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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 Goty on 6/11/2007 2:31:22 PM , Rating: 2
Electricity and magnetism are the same thing (has been proven fundamentally for a long time now), there's no distinction other than the forms they take.


RE: questions...
By aos007 on 6/11/2007 2:43:35 PM , Rating: 2
Yes, and that's part of why I'm confused. I know how induction works, but this "magnetic resonance" business has me baffled. How do they produce magnetic field without using electricity? And if they use electricity, how is the field different from any other normal radiating electromagnetic field?


RE: questions...
By aos007 on 6/11/2007 2:52:52 PM , Rating: 2
Or is the trick that there isn't any self-inductance happening at whatever is the source of the magnetic field? Magnetic field can be produced by the flow of current but if you do it via a normal wire coil then you'd get the magnetic field cause induction current back in the same coil that produced it and then you get the whole traditional EM field business. Perhaps these source "coils" are not inductive (much)? I can't remember much from 20 years ago even though things like these were why I became an EE. Getting old sucks :(.


RE: questions...
By MrDiSante on 6/11/2007 7:03:10 PM , Rating: 2
quote:
Electricity and magnetism are the same thing

No they're not. Electric current is always coupled with magnetic fields, but magnets aren't always coupled with electric current. Take the magnet on your fridge and show me where the current is. Should be obvious to anyone who's taken any physics in high school in Canada, and I'm guessing the US.


RE: questions...
By sxr7171 on 6/12/2007 12:13:31 AM , Rating: 2
Maybe you should read this:

Physics of magnetism

Magnetic forces are forces that arise from the movement of electrical charge. Maxwell's equations and the Biot-Savart law describe the origin and behavior of the fields that govern these forces. Therefore magnetism is seen whenever electrically charged particles are in motion. This can arise either from movement of electrons in an electric current, resulting in "electromagnetism", or from the quantum-mechanical spin and orbital motion of electrons, resulting in what are known as "permanent magnets". Electron spin is the dominant effect within atoms. The so-called 'orbital motion' of electrons around the nucleus is a secondary effect that slightly modifies the magnetic field created by spin.

From here:
http://en.wikipedia.org/wiki/Magnetism#Physics_of_...

"The magnetic force is actually due[3] to the finite speed (the speed of light) of a disturbance of the electric field which gives rise to forces that appear to be acting along a line at right angles to the charges. In effect, the magnetic force is the portion of the electric force directed to where the charge used to be. For this reason magnetism can be considered to be basically an electric force that is a direct consequence of relativity."


RE: questions...
By Chernobyl68 on 6/12/2007 11:52:35 AM , Rating: 2
yes, but permanent magnets don't oscilate.


RE: questions...
By aos007 on 6/12/2007 12:26:03 PM , Rating: 2
Permanent magnets, as any other material, have electrons which are moving (even if just orbiting their nucleus). Any moving charged particle creates a magnetic field. It's just that the atoms in a permanent magnet are aligned so the individual fields of each electron add up instead of (statistically) cancel each other like they would in a usual matter. So you end up with a macro effect of having a measurable magnetic field.


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