A Study Of Brain Magnetic Field Detection In Non-magnetic Sheilded Environment Based On GMI Effect

Brain-Computer Interface(BCI),which is a new type of human-machine interaction technology,can realize the control of peripheral devices by using brain consciousness instead of muscle activity.At present,BCIs mainly use Electroencephalogram(EEG)as signal source for the brain consciousness recognition.However,EEG should be measure contactly,this disadvantange severely restrict BCIs for practical utilization because the contact detection can not meet the demand of practical BCI systems that "plug and play" and "ready-for-use".Magnetoencephalography(MEG)is a non-contact approach for brain consciousness monitoring.Currently,the most effective method to detect brain magnetic field is using Superconducting Quanlum Interference Device(SQUID)in magnetic shielding room(MSR).But the high costs of SQUID make it impossible for BCIs to be used in normal life.In order to promote the development of BCIs for practical utilization,this thesis is drived by the aim of non-contact MEG detection to investigate the bio-sensor design for brain magnetic detection without MSR based on the Giant Magneto-Impedance(GMI)effect.To begin with,this thesis conducts the research on the GMI effect theory,including the introduction of the characterization of GMI effect;the derivation of the calculation formula for amorphous wire impedance;the comparison of the applicable situation of different calculation models;the summarization of the influence factors for GMI perfermance;the factors that need to consider when chosing amorphous wire;the method to optimize working point using geomagnetic field.Based on the above theoretical study,then,the complete magnetic sensor design scheme with 10 pT resolution is introduced,including the design principle,simulation,and circuit realization.Note that circuit design is the key part of this thesis,including the power supply circuit design,sharp pulse generating circuit,phase demodulation circuit,amplifying circuit.Each part of the circuit board is checked carefully and give the specific implementation steps and results.Finally,the sensitivity of the GMI sensor is tested in the non-MSR.The results demonstrate that the sensitivity of the GMI sensor reaches 10 pT.To sum up,this thesis explores a non-contact method that can be used to detection brain magnetic fileld.So this thesis can be referced to promote the BCIs to practical use.