Enhanced sensitivity of magnetic field vector sensor by using UV adhesive-based Fabry-Perot cavity and vernier effect

We have developed a super sensitive fiber optic magnetic field (MF) vector sensor based on a special Fabry-Perot interferometer (FPI) bonded with Galfenol (FeGa) magnetostrictive material. FPI formed by cold fusion splicing of two aligned single-mode fibers with industrial ultraviolet (UV) adhesive has a particularly strong structure. Due to the excellent elastic deformation of industrial UV adhesive, FPI has high sensitivity to axial strain. Then, FPI is straightened and fixed onto the Galfenol rod. Due to the excellent tensile properties of Galfenol rod under the action of MF, so FPI also has high sensitivity to MF. Galfenol rod has a small size, strong elasticity, better toughness, and less prone to fracture, making it more suitable for industrial applications. The experiment found that the MF sensitivity of FPI reached 0.59 nm/mT. Finally, a vernier effect (VE) sensor S1 and a harmonic vernier effect (HVE) sensor S2 were constructed using optical VE technology and FPI. The experiment found that the sensitivities of S1 and S2 to MF strength were -6.48 nm/mT and 19.92 nm/mT, respectively. Additionally, the amount of stretching amount of the Galfenol rod is related to the magnitude and direction of the MF force acting on it. Therefore, the proposed sensors can also determine the direction of MF. In short, the combination of Galfenol rod and special FPI to achieve ultra-high sensitivity MF vector measurement is a latest alternative solution to MF vector measurement.