High-Sensitivity PDMS Film-Based Fabry–Pérot Interferometer for Magnetic Field Sensing via Magnetic Fluid Volume Effect

reflective fiber-optic magnetic field sensor based on the magnetic fluid (MF) magnetic volume effect is proposed. The sensor incorporates a Fabry-Pérot (F-P) interference structure formed by a single-mode fiber (SMF) and a polydimethylsiloxane (PDMS) film. By detecting the volume changes of MF under varying magnetic field strengths, the sensor achieves highly sensitive magnetic field measurement. When exposed to an external magnetic field, the nanoparticles in the MF undergo oriented alignment, resulting in anisotropic volume changes. These changes are transmitted to the F-P air cavity via the PDMS film, enabling precise measurement of magnetic field intensity. Experimental results demonstrate that with a 48.4 μm-thick PDMS film, the sensor achieves axial and radial magnetic field sensitivities of -2.3 nm/mT and -2.73 nm/mT, respectively, within the 0-12 mT range. Furthermore, we observed that reducing the PDMS film thickness significantly enhances magnetic field sensitivity. After optimization to 46.92 μm, the sensor achieved a radial sensitivity of -9.40 nm/mT, a detection limit of 0.0021 mT, and excellent linearity (R2= 0.9988). The sensor combines the advantages of simple structure, high sensitivity and low fabrication cost, which provides a new solution for magnetic field measurement in the fields of power equipment monitoring and aerospace.