1. School of Mechanical and Aerospace Engineering, Seoul National University, 312-203, San 56-1, Shinlim-dong, Kwanak-gu, Seoul, 151-742, Korea, Digital Bio Technology Co., Institute of Advanced Machinery 1304, San 56-1, Shinlim-dong, Kwanak-gu, Seoul, 151-742, Korea, School of Electrical Engineering and Computer Science, Seoul National University, Seoul, 151-742, Korea, and Department of Biomedical Engineering, Korea University, Anam 5-ga, Sungbuk-gu, Seoul, 136-701, Korea