Clean Power

Published on November 12th, 2013 | by James Ayre


Harvesting Lost Wave Energy From The Air — New Device For Generating Electricity From Wireless Energy Achieves 37% Efficiency

November 12th, 2013 by  

An energy-harvesting device capable of utilizing the signals from a wide variety of energy sources — such as microwaves, Wi-Fi signals, satellite signals, and sound signals — has been created by researchers at Duke University’s Pratt School of Engineering.

While the concept itself isn’t anything new, the execution in this case is — the new device has achieved an energy conversion efficiency of up to 37%, putting it on par in that regard with solar cell technology,

This five-cell metamaterial array developed at Duke University has a power-harvesting efficiency of 36.8 percen -- comparable to a solar cell. Image Credit: Duke Photography

This five-cell metamaterial array developed at Duke University has a power-harvesting efficiency of 36.8 percen — comparable to a solar cell.
Image Credit: Duke Photography

The new device works on a similar principle to that used in solar panels, but in this case the energy involved isn’t light energy, it’s other forms of wave energy. The key to the device’s impressive abilities apparently lies in its application of metamaterials — which are, essentially, simply engineered structures that are able to capture various forms of wave energy and tune them for useful applications.

Duke University provides some details:

They used a series of five fiberglass and copper energy conductors wired together on a circuit board 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.

(With regard to potential uses) — 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. Another application could be to improve the energy efficiency of appliances by wirelessly recovering power that is now lost during use. With additional modifications, 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.

(Or) a series of power-harvesting blocks could be assembled to capture the signal from a known set of satellites passing overhead. The small amount of energy generated from these signals might power a sensor network in a remote location such as a mountaintop or desert, allowing data collection for a long-term study that takes infrequent measurements.

“We were aiming for the highest energy efficiency we could achieve,” stated undergraduate engineering student Allen Hawkes. “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.”

“It’s possible to use this design for a lot of different frequencies and types of energy, including vibration and sound energy harvesting,” added researcher Alexander Katko. “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.”

“The properties of metamaterials allow for design flexibility not possible with ordinary devices like antennas,” he continued. “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.”

“Our work demonstrates a simple and inexpensive approach to electromagnetic power harvesting,” stated lead investigator Steven Cummer, a professor of electrical and computer engineering at Duke. “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 new research will appear in the December 2013 edition of the journal Applied Physics Letters.

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About the Author

's background is predominantly in geopolitics and history, but he has an obsessive interest in pretty much everything. After an early life spent in the Imperial Free City of Dortmund, James followed the river Ruhr to Cofbuokheim, where he attended the University of Astnide. And where he also briefly considered entering the coal mining business. He currently writes for a living, on a broad variety of subjects, ranging from science, to politics, to military history, to renewable energy. You can follow his work on Google+.

  • JamesWimberley

    What’s the amount of energy typically available in the form of electromagnetic waves other than light and infrared/ultraviolet? They don’t say and I guess not much. What this will be useful for is energy harvesting. ARM and its ecosystem are working on ultralow-power sensors and processors that can scavenge enough energy from their environment to operate. Not very fast, but who needs a thermometer to be fast? We will be able to get rid of a lot of batteries.

  • sault

    Duke’s statement makes my head hurt…A Volt is neither a unit of energy or power! It is a unit of electrical potential between 2 points. how in the world does Duke University mess this fundamental distinction up? And then they go on to compare this device to a 5V USB port without admitting that a USB connection can move hundreds to thousands of times more current than this “wave harvester”? Maybe thats why they also try to compare it to solar cells even though solar energy again has thousands to millions of times more energy flux than all the wireless signals bouncing around down here on Earth.
    Please do a better job in reporting the basic facts. Slip-ups like this only serve to discredit clean energy and embolden its opponents.

    • Peter Gray

      I agree! Where are the content cops when we need them? This kind of sloppy reporting, all too common, makes me leery of accepting anything that appears on cleantechnica. An article a few months ago on flying cars was another example of gawdawful tech reporting.

      The volts = power error is stunning, but maybe worse is the suggestion that satellite RF signals could be profitably harvested (!?!?). What scale of scientific ignorance can accommodate that? Solar RF flux is orders of magnitude (10^5, 6, 8?) higher than what any satellite can produce, and there’s a good reason we don’t bother trying to harvest the little energy tail of solar radio. Sheesh!

      Newsflash, Duke dudes! We already know how to “power a sensor network in a remote location.” It’s a little thing we call solar PV. check it out someday.

  • Matt

    “including vibration and sound energy harvesting” now that application sound goods. But the one to capture WiFi or cell phone signal and convert to NRG is going to reduce the range of those signals. If I extract NRG from the signal, the signal has less strength.

    • sean

      only in the direction you are in. even then there will be some passive re-radiation. the amount of power you could pull on one of these things will be tiny..

    • Corbin Holland

      Why do you keep calling energy NRG? Most of NRG’s electrical generation comes from fossil fuels. Are you trying to shamelessly advertise for fossil fuels on a clean tech website?

    • Peter Gray

      No, that doesn’t sound good at all, and you don’t need any fancy research to verify it on your own. For example, the world’s loudest air raid siren uses a 180-HP (134 kw) motor to produce 138 dB at 100 feet (ear-shattering at that range, audible miles away). Assuming ALL the input power is converted to sound, none is lost in transit, and 100% is recovered by these harvesting gadgets, they would collect about 10 watts/sq. meter – much less than a decent PV panel. But typical real-world sound energy levels are thousands of times lower than we’d get from that super siren. So forget about it. Not gonna happen.

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