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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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By Chernobyl68 on 6/11/2007 12:36:33 PM , Rating: 2
in the photo the coils seem to be parallel to one another. I wonder if the orientation of the coils matters?

In the future, assuming this scales up well, might you see this replace the electrical distribution network?
Create a standard resonating coil for powerplants, which sends power to the substations in a geographic area, which connect to different coils which send power to coils at your homes. Your home then runs off of a small coil which resonates with the coils in all your electrical appliances.

Would you still need transformers to step voltage from generation to end user?

How is power shared? The example doesn't show the effect of bulbs of different ratings. Also, the resonant frequencies are in the Mhz range according to the article. presumably we'd need to be able to step up current generation frequencies to the coil frequencies, and vice versa. The example works with a light bulb because it is a simple resistor, insensitive to voltage frequency.

RE: Hmmm...
By zsouthboy on 6/11/2007 1:15:12 PM , Rating: 2
Coils have to be parallel to work.

Getting two or more coils into the same "resonate frequency" is a PITA. They did it by hand tuning, in this case.

RE: Hmmm...
By KristopherKubicki on 6/11/2007 1:41:47 PM , Rating: 2
Yes, good point, though I suspect in future revisions this can be done mechanically. As you said they have to be parallel, but I do not believe they need to be parallel on-center. It seems like someone could devise a method for the base station to align with whatever respect the receiver is setup.

RE: Hmmm...
By zsouthboy on 6/11/2007 1:52:58 PM , Rating: 2
It would be neat to see something like - I don't know, a spherical coil - end up working. My guess is that these guys (who are much much smarter than I) have tried such a thing already, though, and it didn't work.

RE: Hmmm...
By Goty on 6/11/2007 2:37:28 PM , Rating: 2
They don't have to be exactly parallel, but you won't be able to achieve any sort of induction if the coils are oriented at right angles to one another since the field produce by the generating coil is polarized.

RE: Hmmm...
By Chernobyl68 on 6/11/2007 5:28:41 PM , Rating: 2
then as a power transmission tool, these are next to pointless. to work on a large scale, broadcast-power type of operation, it would need to be omnidirectional.

if this will only work point to point, you may as well stick with the existing infrastructure.

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