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Calculating Capacitance
Posted Jan 19, 2011, 2:12 a.m. EST 3 Replies
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Hi,
I'm trying to calculate the capacitance between two electrodes (equipotential surfaces) in COMSOL. However I notice I get different answers for capacitance if I change the voltage input to the electrodes.
This doesn't make sense to me. According to electromagnetic theory, capacitance should be determined by the geometry of the electrodes and should not change with vary with the applied.
I have attached the model I'm using. Can someone please tell me what I am doing wrong?
Thanks,
Kevin
I'm trying to calculate the capacitance between two electrodes (equipotential surfaces) in COMSOL. However I notice I get different answers for capacitance if I change the voltage input to the electrodes.
This doesn't make sense to me. According to electromagnetic theory, capacitance should be determined by the geometry of the electrodes and should not change with vary with the applied.
I have attached the model I'm using. Can someone please tell me what I am doing wrong?
Thanks,
Kevin
Attachments:
3 Replies Last Post Jan 19, 2011, 12:59 p.m. EST
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Posted:
1 decade ago
Hi
have you tried to ground one of the plates, and use ONE port with ONE distinct number only (and the sum of the voltage to get the same difference) ?
I believe that should work better. You should not use two input ports, nor two different voltages for the same port id number, in my opinion
--
Good luck
Ivar
have you tried to ground one of the plates, and use ONE port with ONE distinct number only (and the sum of the voltage to get the same difference) ?
I believe that should work better. You should not use two input ports, nor two different voltages for the same port id number, in my opinion
--
Good luck
Ivar
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Posted:
1 decade ago
Hi Ivar,
Thanks for the your response. Making one of the electrodes ground seems to work well. I am now getting a capacitance close to the analytic value I would expect.
However I am curious, why does making both of the electrode ports not work in COMSOL? Physically it seems you should be able to apply a different voltage to each plate (as well as just apply a voltage to one plate and ground the other).
Thanks,
Kevin
Thanks for the your response. Making one of the electrodes ground seems to work well. I am now getting a capacitance close to the analytic value I would expect.
However I am curious, why does making both of the electrode ports not work in COMSOL? Physically it seems you should be able to apply a different voltage to each plate (as well as just apply a voltage to one plate and ground the other).
Thanks,
Kevin
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Posted:
1 decade ago
Hi
first of all you need then two distinc "ports" with different ID numbers, but then the equations underneath requires also to be compatible with the type of excitation for multiple ports with currrent solver.
And everything is relative to a ground, so if you do not define a ground, then how do you define +5V and -2V ?
--
Good luck
Ivar
first of all you need then two distinc "ports" with different ID numbers, but then the equations underneath requires also to be compatible with the type of excitation for multiple ports with currrent solver.
And everything is relative to a ground, so if you do not define a ground, then how do you define +5V and -2V ?
--
Good luck
Ivar