Microwave Power Transmission to a Sensor Terminal for Wireless Sensor Network

Wireless sensor network is becoming an attractive application for monitoring systems such as energy conservation systems of buildings and houses, traffic management systems, environment monitoring systems etc. One of the critical issues of the wireless sensor network is the way to supply electric power for sensor terminals. Primary batteris need to be changed soon or later even though power consumption of the sensor terminals is quite small. Natural energy utilization like solar cells with a charging system will drive the sensor terminal permanently; however their installation location and regular operation are limited because the natural energy is quite unstable. We therefore suggest wireless power supply to the sensor terminals by microwave power transmission (MPT), in order to realize a fruitful wireless sensor network. The objective of the present study is to drive or charge a wireless sensor terminal by MPT. We adopt a ZigBee device as wireless sensor terminal because of its low power consumption. ZigBee is one of the radio communication standards and appropriate for the sensor network for the following reasons: its power consumption is lower than wireless LAN and Bluetooth, its production cost is low, and its network capacity is large. Its low power consumption is beneficial for a MPT system from the viewpoint of electromagnetic compatibility between MPT and ZigBee. We experimentally investigated electromagneti