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Ansys HFSS - Fringing Field Capacitance

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Hello All,

I was wondering if someone might be able to help me determine the fringing capacitance due to a parallel plate with an extended dielectric?

My test project (attached below) is just a simple two parallel plate setup with a Lumped Port connecting the two at the center of the two square plates. I set the resistance to 1ohm and the reactance to 0ohm.

If I use the -1/(2*pi*freq*im(Z)) output, the capacitance is an averaged capacitance across the entire plate, right?

If I use that Q = CV, I would think that I can integrate along the Efield path to determine the Voltage, but I'm not sure how to measure the charge on the plate.

I guess as a follow-up question, how does the modal solution set-up the driving field for a Lumped Port? Is it somehow normalized or is the input field strength variable depending on the dielectric separating a parallel plate?

Thanks for any help you can provide!

View attachment parallel_plate_mixed_dielectric_v01.zip
 

i am not clear about your question.
But you can use HFSS calculator and then you can manipulate your calculated fields the way you want.
 

Thanks for the clarification question.

My apologies, there were actually three related questions there, however the primary question is:

How does one calculate the fringing capacitance separate from the simple averaged parallel plate capacitance using HFSS (calculator or otherwise)?

You can imagine a scenario where the plates are separating by larger and larger distances: Z_tot = Z_para-Z_fringe and C_fringe = -1/(2*pi*Freq*im(Z_tot-Z_para)).

However, I would like to know the capacitance at each point between and beyond the edge of the two plates, which I suspect requires using the Efield.

Regards
 

yeas as far as I can think of this problem calculate E field using HFSS Eigen Mode Solver.
As E field will depend on the geometry of your structure so will be a sort of measure of Impedance of your model which will be predominantly capacitive.
After that use HFSS calculator to implement the mathematical formula for calculation of capacitance at a the area of interest which may be axis or a line depending on the geometry.
After that you can plot your capacitance along the reference line or axis
 

Doesn't the Eigenmode solver require resonant frequencies? As it is a parallel plate capacitor, the resonances do not seem like they would be realistic (i.e. the inductance would be incredibly small).

Concerning the calculation, I think this is the crux of my question, how do I go about that calculation? While I may know the Efield, and thus should be able to calculate C = Q/integ(Efield(s), s). I don't understand how to ascribe the line of integration (for elements dS) or how to determine Q (maybe, integrating the Jfield across the parallel plate surface?).

Any help along these lines (pun intended) would be greatly appreciated.
 

Look I am getting bit confused may be I am not understanding your real problem.
If you have E field calculated which you can calculate with Eigen mode solver then to have a surface integral or line integral of it is just matter of simple HFSS calculator commands.
Have you used HFSS calculator before?
Eigen mode solver calculates resonance frequencies as well as E field and you can see your E field simply by plotting it.
If you have any issues feel free to ask
As far as your calculation formulas are concerned they seem correct but consult the literature
 

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