The cordless cord is a little closer to becoming a reality now that researchers in the US have successfully tested a mechanism to deliver power to devices without the need for wires. In the journal Science, the expiramental system was used to power a 60w light bulb two meters away from the power source. Dubbed "WiTricity", these phsyics exploits could be used to charge several devices and notebooks.
According to Professor Sir John Pendry of the Imperial College of London, "there is nothing in this that would have prevented them inventing this 10 or 20 years ago." One of the reasons this wasn't invented back in the 90's is the lack of wired devices. Now, before mentioning all the things we used to plug in to our TV sets and the newly popular computer systems, the number of portable devices requiring power were much fewer than we see today. It seems that everyone today has their own cell phone, iPod, PDA or other portable electronic device that requires a nightly charge.
The experimental setup involved two 60 cm diameter copper coils, a transmitter attached to a power source, and a receiver placed 2 meters away and attached to a light bulb. Measurements showed that energy could be transferred with 40% efficiency across the gap, and the bulb would even glow when obstructions such as wood or metal were placed in the way.
What's really cool is that this system makes use of resonance, a phenomenon that causes an object to vibrate when energy of a certain frequency is applied. When two or more objects have the same resonance, they exchange energy without having an effect on their surrounding environment.
In this setup, both coils were made to resonate at 10 MHz, allowing a couple of "tails" of energy to flow between them. Using these low frequency electromagnetic waves, which are about 30m long, also has a safety advantage. Typically when transmitters operate at higher frequencies like 2.4 GHz, then it radiates a mixture of magnetic and electric fields. This is in part because the wavelenth is much shorter than the 10 MHz spectrum, and is a characteristic of what is known as the "far field". At a distance of less than one wavelength the field is almost entirely magnetic.
Bodies respond strongly to electric fields, but does not respond to magnetic fields. As far as western science is concerned, we have zero response to magnetic fields in terms of the amount of power absorbed. This results in a low-to-nil health risk for humans and other animals.
Wireless power transfer is hardly a new idea. 19th century physicist Nikola Tesla experimented with long-range wireless energy transfer. His most ambitious attempt was a 29m high aerial known as Wardenclyffe Tower in New York, which failed when he ran out of money.