Research On Detection Technology Of High-sensitivity Miniature Atomic Magnetometer

In recent years,weak magnetic sensor has played an increasingly important role in the fields of medical treatment,magnetic anomaly detection,industrial diagnosis,archaeology and mineral exploration.With the advancement of science and technology,various fields have put forward higher requirements for weak magnetic sensors.In this thesis,the overall scheme of single sensing light and double atomic cell magnetometer based on spin exchange relaxation free(SERF)is adopted.The thesis investigates the method of improving the magnetic field detection sensitivity of atomic magnetometer,the principle of signal detection and the design of architecture,so as to achieve the research goal of high sensitivity and miniaturization.The main research contents of this thesis are as follows:1.The working principle of SERF atomic magnetometer are studied.The influence of Zeeman effect on rubidium atom is discussed,and the working conditions of high-sensitivity atomic magnetometer are analyzed.Based on the structure of single sensing light source atomic magnetometer,its response output to weak magnetic field signal in DC mode and amplitude modulation mode is analyzed,respectively.2.The three-dimensional magnetic field coil is designed and fabricated,matched with the microfabricated weak magnetic sensor probe.According to the Biot-Savart law,the uniformity of the magnetic field and the coil constant generated by the three-dimensional magnetic field coil are simulated and analyzed.In the experiment,in the space area where the atomic cell is located,the non-uniformity of the magnetic field generated by the Helmholtz coil is better than 0.2%,and the non-uniformity of the magnetic field generated by the saddle coil is better than 1.83%,which can meet the uniformity requirements of the system.3.Based On single sensing beam and double cells micro weak magnetic sensing probe,which size is 20 mm×20 mm×80 mm,a weak magnetic field detection system is designed and built.key parameters such as the frequency of the pump light source,the magnetic field modulation amplitude and the modulation frequency are optimized to improve the system's response to weak magnetic signals,thereby improving the sensitivity of the system.In the frequency range of 10 Hz to 40 Hz,the sensitivities of two single-cell are 36 f T/Hz^1/2 and 30 f T/Hz^1/2,respectively.In the gradient magnetic field measurement of the double-cell,the noise of the light source and the common-mode magnetic field are greatly suppressed,which further improves the magnetic field detection sensitivity of the system,reaching 17 f T/Hz^1/2.4.The magnetic field measurement dynamic range of the weak magnetic sensing system is studied and tested.By adjusting the residual magnetic field in the magnetic shielding cylinder,and using the magnetic field coil on the sensing probe to compensate the residual magnetism,the sensitivity of the sensing head under different residual magnetic field is detected by the double cell structure.When the sensitivity of the system is better than 30 f T/Hz^1/2,the dynamic range of the system is ±80 nT.