Duke University's 'superlens' could enable wireless charging via magnetic fields

The concept of ubiquitous "power hot spots" that enable users to wirelessly charge a device wherever it is remains just a dream, but researchers at Duke University have developed a technology that may lay the foundation for bringing that vision to fruition. Duke University researchers used what they call a "superlens" to wirelessly transfer power via low-frequency magnetic fields over distances much larger than the size of the transmitter and receiver.

The experiment, resulting from a partnership between Duke's Pratt School of Engineering and Toyota Research Institute of North America, used a superlens made of metamaterials to translate the magnetic field emanating from one power coil onto its twin nearly a foot away, inducing an electric current in the receiving coil. The square superlens is said to resemble a few dozen giant Rubik's Cubes stacked together.

"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," said Yaroslav Urzhumov, assistant research professor of electrical and computer engineering at Duke. "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."

According to Urzhumov, metamaterial-enhanced wireless power demonstrations have been made previously at Mitsubishi Electric research laboratory. However, in those demos, the distance the power was transmitted was roughly the same as the diameter of the power coils, meaning the coils would need to be quite large to work over any appreciable distance.

"It's actually easy to increase the power transfer distance by simply increasing the size of the coils," Urzhumov said. "That quickly becomes impractical, because of space limitations in any realistic scenario. We want to be able to use small-size sources and/or receivers, and that's what the superlens enables us to do."

Urzhumov said there are advantages to using magnetic fields, rather than electric fields, for wireless power transfer. For one thing, most materials do not absorb magnetic fields very much, making them safer than electric fields.

"In fact, 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," he said.

Urzhumov wants to upgrade the system to accommodate scenarios such as charging mobile devices as they move around in a room. He plans to build a dynamically tunable superlens, which can control the direction of its focused power cone.

The wireless charging field has become a hotbed of activity. For example, during last week's Consumer Electronics Show, MediaTek announced the development of multimode receiver technology for inductive and resonant charging using in-band communications. In addition, the Alliance for Wireless Power (A4WP) launched its global Rezence certification program for wireless charging products based on resonant technology.

For more:
- see this Duke release

Related articles:
Alliance for Wireless Power launches 'Rezence' brand for wireless charging
Qualcomm joins PMA but continues to push for single wireless charging standard
Intel joins A4WP as wireless charging battle heats up
AT&T snubs Qi wireless charging standard with support for Power Matters Alliance
Nokia design chief hints at future NFC support, wireless charging