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Capacitance model in Comsol
Posted May 16, 2011, 7:47 a.m. EDT Low-Frequency Electromagnetics 0 Replies
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I am a bit confused with a basic problem related to capacitances. For info, I am using Comsol 4.0a.
Let's take a very basic 2D model whose geometry consists of a rectangle. The top and bottom lines of this rectangle constitutes the two electrodes of a capacitor and my goal is to compute the value of the capacitance.
First option: I apply a ground boundary condition on the bottom line and a voltage constrained terminal on the top line.After analysis, I can then compute the C11 capacitance matrix component, which is what I am looking for. The obtained value fits with the basic theoretical expression related to parallel plates capacitors.
Second option, where I get my problem: I apply opposite densities of surface charges on the top and bottom lines of the rectangle. In addition, I constrain the bottom line to a zero potential. After analysis, I obtain the difference of potential between the top and bottom electrodes. To determine the capacitance, I consider that it is equal to the quotient of the total electrical charges on one plate over the potential difference between the two electrodes. By this method, I however get twice the value of the capacitance that I get from the other method.
Some ideas of what is not correct in my reasoning?
Hello Michael Renaud
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