Re: gEDA-user: Compiling MMI (electromagnetic simulator)

[Dan McMahill <dan@mcmahill.net>]

On Sun, Aug 22, 2004 at 06:13:34PM +0000, Karel Kulhav? wrote:
> Hello
> 
> MMI promises to compute distributed paramteres of copper strips on
> PCB.

looks neat once it can be built.  I've started and found some issues
with the build system.  Haven't fixed them all yet...


> I am lured by an idea of computing how many picoforad 1cm^2 of PCB trace on my
> 1.5mm FR-4 board makes. 

try out mcalc.sf.net to find impedance (sqrt(L/C)) and velocity (1/sqrt(LC)) of
your line and then solve for L and C.

Thats useful for lines which are relatively long compared to their width.
for a simple parallel plate thing like what you have, you can 

a)  note that 1cm is a good bit more than 1.5 mm so just use C = eA/d
  (e = permitivitty of FR4 which is around 4.8x free space permitivitty)
  (A = area)
  (d = distance)

or 

b)  use something like fastcap if you want a more accurate field solution.


-Dan


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