Duke University researchers have demonstrated the feasibility of wireless power transfer using low-frequency magnetic fields over distances much larger than the size of the transmitter and receiver currently used in portable electronics.
A team of researchers at Duke's Pratt School of Engineering used metamaterials to create a “superlens” that focuses magnetic fields. The superlens translates the magnetic field emanating from one power coil onto its twin nearly a foot away, inducing an electric current in the receiving coil.
“The true functionality that consumers want and expect from a useful wireless power system is the ability to charge a device wherever it is—not simply to charge it without a cable,” said Yaroslav Urzhumov, assistant research professor of electrical and computer engineering at Duke University. “Previous commercial products like the PowerMat have not become a standard solution exactly for that reason; they lock the user to a certain area or region where transmission works, which, in effect, puts invisible strings on the device and hence on the user. It is those strings—not just the wires—that we want to get rid of.”
The researchers created a square superlens, which looks like a few dozen giant Rubik's cubes stacked together. Both the exterior and interior walls of the hollow blocks are intricately etched with a spiraling copper wire. The geometry of the coils and their repetitive nature form a metamaterial that interacts with magnetic fields in such a way that the fields are transmitted and confined into a narrow cone in which the power intensity is much higher.
On one side of the superlens, the researchers placed a small copper coil with an alternating electric current creating a magnetic field around the coil. The magnetic field is focused nearly a foot away with enough strength to induce noticeable electric current in an identically sized receiver coil, according to Urzhumov.
Urzhumov said that magnetic fields have distinct advantages over the use of electric fields for wireless power transfer.
“The FCC approves the use of 3-Tesla magnetic fields for medical imaging, which are absolutely enormous relative to what we might need for powering consumer electronics. The technology is being designed with this increased safety in mind.”
Going forward, Urzhumov wants to drastically upgrade the system to make it more suitable for realistic power transfer scenarios, such as charging mobile devices as they move around in a room. He plans to build a dynamically tunable superlens that can control the direction of its focused power cone.
This would substantially expand the usable volume of “power hot spots.” The follow-up challenge is to maintain the efficiency of the power beam, according to Urzhumov.
The results of the experiment, a partnership with the Toyota Research Institute of North America, are published in Nature Scientific Reports.
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