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# Subject: Calculating inductance, capacitance, and resistance of 3D objects

```At 02:19 AM 12/15/98 -0700, you wrote:

>Original Poster: Jim Lux <jimlux-at-jpl.nasa.gov>
>
>I've just run across some interesting free software from MIT which
>calculates the capacitance, inductance, and resistance of arbitrary
>objects by numerical methods.

A 'field solver'. A web search of electromagnetics will turn up a NASA page
that references many free & commercial codes. There are even plasma
simulation codes available free. Siglo web page has one, but its 2
dimensional (as are many of these codes).

> 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.
Like SPICE to simulate a lamp & switch circuit.

>On a related note, has anyone done any modelling of TC's and their
>environment using a tool like NEC? NEC supports helices, and does
>calculate the turn to turn interactions, etc.

That would give you an excellent theoretical analysis. Field solvers analyze
a structure as if it were a very large array or mesh of inductors,
capacitors and resistors. Conductor thickness is even modeled in NEC.

But once again, the list has fairly well flogged that horse with empirical
measurements too. I gather from the list's posts, that the TC is much better
modeled as lumped rather than distributed (transmission line) with a large
top terminal capacitance. And the big terminal is necessary to store enough
charge for good discharge formation.

After 20 hours of tedious work, you may not learn much you don't already
know. I've tried NEC example files and some of the free & cripple ware for
it, which I'll dredge up references for if you want. It seems to have been
developed by people comfortable with hollerith cards, as conductor
structures are specified by netlists & lists of commands on 'cards'. But
others have made nice Windows GUI interfaces to it, so its not so
cumbersome. Their is another public domain University - sponsored code (I'll
forget) that would probably do a faster job of simulation.

I've been researching writing my own field solver, as I want to model
microwave cavity heated plasma loops. But 3-dimesional (rather, 4-dimension
including time) is computation intensive. Especialy when algorithms require
iteritive solutions. To make full use of the power of the pipelining and
cacheing in pentium processors, and the power of the MMX matrix processor,
code must be optimized. Otherwise performance is no better than 386 class.
Which I bet is the case for the University codes. And the net field solvers
typicaly give you complex impedance at a point or radiation patterns. My
ideal is to have an Open-GL based 3-D animation, with colored fog
visualizing the potentials and currents.

Any Windows - GLUT or Direct-X programmers interested? I'll write the solver
engine. Then on to plasma simulation. I'll stop the post here before I start
raving about MHD engines and giga-volt plasma-wave transformers.

```