0.1pF three-terminal capacitor

Winfield Hill wrote:
Fred Bloggs wrote...

Winfield Hill wrote:


Apparently at these scales fringing-fields have a *huge* effect.
Sloggett, et.al., J Physics A, 19, p2725 (1986), has an accurate
formula with fringing-field correction terms (see a.b.s.e.). **

Adobe 6.0 keeps saying the file is damaged and cannot be repaired.


Testing the posting just now - it downloads and displays fine.
But it's a two-part post, because of the binary file's length.
Perhaps your viewing program didn't successfully download the
second part to complete the file? Would you like me to repost
it to see if that fixes the problem?

I'm think you'd be interested in the article.
Click to expand...
If it's just me, I can get it from the journal directly.
 
Jim Thompson wrote...
Fred Bloggs wrote:

Winfield Hill wrote:

Apparently at these scales fringing-fields have a *huge* effect.
Sloggett, et.al., J Physics A, 19, p2725 (1986), has an accurate
formula with fringing-field correction terms (see a.b.s.e.). **

Adobe 6.0 keeps saying the file is damaged and cannot be repaired.

Doesn't that frost you? Adobe is getting as bad as M$oft for
generating version incompatibilities :-(
Click to expand...
I read it on my computer with Adobe 6.0, so that's not the problem.


--
Thanks,
- Win
 
On 11 Aug 2005 18:15:01 -0700, Winfield Hill <Winfield_member@newsguy.com> wrote:

Fred Bloggs wrote...

Winfield Hill wrote:

Apparently at these scales fringing-fields have a *huge* effect.
Sloggett, et.al., J Physics A, 19, p2725 (1986), has an accurate
formula with fringing-field correction terms (see a.b.s.e.). **

Adobe 6.0 keeps saying the file is damaged and cannot be repaired.

Testing the posting just now - it downloads and displays fine.
But it's a two-part post, because of the binary file's length.
Perhaps your viewing program didn't successfully download the
second part to complete the file? Would you like me to repost
it to see if that fixes the problem?

I'm think you'd be interested in the article.
Click to expand...
I've posted some NBS work that might provide an alternative.
 
On 12 Aug 2005 04:48:38 -0700, Winfield Hill <Winfield_member@newsguy.com> wrote:

The Phantom wrote...

I've posted some NBS work that might provide an alternative.

But only the front page?
Click to expand...
I see 5 TIF files attached to the posting. The front page is only the first. Check
again and let me know if you see the rest or not.
 
On Wed, 10 Aug 2005 15:35:44 -0700, Winfield Hill wrote:

John Larkin wrote...

Incidentally, what hole size actually gets you 0.1 pF?

The FEA says 0.7 inches. Whoa! Too big by far. It must
be time for plan B. Well, heck, what was plan B anyway?
Click to expand...
Get a couple of pieces of aluminum foil, and some mylar shim
stock? ;-)

Cheers!
Rich
 
Glen Walpert wrote:

On 9 Aug 2005 07:01:28 -0700, Winfield Hill
Winfield_member@newsguy.com> wrote:

Is there an easy way to calculate the size of the hole necessary to
create a 0.1pF capacitor in the drawing below? The middle grounded
plate with the hole is 1/8" thick, and the plates are 1/8" apart.

. drive electrode ---,
. |
. #######################
. ,-- hole
. #################### ########################-- GND
.
. ##########################################
. | \
. opamp SJ at GND potential
. measure ac current

Agilent HSFF or other 3D Field Solver would make short work of the
calculation. Assuming you don't have a 3D Field $olver (or you
wouldn't have asked the question) and you don't want to increase the
hole size until you reach 0.1pf, you could try the freeware FastCap
software from:

http://www.fastfieldsolvers.com/

supplemental user manual (main manual included in program download):
http://rleweb.mit.edu/vlsi/codes/FastCapsuppl.pdf

A search will turn up considerable info on FastCap; I haven't used it
but have heard it is a pain to use compared to commercial field
solvers and that it provides quite accurate results if you can figure
it out.
Click to expand...
I've used FastCap quite a lot and I find it generally very good. (I also
like also FastHenry). The main problem with FastCap is that the input file
would be very tedious to generate by hand because you need to list the
x,y,z coordinates of the corners of a lot of triangles or rectangles, so
you would want to write a script to automate that. Another problem is that
the FastCap program relies on you to generate facets that are small enough
that the field can be regarded as constant over the facet. If you make the
facets too big, it will not converge (to a given error tolerance) and if
you make the facets too small you'll run out of memory or computing time.
If the program could decide on the facet size for itself that would be very
handy. At least it's open source so someone could do this if they are keen
enough.
Chris
 
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