1. School of Mechatronics, Gwangju Institute of Science and Technology (GIST), Gwangju 500-712, South Korea
2. Research Institute for Solar and Sustainable Energies (RISE), Gwangju Institute of Science and Technology (GIST), Gwangju 500-712, South Korea
3. Department of Medical System Engineering (DMSE), Gwangju Institute of Science and Technology (GIST), Gwangju 500-712, South Korea