Duke researchers' device pulls energy out of thin air

Breakthrough device converts stray wireless signals into electricity and could be tuned to harvest energy from multiple sources, even sound

By , Computerworld |  Mobile & Wireless

If you've ever wondered where all that errant power from wireless signals goes, you're not alone. Researchers at Duke University wondered the same thing and have invented a cheap device that collects microwave signals and converts them into power for charging batteries.

The energy collection device works similarly to solar panels, which convert light energy into electrical current. The Duke researchers, however, say their converter can collect stray signals from just about anything wireless, including satellite signals, sound or Wi-Fi.

"Our work demonstrates a simple and inexpensive approach to electromagnetic power harvesting," Steven Cummer, a professor of electrical and computer engineering, said in a a statement from the school. "The beauty of the design is that the basic building blocks are self-contained and additive. One can simply assemble more blocks to increase the scavenged power."

The power-harvesting device could become part of a cell phone, allowing it to recharge itself. It could also afford rural areas without access to conventional power a way to harvest energy from cellular towers or satellites, the researchers said.

Duke engineering students Alexander Katko (left) and Allen Hawkes show a waveguide containing a single power-harvesting metamaterial cell, which provides enough energy to power the attached green LED (Image: Duke University).

For example, a series of power-harvesting devices could be assembled to capture the signals from a known set of satellites passing overhead. While minute, the small amount of energy generated from satellite signals might power a sensor network in a remote location, allowing data collection for a long-term study that takes infrequent measurements.

The Wi-Fi energy harvester was invented by undergraduate engineering student Allen Hawkes, who worked with graduate student Alexander Katko and Cummer.

The team was able to use fiberglass and copper energy conductors engineered to capture various forms of wave energy and tune them for useful applications.

The researchers created a series of five fiberglass and copper energy conductors on a circuit board, which was able to convert microwaves into 7.3V of electrical energy. By comparison, Universal Serial Bus (USB) chargers for small electronic devices provide about 5V of power.

This five-cell metamaterial array developed by Duke engineers converts stray microwave energy, as from a Wi-Fi hub, into more than 7 volts of power with an efficiency of 36.8% -- comparable to a solar cell (Image: Duke University).

"We were aiming for the highest energy efficiency we could achieve," Hawkes said. "We had been getting energy efficiency around 6% to 10%, but with this design we were able to dramatically improve energy conversion to 37%, which is comparable to what is achieved in solar cells."

The energy collection device could be tuned for a multitude of frequencies to collect different types of energy, including vibration and sound energy.

"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," Katko said.

Lucas Mearian covers consumer data storage, consumerization of IT, mobile device management, renewable energy, telematics/car tech and entertainment tech for Computerworld. Follow Lucas on Twitter at @lucasmearian or subscribe to Lucas's RSS feed. His e-mail address is lmearian@computerworld.com.

See more by Lucas Mearian on Computerworld.com.

Read more about emerging technologies in Computerworld's Emerging Technologies Topic Center.

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