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PostPosted: 26 Dec 2008, 23:24 
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I'm gonna warn you up front that there may be a lot of math and physics involved. Don't worry if you get lost or don't understand something. If you want it explained ask away. This is the research topic for my paper at the end of my course and questions will benefit all of us.

I'm gonna be talking in particular about resonant induction through evanescent wave coupling. For a more basic understanding think of a transformer. When electrons travel through the primary coil it creates a magnetic field that in turns drags electrons on the secondary coil. Except in this case the coils are much further apart.

I'll add in more later.



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PostPosted: 27 Dec 2008, 01:33 
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Alright, I'll bite. I've thought about wireless energy several times, and I've always run into a few problems.

1. The inverse square law makes it exceedingly difficult to propagate a field to usable proportions without expending a massive amount of energy. Induction works well in transformers because everything is relatively close together. In an open environment, however, a great deal of energy must be used to generate a field powerful enough to induce meaningful current any useful distance away. How do you propose we overcome this difficulty?

2. If I recall correctly, it is fluctuations in magnetic fields relative to the wires that produces the current. Thus, either the wires themselves must be moving, the electro-magnet, or the field itself must be oscillating. Which of these techniques do you suggest we utilize, and why?

3. Induction through a single strand of wire is negligible. We obtain useful amounts of current through coiling the wires, allowing the combined effect of individual inductions to create usable power. Referencing back to point number one, it would seem the number of coils would have to be considerable to obtain useful power from a field originating at an arbitrary distance. At some point, the weight and volume of said coils negates the advantage of wireless power in the first place. How do you propose we alleviate that difficulty?

If I've made a fundamental error in my understanding of the situation, please feel free to let me know. My area of concentration is limited to electromagnetic induction in microphones, so I haven't taken a formal class on this stuff in years.


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PostPosted: 27 Dec 2008, 09:46 
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Deathmagus;22428 wrote:
Alright, I'll bite. I've thought about wireless energy several times, and I've always run into a few problems.

1. The inverse square law makes it exceedingly difficult to propagate a field to usable proportions without expending a massive amount of energy. Induction works well in transformers because everything is relatively close together. In an open environment, however, a great deal of energy must be used to generate a field powerful enough to induce meaningful current any useful distance away. How do you propose we overcome this difficulty?

2. If I recall correctly, it is fluctuations in magnetic fields relative to the wires that produces the current. Thus, either the wires themselves must be moving, the electro-magnet, or the field itself must be oscillating. Which of these techniques do you suggest we utilize, and why?

3. Induction through a single strand of wire is negligible. We obtain useful amounts of current through coiling the wires, allowing the combined effect of individual inductions to create usable power. Referencing back to point number one, it would seem the number of coils would have to be considerable to obtain useful power from a field originating at an arbitrary distance. At some point, the weight and volume of said coils negates the advantage of wireless power in the first place. How do you propose we alleviate that difficulty?

If I've made a fundamental error in my understanding of the situation, please feel free to let me know. My area of concentration is limited to electromagnetic induction in microphones, so I haven't taken a formal class on this stuff in years.



I'll deal with number two first since that's the easiest. We'd be using AC. Numbers one and two I'll deal with together because both are overcome by the same solution. You are quite right when you mention the inverse square law and the size of coils. The amount of power needed to overcome distance issues makes induction unusable and with coils that are too large it becomes impractical to use them. How we get around these problems is with evanescent wave coupling. By resonating the evanescent waves it creates an effect that is mathematically similar to quantum tunneling and allows for smaller coils and less power for the same amount of induction at greater distances.



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PostPosted: 27 Dec 2008, 23:24 
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Kevin;22446 wrote:
I'll deal with number two first since that's the easiest. We'd be using AC.

Good answer - that's likely in most situations to be the easiest to implement.

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Numbers one and two I'll deal with together because both are overcome by the same solution. You are quite right when you mention the inverse square law and the size of coils. The amount of power needed to overcome distance issues makes induction unusable and with coils that are too large it becomes impractical to use them. How we get around these problems is with evanescent wave coupling. By resonating the evanescent waves it creates an effect that is mathematically similar to quantum tunneling and allows for smaller coils and less power for the same amount of induction at greater distances.
The last time I read up on EWC (I think back in '07) the best they'd achieved was less than 50% efficiency over a distance of a few yards using coils that were about 2 feet in diameter. Additionally, the orientation of the coils needed to be the same to transfer the energy properly. That's hardly useful as-is. Has the technology improved meaningfully over the last year or so?

Additionally, has any progress been shown towards solving the alignment dilemma?


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PostPosted: 28 Dec 2008, 10:48 
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Deathmagus;22476 wrote:
The last time I read up on EWC (I think back in '07) the best they'd achieved was less than 50% efficiency over a distance of a few yards using coils that were about 2 feet in diameter. Additionally, the orientation of the coils needed to be the same to transfer the energy properly. That's hardly useful as-is. Has the technology improved meaningfully over the last year or so?

Additionally, has any progress been shown towards solving the alignment dilemma?


Intel demonstrated it's own witricity earlier this year. They greatly improved efficiency as I recall. I don't know what size coils they used though. Commercial versions are being developed already to outfit trucks that charge tools and flashlights wirelessly as they sit on the shelf.



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PostPosted: 30 Dec 2008, 03:00 
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Kevin;22484 wrote:
Intel demonstrated it's own witricity earlier this year. They greatly improved efficiency as I recall. I don't know what size coils they used though.

Hmm.. I hadn't heard that. Any specs you could find would be wonderful to have for future reference.

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Commercial versions are being developed already to outfit trucks that charge tools and flashlights wirelessly as they sit on the shelf.

Blech. Frankly, such an application sounds like a waste of time. If it's on a shelf, there's no reason not to plug it in. I don't really think the technology will be useful until it's at least possible to, say, power a laptop computer anywhere within perhaps a single room, at a variety of angles and distances from the source coil.


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PostPosted: 04 Jan 2009, 18:12 
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Well the distance is the same as the MIT experiment. They just improved efficiency to 75%. This article has a photo of the Intel experiment.

http://www.techinnoventure.com/?p=339



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