Scientists find way to charge wearable devices with common radio waves

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Researchers have figured out how to harvest energy from radio waves to power wearable devices.

From microwave ovens to Wi-Fi connections, the radio waves in the environment are not just used signals of energy but also sources of energy themselves.

Current energy sources for wearable health-monitoring devices have their place powering sensor devices, but each has its setbacks, says Huanyu “Larry” Cheng, professor in the engineering science and mechanics department at Penn State.

Solar power, for example, can only harvest energy when exposed to the sun.

A self-powered triboelectric device can only harvest energy when the body is in motion.

“We don’t want to replace any of these current power sources,” Cheng says. “We are trying to provide additional, consistent energy.”

As reported in Materials Today Physics, researchers developed a stretchable wideband dipole antenna system capable of wirelessly transmitting data collected from health-monitoring sensors.

The system consists of two stretchable metal antennas integrated onto conductive graphene material with a metal coating.

The wideband design of the system allows it to retain its frequency functions even when stretched, bent, and twisted.

This system is then connected to a stretchable rectifying circuit, creating a rectified antenna, or “rectenna,” capable of converting energy from electromagnetic waves into electricity that can power wireless devices or to charge energy storage devices, such as batteries and supercapacitors.

This rectenna can convert radio, or electromagnetic, waves from the ambient environment into energy to power the sensing modules on the device, which track temperature, hydration, and pulse oxygen level.

Compared to other sources, the system produces less energy, but can generate power continuously—a significant advantage, Cheng says.

“We are utilizing the energy that already surrounds us—radio waves are everywhere, all the time,” Cheng says.

“If we don’t use this energy found in the ambient environment, it is simply wasted. We can harvest this energy and rectify it into power.”

The technology is a building block for Chen and his team.

Combining it with their novel wireless transmissible data device will provide a critical component that will work with the team’s existing sensor modules.

“Our next steps will be exploring miniaturized versions of these circuits and working on developing the stretchability of the rectifier,” Cheng says.

“This is a platform where we can easily combine and apply this technology with other modules that we have created in the past. It is easily extended or adapted for other applications, and we plan to explore those opportunities.”

Written by Tessa M. Pick.