Wireless power transfer in low-power sensor networks
With rapid improvements in the reduction of power consumption of modern electronics in recent decades, a batteryless operation can also be achieved in small sensor networks. A common way to power such devices is by energy harvesting from sunlight, heat source, or vibrations. In applications, where none of them can be used, the alternative is to supply energy using wireless power transfer (WPT). Comparing a couple of WPT technologies, a radio frequency (RF) was chosen as a suitable candidate for powering a sensor network.
Wireless power transfer technique refers to the transmission of energy without a direct wire connection. The electric energy is transferred from the transmitter device supplied by a power source to a receiver device through a field between them. The receiver extracts energy from the field, converts it generally to electric current and supplies it to an electrical load. A Block diagram of a dual-band wireless RF powered sensor network is shown in Fig. 1.
Based on this concept, real hardware (Fig. 2) was developed for measurement and testing purposes. It consists of two parts - RF energy harvester and sensor node. Thanks to this modular topology, each part can be used independently as well as it can be upgraded separately.