AbstractMost robots moving autonomously are equipped with batteries as an energy source. Since the energy stored in the batteries is proportional to their volume, the operating time is drastically reduced as the robot is miniaturized. To resolve this problem, it is necessary to supply energy externally. Considering the checking of pipes in electric power generating stations as the target, a microrobot has been developed that autonomously moves inside the pipe with energy supplied by microwaves. A previous report [1] noted the problems that the energy could not be supplied when the robot is rotated and that the power supply method was not suitable for the sensor circuit, since the driving waveform of the actuator was produced by amplitude modulation of the microwaves. In the present paper, a method is proposed to allow the supplying of energy with circular polarization by means of four rectennas. Autonomous reversing motion is successfully achieved by installing a driver control circuit and an infrared sensor on the robot. The microrobot proposed in this paper moves at 10 mm/s, using a power of 200 mW supplied in a pipe with a diameter of 15 mm. © 2001 Scripta Technica, Electron Comm Jpn Pt 2, 84(11): 1–8, 2001