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How It Works: Wi-Tricity

How It Works: Wi-Tricity

By Matt Gibson

Don’t you hate it when you forget to put your mobile phone on charge? Well, take heart — a new technology called WiTricity could mean never having to plug it in again. Welcome to the world of wireless electricity!

An irritated scientist is a dangerous thing. Thomas Edison kept stubbing his toe in the dark and now his light bulbs are busy warming the globe and annoying astronomers with their light pollution.

Marin Soljačić of the Massachusetts Institute of Technology (MIT) was woken up one time too many by the “LOW BATTERY” beep of his mobile phone, and decided that he also wanted to change the world. Since that fateful 3am incident, Soljačić and his team have been researching “WiTricity”- wireless electricity.

A hundred years ago, Nikola Tesla (click here for a short biog) started looking into the idea of transmitting power without wires. Soljačić is one of many people to follow in Tesla’s lightly smouldering footsteps. So why does he think he’s going to succeed where others have failed?

Why the old way sucks
Most previous wireless electricity research has been devoted to power transfer by something called radiative transmission - transmission by long-distance “far field” electromagnetic effects, like microwave beams.

This method sucks in a couple of important ways. Firstly, the power gets broadcast and wasted whether anything uses it or not. Secondly, if you want to power a moving object, you either have to sling the energy in all directions and hope for the best, or you have to track the object and keep the energy beaming in its direction.

Radiative transmission isn’t just complicated, it can be downright dangerous for anything that gets in between the transmitter and the receiver. Take microwaves, for example.

If you want a demonstration of the dangers, pop an egg in your microwave oven for a couple of minutes – and we use the word “pop” advisedly. Now imagine these microwave beams are pointing at a phone in your pocket.

So, what’s Soljačić up to?

Well, if the answer’s difficult, then change the question! The scale of the problem has changed since Tesla's day. We already have massive wired distribution grids strung across our countries, so Soljačić realised that we might as well live with the pylons and solve today’s problems.

We’ve seen a massive increase in the number of gadgets in the last decade. From the mobile phone, through laptops and iPods, we're heading into a future with robotic vacuum cleaners and the like. We’re filling our homes and workplaces with objects that need regular charging, lest they lose our work, beep in the middle of the night, or conk out while hoovering the downstairs toilet.

Therefore, instead of long-distance methods, Soljačić’s team have been looking at non-radiative, near-field transfer. Or, to put it another way, power transfer on the scale of your living room, using the magnetic near-field rather than far-flung electric field transfer.

Why the new way kicks ass
It’s all about resonance, the way a system naturally vibrates more easily at a particular frequency, whether it’s a wine glass being shattered by an opera singer or a Millennium Bridge being wobbled by people marching over it.

With WiTricity, the magnetic transmitter is tuned to a particular resonant frequency. If no receiver is there to pick it up, the transmitter mops up most of the power it is “broadcasting”; only a receiver with a matching resonant frequency will draw power from the system.

The team reckon their method is about a million times more efficient than old fashioned magnetic induction, which is what charges your electric toothbrush.

More importantly, magnetic fields tend not to interact with vital bits of your body. “The fact that magnetic fields interact so weakly with biological organisms is also important for safety considerations,” says Soljačić’s colleague, Andre Kurs - though it may have been hard to hear him over the sound of homing pigeons bouncing off his lab windows.

In a recent demo, the MIT team broadcast enough energy to run a 60 watt light bulb from a distance of two meters, using copper-coil antennae as part of their resonant circuits.

The team hope to send power to mobile devices anywhere in a room, or even robots on a factory floor. Curiously, the research was funded by the US Army's Institute for Soldier Nanotechnologies. The team are keeping quiet about military applications, but the Null wonders if they might be saving the army from buying a few billion very, very small mains adapters.

Several people had invented a light bulb before Edison got his hands on the problem. What got Edison the money was inventing a light bulb that could be mass-produced and used in people’s homes without setting fire to the cat.

Similarly, the basic physics of WiTricity aren’t new. What Soljačić‘s team is busy researching is this: can we engineer this existing science to the point where we’ll never again get woken up by that irritating “LOW BATTERY” beep?

Here’s hoping. Soljačić intends to have the system ready for commercial use within five years.

On Matt's wavelength?  Why not check out his homepage?

Or find out what the Null thinks about...

Books - The Electric Universe
- Straight - Spontaneous human combustion
- Spoof - Transmitting food
- Straight - Nikola Tesla: electric genius

Image: Igor Kasalovic

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30 May 2010
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