Cellular telephones may be heading toward their fifth generation (5G) of wireless networks with billions of cellular handsets around the world, but they are all powered by batteries. That may be about to change, though, with the first generation (1G) of wireless power charging over short distances via inductive power transfer.
Rather than recharge and replace all those batteries contained within mobile communications devices, many researchers are exploring ways to wirelessly move power back into the batteries or power cells of those devices so that they can be used even more frequently during each day. Techniques such as wireless energy harvesting (WEH) and wireless power transfer (WPT) provide the means to transfer energy through the air to a handset in need.
Adoption of WPT will require something of a “modernization” of wireless cell sites and infrastructure equipment, since present-day wireless networks are designed for communications purposes only, and not for transfer and delivery of power to users. Availability of wireless power takes away the dependence of wireless communications devices, such as cell phones, on centralized power sources (e.g., rechargeable batteries).
The use of wireless power has ecological benefits, too, since it eliminates the waste of disposing of “end-of-life” rechargeable batteries. Moreover, it will have significance for strong growth in the use of low-power autonomous devices and Internet of Things (IoT) devices with wireless internet connectivity.
To better understand the current needs for a 1G of wireless power charging, researchers with Imperial College London (London, UK), the University of Bologna (Bologna, Italy), Heriot-Watt University (Edinburgh, Scotland), and University of Aveiro (Aveiro, Portugal) reviewed previous experiments on obtaining wireless power via RF. They felt that WPT and WEH were two approaches with potential for much longer ranges than in those earlier experiments.
For any wireless power network, the researchers felt that several parameters would help to define the network, such as range, efficiency, non-line-of-sight support, seamless integration of wireless communications and wireless power, safety and health, and limiting the energy consumption of RF-powered devices. For example, the operating range might be from 5 to 100 m for indoor and outdoor charging of low-power wireless devices. The researchers point to the growing number of wireless sensors and radio-frequency-identification (RFID) tags that require some small amount of power for operation, often in remote sites.
The thoughtful researchers present a prototype energy-harvesting system with key modules for signal optimization, channel acquisition, and energy harvester. The system employs orthogonal frequency-division multiplexing and demultiplexing for efficiency. The adaptive system transfers information (as in communications) and power simultaneously, making optimum use of available channel bandwidths.
See “Toward 1G Mobile Power Networks,” IEEE Microwave Magazine, Vol. 19, No. 6, September/October 2018, p. 69.