1. Physics Department, Nantong University, No. 9, Seyuan Road, Nantong, Jiangsu 226007, China
2. Jiangsu Key Laboratory of Power Transmission and Distribution Equipment Technology, Hohai University, Changzhou 213022, China
3. Department of Instrument Science and Engineering, Shanghai Jiaotong University, No. 800, DongChuan Road, Shanghai 200240, China