Research On Technologies Of Magnetic Shielding And C-field For Chip Scale Atomic Clock

Micro-PNT technology enables navigation,positioning and timing integration,providing high-precision navigation and positioning time functions for micro-combat platforms,precision-guided weapons and individual electronic countermeasures.Chip scale atomic clock(CSAC)is the core module of the timing unit in Micro-PNT technology,and its miniaturization and optimization of frequency stability have become the focus of current research.The CSAC based on the principle of coherent population trapping(CPT)uses a microwave frequency signal to modulate the laser,so that the laser produces coherent two-color light with a specific optical frequency difference,and locks the frequency at the transition frequency of the alkali metal ground state.The electromagnetically induced transparent spectrum is used as the final microwave discriminating signal.The chip scale atomic clock requires a high-precision uniform external magnetic field,i.e.C-field,to provide the direction of quantization axis for atoms,and at the same time,the atomic hyperfine structure level produces Zeeman splitting,thereby generating a transition under the interaction between light and atoms.Due to the presence of external geomagnetic field and stray magnetic field,the frequency between energy levels is unstable,affecting the interaction between light and atoms,resulting in unstable clock transition frequency.Therefore,magnetic shielding is of great significance to improve the stability of atomic clock.This paper has carried out the following research on magnetic shielding and C-field:First,this paper introduces the principle of atomic interaction between light and magnetic field,explains the Zeeman effect,and focuses on the principle of CPT phenomenon,magnetic shielding principle and Helmholtz coil principle.Secondly,the overall system structure of the CSAC is introduced.The physical system is elaborated,and the preparation process of the MEMS atom cell is mainly described.Thirdly,the shielding effectiveness of the multi-layer cylinder is deduced,and the influence of various structural parameters on the shielding effect is studied.Different simulation models are established to explore the shielding effect of the cylindrical and spherical nested models,and processed according to actual conditions and requirements.The magnetic shielding cylinder required for the experiment,comparing the residual magnetic field in the cylinder and the simulation results,analyzes the cause of the deviation.Fourthly,the uniformity of the Helmholtz coil was analyzed by simulation software respectively.According to the requirement of the magnetic field of the CSAC,the C-field with the magnetic field range of 0~25?T was designed.Finally,absorption line test platform was built to obtain test lines of vapor cell.