Re: those folks at MIT (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Sun, 17 Jun 2007 12:20:35 -0300
From: Antonio Carlos M. de Queiroz <acmdq@xxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: those folks at MIT (fwd)

Tesla list wrote:
> ---------- Forwarded message ----------
> Date: Wed, 13 Jun 2007 17:13:46 -0600
> From: Terry Fritz <terrellfone@xxxxxxxxxxxxxxxxxxxxxxx>
> To: tesla@xxxxxxxxxx
> Subject: Re: those folks at MIT (fwd)
>
>
> I did write up an analysis of their system the best I could figure out
> and it really should work fairly well.
>
> http://hot-streamer.com/temp/WiTricity!/WiTricity.pdf
>
> It is probably not real safe to be around for a long time and you don't
> want to touch anything. Apparently it will radiate enough RF to give HAM 
> radio folks a major cow...  Not sure if it is real practical... But it 
> is cool!!
>
> I updated the paper...
>
> I just added the last page is all. I resolved that the problem where
> their capacitance seemed so low was do to their lack of a ground plane
> (there system is floating in free air) so the parallel capacitance to
> the coils is about 1/2 what Medhurst would predict.
>
> The power supply source impedance and load impedance are coupled to
> their respective coils at about k=0.4. That drastically reduces the
> "Q" to about 15 to 20! Having a "Q" of 1000 on the bare coil does not
> matter... This very low Q gives them a bumpy 2.5 MHz bandwidth as
> shown in the last figure in the paper I wrote. I bet that "dual hump"
> thing really confuses them at MIT if they haven't figure that out yet
> :oD If not, there might still be time to try and convince them that
> the finicky efficiency is due to "effervescent ethereal turbulence" or
> some other hilarious cause >:O)
>
> I have been working to make a much more modest ~4MHz WiTricity system
> simply run from a common 50 ohm signal generator input and a 50 ohm
> resistor at the far end. Waiting for the glue to dry and I hope I can
> slide the coils off the form... ;-)
>
> http://hot-streamer.com/temp/WiTricity!/P6130604.JPG
>
> It should run LEDs and be super
> easy for anyone to reproduce without the need for 5 MIT Ph.d's to help 
> out %:o)
>   
I see that you have ignored the magnetic coupling, considering only the 
electrostatic coupling.
The change, if it exists, will be essentially only in the effective 
coupling coefficient between the
tuned circuits, I think.
I wonder if better efficiency can be obtained using capacitor-discharge 
operation, as in a
"capacitive transformer Tesla coil". Consider, for example, two grounded 
LC tanks with C=20 pF and L=50 uH
coupled trough a capacitance of 1.025  pF. If one of the capacitors is 
charged and connected to the
system (charge the 1.025 pF capacitor too), all the energy is 
transferred to the other side after 10.5 cycles
of  about 5 MHz. Ignoring losses and radiation.
The question is then of how to extract the energy in the output 
capacitor exactly when it is fully charged.

Antonio Carlos M. de Queiroz