High sensitivity fiber optic magnetic field sensor composed of Terfenol-D powder coated on the surface of Fabry-Perot cavity

This paper proposes and validates a high-sensitivity fiber optic magnetic field (MF) sensor based on strain-sensitive Fabry-Perot interferometer (FPI) combined with Terfenol-D powder. Firstly, FPI 1 , FPI 3 , and FPI 4 were designed using single mode fiber (SMF), quartz capillary, and thin core fiber (TCF). They have a TCF cantilever beam structure inserted inside their capillaries, achieving extremely high axial strain sensitivity. FPI 1 and FPI 3 have almost the same cavity length. The cavity length of FPI 4 is longer than that of FPI 3 . Then, the PDMS glue and Terfenol-D powder mixture is evenly coated on the surface of FPI 1 , and the AB adhesive and Terfenol-D powder mixture is evenly coated on the surfaces of FPI 3 and FPI 4 . By utilizing the excellent stretchability of Terfenol-D material under MF action, it is converted into axial strain acting on FPI 1 , FPI 3 , and FPI 4 , enabling them to indirectly measure MF. The MF sensitivities of FPI 1 , FPI 3 , and FPI 4 measured experimentally were 9.17 pm/mT, 24.35 pm/mT, and 2.98 pm/mT, respectively. The results showed that the sensitivity of FPI 3 coated with the mixture of AB glue and Terfenol-D was highest, while FPI 4 with a longer cavity length than FPI 3 has lower sensitivity. To achieve higher MF sensitivity, we prepared FPI 2 using SMF and capillary splicing. Then, FPI 1 parallels with FPI 2 to produce vernier effect (VE) sensor S 1 . FPI 3 parallels with FPI 2 to produce VE sensor S 2 . The MF sensitivity of S 1 and S 2 reached −149.76 pm/mT and −294.05 pm/mT, respectively, which increases the sensitivity of FPI 1 and FPI 3 by 16 and 12 times, respectively. This new sensor structure composed of Terfenol-D powder has compact size, good repeatability and stability, and high MF sensitivity, indicating that this sensor has good application prospects in the field of MF measurement.