Research On Magnetic Sensor Of Amorphous Film/Planar Coil Laminated Structure

Covering a planar coil with a high permeability soft magnetic film enhances the inductance of the coil.Due to the nonlinearity of the magnetization process of soft magnetic materials,the magnetic permeability changes with the external magnetic field,which leads to the sensitivity of the coil inductance to the external magnetic field.With this feature,a magnetic film/planar coil/magnetic film laminated structure magnetic sensor is designed.In this paper,the amorphous film/planar coil laminated structure is studied.The planar laminated structure has the advantages of easy miniaturization,low excitation frequency,high sensitivity,and so on.In this paper,the influence of the structural geometry and the demagnetization effect of the amorphous film on the magnetic field sensitivity of the laminated structure is analyzed.Finally,we proposed a mutual coupling laminated structure,whose sensitivity is improved by the mutual inductance coupling structure design,and the noise level is reduced.In terms of the analysis of the influence of geometric on the magnetic sensitivity of laminated structure,the paper further deduced and analyzed the inductance model of magnetic material/conductor/magnetic material sandwich structure.Based on the model,the influence of the relative position of magnetic material and conductor,the width of magnetic material,the thickness of magnetic material,the gap of upper and lower magnetic material of sandwich structure and the width of conductor on sensitivity of the laminated structure was studied.The analysis results show that when designing the geometrical dimensions of the laminated structure,the ratio of the gap and the width of conductor should be minimized and the ratio of the width of the magnetic material to width of the conductor should be increased as much as possible,so that the sensitivity can be effectively improved.In terms of the influence of demagnetization effect on the magnetic sensitivity of laminated structure,the paper firstly analyzed the magnetization distribution of magnetic materials with different shapes and aspect ratios under external magnetic field.Results show that the overall effective magnetic permeability of the rectangular magnetic material is higher that of the elliptical shape under the same aspect ratio,and the demagnetization factor of each sample is smallest in the central region,largest at the edge.The magnetic sensitivity analysis of samples with rectangular and elliptical magnetic materials shows that the sensitivity of rectangular magnetic material samples is higher under the same aspect ratio.Under the same magnetic material shape,the larger the aspect ratio,the larger the sensitivity,Therefore,for improving the magnetic sensitivity of the laminated structure,the rectangular magnetic material is more effective than the elliptical shape,and the aspect ratio of the amorphous the amorphous film should be increased as much as possible.Furthermore,the mutual coupling laminated structure is proposed to further improve the magnetic field detection sensitivity by mutual inductance coupling between coils.The experimental results show that under the excitation of 500 kHz,the proposed mutual coupling laminated structured can increase the sensitivity by about 5 times compared with the amorphous film/coil/amorphous film structure.In addition,we also find that the noise level of the proposed mutual coupling structure is about 1.8?V at 1Hz,which is lower too.By increasing the number of layers of the pickup coil to three,the proposed mutual coupling structure can achieve a sensitivity of 3.45mV/Oe and a field detection resolution of 52.17nT(0.52mOe).When the gap between the magnetic films is largely reduced by MEMS technology,the sensitivity and resolution of the proposed mutual coupling structure can be further greatly improved.