Charging Tiny Electronics With WiFi

A Singapore-Japan team has devised a method to harness WiFi signals and convert them into energy, powering small electronics like LEDs in the process.

AsianScientist (Jun. 16, 2021) – Though we often use WiFi to connect to the Internet, researchers from Singapore and Japan have found that the signals could also be harnessed to wirelessly power small electrical devices—no batteries needed! Their results are described in Nature Communications.

Head over to a nearby café or visit a friend’s place and chances are, the first thing you’ll do is connect to the WiFi. By allowing millions—if not billions—of people worldwide to connect their devices wirelessly to the Internet, there’s no doubt that WiFi is an essential service, especially with remote work on the rise.

Typically, WiFi routers use radio frequencies like 2.4 GHz and 5GHz to wirelessly transmit data across devices. However, when these frequencies aren’t being used to access the Internet, the excess signals are wasted.

Seeking to put ambient WiFi signals to good use, a research team from the National University of Singapore (NUS) and Japan’s Tohoku University developed a technique to harvest wireless radio frequencies and convert them into energy to power small electronics.

The team’s method relies on tiny smart devices called spin-torque oscillators (STOs), which can generate and detect microwaves. Interestingly, both microwave ovens and WiFi operate on the same 2.4 GHz frequency, explaining why cooking in the microwave sometimes interferes with the WiFi connection.

After arranging eight oscillators in a series, the team found that they could convert the 2.4 GHz WiFi signal into a direct voltage capable of charging a capacitor. By charging the capacitor for a mere five seconds, the device managed to power a 1.6-volt LED for one minute even after WiFi was switched off.

The authors also assessed if arranging the oscillators in series or in parallel could impact their ability to broadcast microwave signals. When the oscillators are connected in series, each oscillator has a different voltage. In contrast, in a parallel circuit, the same voltage exists across all oscillators. Accordingly, they found that the parallel arrangement was more stable—making it suitable for wireless transmission.

Moving forward, the researchers are set to explore how increasing the number of oscillators in the array could enhance their energy harvesting ability. In addition, they hope to soon test if their energy harvesters can also wirelessly charge other electronic devices and sensors—paving the way for self-sustaining smart systems.

“Our 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,” said project leader Professor Yang Hyunsoo from NUS. “With the advent of smart homes and cities, our work could give rise to energy-efficient applications in communication, computing and neuromorphic systems.”

The article can be found at: Sharma et al. (2021) Electrically Connected Spin-torque Oscillators Array for 2.4 GHz WiFi Band Transmission and Energy Harvesting.


Source: National University of Singapore.
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