Research On Magnetoelectric Coupling In Miniaturized Active Magnetic Sensors

In recent years,the weak magnetic detection has been widely used in resource exploration,marine rescue,military defense and other fields,and is an important means of non-acoustic detection.Among them,the magnetic sensor based on the magnetoelectric coupling effect has the advantages of high sensitivity and miniaturization,is becoming a powerful tool in weak magnetic detection.The sensitive element of the magnetoelectrically coupled magnetic sensor is a magnetoelectric composite structure,and there are two mainstream designs of structures called 2-1structure and 1-1 structure.Among them,the 2-1 structure has good detection performance at low frequency,but its performance is severely limited in resonance state.The 1-1 structure is more suitable for the magnetic target in the resonance state,and it perform badly in the detection of low-frequency targets.Aiming at this problem,this paper designs a fishtail structure that can take into account the detection capability at low frequency and resonance state.The design is completed by simulation,and then the device is fabricated and verified by experiments.This thesis firstly carries on the simulation analysis to the magnetoelectric composite structure.The simplified model is simulated and calculated by using the magnetic concentration effect in the magnetic design and the modal analysis in the structural mechanics;comprehensively considering the two factors of the magnetic and structural mechanics,the amplitude-frequency response analysis of the model is carried out,and the results are obtained that called fishtail design with good detection ability at low frequency and resonance;select the appropriate optimization solver,and use the iterative optimization method to obtain its optimal size.The structure that satisfies both shape optimization and size optimization is named Design No.1,and its geometric size can be expressed as:a=0.2cm,x₁=3cm,l₁=2cm,w₁=0.075cm.Secondly,the equivalent circuit model and mechanical response model of the L-T magnetoelectric composite structure are constructed to guide us in selecting magnetostrictive materials and piezoelectric materials.Choose untreated domestic Cloud Road material as piezomagnetic material,its magnetostriction coefficientλ=28ppm,piezomagnetic coefficient d_33,m=3ppm/Oe,piezoelectric material choose piezoelectric single crystal PMN-PZT,piezoelectric constant d_33,p=1530p C/N.Using the selected materials,a magnetoelectric composite structure was prepared according to the simulation results and the performance was characterized.The simulation results were consistent with the experimental measurement results in terms of modal frequency and output response,which verified the rationality of the simulation design.Among them,the low frequency output response of No.1 design is:_（1,16）=27.2V/cm·Oe,the response in the resonance state is:_（1,1）=6239V/cm·Oe.The magnetoelectric composite structure shows good detection ability at both low frequency and resonance,which proves the effectiveness of the simulation design.Thirdly,the modulation and demodulation is performed on the target magnetic field to reduce frequency noise.Due to the 1/f noise inversely proportional to the frequency,the detection ability of the magnetoelectric composite structure to extremely low frequency magnetic targets is severely limited.We use the magnetic field modulation method to modulate the target magnetic field to the high frequency region to suppress 1/f noise.We first mathematically deduce the output response of the magneto-electric composite structure,and prove that it is approximately electrically equivalent to a multiplier,which can be modulated to high frequencies by the carrier magnetic field;After that,the output signal is demodulated by the reference signal;Finally,the output signal is passed through a low-pass filter to obtain the target magnetic field with significantly reduced noise.Fourthly,the magnetic field modulation process is optimized according to the power spectrum analysis.The enhancement of the target signal and the suppression of noise are realized by adjusting the carrier magnetic field and the DC bias magnetic field.We compared the right band signal（RSB）and the signal-to-noise ratio（SNR）two evaluation indicators,and found that the SNR can better represent the output response of the magnetoelectric composite structure.The results show that:when the carrier magnetic fieldB_c=20.4uT and the frequency f_c=11580Hz,it has the best enhancement effect on the target signal,and SNR=44.39dB;To DC bias magnetic field,we found that the bias magnetic field has a small enhancement effect on the target signal in a small range of（0,±2.93）Oe,and the target signal will be significantly inhibited beyond this range.Considering the factors of signal-to-noise ratio（SNR）and signal-to-carrier ratio（SCR）,we found that avoid applying DC bias magnetic field is a better choice.Fifthly,after completing the frequency domain analysis,we tested in the time domain.The results show that by optimizing the conditions of the magnetic field modulation,the low-frequency detection limit of the magnetoelectric composite structure is reduced to 0.8nT from 2nT,which proves the effectiveness of the magnetic field modulation optimization.