1. School of Instrumentation Science and Optoelectronics Engineering, Beihang University, Beijing, China
2. Key Laboratory of Ultra-Weak Magnetic Field Measurement Technology, Ministry of Education, School of Instrumentation and Optoelectronic Engineering, Beihang University, Beijing, China
3. Beijing Engineering Research Center of High-Speed Magnetically Suspended Motor Technology and Application, Beihang University, Beijing, China
4. National Institute of Metrology, Beijing, China