A fabrication process was proposed to achieve ultra small electromagnetic motor of radial gap type. Based on this process, the motor stator was formed by such manner that flexible coils were rounded and fixed around the cylindrical core. A rotor consisted of a permanent magnet was made, and then, this rotor and the stator were put together. The fabricated ultra small electromagnetic motor was 1.6 mm in diameter and 2 mm in length. As a radial gap type electromagnetic motor with core, it is the smallest in the world. The torque, efficiency, and losses were evaluated, and the performance of the motor was investigated. From these experiments, the following conclusions were obtained. (1) The efficiency reached the maximum, when the radial gap between the rotor and stator was kept at 20 μm. (2) The power density of the fabricated micro motor was seven times larger than that of small size DC motor used in a cellular phone, and the torque of 1.5×10-6 Nm was achieved. (3) The mechanical loss due to the friction of bearings occupied approximately 90% of the total losses.
