Spatial Magnetic Field Distribution Design Technology And Application Research Of Tunneling Magnetoresistance Acceleration Measurement System

Accelerometer is an instrument used to measure the acceleration of moving objects,which is widely used in aerospace,seismic monitoring,petroleum exploration and other fields.Material noise and ambient temperature restrict the improvement of the precision of silicon-based microelectromechanical(Micro-Electro-Mechanical Systems,MEMS)accelerometer.It is of great significance to explore the research of high-precision accelerometer with new materials,new devices or new technology.Micro and nano technology is constantly developing,especially in the field of magnetic sensors.The development of highly sensitive tunneling magnetoresistance(Tunneling Magnetoresistance,TMR)provides an important and effective way for the development of high-precision accelerometer.Based on the high sensitivity characteristic of TMR,the high-precision acceleration measurement system is realized by the multi-physical field coupling principle of"force-magnetic field-electricity",including:the cantilever beam converting the change of acceleration to displacement,the magnetic source placed on the cantilever beam converting the displacement of the cantilever beam to magnetic field,the TMR sensing the magnetic field and the TMR processing circuit outputting voltage which carrying acceleration signal.The core problem of the system is to convert the acceleration change to the linear magnetic field change sensed by TMR.In this paper,the magnetic field distribution requirements of the acceleration measurement system are studied to design a spatial magnetic field with large linear variation for TMR.Firstly,the magnetic source is designed with permanent magnet material.The magnetic field of cylindrical and rectangular magnets is analyzed theoretically and simulated.With the summarized laws of linear magnetic field with the influencing factors such as magnet' s size,magnet's material and spatial position,the cylindrical permanent magnet made of NdFeB N42 is the optimized design of the acceleration measurement system,which meets the demand of the linear working range of TMR2104.The system prototype constructed with magnet source realizes the function of acceleration measurement.Secondly,in order to eliminate the influence of low-frequency noise of TMR on the accuracy of system,the excitation coil is designed for generating spatial alternating magnetic field to make the TMR working at low-noise kHz frequency.For further improving the sensitivity of the system,the I-shaped magnetic core and flux concentrator are designed.So the sensitivity of the spatial magnetic field is improved and the amplitude of alternating magnetic field coincides with the linear working range of TMR2104.The experimental results show that the sensitivity of the prototype with permanent magnet source is 1076.29mV/g in the range of 0?0.5g,and the linearity is 1.49%.The sensitivity of the prototype with coil is 21.18mV/g in the range of 0-1.6g,and the linearity is 3.81%.With the magnetic modulation,the system noise is decreased from 178.94?g/?Hz(@1Hz)to 15,11?g/?/Hz(@1Hz).The above results show that the static magnetic field and alternating magnetic field distribution designed in this paper are in agreement with the experimental results,and the two system prototypes realize the function of acceleration measurement.The application of alternating magnetic field generated by coil reduces the low-frequency noise of TMR.This study provides theoretical support for the further development of a high-precision TMR acceleration measurement system.