The proposed prototypes were designed in geometrical configurations that allowed a massive reduction of more than 98% in the amount of Terfenol-D employed compared to FBG-based FOCS proposed previously. Using only 5.6 and 2.0 g of Terfenol-D in each prototype, we show that not only the cost of the sensor can be reduced but also greater sensitivity, linearity, and fast response-time to transient events were achieved.

In this paper, a compact fiber-optic current sensor (FOCS) based on in-fiber Fabry-Perot interferometer (FPI) and magnetostrictive transducer is presented. The in-fiber FPI sensor employed in the proposed FOCS was fabricated with a 273-μm section of capillary fiber spliced between two pieces of standard single-mode fiber (SMF). The in-fiber FPI sensor and a commercial fiber Bragg grating (FBG), which was used as a reference sensor for sensitivity comparison, were bonded to a small magnetostrictive actuator (Terfenol-D) and assembled in the proposed FOCS for electric current monitoring up to 800 A _rms using a commercial FBG interrogator. The in-fiber FPI sensor presented a sensitivity 84.4% higher than that of the FBG sensor. An alternative interrogation system based on an edge-filter technique with temperature compensation was also developed and employed for characterization of the proposed FOCS under the same range of electric current. Using the edge-filter interrogation system developed, the in-fiber FPI sensor presented a sensitivity 169.8% higher than that shown by the FBG. The results show that the proposed FOCS using an in-fiber FPI sensor presented high sensitivity to electric current sensing and, therefore, is a potential candidate for current monitoring in complement to conventional current transformers (CTs) as well as to conventional optical current transformers (OCTs).