Fundamental Mode Micro Orthogonal Fluxgate Sensor And Its Application In Biological Detection

High precision micro magnetic sensors are widely used in geological exploration,space magnetic field detection,environmental monitoring,traffic control,magnetic storage,consumer electronics and biomedical fields.Conventional fluxgate sensors have the advantages of high sensitivity,high linearity,low temperature drift,and operation at room temperature.As a special type of fluxgate device,the orthogonal fluxgate sensor has two unique advantages in addition to the advantages of conventional fluxgate sensors:on the one hand,the orthogonal fluxgate sensor is composed of a pickup coil and a sensing element of single magnetic core in which an excitation current is fed directly,and no excitation coil is needed,it has shown better potential for miniaturization due to its simpler structure;on the other hand,it can be operated in fundamental mode by superimposing a suitable dc bias current,which allows for decreasing the Barkhausen noise.The amorphous ribbon and electroplated FeNi thin film materials are used as the core of the orthogonal fluxgate sensor,and the Micro-Electro-Mechanical System(MEMS)technology is used to miniaturize the probe of the orthogonal fluxgate sensor.The magnetic core structure directly affects the performance of the micro orthogonal fluxgate sensor.In this paper,the use of meander-core structure ensure high sensitivity and low noise,while improving the linear working range of the sensor,which can further expand the application field of the micro orthogonal fluxgate sensor.In recent years,the magnetic biosensors based on magnetic tags have been greatly developed in the field of biomedical detection,but there are still some shortcomings,such as low sensitivity,poor stability and the need for a high external magnetic field,which make them unable be widely used.The micro orthogonal fluxgate sensor with high sensitivity,low noise and wide linear range is very suitable for the requirements of magnetic biosensors,and has good application potential in the field of biological detection.Based on the above considerations,systematic researches on the device manufacturing and biological detection applications based on the fundamental mode micro orthogonal fluxgate sensor are carried out in this paper.On the one hand,a high-performance micro orthogonal fluxgate sensor based on MEMS technology is developed.On the other hand,the micro orthogonal fluxgate sensor is applied in the field of biological detection,which lays a foundation for the establishment of a perfect biological detection system based on the micro orthogonal fluxgate sensor.The main research works of this thesis are as follow:(1)A novel fundamental mode orthogonal fluxgate sensor based on meander-core structure is proposed and the theoretical research is carried out.According to the Faraday's law of electromagnetic induction and the mechanism of permeability modulation,the mathematical formula of the output voltage of orthogonal fluxgate sensor based on single strip ribbon magnetic core is derived in the fundamental mode.A demagnetization model of the meander-core structure of the orthogonal fluxgate is established.Using the finite element simulation and theoretical calculation,the influence of the number of the strip,the line width and the spacing of the meander-core on the sensitivity of the sensor is discussed.The results provide theoretical support for the subsequent fabrication of micro orthogonal fluxgates.(2)The experimental studies of the magnetic core structure and magnetic field annealing based on Co-based amorphous ribbons are carried out.A simple orthogonal fluxgate sensor probe is assembled by winding an induction coil on the meander-cores,and the effect of the meander-core structure on the performance of sensor is studied.The experimental results are in good agreement with the simulation results,which proves the correctness of the demagnetization model and obtains an optimized magnetic core structure.The reaserch on magnetic field annealing of Co-based amorphous ribbon materials is carried out.The changes of magnetic properties and sensor performances with different annealing temperatures and different magnetic field annealing directions are studied.The magnetic properties of the material are tested by various magnetic material testing methods,such as the vibrating sample magnetometer(VSM),X-ray diffraction(XRD)and the magneto-optical Kerr effect(MOKE)microscope.The test results show that the Co-based amorphous ribbons annealed at 300°C can obtain better soft magnetic properties and sensor performance.In addition,the longitudinal field annealing makes the sensitivity higher,and the transverse field annealing makes the noise lower.This research provides a guarantee of magnetic core structure and materials for the development of high-performance micro orthogonal fluxgate sensors.(3)The fabrication process and performance test of micro orthogonal fluxgate based on MEMS technology are carried out.Three-dimensional micro-coil orthogonal fluxgate sensors based on Cu/FeNi core and Co-based amorphous ribbon core are fabricated by MEMS technology.The performance of fabricated micro orthogonal fluxgate sensor is tested and analyzed by the fundamental mode orthogonal fluxgate test system.The sensitivity,linear range,noise,perming error and stability of micro orthogonal fluxgate sensors are tested in the different excitation conditions.The size of the micro orthogonal fluxgate sensor based on the Co-based amorphous ribbon core is below 0.4 cm~2,the sensitivity reaches 660V/T,the linear range is 600?T,and the minimum noise is as low as 0.05 n T/?Hz@1 Hz.Compared with the same type of micro fluxgate sensor,the linear range,sensitivity and noise level have been greatly improved.(4)The application research of biological detection based on micro orthogonal fluxgate sensor is carried out.Firstly,the My One superparamagnetic magnetic beads with the diameter of 1?m are detected by the developed micro orthogonal fluxgate sensor,and the quantitative detection of magnetic beads in the concentration range of 0.1?50?g/m L is successfully achieved.Then,biological samples of alpha-fetoprotein and E.coli O157:H7are prepared based on superparamagnetic bead labeling technology,self-assembled membrane technology,and double-antibody sandwich method.And the sensitivity and specificity are tested.The experimental results show that the detection limit of AFP antigen can reach 0.1 ng/m L,and in the concentration range of 0.1?10 ng/m L,the output signal difference has a good linear relationship with the logarithm of the concentration.The detection limit of E.coli O157:H7 can reach 100 CFU/m L,and it has a good linearity in the concentration range of 100?1000 CFU/m L.The separated biological detection method based on the micro orthogonal fluxgate sensor has the advantages of fast,simple,high sensitivity,high specificity,and good stability.