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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 Souka on 6/11/2007 12:20:34 PM , Rating: 3
What is maxinum power transfer?

What is range?

It would be nice if:....
There was a graph showing power transfer rate in relation to range?

RE: questions...
By KristopherKubicki on 6/11/2007 12:23:42 PM , Rating: 4
The MIT release was a little light on details, though I suspect the maximum power transfer is fairly high if they're able to do a 60W lightbulb already.

Range seems limited to two meters right now with very large coils. If you look at the image, you can see the team is actually sitting between two coils -- and they're big. I suspect they way they'll make progress with this technology is by increasing the magnetic resonance frequency.

RE: questions...
By spillai on 6/11/2007 12:30:28 PM , Rating: 2
If the MIT Team is successful with transfering 60 Watts, it is great achievement. Now they can definetly work with low power equipments like laptops etc.

Size of the coils will also be low.and the article does not make any statements about electromagnetic wave pollution in the atmosphere.

Good Luck MIT


RE: questions...
By KristopherKubicki on 6/11/2007 1:20:19 PM , Rating: 1
Well, right now its hard to say whats going on with the size of the coils -- though I emailed the team.

The "electromagnetic wave pollution" you state doesn't really exist with this technology. The fields created are only magnetic, which is one of the big advantages of this tech -- there is no electromagnetic radiation emitted.

RE: questions...
By Oregonian2 on 6/11/2007 1:30:30 PM , Rating: 1
there is no electro magnetic radiation emitted.


RE: questions...
By KristopherKubicki on 6/11/07, Rating: 0
RE: questions...
By aos007 on 6/11/2007 2:07:59 PM , Rating: 3
I'm an electrical engineer... but I can't wrap my head around having just the magnetic field which is rapidly changing (oscillating) without the electrical component. Other than making a permanent magnet vibrate, I can't think of anything. Are there any articles on this subject?

RE: questions...
By KristopherKubicki on 6/11/07, Rating: 0
RE: questions...
By Goty on 6/11/2007 2:34:20 PM , Rating: 2
That's easy. An oscillating magnetic field causes the electrons in the coil to oscillate as well, producing an alternating current. Simple magnetic induction.

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
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:

"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.

RE: questions...
By thatguy39 on 6/12/07, Rating: 0
RE: questions...
By theapparition on 6/12/2007 6:50:02 AM , Rating: 2
I don't know your background, so let me just say this.

The core tennant of a scientist is to question everything. When some scientists unveiled "cold fusion" decades ago, should the community just blindly accept their findings because we should "trust" them? No, they were continually questioned and their theory/experiments fell apart. It is in everyones best interest to question everything and get a resonable answer. BTW, some of the posters here are scientists. One of the reasons I like Dailytech is its diversity of comments.

Going back to the original point, there are only 4 known forces in this universe. The two nuclear forces, gravity, and electromagnetism . They are clearly generating the magnetic waves with electricity, and the corresponding coupling is converting that energy back into electricity. This would create (at low frequencies) an E (electric) and and H (magnetic) field. It is possible, with the use of a waveguide, to effectively cancel out the E fields. Don't know if that's what they are doing, but it is possible.

RE: questions...
By AntDX316 on 6/12/2007 10:55:54 AM , Rating: 2
if basically u want more power and i mean more power its more like a rail gun in the power transfer path

RE: questions...
By Amiga500 on 6/11/2007 12:50:28 PM , Rating: 2
This is probably a proof-of-concept as much as anything.

I guess there will be a few papers published on this somewhere... maybe have a look for IEEE (Institute of Electrical & Electronics Engineers) conferences - I'd guess they'd be presenting some stuff there.

It'll be refined in time of course :-)

RE: questions...
By Oregonian2 on 6/11/2007 1:58:02 PM , Rating: 2
It strangely resembles the concept of the spark transmitter first demonstrated, what, over a century ago? Except back then they keyed it on and off and used the receiving coil for data transmission rather than power. The transmitting coil was resonate, that picked it's operating frequency. I think the receiving coil "antenna" was tuned as well, but I don't recall (I wasn't there). The receiving coil just had an airgap to spark as the "signal" rather than having a light bulb load (but the sparks made certainly indicated power being transferred). They were use for quite a distance as I recall as well (although they got really BIG to gain the distance).

There have been tuned transformers nearly forever as well, although those used an iron core rather than air (and were a LOT more efficient than 40%).

Having two tuned circuits couple power from one to other is about as old as using iron for knives, so I'm not quite sure what's new here other than perhaps the demonstration application, the PR, and the implementation details.

RE: questions...
By Amiga500 on 6/11/2007 2:05:45 PM , Rating: 2
Yeah, it could be based on it all right (as a principal at the very least).

But, from what I understand, the spark transmitter was more of a signal generator (akin to radio) rather than a means of transmitting significant amounts of power.

RE: questions...
By Spivonious on 6/11/2007 2:43:27 PM , Rating: 2
I just thought of this. Big powerplant has a giant transmitter magnet thingy which beams power to the town. Every house and car in the town has a receiver magnet thingy and thus are powered everywhere. The need for batteries disappears. The power companies control the world.

RE: questions...
By FITCamaro on 6/11/2007 3:44:07 PM , Rating: 1
The only way we'd ever make that much power reliably though would be to use nuclear power. And at least the US has made its view abundantly clear with nuclear power in that its satan. I personally hate this fact since I live in the US and want cheap electric power thats not tied to the price of oil.

But thanks to environmental groups we don't get it.

RE: questions...
By agentcooper on 6/11/2007 6:56:22 PM , Rating: 1
sure, blame the environmentalists. Sheesh, what an ignorant statement. I'm an environmentalist and I support more nuclear power.

Don't you think big oil and the coal industry would make a big stink about nuclear taking a huge share of energy production?

And then there's the NIMBY attitude which would be adopted by everyone, everywhere.

RE: questions...
By Ringold on 6/12/2007 12:26:20 AM , Rating: 2
Not to start a flame war, but you're a minority amongst your own people. I watch Bill Maher's show (entertainment) and virtually without fail every liberal/environmentalist he has on his show is against nuclear power, and he doesn't understand it because he, like you, supports it in recognition of its great track record. It's sad..

RE: questions...
By Dactyl on 6/12/2007 2:47:15 AM , Rating: 2
The only reason for NIMBY attitudes towards nuclear power is enviro scare tactics.

It's true there are legitimate reasons to oppose nuclear power (for instance, the waste it creates). But those aren't NIMBY issues, because the waste gets dumped in Nevada or some other desolate place, not near the power plant.

No, the only reason people oppose nuke plants near them is that they're afraid some horrible thing will happen (mutations, cancer, radioactive gas leak, going critical, etc.)

RE: questions...
By Chernobyl68 on 6/12/2007 11:55:44 AM , Rating: 2
actually for quite a while waste is stored on site. Until Yucca mountain is open and legal for permanent waste storage...

RE: questions...
By theapparition on 6/12/2007 6:58:17 AM , Rating: 2
Kudo's to you, but you are a signifigant minority in the enviromenalist group.

However, we see the power (or lack thereof) of enviromentalists lobbying the government. They are not organized, don't have an effective platform, not to mention policies that are ludacris at best. So to blame enviromentalists for lack of nuclear power is wrong.

My own opinion is that the biggest issue is political. How can you stand before the world and say you need to make more nuclear power plants, it's the future of energy. Then tell other countries (cough, Iran, cough) they shouldn't have it?

RE: questions...
By vortmax on 6/12/2007 3:05:31 PM , Rating: 2
Because (cough, Iran, cough) is really creating nuclear weapons to kill people with. Why else would a nation with enough oil within their borders to last many centuries push so hard to create nuclear plants for power? I'm sure they aren't just being proactive....

RE: questions...
By theapparition on 6/13/2007 6:55:17 AM , Rating: 2
And just how many power plants do you know that burn crude oil?

I don't disagree that the thought of an unstable country like Iran posessing nulear fuel is quite unsettling. There is no doubt that their ultimate goal is to enrich uranium enough for weapons grade material. However, that doesn't change my original post, which states that (IMO) the US isn't pushing nuclear energy at home, because it wants to prevent other countries from thinking nuclear is the way to go. And that is directly related to the potential proliferation of nuclear weapons.

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?

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