High-Resolution Magnetic Field Sensor Utilizing a Fabry-Perot Cavity Assembled on Terfenol-D Slab

We propose and experimentally demonstrate a novel, high-resolution, and high-sensitivity magnetic field sensor based on an extrinsic Fabry-Perot interferometer (EFPI), where two precisely-cleaved single-mode fibers (SMFs) are meticulously bonded face-to-face with a precise gap on the surface of a Terfenol-D slab to form a Fabry-Perot (FP) cavity. Variations in magnetic field intensity will directly change the length of the magnetostrictive material, thereby leading to a substantial phase difference variation between the two reflective mirrors of the EFPI. Instead of using the traditional wavelength demodulation method, which suffers from the drawback of very limited resolution due to the use of optical spectrum analysis devices, such as optical spectrum analyzers (OSA), the proposed sensor is interrogated by a microwave photonics filter (MPF) system, which is capable of providing significantly enhanced measurement resolution at the KHz level. As a result, the proposed sensor exhibits a high-sensitivity response over the measurement range of 0 to 217.06 mT. Particularly, within the range of 11.424 mT to 24.276 mT, the sensor achieves a maximum sensitivity of 4.61 MHz/mT and an impressive resolution of 54.23 μT. Compared with the traditional optical wavelength demodulation method, the proposed sensor exhibits a more than 22-fold increase in resolution and over a hundredfold improvement in the measurement range. Moreover, the MPF system has been demonstrated to surpass the traditional optical wavelength demodulation method in multiplexing ability, which can measure multiple EFPIs simultaneously, achieving quasi-distributed, high-resolution magnetic field measurements. The proposed sensor possesses unique advantages of high sensitivity, superior resolution, and multiplexing ability over the state-of-the-art technology, which is very promising for high-precision magnetic field intensity measurement in the future.