WIRELESS DEVICE GRABS ‘LOST’ ENERGY

[Andre Kesteloot]

http://scitation.aip.org/content/aip/journal/apl/103/16/10.1063/1.4824473


  WIRELESS DEVICE GRABS ‘LOST’ ENERGY FROM WI-FI

DUKE UNIVERSITY 
<http://www.futurity.org/university/duke-university/>rightOriginal Study 
<http://scitation.aip.org/content/aip/journal/apl/103/16/10.1063/1.4824473>
Posted by Karyn Hede-Duke 
<http://www.futurity.org/author/karyn-hede/> on November 8, 2013

Using inexpensive materials configured and tuned to capture microwave 
signals, researchers 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 cell phone battery or other small 
electronic device, according to a report appearing in /Applied Physics 
Letters/ 
<http://scitation.aip.org/content/aip/journal/apl/103/16/10.1063/1.4824473>.
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.


      ENERGY EFFICIENCY

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 energy efficiency we could achieve,” 
says 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 
says. “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.”


      METAMATERIAL POSSIBILITIES

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 says. Another application could be to improve the energy 
efficiency of appliances by wirelessly recovering power that is now lost 
during use.
“The properties of metamaterials allow for design flexibility not 
possible with ordinary devices like antennas,” says 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 say 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,” 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.”
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 explain.
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.
The Army Research Office supported the research.


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