Study and development of a microwave power receiving system for ZigBee device

Battery exchange cost or the battery itself of sensor terminals is a serious problem to construct a wireless sensor network. The objective of the present study is to develop a ZigBee sensor network powered by external microwave in order to realize a battery-less or wirelessly-charged wireless sensor network. Our designed microwave power receiving system consists of a power receiving antenna, a rectification circuit and a dc-dc converter. We conducted ZigBee communication experiments while the ZigBee device was irradiated by the external microwave. The results indicate that there are available frequencies for the microwave power supply even in 2.4 GHz band, which is also used for the ZigBee communication. We made two prototypes of rectification circuits whose optimum loads were 140 Ω, and whose efficiencies were 65 % and 27 %, respectively. We demonstrated operation of a ZigBee device with the external microwave power. We confirmed that microwave power receiving circuit can operate ZigBee device. We made a rectenna from nine rectification circuits and nine patch antennas. This rectenna could output voltage to operate the ZigBee device with wireless power.