Re: Wire Length (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

Moderated and approved by: Gerry Reynolds <greynolds@xxxxxxxxxx>



---------- Forwarded message ----------
Date: Sun, 24 Dec 2006 06:13:05 GMT
From: Paul Nicholson <paul@xxxxxxxxxxxxxxxxxxx>
To: tesla@xxxxxxxxxx
Subject: Re: Wire Length (fwd)

Bart, All,

There doesn't seem to be a coding error involved with this Cint
problem.  Removing the interpolation (ie running the internal
capacitance extraction at the same resolution - 91 segments - as
the network model) doesn't help.   What does make a difference,
and accounts for the discrepancy between the two programs,
is the precise manner in which the disc of the secondary is
segmented within the model, especially in the region near the
grounded rim where dQ/dx and dI/dx are very high.

It's a matter of taking the approximately smooth and continuous
charge distribution across the disc and representing it by
a matrix of finite size.  That means chopping the disc into
a set of concentric rings and we have some free choice over
where to set the boundaries between the rings.   Normally,
with a large enough number of rings, variation in the placement
of ring boundaries doesn't make much difference to the final
results, and that gives us confidence that the model is stable
and reliable.    Difficulties usually only arise when looking
at the overtones (in which the in-coil wavelength spans fewer
segments so is more sensitive to segmentation, especially at
the ends).

For some reason, in the rim-grounded flat coil, there's a
lot going on in the outer few turns and this is stressing
the model.  With various slight changes in segmentation, I can
vary Fres from 460kHz to 500kHz, which is not much good at all.
The only prediction then is 480kHz +/-5%.

I'll try to put in the primary and center load.  Perhaps that
will settle things down in the model... one wonders if the
electrical stresses in the coil will appear in the same place,
perhaps for the same reason.

When rim-grounded flat coils fail, do they fail in the outer
few turns?

--
Paul Nicholson
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