1. a Dept. of Physics , Hong Ik Univeristy , Mapoku, Seoul , KOREA
2. b Dept. of Electrical and Control Engineering , Hong Ik Univeristy , Mapoku, Seoul , KOREA
3. c Dept. of Electronic and Computer Engineering , Hong Ik Univeristy , Jochiwon, Chungchungbukdo , KOREA
4. d Goldstar Central Research Lab , Umyundong, Seochoku , Seoul , KOREA