Duke wireless device converts "lost" energy into electric power

Nov. 09, 2013 @ 02:42 PM

Researchers at Duke University’s Pratt School of Engineering have designed a power-harvesting device with efficiency similar to that of modern solar panels.

The device wirelessly converts a microwave signal to direct current voltage capable of recharging a cell phone battery or other small electronic device, according to a report appearing in the journal Applied Physics Letters this December.

It operates on a similar principle to solar panels, which convert light energy into electrical current. But this versatile energy harvester could be tuned to harvest the signal from other energy sources, including satellite signals, sound signals or Wi-Fi signals, Duke researchers say.

The key to the power harvester lies in its application of metamaterials, engineered structures that can capture various forms of wave energy and tune them for useful applications.

Undergraduate engineering student Allen Hawkes, working with graduate student Alexander Katko and lead investigator Steven Cummer, professor of electrical and computer engineering, designed an electrical circuit capable of harvesting microwaves.

“It’s possible to use this design for a lot of different frequencies and types of energy, including vibration and sound energy harvesting,”  Katko said. “Until now, a lot of work with metamaterials has been theoretical. We are showing that with a little work, these materials can be useful for consumer applications.”

For instance, a metamaterial coating could be applied to the ceiling of a room to redirect and recover a Wi-Fi signal that would otherwise be lost, Katko said. Another application could be to improve the energy efficiency of appliances by wirelessly recovering power that is now lost during use.

“The properties of metamaterials allow for design flexibility not possible with ordinary devices like antennas,” Katko said. “When traditional antennas are close to each other in space they talk to each other and interfere with each other’s operation. The design process used to create our metamaterial array takes these effects into account, allowing the cells to work together.”

With additional modifications, the researchers said the power-harvesting metamaterial could potentially be built into a cell phone, allowing the phone to recharge wirelessly while not in use. This feature could, in principle, allow people living in locations without ready access to a conventional power outlet to harvest energy from a nearby cell phone tower instead.