Fiber Magnetic Field Sensor With Extended Linear Measuring Range Based on Magneto-Shape Effect

The linear measuring range is limited by the relative magnetic permeability of magnetic fluid (MF) in tradition fiber magnetic field sensors utilizing MF refractive index modulation effect. The article proposes a fiber optic sensor with the help of MF magneto-shape effect, which can extend linear measuring range. The magneto-shape effect is not only related to the relative magnetic permeability of MF, but also to the magnetic field distribution on the concave, which can expand the linear measurement range of magnetic field. The sensing probe consists of single mode fiber (SMF)-air-MF-air-SMF. The measuring range of sensing structure can reach 402.1 Gs, the sensitivity is 180 pm/Gs from
$0\sim 205.9$
Gs and 81 pm/Gs at
$205.9\sim 402.1$
Gs. The response times of structure reach 50 ms and 137 ms at 45.5 Gs and 91.2 Gs, respectively. In addition, the linear measurement range of structure with magneto-shape effect is twice as high as that based on magneto-refractive index modulation effect under the premise of using the same MF. The sensing structure possesses the characteristics of fast response time, highly sensitive and large linear measurement range.