Scientists at Duke University have developed a new method of transmitting power wirelessly over much greater distances than previously achieved, bringing us closer to the possibility of a society where mobile electronic devices can be charged virtually anytime, anywhere.
While the idea of wirelessly transferring power to an electronic device is not a new concept, experimental attempts thus far have yielded somewhat bulky devices that must be either close to or touching a device in order to transfer power. These power transfer devices also often must be connected to a power source of their own, limiting possible locations for where they can be used.
Now, researchers at Duke University’s Pratt School of Engineering have demonstrated the transfer of power wirelessly using low-frequency magnetic fields over distances much larger than the size of the transmitter and receiver. The technique utilizes a square “superlens” capable of “translating” a magnetic field emanating from one power coil onto another coil placed almost a foot away, inducing an electric current in the second coil. The results are published in the journal Nature Scientific Reports.
“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,” Yaroslav Urzhumov, assistant research professor of electrical and computer engineering at Duke University, said. “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.”
Together with researchers from the Toyota Research Institute of North America, Urzhumov and his team built the superlens, which resembles multiple giant Rubik’s cubes stacked together. All exterior and interior surfaces of the hollow blocks are intricately etched with a spiraling copper wire; the pattern effectively forms 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.”
To create the necessary magnetic field, a small copper coil with an alternating electric current running through it was placed on one side of the superlens. The magnetic field, however, drops in intensity and power transfer efficiency the further away from the coil it is, Urzhumov explained.
“If your electromagnet is one inch in diameter, you get almost no power just three inches away,” he said. “You only get about 0.1 percent of what’s inside the coil.” The superlens, however, increases the range of the magnetic field to almost a foot away, enabling it to induce a noticeable electric current in the other receiver coil.
However, the system still requires a lot of work before it can be used for everyday purposes. The team must figure out how to eventually provide power to larger electronic devices while keeping the power transfer device at a reasonable size, and to prevent the magnetic fields from producing undesirable effects. Urzhumov hopes to upgrade the system to make it more suitable for realistic power transfer scenarios, such as charging mobile phones as they are carried around a room, in the near future. He plans to build a dynamically tunable superlens, which can control the direction of its focused power cone.
“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,” he said. “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.”
