Alive Monitoring Sensor System with 2.45-GHz Wireless Power Transfer for Self-powered Wireless Sensor

An alive monitoring system with a 2.45-GHz wireless power transfer utilizing a 4.9-GHz harmonic wave generated from a receiving rectenna supplying DC power to a self-powered wireless sensor has been developed. The system consists of a power transmitter and a power receiver embedded in the sensor. The power transmitter has a 2.45-GHz power transmitting antenna and a 4.9-GHz receiving antenna. The power receiver has a 2.45-GHz power receiving rectenna and a 4.9-GHz transmitting antenna. To reduce transmitted power, the system searches for the sensor location with a harmonic wave using an intermittent wireless power transfer and then performs the alive monitoring with continuous wireless power transfer. A Yagi-Uda composite antenna structure at the power transmitter and a dipole-sleeve composite antenna at the power receiver make it possible to check the operation of a wireless self-powered sensor at distance of over 1 m. We evaluated the alive monitoring system for a self-powered water leakage sensor and found that it could detects the sensor at a distance of 1 m within 2 seconds by using the intermittent wireless power transfer that utilizes the harmonic 4.9-GHz wave generated at the sensor’s rectenna. The average transmitting power was 1 W. We also performed alive monitoring of the sensor using continuous wireless transfer with the transmitted power of 10 W and found that the response time of the sensor was 10 seconds at a distance of 1.2 m.