A Resonant Magnetic Field Sensor With High Quality Factor Based on Quartz Crystal Resonator and Magnetostrictive Stress Coupling

A resonant magnetic field sensor is developed by using a piezoelectric quartz crystal double-ended tuning fork (DETF), two FeGa thin plates, and four quartz spacers. The double ends of the DETF are bonded to the ends of the magnetostrictive thin plates through four spacers with adhesive, allowing the magnetostrictive force to be converted into the longitudinal force in the DETF which leads to an increase of the resonant frequency of the DETF. This design brings the advantage of field-independent damping, i.e., the quality factor (Q-factor) of the sensor is found to be independent on the dc field, with an average value of about 3318 in the air due to the low internal loss in quartz. After an initially slow increase before the field reaching ~50 Oe, the resonant frequency of the sensor increases linearly with the increase of the applied dc field before reaching 280 Oe. The total frequency shift, sensitivity of the frequency shift per magnetic field, and field resolution in the linear region are 2.12% (~808.3 Hz), 3.5 Hz/Oe and 8 mOe, respectively. The results demonstrate a possibility and promising to realize a highly sensitive magnetic sensor with high-Q-factor quartz crystal as well as direct digital frequency output.