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Capacitance matrix varies as you change the voltage

Posted 1 juin 2017, 06:13 UTC−4 Low-Frequency Electromagnetics Version 5.3 8 Replies

Hiroki Ikegami
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I have a 3D grounded box and a set of plate on a silicon chip in a 2D plane, and I was trying to calculate the capacitance matrix by assigning certain voltages to three plates using the electrostatic module. Apparently it turns out that the capacitance matrices has a dependence on the voltage we apply which does not make any sense to me. But If independently excite just one terminal applying 1V keeping all others 0V, then it would give you the correct result.Could any one explain why this happen.Now the issue is that if I have a say 20 plates, it would be difficult to get the capacitance matrix and the job is painful.
8 Replies Last Post 10 juin 2017, 02:16 UTC−4
Sergei Yushanov Certified Consultant
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Posted: 7 years ago 1 juin 2017, 12:59 UTC−4
Hiroki,

As you say, capacitance matrix is obtained by exciting one terminal at a time, not by applying voltage at several terminal simultaneously - see example problems

www.comsol.com/model/touchscreen-simulator-30841
www.comsol.com/model/download/420531/Capacitance_Matrix_2Spheres.pdf

Regards,
Sergei
Hiroki, As you say, capacitance matrix is obtained by exciting one terminal at a time, not by applying voltage at several terminal simultaneously - see example problems https://www.comsol.com/model/touchscreen-simulator-30841 https://www.comsol.com/model/download/420531/Capacitance_Matrix_2Spheres.pdf Regards, Sergei
Sergei Yushanov Certified Consultant
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Posted: 7 years ago 1 juin 2017, 13:31 UTC−4
Hiroki,

You can use Terminal sweep option to calculate capacitance matrix for multiple plates in a single run, as shown in the attached slides.

Regards,
Sergei
Hiroki, You can use Terminal sweep option to calculate capacitance matrix for multiple plates in a single run, as shown in the attached slides. Regards, Sergei
Hiroki Ikegami
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Posted: 7 years ago 6 juin 2017, 04:04 UTC−4
Thank you very much Sergei, but could you give me an example file where we have this parametric sweep. I am not familiar with the parametric sweeping . As per the slide i have activated the terminal sweep option, then the slide does not explain well , how to perform this operation.
Thank you very much Sergei, but could you give me an example file where we have this parametric sweep. I am not familiar with the parametric sweeping . As per the slide i have activated the terminal sweep option, then the slide does not explain well , how to perform this operation.
Sergei Yushanov Certified Consultant
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Posted: 7 years ago 6 juin 2017, 08:00 UTC−4
Hiroki,

Attached is example model calculating Maxwell capacitance matrix for coplanar waveguide.

Regards,
Sergei
Hiroki, Attached is example model calculating Maxwell capacitance matrix for coplanar waveguide. Regards, Sergei
Hiroki Ikegami
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Posted: 7 years ago 6 juin 2017, 23:06 UTC−4
Updated: 7 years ago 6 juin 2017, 23:19 UTC−4
Sergei,

Thank you very much.That was helpful. I have just one last question; In your example, why do the Maxwell capacitance and the mutual capacitance give absolutely the same result ?

I appreciate your help.
Sergei, Thank you very much.That was helpful. I have just one last question; In your example, why do the Maxwell capacitance and the mutual capacitance give absolutely the same result ? I appreciate your help.
Sergei Yushanov Certified Consultant
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Posted: 7 years ago 7 juin 2017, 08:00 UTC−4
Hiroki,

Not sure why you are saying that mutual and Maxwell matrices are the same - they are different, as shown in the attached image.

Regards,
Sergei
Hiroki, Not sure why you are saying that mutual and Maxwell matrices are the same - they are different, as shown in the attached image. Regards, Sergei
Hiroki Ikegami
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Posted: 7 years ago 8 juin 2017, 02:21 UTC−4
Updated: 7 years ago 10 juin 2017, 02:24 UTC−4
Sergei,

Sure , in your file, you have plotted the first one under Transformation: None
the second one is under Transformation: Maxwell to mutual

Please try the following option under Transformation : mutual to Maxwell, you will get exactly the same answer for, may be that is an error or something I guess.

Transformation: Maxwell to mutual and mutual to Maxwell.
Sergei, Sure , in your file, you have plotted the first one under Transformation: None the second one is under Transformation: Maxwell to mutual Please try the following option under Transformation : mutual to Maxwell, you will get exactly the same answer for, may be that is an error or something I guess. Transformation: Maxwell to mutual and mutual to Maxwell.
Hiroki Ikegami
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Posted: 7 years ago 10 juin 2017, 02:16 UTC−4
Dear Sergei,

Thank you very much
Now I am trapped in a weird situation. I have a co planar wave guide where I want to calculate the capacitance with two pads. I have been getting asymmetric and positive elements on the capacitance matrix(non diagonal elements). Do you have some idea why?

C11=221fF
C12=-2.6fF
C13=+5.33fF
C21=-2.61fG
C31=+3.99fF



Dear Sergei, Thank you very much Now I am trapped in a weird situation. I have a co planar wave guide where I want to calculate the capacitance with two pads. I have been getting asymmetric and positive elements on the capacitance matrix(non diagonal elements). Do you have some idea why? C11=221fF C12=-2.6fF C13=+5.33fF C21=-2.61fG C31=+3.99fF

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