Scientists achieve wireless electricity

A team of American scientists have achieved something that could signal the beginning of a completely wireless lifestyle: They have powered a device with no physical connection to the power source.

Prof Marin Soljacic and a team from MIT have succeeded in lighting a 60 W light bulb from a power source more than 2 m away with no wiring connecting the source to the appliance.

Rather than using normal electromagnetic transmission such as radio waves, which is too inefficient, or directed radiation such as lasers, the researchers have developed a system based on magnetically coupled resonance.

The system is based on the idea that two resonant objects of the same resonant frequency tend to exchange energy efficiently, while interacting weakly with off-resonant objects. The energy transfer can be most efficient when the resonators are ‘in tune’.

The scientists say magnetic coupling is particularly 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 experimental system is based on two electromagnetic coils, each a self-resonant system. The coil attached to the power source is the sending unit, which fills the space around it with a non-radiative magnetic field oscillating at a high frequency. The receiving unit is designed specifically to resonate with the field.

The resonant nature of the process ensures the strong interaction between the sending unit and the receiving unit, while the interaction with the rest of the environment is weak.

Because the field is localised around the sending coil, wasted energy is minimal. It is suggested that a laptop-sized coil could power levels more than sufficient to run a laptop over room-sized distances, nearly omni-directionally and efficiently.