Post subject: Analytical parasitic estimation Posted:
Thu May 10, 2007 9:26 am
Joined: Fri Jan
19, 2007 10:36 am
I hope it is not a too
much weird question…
We all know that if you have two metal layer
with a distant d and thickness th1, th2, we could calculate the
capacitance for area unit with C = (Er*Eo)/d. My question is, in
order to get merely an estimation, does someone know if exists such
as similar formula for calculating the capacitance for perimeter
unit between the edge th1 of the first layer with the surface (with
infinite extension) of the second?
Thank you very much!
Post subject: Posted:
Fri May 11, 2007 10:33 am
Feb 17, 2006 12:07 pm
Location: London UK
I suspect that the structure you are enquiring about
is the structure that actually makes the formula value of C = the
measured value of C.
The classic formula assumes the electric
field is perpendicular to the plane of the plates. Without the device
you seem to be mentioning, the field at the edge of both plates
actually curves outwards before returning to the plates. In consequence
the formula in that case does not predict an accurate answer corresponding
to what you will measure with a bridge.
The extra plate is called
a fringing plate (I think) and is always used for constructing a
standard reference capacitor. It has the effect of restoring parallelism
to the E field between the plates, a situation for which the formula