Study On A Novel Accelerometer Based On Tunnel Magnetoresistence

Accelerometer is one of the most mature sensors with MEMS technology.Conventional MEMS accelerometers are typically based on capacitive,piezoresistive,piezoelectric,tunnel current,resonant and thermal convectional current transduction mechanisms.As research on TMR rises in recent years,accelerometer based on TMR begins to enter the research field of MEMS accelerometer,which uses TMR as signal converter.The working principle of this novel accelerometer is concerned with multiple converting procedures including acceleration to displacement,displacement to magnetic field,magnetic field to electrical resistance to voltage output.The high TMR ratio can be applied to the accelerometer to improve the conversion efficiency and precision of the traditional accelerometer,which has broad research prospect in the field of high-precision accelerometer.Institutions all over the world have studied on displacement sensors/accelerometer based on GMR/TMR sensitive structure,while the excitation structure mostly adopts permanent magnets,which attenuates with time and limits flexibly design in structure.In this paper,a new type of TMR accelerometer is presented,which produces magnetic field by excitation coil and modulates by fixing soft magnetic film on proof mass.The new TMR accelerometer could flexibly excite magnetic field by adjusting the current in excitation coil.At the same time,the noise of the TMR can be reduced by the change of excitation frequency to optimize the stability of the accelerometer.The content of this thesis could be divided into five parts.Firstly,this paper introduces the development history of accelerometer and magnetic sensors,and explains the advantages of TMR as the signal converter of accelerometer.Secondly,the working principle of the TMR accelerometer are verified,including the analysis of the excitation characteristics of the coil,the mechanical analysis of the mass proof mass structure,the feasibility analysis of the magnetic field modulated by soft magnetic film,etc.Thirdly,the excitation structure and the modulation structure are designed applied on Maxwell as a finite element simulation tool,so that the modulation efficiency of the structure could be as high as possible under the condition that the technology allowed.Then,sensitivity structure with proof mass is designed applied on ANSYS Workbench is used as simulation tool,so that the modulation structure designed before can be realized.In the last part,the whole TMR accelerometer prototype was tested,including excitation current test,scale factor and range test,stability test,etc.In the control group,the prototype with the best performance has a sensitivity of 24.5m V/g,a range of±2.5g,a stability(1?)of8.324×10^-5g.The experimental results show that this structure design has advantages and great research prospect.