January 11, 2014
Superlens Approach Allows For Longer-Distance Wireless Device Charging
redOrbit Staff & Wire Reports - Your Universe Online
Researchers from Duke University have come up with a method of wirelessly charging electrical devices using low-frequency magnetic fields, according to a study appearing in Friday’s edition of the journal Nature Scientific Reports.“The ability to wirelessly power electrical devices is becoming of greater urgency as a component of energy conservation and sustainability efforts,” the researchers wrote. However, due to health and safety concerns, the majority of wireless power transfer methods rely on very low frequency, quasi-static magnetic fields that require oversized devices capable of charging devices over fairly short distances.
In the newly-published study, researchers from Duke’s Pratt School of Engineering have demonstrated the feasibility of a technique which uses metamaterials to create a “superlens” to focus magnetic fields. This superlens translates the magnetic field emanating from one power coil onto another located approximately one foot away, inducing an electric current in the second coil, the study authors explained in a statement Thursday.
“The experiment was the first time such a scheme has successfully sent power safely and efficiently through the air with an efficiency many times greater than what could be achieved with the same setup minus the superlens,” said the researchers, who conducted the research in collaboration with the Toyota Research Institute of North America.
“For the first time we have demonstrated that the efficiency of magneto-inductive wireless power transfer can be enhanced over distances many times larger than the size of the receiver and transmitter,” explained Duke University assistant research professor of electrical and computer engineering Yaroslav Urzhumov. “This is important because if this technology is to become a part of everyday life, it must conform to the dimensions of today’s pocket-sized mobile electronics.”
Urzhumov and his colleagues created a square superlens which they said resembled a few dozen giant Rubik’s cubes stacked one on top of another. The blocks are hollow, and both the interior and exterior walls were etched from a spiraling copper wire similar to a microchip. The coils’ structure allows them to form a metamaterial that allows magnetic fields to be transmitted and confined inside a narrow cone, where the power intensity increases.
The engineers placed a small copper coil with an alternating electric current running through it on one side of the superlens, creating a magnetic field around the coil. However, that field drops in intensity and power-transfer efficiency extremely quickly as it gets further away.
Yet with the superlens in place, the magnetic field is focused nearly one-foot away, allowing it to remain strong enough to induce noticeable electric current in an identically sized receiver coil, Urzhumov said. He added that previous experiments involving metamaterial-enhanced wireless power devices were only capable of transmitting power approximately the same as the diameter of the power coils.
These types of charging methods would require very large coils in order to work over larger distances. However, as Urzhumov explained, space limitations make this approach “impractical.” Conversely, the superlens allows them “to use small-size sources and/or receivers” in order to allow for longer-distance wireless charging.
“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,” the university added. "He plans to build a dynamically tunable superlens, which can control the direction of its focused power cone… If successful, the usable volume of ‘power hot spots’ should be substantially expanded.”