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Re: Calculating inductance, capacitance, and resistance of 3D objects

At 06:35 PM 12/16/98 -0700, you wrote:

>Original Poster: Jim Lux <jimlux-at-jpl.nasa.gov> 

>> Original Poster: Scott Stephens <Scott2-at-mediaone-dot-net>

>> > I haven't had a chance to work with it
>> >yet, but, it might prove useful to some for calculating Cself and Ctop
>> >for all those weird toroid shapes, etc... It's at:
>> >
>> >ftp://rle-vlsi.mit.edu/pub/
>> 
>> I would use book equations for such things. A field solver is over-kill.
>

>But there isn't a good book equation for the capacitance of a cylinder
>over a ground plane or for a toroid on top of a cylinder. All you have
>are empirical approximations for parts of the problem such as those of
>Medhurst. I think it would be useful to run a field solver with a very
>large number of cases of various combinations of "top load" and
>cylinder, etc. then derive some empirical relations. 

In that case the electro-static (laplace?) program at
ftp://rle-vlsi.mit.edu/pub/ might be a good choice. Also (Free-FEM?) a 2-D
commercial Finite Element Analysis cripple-ware code for structural,
thermal, electro-static, and magnetic might be good, because it is simple,
all GUI, with no arcane syntax. Fast learning curve, like using schematic
editor in SPICE rather than attempting to edit a text netlist file.

For voltage & capacitance, an electro-magnetic solver isn't required, so you
can use a simple and faster static simulator. But it will still take some
skill structuring the problem, in 2 dimensions.

There is a graphical technique, (IIRC called logicaly enough "the graphic
technique") that requires only graph paper and pencil. I would look to that,
or Free-FEM, before using NEC. Probably is described in most decent physics
or electro-magnetic textbooks.

>but it would be nice to have an understanding in a sort of
>semiquantitative way of the effects of toroid size/spacing above the
>secondary, working against a flat primary of various sizes, etc.

And getting a printout of the voltage gradient along the coil and terminal,
and varying terminal geometry and location would help a lot with optimizing
area, and avoiding destructive and unwanted arcing along the coil and
terminal.

>I, for one, would be interested to know the effects of ground planes and
>counterpoises of various configurations over various substrates.
>Concrete floors aren't infinitely conducting groundplanes....

Great point. Have a look at the coils complex impedance change with
imperfect ground planes too. But now, were back to a dynamic EM solver,
rather than a static solver. Then again, the concrete could possibly be
modeled electonicaly in SPICE, as a lossy R-L-C ladder network. At high
frequency, the RC would probably be good enough.

>A better answer may be to develop a solver that can run on a distributed
>network of PC's (much like the digits of PI or prime number searches).

How long ago? Now PC's have >10MB ram, >2 gig HD's & >100 MIP, maybe a
single PC could handle that app?

> I
>did this for a Computational Fluid Dynamics code based on numerical
>integration of the Navier-Stokes equation. Let it run for a week as a
>screen saver on 30 PCs...

For a plasma field solver, I had in mind something like your fluid dynamics
solver, and an EM solver. Both run independently, but swap data, with the
Navier-Stokes modified to accept EM forces and magnetic viscosity. I've done
some rough calculations for a FEM EM solver that estimate it could solve my
problems in < 1hr, but am afraid I'll find I need MIP-centuries to solve
plasma fields like I want. But I wont know till I try.