Abstract
This paper proposes an alive monitoring system for small self-powered sensors that uses 2.45-GHz microwave power transfer, where a second harmonic generated by a receiver is directly radiated through an antenna and monitored by the transmitter for location detection at ultra-low energy. The location is detected by intermittently transmitting and receiving the harmonic in the transmitter and then executing alive monitoring with continuous transmission to reduce the transmitting energy. The key technology of our alive monitoring system is the slim dual-band antenna configuration, which includes a 2.45-GHz sleeve receiving and 4.9-GHz dipole transmitting single-feed antennae for the receiver, enabling omnidirectional power reception and transmission. The configuration also includes 2.45-GHz transmitting and 4.9-GHz receiving Yagi-Uda antennae for the transmitter, which makes it feasible to improve the harmonic-reception sensitivity by arranging the polarization vertically and shortening the distance between the antennae. To demonstrate the effectiveness of this system, we prototyped our system for 2.45-GHz microwave power transfer targeting self-powered water-leakage sensors. The system was evaluated under simulated test conditions in which the transmitter performed intermittent operation with a duty ratio of 10%. The test results confirmed that the energy consumption could be reduced by 62.5% compared to that of continuous transmission alone.
