Research On Key Technologies Of Giant Magneto-impedance Magnetic Sensor And Its Application

The giant magneto-impedance?GMI?effect is a magnetic phenomenon that a large change in the AC impedance of a ferromagnetic conductor with an axial external magnetic field when a high frequency current is passing through the conductor.When compared with the traditional magnetic sensors,the GMI magnetic sensor has many advantages,like a high sensitivty,fast response,low consumption and small size.Therefore,it has a potential to be widely used in many applications.However,the researches on the GMI sensor have some shortcomings.For example,the theories of the GMI effect are still uncertain;a suitable equivalent circuit model is required for the simulation of the GMI magnetic sensor;the published circuit of the GMI sensor is not impeccable,and the application of the GMI sensor is still not enough.Hence,some problems about the GMI sensor are researched in this present dissertation.The main contents are like the follow:?1?The theory about the GMI effect has been researched.The influences of the length of amorphous wire,the frequency of the excitation current,the peak to peak amplitude of the exciation current and the DC bias of the excitation current on the GMI effect have been researched.With the experiments,the main influence factors on the GMI effect have also been found.The maximum rate of change of the amorphous wire's impedance for different conditions have been calculated,which can be used to facilitate the design of the sensor.?2?The equivalent circuit model of the GMI sensor has been researched.With the description of the ferromagnetic conductor impedance,the impedance of amorphous wire was equivalent to a Cauer's type 2 network that combined with resistors and inductances with the Pade approximation.Then the relations between the external magnetic field and the circular permeability have been concluded with the method of free energy minimum principle.Then the designed model has been test with the numerical simulation.Firstly,the external magnetic field was fixed,and the relations between the excitation frequency and the impedance amplitude were measured with the impedance analyzer,which was compared with the simulation results.Secondly,the exciation frequency was fixed,and the relations between the external magnetic field and the impedance amplitude were measured and compared with the simulation results.These comparations can prove that the designed model is effective.?3?The GMI sensor based on the amorphous wire was designed.In order to protect the GMI sensor from the external magnetic field that can influence its operating point,an operating point regulator has been designed.Therefore the performance of the GMI sensor has been improved.Moreover,a phase-lag compensation network was designed in the regulator.This compensation network can depress the noise in the GMI sensor that introduced by the operating point regulator.With the measurement results,the designed GMI magnetic sensor has performed a sensitivity of about 3.4mV/nT,and a noise level of about 2 nT/Hz¹/2/2 in 0⁷Hz,and 0.38 nT/Hz^1/2 in 7¹5Hz.The resolution of the GMI sensor was about 8.3nT.?4?Then the designed GMI sensor was applied in the magnetic anomaly detection?MAD?.An EMD trend filtering based magnetic anomaly energy detector has been designed.It needs not any a priori knowledge about the target or the background noise.Therefore the proposed detector can effectively detect the target in low SNR environment and 1/f background noise.Moreover,the proposed detector has a stable performance for the magnetic anomaly signals with different characteristics.The main contributions of this dissertation are like the follows:?1?A GMI sensor with new structure has been designed.This kind of GMI sensor has an operating point regulator,which can depress the influence of low-frequency changing external magnetic field on the operating point.Therefore the GMI sensor can achieve a stable performance even in different external magnetic field.Moreover,a compensation network is designed to eliminate the noise that introduced by the regulator,and then improve the resolution of the GMI sensor.?2?A magnetic anomaly detector based on the EMD trend filtering has been designed.The advantages of this detector are like the follows:1.the detection will not be disturbed by the 1/f background noise;2.for the magnetic anomaly signals with different charateristics,the proposed detector can achieve a similar performance;3.the proposed detector requires not any a priori knowledge about the target or the background noise.?3?The impedance of the amorphous wire has been presents as a Cauer type?network that consist of registors and inductances with the Pade approximation.Moreover,the relations between the network and the external parameter,for example,the external magnetic field,have been concluded with the free energy minimum principle.