Present-day wireless charging makes use of induction to charge through a special case adapted to the device and a charging base connected to an electrical socket. A magnetic field is generated when the device is placed on top of the base, creating an electric current inside the case and, without the need of using any cables, the device is charged. However, if the device is separated from the base, the energy is not transferred efficiently enough and the battery cannot be charged.

The system created by the researchers overcomes these limitations. It is made up of metamaterials that combine layers of ferromagnetic materials, such as iron compounds and conductor materials such as copper. The metamaterials cover the emitter and receiver and enable transferring energy between the two, allowing a trade-off of higher efficiency for a longer distance. With the use of metamaterial crowns researchers were able in the lab to increase the transmission efficiency 35-fold.

"There is much more room for improvement, since theoretically the efficiency can be increased even more if conditions and the design of the experiment are perfected," said Alvar Sanchez, director of the research.

Metamaterial Figure 1: Researchers at the University of Barcelona in Spain have used metamaterials to improve the performance of wireless charging systems.

"Enveloping the two circuits with metamaterial shells has the same effect as bringing them close together; it's as if the space between them literally disappears", said Jordi Prat, lead author of the paper.

Moreover, the materials needed to construct these crowns such as copper and ferrite are easily available. The first experiments conducted with the aim of concentrating static magnetic fields required the use of superconductor metamaterials, unfeasible for everyday uses with mobile devices. In contrast, low frequency electromagnetic waves, the ones used to transfer energy from one circuit to the other, only need conventional conductors and ferromagnets.

The device has been patented by the University and the researchers said companies from several different countries have shown interest in applying the technology. The research was funded by the PRODUCTE project of the Government of Catalonia, the European Regional Development Fund (ERDF) and the Spanish Ministry for Economy and Competitiveness.