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Re: Non-Radiative Evanescent Waves are back in the news... (fwd)



---------- Forwarded message ----------
Date: Fri, 08 Jun 2007 09:53:16 -0500
From: Bert Hickman <bert.hickman@xxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: Non-Radiative Evanescent Waves are back in the news... (fwd)

I was able to access a copy of their new paper, "Wireless Power Transfer 
via Strongly Coupled Magnetic Resonances" which appears in the June, 
2007 issue of Science Express. You need to be a member of AAAS or have 
access (as a university student or staffer or through a university 
library) to access the article. Following is a very "quick and dirty" 
summary.

They used identical self-resonant helical coils, each 60 cm in diameter 
and 20 cm high, wound with 3mm copper wire, separated by abut 2 meters. 
Each coil has 5.25 turns, each self-resonates at 9.9 MHz, and both are 
aligned along a common axis of rotation (although the authors claim this 
is not essential). Interestingly, they predict a theoretical Q of 2500 
and measure an actual Q of 950 +/- 50 for the coils. This is 
unexpectedly high for regular (non silver-plated) copper wire.

RF power was inductively coupled from a 400 watt Colpitts power 
oscillator into the "sending" coil via a single-turn 50 cm diameter 
loop. Power is extracted via a single-turn loop in close proximity to 
the resonating receiving coil. Schematically the system looks like this:

http://CapturedLightning.com/photos/WirelessPower1.png

For this system, they predict an efficiency that's proportional to the 
coupling coefficient, and inversely proportional to the square root of 
the product of sending and receiving coil inductances. They adjusted the 
distance between the receiving coil and load loop for optimal 
performance. By measuring current in the transmitting and receiving 
coils, they were able to calculate transmission efficiency (the stated 
40%). However, actual wall plug power into the RF driver was 400 watts, 
so by lighting the 60 watt lamp 2 meters away, they actually saw an 
overall power transfer efficiency of about 15%.

The inventors also claim that the receiving coil can be made 
considerably smaller without decreasing efficiency (as long as resonance 
is maintained). However, as the receiving coil becomes smaller, so does 
he effective coupling coefficient, so a smaller coil will need to be 
closer to maintain the same efficiency. Here are a couple of charts 
showing predicted and measured results:

http://CapturedLightning.com/photos/WirelessPower2.png
http://CapturedLightning.com/photos/WirelessPower4.png

Bert

Tesla list wrote:
> ---------- Forwarded message ----------
> Date: Fri, 8 Jun 2007 09:58:18 +0100
> From: Chris Rutherford <chrismrutherford@xxxxxxxxxxxxxx>
> To: Tesla list <tesla@xxxxxxxxxx>
> Subject: Re: Non-Radiative Evanescent Waves are back in the news... (fwd)
> 
> After a bit of digging I found the papers.
> 
> http://www.mit.edu/~soljacic/AIP_press.pdf
> http://arxiv.org/ftp/physics/papers/0611/0611063.pdf
> 
> Here's an interesting paragraph.  Does this 'breakthrough' seem familiar to
> anyone?
> 
> "However, Solja�i� realized that the close-range induction taking place
> inside a
> transformer -- or something similar to it -- could potentially transfer
> energy over longer distances, say, from one end of a room to the other.
> Instead of irradiating the environment with electromagnetic waves, a power
> transmitter would fill the space around it with a "non-radiative"
> electromagnetic field. Energy would only be picked up by gadgets specially
> designed to "resonate" with the field. Most of the energy not picked up by a
> receiver would be reabsorbed by the emitter."
> 
> <sarcasm>
> Maybe he uses 'scalar waves', but thats been classified so he cant tell us
> what the real breakthrough is.
> <\sarcasm>
> 
> Thanks
> 
> Chris
> 
> On 6/8/07, Tesla list <tesla@xxxxxxxxxx> wrote:
>>
>> ---------- Forwarded message ----------
>> Date: Thu, 07 Jun 2007 20:36:37 -0500
>> From: Bert Hickman <bert.hickman@xxxxxxxxxx>
>> To: Tesla list <tesla@xxxxxxxxxx>
>> Subject: Non-Radiative Evanescent Waves are back in the news...
>>
>> By using a weakly coupled resonant receiving coil 1/2 meter in diameter,
>> the research team that rediscovered induction and Tesla wireless power
>> transmission last year have successfully lit a 60 watt bulb 2 meters
>> away from a transmitting  coil. I wonder if the lamp was continuously
>> illuminated or a flash (when the lamp was connected across the fully
>> "rung up" receiving LC circuit). The researches claim 40% efficiency.
>> Will be interesting to get the complete story instead of this snippet:
>>
>> http://physicsweb.org/articles/news/11/6/5
>>
>> Bert
>> --
>> ***************************************************
>> We specialize in UNIQUE items! Coins shrunk by huge
>> magnetic fields, Lichtenberg Figures (our "Captured
>> Lightning") and out of print technical Books. Visit
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