Study On Key Techniques Of The Flexible Substrate Fluxgate Sensor Based On MEMS Technology

Fluxgate sensor becomes the best vector magnetic field sensor with comprehensive properties because of characteristics of simple structure,the ability to measure the static and low frequency magnetic field,and its stability in temperature sensitivity and resolution as well as accuracy.With the development of MEMS(micro-electro-mechanical system)technology,and the enlargement of the research and application of flexible substrate,combining with the advantage of fluxgate sensor and flexible substrate,the research of flexible substrate fluxgate sensor based on MEMS technology,would further expand its application in measuring the magnetic field in the non-planar surface,on-line current measurement,biomedical,wearable sensors,and flexible electronics and so on.However,the technology of MEMS and the flexibility also brought many new challenges and problems to fluxgate,MEMS technology is compatible with microelectronic technology,thus micro fluxgate and processing circuit can be integrated into one chip,which requires a overall design method to optimize system performance;Compared with the three-dimensional structure,the implementation of flat structure fluxgate in MEMS technology does not require the lower and upper coils to be connected,which reduces the difficulty of craft,but it has poor coil excitation efficiency and high power consumption,and the problem of how to optimize the topology structure of the coil and core remains to be further researched;Based on MEMS technology,fluxgate adopted film core,which has a sharp decline in the soft magnetic properties comparing with traditional fluxgate strip core,and noise increases significantly with decrease of the volume,it is necessary to study the improvement of soft magnetic film core performance;In the field of application,combining with the advantages of the fluxgate and flexible substrate,research of flexible substrate current sensor on the basis of the principle of fluxgate,is expected to improve the capability of current sensor in online testing and measurement accuracy.In view of the challenges and problems mentioned above,in this paper,on the basis of theoretical analysis,optimize the performance of the sensor in two aspects: topological structure of fluxgate sensor core and coil and the soft magnetic properties of core,make use of MEMS technology to fabrication the flexible substrate fluxgate sensor,and used them to measure magnetic field and current.In this paper,the main work and innovative research results are as follows:1?A method of preparation of flexible substrate fluxgate on MEMS technology was proposed,and applied the prepared flexible substrate fluxgate as current sensor for online measurement.Based on the technology of MEMS,we combined that with the high precision,high stability features of fluxgate,and the flexible and extension characteristics of flexible substrate,the preparation of a kind of fluxgate current sensor with flexible substrate,and used it as current sensor for online measurement.This prepared flexible substrate fluxgate current sensor not only has the characteristics of fluxgate sensor with high precision,but also has the advantages of convenient online measurement of Rogowski coil(hollow induction coil).2?A simulation program with integrated circuit emphasis(SPICE)circuit model of voltage excitation fluxgate was proposed,and used this model to optimize the fluxgate core structure and magnetic parameters,the coil structure parameters,and the excitation voltage parameter.Fluxgate SPICE model can be helpful for united simulation of fluxgate sensor and processing circuit,and then to optimize system as a whole,while the existing fluxgate SPICE models are current excitation,which have a certain gap with actual situation.It used the arctangent function to describe the hysteresis loop of fluxgate core,the excitation and measurement coils of the fluxgate were equivalent to a circuit model that contains a kind of non-linear time-varying inductance,finally the solving of the model is realized by using the SPICE.This model can quickly and conveniently get input and output characteristics of fluxgate under knowing excitation voltage,coil turns,core size,magnetic hysteresis loop data of core and the external magnetic field.3?A preparation method of film core with different adhesive layer based on MEMS technology used for fluxgate was proposed.Fluxgate used soft magnetic film materials based on MEMS technology as the core,though film core has a sharp decline in soft magnetic performance compare to strip core for traditional fluxgate,and the noise increases significantly as the volume of the core reduces.Based on theoretical analysis of what kind of soft magnetic materials the fluxgate needed,we studied on the effect of four different adhesive layer on the soft magnetic properties of film core Ni81Fe19 by the sputtering process,the effect on the soft magnetic properties of NiFe alloy under different plating processes were studied,and effects on the soft magnetic properties of film core under different stress conditions.Results showed that the adhesive layer of tantalum in common metal materials is best for Ni81Fe19 film core adhesive layer,the best electroplating conditions of NiFe alloy electroplating and different direction stress have different effect on the soft magnetic performance of core.4?The method for lowering power consumption of flat structure fluxgate based on the theory of demagnetizing field was proposed,to optimize the structural of flat fluxgate according to this method,and to simulate for verification.Flat structure fluxgate possesses the advantages of simple structure and easy preparation,but its large power consumption which caused by poor excitation efficiency and large drive coil resistance needs to be researched.On the basis of analysis of plane structure fluxgate theory,we provided the method for reducing the power consumption of the sensor using the theory of demagnetizing field,and designed several flat structure fluxgate based on this method,finally made the magnetic field simulation.The method provided the theoretical support for further devices preparation.The dissertation was supported under the national natural science fund project "research on low-power technology of micro fluxgate(No.60874101)" and the specialized research fund for the doctoral program of ministry of education higher education " research on low-power technique of micro fluxgate based on porous soft magnetic film core"(No.20126102110031),which is important for overall design and optimization of micro fluxgate sensor,reducing power consumption,preparation of film core,non-planar magnetic field measurement,current measurement,and the research results can be used in the fields of current detection,non-planar magnetic field measurement,flexible electronics,biomedical,wearable sensors,small robot control,nondestructive detection,magnetic markers detection,aircraft navigation,and so on.