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tomed
France
28 Posts |
 Posted - May 06 2015 : 18:24:49
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Dear Enrico,
I'm beginning right now with Fastcap.
I'm going through the user's guide and i've got a question:
is there any way to get the frequency dependence of capacitance like what we've got using FastHenry for Resistance and inductance?
Thank you
Appreciate your time & support,
Best regards,
Tomed |
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Enrico
545 Posts |
Posted - May 07 2015 : 12:07:01
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No, this is not possible.
Actually both solvers work in the quasi-static regime. The only reason why you can see a frequency dependence with FastHenry is that, while still in the quasi-static regime, some effects already take place when increasing the frequency, i.e. the skin and proximity effects.
This is not the same for the electric field alone (in a static or quasi-static field, just for completeness, the charges in the conductors are already on the surface).
Other kind of effects will kick-in out of the quasi-static regime, with the interaction of the electric and magnetic field, so you will start talking about the overall impedance of the structure.
Best Regards,
Enrico
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tomed
France
28 Posts |
Posted - May 07 2015 : 16:02:20
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Dear Enrico,
In fact, i've learned that in homogeneous area LC=mu*epsilon. This is why i was wondering about frequency dependence of capacitance.
So if i understand all, do Fastcap only give the capacitance regarding low frequency(DC case)?
Thank you.
Best regards,
Tomed
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Enrico
545 Posts |
Posted - May 07 2015 : 23:33:48
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I guess you are thinking about a transmission line.
Now, the capacitance is calculated in DC, but this value is still valid up to a certain frequency, i.e. in quasistatic regime. The frequency depends on the dimensions of the structure w.r.t. the wavelength. If the dimensions are much smaller than the wavelength, the approximation holds.
However, in a txline, where the section is uniform along the length, if on the section the quasistatic assumption is valid, you can use quasistatic solvers to find the L/m and C/m (as these are distributed parameters: capacitance per meter, inductance per meter) of the txline.
For this txline also LC=mu*epsilon will hold (note: L is the L calculated when the skin effect is already pronounced)
Best Regards,
Enrico
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frequency dependence of capacitance
