A team of U.S. researchers was able to power a light bulb from a power source more than two metres away, an advance in wireless power transfer that could cut the final cord required by portable technology.

Researchers at the Massachusetts Institute of Technology said the technology they call WiTricity — as in wireless electricity — allows power to cross distances even when there is no physical connection or straight path between the power source and the object to be charged.

The work, led by MIT physics professor Marin Soljacic, is reported in the June 7 issue of Science Express, the advanced online publication of the journal Science.

The concept of sending power wirelessly is not new — a century ago inventor Nikola Tesla dreamed of powering entire neighbourhoods without physical connections. And devices such as radio frequency ID tags already exist that can send wireless power through radio signals, though the method is not seen as a practical form of energy transfer for more powerful devices because the signals travel in all directions.

Instead of radio signals, the MIT scientists used the principle of coupled resonance. Just as an opera singer hitting a particular note might shatter a glass that resonates at the same frequency, the researchers found an electromagnetic resonator can send out energy at a frequency that only a particularly tuned receiver can receive.

The researchers successfully tested the principle in powering a 60-watt light bulb from seven feet, more than two metres, away.

"It was quite exciting," said Soljacic.

The process is "very reproducible," he added. "We can just go to the lab and do it whenever we want."

The design of the device includes two copper coils, one attached to the power source and the other to the light bulb.

Instead of sending out waves of radio signals, the coil attached to the power source filled the space around it with a magnetic field that oscillated at a particular frequency in the MHz range. The receiving coil then vibrates in response to that frequency.

The researchers say the magnetic resonance is safe for humans and won't affect other electronic devices.

It's not the first technology to use magnetic fields to power a device. Michigan-based Fulton Innovation unveiled a product dubbed eCoupled at the Consumer Electronics Show that can send power over very short distances (about 2 centimetres) via a magnetic field that doesn't interfere with other short-range signals or demagnetize credit cards.

But the MIT researchers say the use of coupled resonance is unique, though the technology likewise has a limited range: it can only travel over distances of up to eight times the radius of the coils used to send and receive the signals. The power transfer is also only 40 per cent efficient.

The researchers plan to test the technology next on more advanced devices such as laptops.

With files from the Associated Press