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problem with capacitor having conductive media

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I am using this one as example:
www.comsol.com/model/frequency-domain-modeling-of-a-capacitor-12693
in the example, it use glass as media and conductivity is 0;
if I change the media to pbs buffer, which has conductivity 1.5 and permittivity 78, I get following result:
Frequency Capacitance(f)
0.0010000 250.00
0.010000 25.000
0.10000 2.5000
1.0000 0.25000
10.000 0.025000
100.00 0.0025000
1000.0 2.5000E-4
10000 2.5000E-5+7.2774E-10i

I found frequency*capacitance is a constant number. This is not going to happen in real world because when I input very very small frequency the result will go to infinity. In real case it should become a constant when frequency approaches to zero.

Can anybody help me with this? Is it possible to use comsol to simulate conductive media?

3 Replies Last Post 2015年8月7日 GMT-4 07:05
Edgar J. Kaiser Certified Consultant

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Posted: 9 years ago 2015年8月6日 GMT-4 14:44
Jiantao,

in a nonconductive medium the capacitor's impedance is purely reactive (imaginary) and can be described by a capacitance. In a conductive medium the impedance gets complex. A real resistive component and the imaginary capacitive component. Looking at the complex impedance is much more appropriate in this situation.
You can also interpret it as a parallel circuit of resistor and capacitor.

Cheers
Edgar

--
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
Jiantao, in a nonconductive medium the capacitor's impedance is purely reactive (imaginary) and can be described by a capacitance. In a conductive medium the impedance gets complex. A real resistive component and the imaginary capacitive component. Looking at the complex impedance is much more appropriate in this situation. You can also interpret it as a parallel circuit of resistor and capacitor. Cheers Edgar -- Edgar J. Kaiser emPhys Physical Technology http://www.emphys.com

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Posted: 9 years ago 2015年8月6日 GMT-4 15:13
Thanks for your reply. After I change to conductive media(pbs buffer conductivity=1.5), the impedance is independent with frequency. Does it look like right? On a paper, I found in experiment, pbs buffer impedance is dependent on freq.


Jiantao,

in a nonconductive medium the capacitor's impedance is purely reactive (imaginary) and can be described by a capacitance. In a conductive medium the impedance gets complex. A real resistive component and the imaginary capacitive component. Looking at the complex impedance is much more appropriate in this situation.
You can also interpret it as a parallel circuit of resistor and capacitor.

Cheers
Edgar

--
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com


Thanks for your reply. After I change to conductive media(pbs buffer conductivity=1.5), the impedance is independent with frequency. Does it look like right? On a paper, I found in experiment, pbs buffer impedance is dependent on freq. [QUOTE] Jiantao, in a nonconductive medium the capacitor's impedance is purely reactive (imaginary) and can be described by a capacitance. In a conductive medium the impedance gets complex. A real resistive component and the imaginary capacitive component. Looking at the complex impedance is much more appropriate in this situation. You can also interpret it as a parallel circuit of resistor and capacitor. Cheers Edgar -- Edgar J. Kaiser emPhys Physical Technology http://www.emphys.com [/QUOTE]

Edgar J. Kaiser Certified Consultant

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Posted: 9 years ago 2015年8月7日 GMT-4 07:05
The reactive (imaginary) component has to be frequency dependent, whatever medium you are using:
Xc = 1/(omega*C).

--
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
The reactive (imaginary) component has to be frequency dependent, whatever medium you are using: Xc = 1/(omega*C). -- Edgar J. Kaiser emPhys Physical Technology http://www.emphys.com

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