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,
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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