Magnetostrictive Behavior of Metglas® 2605SC and Acoustic Sensing Optical Fiber for Distributed Static Magnetic Field Detection

Fiber optic technologies have strong potential to augment and improve existing areas of sensor performance across many applications. Magnetic sensing, in particular, has attracted significant interest in structural health monitoring and ferromagnetic object detection. However, current technologies such as fluxgate magnetometers and inspection gauges rely on measuring magnetic fields as single-point sensors. By using fiber optic distributed strain sensors in tandem with magnetically biased magnetostrictive material, static and dynamic magnetic fields can be detected across long lengths of sensing fiber. This paper investigates the relationship between Fiber Bragg Grating (FBG)-based strain sensors and the magnetostrictive alloy Metglas® 2605SC for the distributed detection of static fields for use in a compact cable design. Sentek Instrument’s picoDAS system is used to interrogate the FBG based sensors coupled with Metglas® that is biased with an alternating sinusoidal magnetic field. The sensing system is then exposed to varied external static magnetic field strengths, and the resultant strain responses are analyzed. A minimum magnetic field strength on the order of 300 nT was able to be resolved and a variety of sensing configurations and conditions were also tested. The sensing system is compact and can be easily cabled as both FBGs and Metglas® are commercialized and readily acquired. In combination with the robust and distributed nature of fiber sensors, this demonstrates strong promise for new means of magnetic characterization.