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

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Fri, 8 Jun 2007 15:44:46 -0700 (PDT)
From: Ben McMillen <spoonman534@xxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: Non-Radiative Evanescent Waves are back in the news... (fwd)

Hello All,
   Can someone explain to me why the word 'Evanescent' is used? I'm an
optics guy, and an evanescent field is hardly seen a few meters away from
the source, let alone within a few microns of the surface. Forgive me if I
don't understand. My background is (heavily) in optics, so I'm not well
versed in RF.

Coiling In Pittsburgh
Ben McMillen

Tesla list <tesla@xxxxxxxxxx> wrote: 
---------- Forwarded message ----------
Date: Fri, 8 Jun 2007 18:44:21 +0100
From: Chris Rutherford 
To: Tesla list 
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  '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  wrote:
>
>
> ---------- Forwarded message ----------
> Date: Fri, 08 Jun 2007 09:36:13 -0700
> From: Jim Lux 
> To: Tesla list , 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 
> >To: Tesla list 
> >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...
>
>
>
>
>
>




       
---------------------------------
Choose the right car based on your needs.  Check out Yahoo! Autos new Car Finder tool.