1. Key Laboratory of Ultrafast Photoelectric Technology and Terahertz Science in Shaanxi, Xi'an University of Technology, Xi'an, China
2. School of Electrical Engineering, Xi'an University of Technology, Xi'an, China
3. School of Physics Electrical Engineering, Weinan Normal University, Weinan, China
4. State Key Laboratory of Electrical Insulation and Power Equipment, School of Electrical Engineering, Xi'an Jiaotong University, Xi'an, China