Development Of Digital Detection System For Optically Pumped Helium Magnetometer

Optically pumped helium magnetometer is a high sensitivity magnetometer, widely usedin the fields of space magnetic survey, military anti-submarine and geophysical exploration.Digitization of helium optical pumping magnetometer detection system is the main develop-ment direction of improvement the accuracy of the instrumentation, digital optically pumpedmagnetometer is easy to implement the miniaturization of the instrumentation, and can extendthe field of application of the magnetometer, such as mounting on a small unmanned aerial vehi-cle. Introduce the optically pumped helium magnetometer applications and development in theworld, summed up the optically pumped helium magnetometer detection system. On this basis,propose the objective of this paper is development of all-digital detection system for opticallypumped helium magnetometer, the main research work and achievements can be summarizedas the following aspects:1. Based on the theory of the helium optical pumping magnetometer, explain the magneticmeasurement principle and signal characteristics, analyse the instrument sensitivity estimationmethod and magnetic resonance angular correlation efect on sensitivity, introduce frequencymodulation resonance detection principle and signal characteristics, derive the optimal frequen-cy modulation parameters, propose monolithic FPGA chip based digital detection system.2. Design the digital frequency modulation RF field based on DDS and FPGA technolo-gies. According the frequency stability, modulation frequency resolution and performance re-quirements, realize the FPGA square wave frequency synthesizer, frequency modulator and itsperipheral circuits.3. To detect the fundamental modulation signal from the photodiode, design and imple-ment FPGA quadrature digital lock-in amplifier module, using CORDIC algorithm to completethe digital phase-sensitive detection and square root computing, using the multirate techniquesto achieve efcient narrowband low-pass filters.4. Test the system module and the prototype system. Simulation of the digital frequencymodulator, simulation of digital lock-in amplifier and compared the measurement result with the commercial instrument, detect the fundamental signal amplitude characteristic curve withthe commercial LIA instrument and the prototype detection system.