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

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Fri, 8 Jun 2007 18:44:21 +0100
From: Chris Rutherford <chrismrutherford@xxxxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: Non-Radiative Evanescent Waves are back in the news... (fwd)

In this case the hype appears to be a good thing.  Buzzwords and hype
usually get the attention of the non technical people who control the purse
strings.  i.e.  Funding for <grimace> 'WiTricity' <\grimace> projects...  If
wireless power really is feasible then surely the first steps have now been
taken.  Light bulbs today, planes tomorrow (or maybe in the next 50 years).

On 6/8/07, Tesla list <tesla@xxxxxxxxxx> wrote:
>
>
> ---------- 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...
>
>
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>