[1] Univ Calif Davis, Dept Elect & Comp Engn, Davis, CA 95616 USA
[2] Zhejiang Univ, Dept Informat & Elect Engn, Hangzhou 310027, Peoples R China
[3] Zhejiang Univ, Electromagnet Acad, Hangzhou 310027, Peoples R China
[4] Royal Inst Technol, Joint Res Ctr, Ctr Opt & Electromagnet Res, Stockholm, Sweden
[5] Zhejiang Univ, Hangzhou 310058, Peoples R China