[1] Department of Physical Electronics, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8552, Japan
[2] Tokyo Bio R and D Center, Motortronics Laboratory, Tamagawa Seiki Co., Ltd., 4259-3 Nagatsuta-cho, Midori-ku, Yokohama 226-8510, Japan
[3] Integral Research Institute, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8552, Japan