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Power-harvesting device converts microwave signals into electricity


November 7, 2013

The five-cell metamaterial array developed by Duke engineers that converts stray microwave energy, as from a Wi-Fi hub, into more than 7 V of power with an efficiency of 36.8 percent

The five-cell metamaterial array developed by Duke engineers that converts stray microwave energy, as from a Wi-Fi hub, into more than 7 V of power with an efficiency of 36.8 percent

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Joining the ranks of devices designed to harvest energy from ambient electromagnetic radiation comes an electrical circuit from researchers at Duke University that can be tuned to capture microwave energy from various sources, including satellite, sound or Wi-Fi signals. The researchers say the device converts otherwise lost energy into direct current voltage with efficiencies similar to that of current solar cells.

Duke University students Allen Hawkes and Alexander Katko, working with lead investigator and Duke professor of electrical and computer engineering Steven Cummer, built the device using five fiberglass and copper energy conductors wired up to a circuit board to form a five-cell metamaterial array. The team says the resulting electrical circuit is able to harvest microwaves and convert them into 7.3 V of electrical energy. They compare this to USB chargers for mobile devices that provide around 5 V of power.

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

In addition to microwaves, the researchers say the metamaterial array could be tuned to harvest power from a range of frequencies, as well as vibrations and sound waves.

“Until now, a lot of work with metamaterials has been theoretical,"says Katko. "We are showing that with a little work, these materials can be useful for consumer applications. The properties of metamaterials allow for design flexibility not possible with ordinary devices like antennas. 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.”

Katko also suggests that a metamaterial coating could be applied to the ceiling of a room to harvest Wi-Fi signals or recover otherwise lost power from home appliances to improve their energy efficiency. But one of the most attractive potential uses would be to embed the energy-harvesting metamaterial in a mobile phone. The researchers say this could be accomplished with some modifications to the technology and provide people in remote locations with the ability to harvest energy from a mobile phone tower.

“Our work demonstrates a simple and inexpensive approach to electromagnetic power harvesting,” says 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.”

In this way, a series of blocks could be set up to harvest energy from satellites passing overhead. Although this wouldn't yield a large amount of power, the researchers say it could be enough to a remote sensor network used for infrequent data collection in remote locations.

The team's power-harvesting device is detailed in a paper in the journal Applied Physics Letters.

Source: Duke University

About the Author
Darren Quick Darren's love of technology started in primary school with a Nintendo Game & Watch Donkey Kong (still functioning) and a Commodore VIC 20 computer (not still functioning). In high school he upgraded to a 286 PC, and he's been following Moore's law ever since. This love of technology continued through a number of university courses and crappy jobs until 2008, when his interests found a home at Gizmag. All articles by Darren Quick

Okay, time to send up solar-energy-harvesting geo-synchronus satellites equipped with focused microwave beams targeted at precisely tuned receptors on the ground as a way to take harvesting solar energy to the next level! ☺


@ MzunguMkubwa more stuff in space is risky. keep it on the ground.

Jay Finke

thank you Dr Teslamm

Robert Margouleff

Doesn't need to be in orbit. Microwaves are everywhere. Just take a few hundred square miles of uninhabitable land, and spread them all over. Just a few transformers in the circuit, and kiss nuke power , and fossil fuel generators, good bye. Oh... might be a little resistance to that last one. I just really hope that this isn't an idea that takes 30 years to implement, like (sadly) so many other essential ones seem to take..


I think this technology could really be useful. But considering what microwaves can do to my lunch, I wonder just how good it is that we have them scattered all over the place.


@ Jay Finke putting it on the ground means that for over half the time it is not generating electricity.


This article suggests using metamaterials to scavenge power for cell phones. Great!! However it is disappointing that cell phones are not already routinely equipped with solar cells for "scavenging" power from light. Odd as this technology exists. The only use of solar always seems to be an external add-on or a case. Remember the solar powered calculator? Every phone should have an integral solar charger/battery extender. While solar may not fully power the phone it can extend battery life.

Don Betton

It would be interesting to get some idea of possible wattage per sqft of panels. Voltage and energy conversion say nothing about the power potential. Further there is the slight issue of economics. What investment is needed to get a watt under assumed mass scale conditions? I moderate the 2700+ member Yahoo's Alternatepower Group where we have had some highly skeptical exchange on Hawkes, Katco and Cummer's findings. I'd be delighted to get feedback.

Alex Markin
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