| Due to the high sensitivity and stability,optically pumped atomic magnetometers are widely used in magnetic field measurements.In this work,we focus on a vetor magnetometer used for weak field detections newly developed in our lab.The performance of this sensor has been demonstrated in the lab using commercial electronics.In order to realize the miniaturization of this device,we designed signalprocessing and data-acquisition electronics for this sensor based on FPGA in this thesis.The signal processing mode of ADC+FPGA+DAC is adopted while FPGA is used as the signal processing core.We also designed circuits for the interface between the FPGA and the sensor head or the host computer,and these circuits realize the functions of power supply,parameters configuration,the calculation and filtering of the analog signals and the conversion of reference volage.FPGA firmware integrates digital signal generators,lock-in amplifiers and proportional-integral control modules to realize the modulation and demodulation of magnetic field signal in a closed-loop way.For the data acquisition,we designed a set of variable data transfer protocol based on UART communication protocol,which realizes the functions of real-time modifications of FPGA working parameters through the host computer and continuous reading of scientific data from the signal processing module.The magnetometer uses three different modulation frequencies to realize a full three-dimensional closed-loop operation.The interference between these modulation fields in the signal processing may lead to instability in the measurements.We eliminate this problem by choosing the frequencies of the modulation fields to match the zero response points of CIC filters used in the demodulation process.Based on our homemade signal-processing electronics design,the magnetometer shows a dynamic range of±130 nT,a sensitivity better than 40 fT/(?)@1 Hz and 70 fT/(?)@0.1 Hz for all three axes,and a long-term stability better than 1 pT for an integration time of 104 s.These performances are comparable with the results using the state-of-art commercial devices. |
