There is wireless communication - now also wireless electricity

The tangle of cables and plugs needed today to charge electronic gadgets may soon be a thing of the past. American researchers have outlined a relatively simple system that could provide power to devices such as laptops or MP3 players without cables

The tangle of cables and plugs needed today to charge electronic gadgets may soon be a thing of the past. American researchers have outlined a relatively simple system that could provide power to devices such as laptops or MP3 players without cables. The idea uses century-old physics and would be able to operate over distances of many meters, the researchers said. Although the team has not built and tested a system, computer modeling and mathematics suggest it will work.

"There are so many stand-alone devices such as cell phones and laptops that have been developed in recent years," said Professor Marvin Suliaczyk of the Massachusetts Institute of Technology (MIT) and one of the participating researchers.

"We started thinking, 'It would be really convenient if we didn't have to load all these things.'

"And because we are physicists, we asked 'what physical phenomenon can be used to carry out the wireless transfer of energy?'"

The answer the team found was "resonance", a phenomenon that causes an object to vibrate when energy is applied to it at a certain frequency.

"When there are two objects resonating with the same frequency they tend to create a very strong coupling," Professor Suliacik told the BBC news website.

You can see resonance in musical instruments, for example. "If you play a tone on one instrument, then another instrument with the same acoustic resonance will pick up the tone and it will be possible to see its vibrations with the eye," he said. Instead of using acoustic vibrations, the team's system utilizes the resonance of electromagnetic waves. AM radiation includes radio waves, infrared and X-rays.

Generally, systems that use AM radiation, such as radio antennas, are not suitable for efficient energy transfer because they scatter the energy in all directions, wasting a large amount of it into the free air.

To overcome this problem, the researchers studied a special type of "non-radiating" objects with so-called "long-lived resonances". When energy is applied to these objects, it remains attached to them, and does not escape into the air. "Tails" of energy, which can reach many meters in length, flash above the surface.

"If you bring another object resonating with the same frequency close enough to these tails, it turns out that the energy can pass through a tunnel from one object to another," said Professor Suliaczyk. Thus, a simple copper antenna designed to have a long-lived resonance can transmit energy to a laptop whose antenna resonates at the same frequency. The computer could be truly wireless. The energy that is not directed to the device is simply reabsorbed.

The systems the team described would be able to transfer energy over three to five meters. "This system will work, we say, in a room, but it can be adapted so that it works in a factory," he said. "It will also be possible to reduce it to the microscopic or nanoscopic world."

Old technology

The team from MIT is not the first to propose the wireless transfer of electricity. Nineteenth-century physicist and engineer Nikola Tesla experimented with long-range wireless transmission of energy, but his most ambitious attempt—the 29-meter-high antenna known as Wardencliffe Tower, in New York—failed when he ran out of money. Others have worked on highly directional energy transfer mechanisms such as lasers. However, these require an unobstructed line of sight, and are therefore not good for operating objects in the home.

A British company called Splashpower has also designed wireless charging pads that gadget lovers can place their phones and MP3 players directly on to charge them. The surfaces use an induction charger to charge devices, the same process used to charge electric toothbrushes.

Splashpower co-founder James Hay said the MIT team's work is "clearly early stage" but "interesting for the future." "Consumers want a simple general solution that will free them from the hassle of chargers and adapters," he said. "Wireless electricity technology has the potential to meet all these needs."

However, Hay said the power transfer is only part of the solution. "There are several aspects that need to be addressed to ensure efficient conversion of the energy into a form that can be fed to devices."

Professor Soliaczyk will present the work at the American Institute of Physics' Industrial Physics Forum in San Francisco on November 14. The work was carried out together with his colleagues Aristadis Karalis and John Joannopoulos.

For news on the subject at the BBC

For further information from June 2007 - Suliacic's team managed to light a light bulb from a distance of 2 meters