A device similar in size and shape to a flat-screen TV could soon be remotely charging any device within its line of sight.

Engineers at Duke University, the University of Washington and Intellectual Ventures’ Invention Science Fund have shown that the technology already exists to build such a system—it is only a matter of taking the time to design it.

A device the size and shape of a flat-screen TV could continuously charge multiple devices throughout a room. Image credit: Duke University. “Whether it's headphones, cell phones, watches or even your mouse and keyboard, a major irritation for consumers is the hassle of being tethered to cords to recharge batteries,” notes David Smith, chair of Duke's Department of Electrical and Computer Engineering. “Our proposed system would be able to automatically and continuously charge any device anywhere within a room, making dead batteries a thing of the past.”

Some wireless charging systems already exist to help power speakers, cell phones and tablets. But these technologies rely on platforms that require their own wires, and the devices must be placed in the immediate vicinity of the charging station.

This is because existing chargers use the resonant magnetic near-field to transfer energy. However, the magnetic near-field approach is not an option for power transfer over larger distances because the coupling between source and receiver drops rapidly with distance.

The proposed wireless power transfer system instead would operate at much higher microwave frequencies, at which the power transfer distance could extend well beyond the confines of a room. To maintain reasonable levels of power transfer efficiency, the key to the system is to operate in the Fresnel zone—a region of an electromagnetic field that can be focused, allowing power density to reach levels sufficient to charge many devices with high efficiency.

The solution proposed by Smith and his colleagues relies on metamaterials—a synthetic material composed of many individual, engineered cells that together produce properties not found in nature.

“Imagine you have an electromagnetic wave front moving through a flat surface made of thousands of tiny electrical cells,” says Smith. “If you can tune each cell to manipulate the wave in a specific way, you can dictate exactly what the field looks like when it comes out on the other side.”

The team's approach anticipates the use of flat reconfigurable satellite antennas, of the sort that could be manufactured at the same plants that produce LCD televisions. A flat metamaterials-based wireless power system no bigger than a flat-screen TV would be capable of focusing beams of microwave energy down to a spot about the size of a cell phone within a distance of up to 10 meters, they calculate—and should also be capable of powering more than one device at the same time.

There are challenges to engineering such a system. A powerful, low-cost, highly efficient electromagnetic energy source would need to be developed. And the system would have to automatically shut off if a person or a pet were to walk into the focused electromagnetic beam.

“All of these issues are possible to overcome,” says Smith. “We actually came up with some nice analytical formulas for coverage areas and efficiencies that would be possible. I think building a system like this, which could be embedded in the ceiling and wirelessly charge everything in a room, is a very feasible scheme."