Researchers at Duke University's Pratt School of Engineering have designed a wireless power-harvesting device that converts a microwave signal to direct current with efficiency similar to that of modern solar panels by using inexpensive metamaterials configured and tuned to capture microwave signals.
Metamaterials are engineered structures that can capture various forms of wave energy and tune them for useful applications.
The device operates on a similar principle to solar panels, which convert light energy into electrical current, but in addition could be tuned to harvest the signal from other energy sources, including satellite signals, sound signals or Wi-Fi signals, the researchers say.
The researchers 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, USB chargers for small electronic devices provide about 5V of power. The number of conductors can be expanded 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 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.
"With this design we were able to dramatically improve energy conversion to 37 percent, which is comparable to what is achieved in solar cells," said researcher Allen Hawkes.
The technology potentially has 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. Another application could be to improve the energy efficiency of appliances by wirelessly recovering power that is now lost during use.
The researchers said a modified array of power-harvesting metamaterial could potentially be built into a cellphone, allowing the phone to recharge wirelessly by harvesting energy from a nearby cellphone tower via a conventional power outlet when the cellphone is not in use.
The research was supported by a Multidisciplinary University Research Initiative from the Army Research Office.
A report on this research appearing in the journal Applied Physics Letters in December is available online now.
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