Research On Weak Magnetic Field Sensor Based On Magnetoelectric Coupling Effect

Since the beginning of this century,with the in-depth research of multiferroic materials,magnetic field sensors based on magnetoelectric coupling effect have advantages such as high sensitivity,low cost,easy miniaturization and integration compared with other magnetic field sensors,and become the research focus in the field of weak magnetic field signal detection.In this paper,the work is carried out from the sensor preparation,the construction and optimization of the test system,the influencing factors of sensors'performances and the detection of weak magnetic signal,etc.The main research results are as follows:1.Preparation and characterization of magnetoelectric coupling sensor materials and construction of test systemLead zirconate titanate Pb(Zr,Ti)O₃piezoelectric ceramics(PZT)with high purity and good piezoelectric properties were prepared by solid state sintered technology.The piezoelectric coefficient d₃₁reached-280 pC/N,and the dielectric loss tan?=1.5%.FeCoB ferromagnetic thin films with good soft magnetic properties(H_c=12 Oe)and high flatness(0.521nm)were prepared by magnetron sputtering.After the sensor was prepared by adhesive with epoxy resin or sputtering,the test system based on magnetoelectric coupling effect was built independently and optimized in this work:Firstly,a set of ME based measuring device was built,which can collect and process a series of output AC/DC signals of the sensor,and then obtain the important performance indexes such as magnetic field resolution,sensitivity,linearity,output waveform and power spectral density of the sensor.The shock absorption-vacuum-magnetic shielding device can effectively reduce the interference of external vibration noise and magnetic noise on the output signal of the sensor,thus improving the measurement accuracy.And a resistance strain gauge measuring device was built to measure and characterize the magnetostrictive properties of ferromagnetic materials.The charge amplifier(AD745)amplifies the small amount of charge generated by the sensor,thus increasing the sensitivity.The second order low pass filter circuit can filter out the high frequency noise when measuring the low frequency signal.AC signal can be converted to DC signal by full wave precision rectifier circuit.The application of these three electronic devices plays a gain effect on the measurement of the signal,so that the performance of the test system is optimized.Sensor preparation and test system construction are the prerequisites for the follow-up work.2.The exploration of influencing factors based on the performances of magnetoelectric coupling sensorThe exploration was carried out from the sensor's working environment(including the measuring frequency and DC bias magnetic field)and the materials(including the size and structure of the material,the anisotropy of ferromagnetic materials,doping modification of piezoelectric ceramic and polarization of piezoelectric ceramic),and a number of conclusions were drawn,which lays a foundation for the follow-up measurement of weak magnetic field signals.3.Weak magnetic field detection based on magnetoelectric coupling effect(1)The PZT/Fe Co Si B Metglas magnetoelectric coupling sensor whose resonant frequency is 72.2 kHz was prepared,and the resolution is less than 1.0 nT in the frequency range of 70.0-73.4 kHz,which has high practical application value;(2)The sensor works at the optimal working point where the sensor is at resonant frequency and most sensitive to changes in the external magnetic field.The working point perturbation method is used to measure the DC resolution.As a result,a DC resolution of 0.9 nT was measured in the prepared PZT/Fe Co Si B Metglas magnetoelectric coupling sensor.And the noise power spectral density of the sensor was as low as 0.1 nT Hz;(3)Frequency modulation method is used to preserve the high ME performance of the sensor at resonant frequency and reduce the impact of 1?f noise effectively.Based on this measurement method,the prepared PVDF/FeCo SiB Metglas magnetoelectric coupling sensor obtains the AC resolution of 0.8,1.6,3.2,8 and 16 nT at 84,11,6,0.8 and 0.1Hz respectively,the white noise level of the sensor is approximately 50pT(Hz)^1/2.