1. Department of PhysicsSUPAUniversity of StrathclydeGlasgowG4 0NGScotlandUK
2. School of Electronic Science and EngineeringUniversity of Electronic Science & Technology of ChinaChengdu610054People's Republic of China
3. College of Electronic Science and TechnologyShenzhen UniversityShenzhen518060People's Republic of China
4. High Voltage DivisionSchool of Electrical EngineeringXi'an Jiaotong UniversityXi'an710049People's Republic of China
5. Department of Electronic EngineeringQueen Mary University of LondonLondonUK