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Researchers have developed technology that harvests unused energy from WiFi signals to power small electronic devices or for wireless charging

As the number of wireless devices has grown, so has the number of WiFi sources, and the widespread use of the 2.4 GHz radio frequency used by WiFi. It makes sense to then consider ways to harvest the untapped energy contained in these ambient radio waves. Now, a team of researchers at the National University of Singapore (NUS) and Japan’s Tohoku University (TU) may have found a way.

The team has developed a technology that uses tiny devices called spin-torque oscillators (STOs). The STOs generate microwaves, but their low output power and broad linewidth have prevented their use in harvesting and converting wireless radio signals into energy. Previous attempts to overcome this limitation have led to several STOs working together on a single chip, but until now these efforts have been plagued by spacing issues and low frequency responses.

The current team overcame these problems by developing an array in which eight STOs are connected in series. Using the array, the researchers were able to convert the 2.4 GHz electromagnetic radio waves used by WiFi into a direct voltage signal, which was then transmitted to a capacitor to light up a 1.6-volt LED. A five second charge of the capacitor resulted in the ability to light an LED for one minute after the wireless power was switched off.

Professor Yang Hyunsoo, who headed the project, explained that since the WiFi signals are always on, not using them to provide power is a huge waste. He added that the team’s latest result, “is a step towards turning readily-available 2.4GHz radio waves into a green source of energy, hence reducing the need for batteries to power electronics that we use regularly. In this way, small electric gadgets and sensors can be powered wirelessly by using radio frequency waves as part of the Internet of Things.”

This research is part of a growing trend in searching for ways to save energy, by better utilising the power sources that are already ubiquitous. Other recent research in this area includes a novel way to revive dead lithium-ion batteries and using food waste to generate electricity.

Written By: Lisa Magloff

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