In brief
WiFi charging experiments showed that radio-wave energy could be converted into electricity, but continuous transmission and sufficient power remained challenges. The article also describes Ossia’s Cota system and potential uses for wireless-powered sensors in future cities and smart homes.
Researchers in the United States are investigating how to use surrounding wireless network signals (WiFi) to charge mobile phones.
In the homes used for the experiment, they modified electronic devices and wireless routers so that the devices would charge through signals transmitted by the routers over a 24-hour period. The routers could still perform their primary function as normal: providing WiFi.
The principle is similar to how solar panels convert light into electricity. The equivalent of the “solar panel” in this experiment is a component called a “rectifier”. It converts the energy in radio waves emitted by the router into a DC voltage. A DC converter then raises that voltage to a usable level, allowing devices to charge.
The experiment demonstrated that the device was feasible, but the challenge was how to make the router supply enough energy continuously. After all, WiFi signals become more active only when someone is using the internet, at which point they can be used to charge devices. When no one is online, WiFi signals are not transmitted, making charging impossible.
To address this problem, the researchers developed software that sends meaningless data when no one is using the internet, providing a continuous stream of signals that can be converted into usable electricity.
However, solving the problem of signal continuity raised another question: “Are WiFi signals powerful enough to fully charge a mobile phone?” In many countries, including the United States, WiFi network power is limited to 1 watt, while an iPhone charger requires at least 5 watts. How, then, can charging work?
A company called Ossia proposed a system named Cota. It designed a “wireless network hub” that transmits radio waves at wireless network frequencies without sending communication signals. The Cota setup can generate up to 20 watts of power, but it can supply only 1 watt to a single phone. If WiFi signals can be received continuously, it could charge an iPhone countless times within a day.
Regarding this type of technology, researchers at Navigant, a consultancy in London, UK, said: “Many sensors in future cities and smart homes will need this type of technology. Sensors powered by wireless networks could be used to monitor air quality or the status of systems across an entire city. Eliminating concerns about batteries would remove one of the barriers to exploring this kind of technology.”