Study On High-temperature Superconducting Magnetometer With Counting Type

Superconducting magnetometer is the highest sensitivitively magnetometer.It has two kinds of work modes:the zero closed-tracking magnetometer is a closed loop tracking loop,it has high sensitivity but the range is limited,the locking of single component tracking type superconducting magnetometer can not be directly used in magnetic measurement.In order to elimilate problems of zero flux closed-tracking magnetometer,a prospective study to launch to the counting type high temperature superconducting magnetometer in the project.It supported by the National 863 plan project.We designed ans tested the prototype.The main research contents and achievements of this paper are as follows:(1)Study the principle of counting type superconducting magnetometer.Study on the characteristics of superconducting junction's weak link,Irf-Vrf and Vrf-?e.Through the analysis of the deficiencies of zero flux locked tracking mode,which leads to the need of counting scheme,clarifies the research of counting scheme focus and theoretical basis.(2)Developed a prototype of high temperature superconducting magnetometer.The prototype contains radio frequency unit,control unit,the magnetic flux quantum counting unit based on FPGA and DSP,display control unit.The RF unit comprises a RF oscillator,RF attenuator,directional coupler,the RF amplifier and mixer detector;control unit comprises a singlechip controller,multi DAC and multi ADC;flux quantum counting unit contains a high speed signal acquisition,modulation signal output,FPGA and DSP system;display control unit contains the best working point of intelligent search software and flux quantum display software.(3)Studyed two key technical method of counting type superconducting magnetometer,the intelligent adjusting algorithm of working point and the counter state judgement.In order to enable RF-SQUID to enter and entered the best working pointwith the fastest speed,this paper studies the nonlinear steepest descent method based ontwo element function extremum search method and its application to the operating point of intelligent software.Discrimination in the counter state method,we study and the spectruminatching technology to check and confirm the status of count,make up the one or two hannonic amplitude rely solely on the lack of state identification,and laid the foundation for the counting accuracy.(4)Launch the in door test of counting type superconducting magnetometer.By applying static external magnetic flux were technical testing,the counting result is correct,the instrument is working correctly,and laid the foundation for the further application.The innovation of this paper is as follows:(1)After the study of the working principle of counting type high temperature superconducting magnetometer,puts forward the thought method of distinguishing the counter state units,ultimately based on FPGA+DSP architecture to realize magnetic flux quantum countingscheme.(2)In order to reach the best working point RF-SQUID,we using search method of nonlinear steepest descent method for two dimession on the extreme value of function,and take a good effect,the tedious process of manual adjustment of the working point is omitted.(3)In discrimination of counting state method,in addition to the one or two harmonic amplitude variation,also uses a spectrum matching technique,check and confirm thecounter state,to ensure the accuracy of counting.Through this study,confirmed the principle of counting type high temperature superconducting magnetometer scheme,solving some key technical counting type high temperature superconducting magnetometer required.In this paper,the principle prototypes developed in the quasi static external magnetic flux test,normal work,and technical accuracy,broaden the range of instruments,have the vital significance to the future development ofsuperconducting magnetometer with wide range and high sensitivity.