by Minnie Glymph
7 November 2013
Designed by Duke Engineers
Power as Efficiently as Solar Panels
How do you define free energy?
A cheap device
that converts freely available background
energy to run gadgets or charge
No fossil fuel needed. No turbines
need to be spun.
A clean energy whether or not
the sun shines or the wind blows.
Today, researchers from Duke University
announced a breakthrough new device that
harvests WiFi and converts it into direct
current to charge batteries. The team achieved
an astonishing energy conversion rate
to current solar panels.
five-cell metamaterial array developed at Duke University
power-harvesting efficiency of 36.8 percent - comparable to a solar
Click here for more information.
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
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 the
journal Applied Physics Letters in December 2013 (A
Microwave Metamaterial with Integrated Power Harvesting
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
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
energy efficiency 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
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 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."
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
"Our work demonstrates a simple and
inexpensive approach to electromagnetic power harvesting," said
"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
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
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 research was supported by a
Multidisciplinary University Research Initiative from the
Army Research Office (Contract No. W911NF-09-1-0539)