At 09:37 PM 2/23/2004 +0000, you wrote:

>C = E0.A/D
>
>where A = area of the plates, D is the distance between them and E0 = the
>permeability of the dielectric.

Mmm.. I think that you mean "permittivity", and e0 is the permittivity of
free space = 8.854E-12 F/m. Multiply that by k = the dielectric constant
of the dielectric (relative to vacuum) to get e, the permittivity of the
dielectric. You look up the dielectric constant for the material.

This simple formula ignores edge effects.

Eg. a 100mm x 100mm pair of plates separated by 4 mil = 0.1mm  thick
polyethylene film (dielectric constant = 2.3)

C = k*e0 * A/D

C =8.8E-12 * 2.3 * 0.1 * 0.1 /0.1e-3 ~= 2nF = 2000pF.

If you stack n plates, just multiply that number by n-1. Eg. 100 plates,
100mm (~4") square would have a capacitance of 0.2uF.

You can get some idea of the voltage capability by looking up the
dielectric strength (typically specified in North America in volts/mil,
and multiplying by the thickness, but that might not be the whole story.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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