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The team consists of (top to bottom, left to right) Andre Kurs, Prof. John Joannopoulos, Aristeidis Karalis, Prof. Marin Soljacic, Prof. Peter Fisher, and Robert Moffatt. (Source: MIT, Aristeidis Karalis)
A 60-watt bulb illuminates for the future of wireless power

"Wireless" isn't exactly a new concept to computing. Network connectivity, USB devices and even displays had their cords cut in recent years.  Researchers from the Massachusetts Institute of Technology took the final steps towards cutting the last tether of the laptop user: the power cord.

Transmitting power wirelessly is traditionally limited to line-of-sight methods such as microwave or laser, which have a "significant negative effect" on anyone or anything unfortunate enough to be caught in the middle.

Playfully dubbed "WiTricity" by the team, the researchers were able to power a sixty-watt lightbulb from seven feet away using the principle of magnetically coupled resonance. The basic concept is similar to existing electromagnetic inductive chargers, but does not suffer the massive drop in efficiency when distance is increased.

The experiment works as follows. Two magnetic coils resonate at the same frequency.  When one of these coils is attached to a power source, the resonant magnetic field produced by the coil increases dramatically.  The second, unpowered coil "couples" with the resonating magnetic field.  The resonance from the second coil is then converted back to electricity for the device.

The MIT researches are quick to tout magnetically coupled resonance over electromagnetic induction.  Aristeidis Karalis, an MIT graduate student that worked on the project, states, "Here is where the magic of the resonant coupling comes about. The usual non-resonant magnetic induction would be almost 1 million times less efficient in this particular system."

In addition to increased efficiency, the WiTricity project does not transmit biologically harmful electromagnetic radiation during operation.  Additionally, line-of-sight issues present in microwave technology disappear with WiTricity; magnetic fields are more-or-less unaffected by non-metallic materials in most environments. 

The most current WiTricity experiments use coils approximately 20" in diameter and operate at distances of approximately two meters.  The team hopes to eventually power a notebook from a several meters away.

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RE: questions...
By arazok on 6/11/2007 12:59:08 PM , Rating: 3
If they are getting 60W already, I would suspect that power transfer is limitless, bounded only by the size of the coils and the amount of power supplied. Range is, as stated, limited.

I read elsewhere that these are only 40% efficient, so it would have taken much more power to light the bulb. They need to shrink these down, and get the efficiency to at least 80% before these are practical. I'd expect initial commercial versions powering mice, speakers and other low power nick-knacks. I can't wait!

RE: questions...
By audiophi1e on 6/11/2007 1:59:50 PM , Rating: 2
The gas engine in your car is less than 40% efficient (I remember it's something closer to 15%). The incandescent bulb is also something around 20% or less. I'd frankly be impressed if this thing was actually 40% efficient. That's amazing to me.

RE: questions...
By Kuroyama on 6/11/2007 3:44:09 PM , Rating: 2
If their incandescent bulb was 20% efficient and the electricity transfer was 40% efficient then the combination of the two is only 8% efficient. That's pretty bad, and even worse when you factor in transmission losses too. Would be cool if efficiency improves and in the future we could make a wireless house, say put a central hub in the middle of the house and just tape or otherwise attach some glowing light panel or super thin TV wherever the mood strikes you.

However, even if efficiency doesn't improve but size decreases then it'd still be worth putting up with the energy loss to make those rarely used or low power items truly wireless: laptop, printer, rear speakers, etc.

RE: questions...
By arazok on 6/11/2007 6:01:07 PM , Rating: 2
When converting gas, hydro, nuclear etc to electric current, you are always dealing with low efficiencies. We're dealing with electric current to electric current, so that loss is already accounted for. A further 60% loss just adds to the total. PSU's in computers are over 90% efficient, and this is what you need to compete with to make this a practical application for home use. People complain about needing 600W PSU's to run their computers. Replacing those with 1200W coils is not an option.

RE: questions...
By audiophi1e on 6/11/2007 8:01:24 PM , Rating: 2
I disagree. This thing would probably still be very useful at 40% efficiency. Most things that you would like to be truly wireless don't consume *that* much power: laptop, satelite speakers (rear channel), etc. If a laptop requires let's say 60W, you only need to deliver about 200W~250W to ensure 60W delivery. Rear channels consume maybe 50W each maximum. Same story. You only need to deliver 200W each to power those babies. Some people will be more than happy to pay for that difference for the convenience and aesthetic advantage and having no power cords for certain things.

Now here's the catch: once this thing becomes commercial, and assuming the maximum range becomes fairly good--let's say 100ft--how do you prevent your neighbor from stealing your power?

It's just like your neighbor leeching your unsecured Wifi connection.

RE: questions...
By RubberJohnny on 6/11/2007 8:52:40 PM , Rating: 2
I'd expect initial commercial versions powering mice, speakers...

Does anyone else see a problem with powering speakers this way? Surely there would be major problems with the magnetic field vibrating the voice coils of the speaker?

"Google fired a shot heard 'round the world, and now a second American company has answered the call to defend the rights of the Chinese people." -- Rep. Christopher H. Smith (R-N.J.)

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