Tri-axial magnetic field mapping via magneto-strain modulated whisk-shaped fiber interferometer

A tri-axial magnetic field fiber optic sensor based on a whisk-shaped single-mode fiber (WSMF) coated with soft magnetic elastomer is proposed. The sensor operates by exploiting the magneto-straining effect of Fe₃O₄@polydimethylsiloxane (PDMS) composite under an external magnetic field, combined with two orthogonally arranged balloon-like single-mode fiber (BLSMF) structures. When the fiber is bent into a balloon-like shape, variations in the refractive index distribution of the cladding and core induce optical leakage, forming a Mach-Zehnder interferometer. Finite element analysis reveals that a single Fe₃O₄-PDMS-coated BLSMF exhibits anisotropic deformation characteristics under the magnetic field. By cascading two BLSMFs in orthogonal configuration, the dip shift of the resonant wavelength is correlated not only with the magnitude of the magnetic field but also with its direction. This demonstrates that the whisk-shaped SMF configuration enables three-dimensional magnetic field measurement. In this study, the mass ratio of Fe₃O₄ nanoparticles in preparing the magnetic elastomer was varied from 10% to 50%. The optimized tri-axial magnetic field sensor achieves a magnetic sensitivity of 242.1 pm/mT and a rapid response time of 0.28 s. The proposed sensor shows great potential for applications in intelligent robotic control and human-machine interactions.