Magnetic Field Sensing With Magnetic Shape Memory Alloy and Fiber Bragg Grating on Silica and Polymer Optical Fibers

Optical fiber magnetic field sensors based on magnetostrictive materials have attracted significant interest. However, most existing sensors utilizing optical fibers and magnetostrictive materials have a limited measurement range up to 200 mT, posing a challenge for applications requiring the detection of strong magnetic fields, such as in maglev train systems. In this study, we introduce two magnetic field sensors: one based on a magnetic shape memory alloy-silica fiber Bragg grating (MSMA-SFBG) and the other on an MSMA-polymeric fiber Bragg grating (MSMA-PFBG). These sensors couple magnetic field-induced strain in the MSMA transducer with fiber Bragg gratings (FBGs) inscribed in the silica optical fiber and the polymer optical fiber, respectively. We evaluated the performance of these sensors in terms of sensitivity, measurement range, and saturation magnetic field. The MSMA-SFBG sensor exhibited a linear response with a sensitivity of approximately 2 pm/mT over the magnetic field range from 250 to 550 mT. The MSMA-PFBG sensor demonstrated a sensitivity of 46.02 pm/mT at 400 mT, outperforming Terfenol-D-based magnetic field sensors by about four times in sensitivity. By applying dc bias fields up to 268 mT, the sensitivity of the MSMA-SFBG sensor decreased from 2.01 to 0.56 pm/mT, while the linear measurement range expanded from 250–550 to 50–550 mT. Conversely, the sensitivity of the MSMA-PFBG sensor increased from 2.30 to 18.68 pm/mT at weak magnetic field of 150 mT, although both the measurement range and the saturation magnetic field decreased. These findings suggest that the two proposed MSMA-based magnetic field sensors complement one and other, are well-suited for applications requiring extensive range, and high-sensitivity magnetic field measurements.