| Magnetic field sensors are widely used in storage,navigation,medical and other fields.In recent years,the research on the resonant magnetic field sensors based on MEMS technology has received widespread attention.In the early stage,the research group combined the magnetostrictive material with a quartz tuning fork resonator with force-frequency conversion characteristics,and designed a resonant magnetic sensor with magneto-force-frequency conversion.In order to increase the magnetic-force-frequency conversion coefficient,this paper improves the sensor performance from the perspective of improving the magnetostrictive performance,that is,improving the magnetic-force conversion capability.The main work is provided as follows:Fe Ga alloy with large saturation magnetostriction coefficient and small hysteresis is selected as the magnetic sensitive material.The demagnetization factors of Fe Ga magnetostrictive alloys with the same cross-sectional area and different lengths are analyzed by conbining the empirical formula of demagnetization factor and Maxwell electromagnetic simulation.And the influences of demagnetization on the magnetostrictive properties of Fe Ga alloy and the sensitivity of the resonant magnetic sensor are analyzed and predicted.The demagnetization factor decrease and sensitivity increase with the increase of the length of Fe Ga alloy,respectively.The sensitivities of the sensor with different lengths of 10.6mm,20 mm and30mm are 3.7Hz/Oe,5.8Hz/Oe and 9Hz/Oe,respectively.And the magnetic field when the sensitivity reaches the maximum value decreases with the increase of length,which are 230 Oe,150 Oe and 60 Oe,respectively.According to the nonlinear constitutive equation of the magnetostrictive material,the influence of different prestresses on the magnetostrictive response curve of Fe Ga alloy is analyzed,and the prestressed structure is designed.The magnetostrictive plate with proper compressive pre-stress has better magnetostrictive performance;The sensitivity in the linear region is determined to be 2.85 Hz/Oe,6.86 Hz/Oe,and 5.43 Hz/Oe when Fe Ga alloy is prestressed with 0MPa,4.8MPa,and 9.6MPa,which is increased by 2.4 times and 1.9 times to 2.85 Hz/Oe.And field resolution in the linear region is30 n T.Considering the influences of prestress and demagnetization,a differential resonant magnetic sensor is designed,which can effectively reduce temperature interference.Permanent magnets provide bias magnetic fields of the same magnitude and opposite directions for the two sensitive units respectively,and temperature interference plays a common mode effect.Therefore,the sensitivity of the sensor is the superposition of the sensitivity of the two signals,and the temperature interference is suppressed.The fabricated device show that: 1)The sensitivity of the magnetic sensor first increases and then decreases with the increase of the prestress,which reaches the maximum after loading the 7.2MPa prestress;2)In the linear region the sensitivity,resolution of the 10.6mm sensor is 7.6Hz/Oe,30 n T,respectively;3)In the linear region the sensitivity,resolution of the 30 mm sensor is 32Hz/Oe,10 n T(DC magnetic field),12 n T(AC magnetic field),respectively;4)The temperature fluctuation after the differential output is greatly reduced,effectively restraining the influence of temperature drift. |
