1. School of Science and Technology, Kwansei Gakuin University, 2-1 Gakuen, Sanda, Hyogo 669-1337, Japan
2. Aoi Electronics Co. Ltd., 455-1, Kohzai Minamimachi, Takamatsu, Kagawa 761-8014, Japan
3. Faculty of Engineering, Kagawa University, Hayashicho 2217-20, Takamatsu City, Kagawa Prefecture 761-0396, Japan