Wireless device converts 'lost' energy into electric power

Nov 07, 2013
This five-cell metamaterial array developed at Duke University has a power-harvesting efficiency of 36.8 percen -- comparable to a solar cell. Credit: Duke University

Using inexpensive materials configured and tuned to capture microwave signals, 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 the microwave signal to direct current voltage capable of recharging a battery or other small electronic device, according to a report appearing in the journal Applied Physics Letters in December 2013. (It is now available online.)

It operates on a similar principle to , 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.

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.

"We were aiming for the highest we could achieve," said Hawkes. "We had been getting energy efficiency around 6 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."

"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 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."

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."

For example, a series of power-harvesting blocks could be assembled to capture the signal from a known set of satellites passing overhead, the researchers explained. The small amount of 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.

Explore further: The very idea: Kitchen gadgets powered by microwave leaks

More information: "A microwave metamaterial with integrated power harvesting functionality," Allen M. Hawkes, Alexander R. Katko, and Steven A. Cummer. Applied Physics Letters 103, 163901 (2013); DOI: 10.1063/1.4824473

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User comments : 14

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Eikka
2 / 5 (16) Nov 07, 2013
7.3V of electrical energy. By comparison, Universal Serial Bus (USB) chargers for small electronic devices provide about 5V of power.


Okay. I stopped reading there.

If the author is so oblivious as to call Voltage both energy and then power, without noticing that something is wrong, the rest of the text cannot be any better.
axemaster
4 / 5 (3) Nov 07, 2013
Wow, are they still doing this? Wireless energy harvesting has been debunked countless times. And they're trying to do this with "satellite signals, sound signals or Wi-Fi signals". They'll be lucky to harvest even a few tens of microwatts. There simply isn't a useable amount of energy out there to be harvested, so it makes no difference how efficient your capture device is.

Here's a video from EEVBlog tearing apart a similar device:

http://www.youtub...3Xjeg0sk
Humpty
1.6 / 5 (15) Nov 07, 2013
I have a mind energy capturing devise that captures the energy from peoples life forces and thoughts.

I have mind wave panels, that charge batteries and give lighting and power to peoples homes.

It is cyclic, in that when it's dark and people are asleep, the net gain is almost zero - but during the daytime, they come up to full capture efficency.

I call them Brain Wave Day Panels.
WillieWard
1 / 5 (12) Nov 08, 2013
A device able to convert wasted heat energy into electric power with a power-harvesting efficiency higher than 36.8% can be possible by using opposing moving magnetic fields. http://www.youtub...---y5E2c

Disproselyte
1 / 5 (11) Nov 08, 2013
W(h)at(t) power, finally?
WillieWard
1.1 / 5 (11) Nov 08, 2013
designed a power-harvesting device with efficiency similar to that of modern solar panels
Such a device will block the signal for another receivers of WIFI signal, thus working as an effective jammer of it. It's nothing else but a tiny http://home.comca...e001.jpg for microwaves and it can suck the signal from wide area. I'm sure, such a device would be banned in cities if it would get a wider widespreading.

As a resonant circuit that absorbs significant amounts of energy from an RF source?
http://en.wikiped...cillator
tadchem
1.4 / 5 (11) Nov 08, 2013
This looks like a cascade receiver unit for Tesla's broadcast power - about 100 years too late.
MR166
1 / 5 (12) Nov 09, 2013
You see, they get these green energy grants from the federal government and have to show some sort of published end result. Thus, articles like this.

Perhaps if we ever had solar cells in orbit and beamed the power back to earth in the form of microwave energy this sort of device could be useful.
Q-Star
2.3 / 5 (3) Nov 09, 2013
Serious question. Since electrical engineering is not my forte, it's okay if ya give me a drubbing for it.

Is there enough radiation randomly passing through the environment at any point or place that is intense and concentrated enough to make it cost effective to pursue this technology? Or is it just a novelty? Collecting E-M radiation is not new. But nothing compares to the solar E-M in quantity, 1300 watts/meter^2, is that right? Seems like that is the place to go. Why go for microwatts when ya have kilowatts sitting right there.
MR166
1 / 5 (11) Nov 09, 2013
The short answer is no. The power levels involved are in the microwatts unless you are directly in the beam of a microwave horn and close to it.
Q-Star
2.3 / 5 (3) Nov 09, 2013
The short answer is no. The power levels involved are in the microwatts unless you are directly in the beam of a microwave horn and close to it.


Thanks, that's what I was thinking but wasn't certain. I suppose if ya were to put a collector close to and directly in the beam, the owner of said beam might take umbrage to ya sucking up his signal and blocking it from going where he intended.
MR166
1 / 5 (11) Nov 09, 2013
It is funny how all of these useless energy collection devices are touted as a way to charge a cell phone. Perhaps it is a age bracket that these articles are aimed at, the young, ignorant and gullible.
evropej
1 / 5 (10) Nov 09, 2013
You can harvest electromagnetic waves but the power per square meter for example is so tiny that it is pointless. Unless you are sitting in front of a 1 megawatt radar dome or a radio transmitter, this concept is useless and pointless. Whats disappointing is not the article, it is disappointing because its on this site.
MR166
1.3 / 5 (12) Nov 09, 2013
I am starting to think that articles like this are not created directly by the authors of the research but interpreted by some idiot at Physics.Org. Duke is a major US university and I cannot believe that the researches there actually think this device is capable of recharging a cell phone.

Note to the editor of Physics.org: Hire someone that at least passed High School physics.