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

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Fri, 08 Jun 2007 09:36:13 -0700
From: Jim Lux <jimlux@xxxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>, tesla@xxxxxxxxxx
Subject: Re: Non-Radiative Evanescent Waves are back in the news...  (fwd)

Thanks, Bert..
Comments below.
>---------- 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)
>
>  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.

Hmmm.. have they done tests to confirm the surprising assertion of 
alignment not being important? Considering that goniometers have been 
built for, oh, better than a century, which rely on misalignment to 
change the coupling.  Maybe it's not important in a system with a 
transmitter and receiver and nothing else.. Sure, the coupling is 
less, but as long as the coils are relatively "lossless" energy is coupled.



>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


So nothing novel here, really...