The science fiction idea of wireless electricity inched closer to fact this week as Finnish handset giant Nokia made headway in using ambient radio waves as a power source.

Boffins at the Nokia Research Centre have been using the electromagnetic radiation emitted from wifi transmitters, mobile phone antennas, TV masts and the like to harvest 3-5 milliwatts using current prototypes test circuits in the lab.

The target is to hit 50 milliwatts, which would be enough to eventually re-juice a phone that has run its battery flat.

Nokia researcher Markku Rouvala said that the concept is based on the idea behind an RFID tag – converting electromagnetic waves into an electrical signal. Rouvala’s team is working on increasing the range of frequencies from which power can be harvested from the ambient radio waves. By focusing on everything from 500MHz to 10GHz they expect to increase the chances of getting enough juice.

If Nokia is successful, and that’s a big ‘if’, the technology could find its way into mobile devices that would charge themselves wherever they are in your home. However the company is keen to point out that this research project is still in the early stages and the end game may be very difficult or impossible to achieve.

In the past, researchers are the Massachusetts Institute of Technology (MIT) have focused on magnetically coupled resonance as a way of providing wireless electricity.

In 2007, the MIT team discounted electromagnetic radiation, such as radio waves, which spread in all directions, and focused on findings that two resonant objects of the same resonant frequency tend to exchange energy efficiently, while interacting weakly with extraneous off-resonant objects. For example, a child on a swing must pump her legs at the natural frequency of the swing in order to impart substantial energy.

Electromagnetic resonators couple mostly through their magnetic fields and are able to identify the strongly coupled regime in this system, even when the distance between them is larger than the size of the resonant objects. This way, efficient power transfer is enabled.

The MIT team said that magnetic coupling is suitable for everyday applications because most common materials interact only very weakly with magnetic fields, so interactions with extraneous environmental objects are suppressed even further.

The 2007 demonstration design consisted of two copper coils, one attached to the power source, which filled the space around it with a non-radiative magnetic field oscillating at MHz frequencies. The non-radiative field mediates the power exchange with the coil on the receiving unit, specially designed to resonate with the field.

Power levels more than sufficient to run a laptop could be transferred over room-sized distances nearly omni-directionally and efficiently, without line of sight. Eventually, this could eliminate the need for batteries altogether.