1. Key Laboratory of Advanced Display and System Applications, Ministry of Education; Shanghai University; Yanchang Road 149 Shanghai 200072 P.R. China
2. Department of Electrical Engineering; Iowa State University; 4565 Union Dr Ames IA 50011 USA
3. School of Mechanical and Electrical Engineering; Guilin University of Electronic Technology; 1 Jinji Road Guilin 541004 P.R. China