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kecman
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Capacitance Calculator for 2D Geometry

05/24/2012 7:11 AM

Does anyone know of a free or inexpensive software package for calculating capacitance in 2D geometry?

We cannot afford one of those CAD systems used in device modeling that could certainly do the job, but our goal is to calculate inter-contact capacitances of a thin, Al-plated, Si detector typically used in scientific cosmic-ray instruments. The surface of the detector is partitioned into several closely spaced regions, each connected to its contact on the perimeter of the detector. Often there is a tiny Al trace bringing the signal of a region "X" and running in between two other regions, "Y" and "Z". The inter-contact capacitances are very important in estimating the future cross-talk between the detector regions for the design purposes, i.e., before any detectors are made.

Sorry, not allowed to post any photos. Thanks!
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redfred
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#1

Re: Capacitance Calculator for 2D Geometry

05/24/2012 10:30 AM

Capacitors do not exist in two dimensions! Capacitance is determined by the overlapping area of two conductors separated by an insulator with a certain permittivity between the two conductors.

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kecman
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#2
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Re: Capacitance Calculator for 2D Geometry

05/24/2012 2:42 PM

This is a little more exotic case of capacitance where the electric field lines between the adjacent co-planar detector segments close through both the air and silicon. Another example is a thin Al trace running next to a co-planar Al plate or between two co-planar Al plates. They all make a "2D" capacitor, and no matter how small its capacitance is, we would like to calculate it.

There is also the bulk capacitance of each detector segment in the classical sense of two parallel plates since the back side of the Si detector is Al-plated and serves as the common electrode for the partitioned segments of the front side. But that is a 3D geometry case, not of interest here.
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redfred
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#3
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Re: Capacitance Calculator for 2D Geometry

05/24/2012 5:04 PM

There are no capacitors possible in Flatland.

Don't tell me that this is an exotic exception, either. I've worked on the designs and electronics for a Segmented Wire Ion Chamber (SWIC) and many other beam profile monitors where thin wires run parallel to many plates. This is done all the time in RF strip line designs to make directional couplers, too.

So do your homework, crack open that old textbook or hire a consultant. But don't wave the proprietary flag while asking for help in solving a fundamental Physics / Electrical Engineering problem. That is insulting.

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ci139
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#5
In reply to #3

Re: Capacitance Calculator for 2D Geometry

05/26/2012 11:05 AM

CR4 ADMIN: Deleted Post

Abuse/Attack: This post was deleted because it was an attack on another user. Please review the CR4 Site FAQ and the CR4 Rules of Conduct.
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ci139
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#6
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Re: Capacitance Calculator for 2D Geometry

05/26/2012 4:18 PM

i haven't needed net capacitance so i dont have these formulas

but i 've needed inductances so

http://www.hot.ee/rjc/files/CR4/Untitled-7old.jpg

http://www.hot.ee/rjc/files/CR4/Untitled-220new.jpg

µ(1)=1
µo(N/A²)=1.25664E-06
n(1)=100
l(m)=0.01
r(m)=0.003
d(=2r)=0.006
L.1stPass(H)=5.672E-05
L.2ndPass(H)=4.264E-05
L.from[http://www.qsl.net/in3otd/indcalc.html](H)=2.800E-05

i trust the least coz i don't trust myself (not fully into this subject)

you tell me witch is by the book & if any is correct ... in ... real
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redfred
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#7
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Re: Capacitance Calculator for 2D Geometry

05/26/2012 4:53 PM

That image is so large I cannot fit a page onto my laptop to tell what you are trying to do, let alone if you made an honest mistake somewhere.

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SolarEagle
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#4

Re: Capacitance Calculator for 2D Geometry

05/24/2012 6:23 PM
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amnakhan1245
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#8

Re: Capacitance Calculator for 2D Geometry

06/07/2012 1:53 PM

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