New device converts microwave signals into electricity

A new wireless device that converts microwave signals into electricity capable of charging cell phones or other small gadgets has been developed, scientists say.
Using inexpensive materials configured and tuned to capture microwave signals, researchers from Duke University designed the power-harvesting device with efficiency similar to that of modern solar panels.
The device wirelessly converts the microwave signal to direct current voltage, researchers said.
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, the 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.

"The properties of metamaterials allow for design flexibility not possible with ordinary devices like antennas," said Katko.
"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," said Katko.

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.
"Our work demonstrates a simple and inexpensive approach to electromagnetic power harvesting," said Cummer.
"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," Cummer said.
The study will appear in the journal Applied Physics Letters.