1. School of Electrical Engineering, Chungbuk National University, 1 Chungdae-ro, Cheongju 362-763, Republic of Korea.
2. School of Electronic Engineering, Daegu University, Gyeongsan 712-714, Republic of Korea.
3. Department of Biomedical Engineering, School of Medicine, Chungbuk National University, 1 Chungdae-ro, Cheongju 362-763, Republic of Korea.