Sensing Technology Of Weak Magnetic Field Based On Gaint Magneto Impedance Effect

With the development of new magnetic materials, the types of magnetic sensor has been greatly enriched, at the same time, the sensitivity, power consumption, size and other performance indicators of the magnetic sensor have been highly required. it has become increasingly difficult to meet these requirements by using the traditional sensors,like the hall sensor and the fluxgate sensor.The giant magneto impedance(GMI) effect is a new effect discovered by Mohri et al. In the early 1990 s, this effect is the phenomenon that the AC impedance of amorphous alloy changes with the change of external magnetic field. The magnetic sensor based on the GMI effect has the advantages of high resolution, low power consumption and small size. It can be widely used in navigation, positioning, vehicle flow detection and other fields, which has attracted great attention. Based on the theory of GMI effect, a research has been made on the technology of the weak magnetic field with the support of the 863 project.Firstly, based on the simplified model of the GMI effect, the permeability tensor can be calculated through the magnetization motion equations. With the permeability brought into Maxwell’s equations, the impedance expression in amorphous wire can be solved by using the characteristic of electromagnetic wave spreading on the surface of the amophous wire. The effect factor and the influence mechanism can ben known by the impedance expression. Based on the GMI effect theory and mathematical model, the relationship between the impedance variation rate, the excitation mode, the excitation frequency,the equivalent magnetic field, the probe size, the external magnetic field and other parameters of the GMI effect are analyzed.Secondly, the overall structure of the sensor is established, the output transfer function and the error transfer function have been solved. According to the overall structure, the sensor probe and relevant circuits were designed. The differential probe with the form of “ring incentive and nondiagonal extraction” is designed to improve the sensitivity of the sensor and suppress the common mode noise of the sensors.By using the closed-loop feedback structure with a PI controller, the working range、the linear degree and other performance of the sensor are greatly improved. A set of sensor characteristic test device was designed in order to get the sensor parameters adjusted quickly. The device can not only get the sensor characteristic curve and parameters quickly, but also screen the sensor according to characteristics of the output, which enhance the engineering practicality of the sensor. Finally, the sensor was tested. The test results show that working range of the sensor can reach-10-4T~10-4T, the sensitivity is 41.7μV/nT, the nonlinearity is 1.03%FS, the peak to peak time domain noise is 2.5n T in the frequency range of 0~40Hz.The test results showed that, the sensor can be used for measurement of weak magnetic field.