Wireless energy transfer charges batteries

Friday, 24 November, 2006

Recharging your notebook computer and mobile phone and a variety of other gadgets might one day be possible in the same way many people now surf the web: wirelessly.

Massachusetts Institute of Technology research on the physics of electromagnetic fields shows how wireless energy could power future gadgets.

The MIT team is also working on demonstrating the technology in practice.

Scientists and engineers have known for nearly two centuries that transferring electric power does not require wires to be in physical contact all the way. Electric motors and power transformers contain coils that transmit energy to each other by the phenomenon of electromagnetic induction.

A current running in an emitting coil induces another current in a receiving coil; the two coils are in close proximity, but they do not touch.

Later, scientists discovered electromagnetic radiation in the form of radio waves, and they showed that another form of it " light " is how we get energy from the sun. But turning light into electrical power is notoriously difficult and requires a direct line of sight between transmitter and receiver.

Radio waves, and especially microwaves, can be used to transfer energy, which can then be picked up with an antenna. But transferring energy from one point to another through ordinary electromagnetic radiation is typically very inefficient, and can even be dangerous.

The waves tend to spread in all directions, so most of the energy is lost to the environment.

The researchers realised that the close-range induction taking place inside a transformer " or something similar to it " could potentially transfer energy over longer distances, say, from one end of a room to the other.

Instead of irradiating the environment with electromagnetic waves, a power transmitter would fill the space around it with a "non-radiative' electromagnetic field.

Energy would only be picked up by gadgets specially designed to "resonate' with the field. Most of the energy not picked up by a receiver would be reabsorbed by the emitter.

While rooted in well-known laws of physics, non-radiative energy transfer is a novel application no one seems to have pursued before.

Working out the details was not easy but was achieved through theoretical calculations and computer simulations.

With the proposed designs, non-radiative wireless power would have limited range and the range would be shorter for smaller-size receivers. But the team calculates that an object the size of a notebook computer could be recharged within a few metres of the power source.

Placing one source in each room could provide coverage throughout a home.

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