Research On Improving The Gradient Tolerance Of Magnetometer

When there is no gradient in the magnetic field,the frequency measurement time can reach more than 900 ms.When there is a gradient field,the attenuation constant of the Larmor signal becomes smaller,and the signal attenuates sharply.At this time,the time of the frequency measurement will be correspondingly reduced.In the weak field,the signal induced by the signal sensor is weak,and the signal-to-noise ratio of the amplified signal is very low.As the signal is attenuated,the signal-to-noise ratio will be drastically reduced,and the time of the frequency measurement will be reduced accordingly.How to determine the frequency measurement time according to the signal quality is one of the main methods to improve the gradient tolerance,and it is also one of the important methods to improve the weak field detection capability.In this paper,the Larmor signal is generated by Matlab simulation,and the Larmor sinusoidal signal Ae^(-t/τ)sinωt with a frequency of 2.3KHz is simulated by MATLAB.The analog shaping circuit function converts the Larmor signal into a square.Wave,through the square wave count,to achieve frequency analog measurement.The influence of signal amplitude and decay time constant on the frequency sensitivity is studied,which lays a theoretical foundation for determining the optimal frequency measurement time.Through the rigorous mathematical argumentation,the theoretical basis of sensitivity time domain and frequency domain representation is given.This provides theoretical support for estimating sensitivity using gradient and synchronization methods.On this basis,the 7000nT/m gradient field is generated by the laboratory-made gradient coil,and the signal envelope under the gradient is obtained.The sensitivity of the Overhauser magnetometer is estimated under this gradient,and the sensitivity is 19 nT in one cycle of 3s..In summary,the method of appropriately adjusting the frequency frequency according to the signal quality can effectively improve the frequency measurement sensitivity of the high gradient condition and improve the gradient tolerance of the magnetometer.Experiments show that the magnetometer can still be stabilized at 7000 nT/m.reading.