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How to Couple Electrostatics with Charge Density Continuity Equation?

Posted May 19, 2020, 5:46 p.m. EDT Electromagnetics, Low-Frequency Electromagnetics, Microfluidics Version 5.5 3 Replies

Nazanin Farjam
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Hello,

I am trying to couple electrostatics module with charge density continuity equation, for which these three equations need to be coupled:

The first two equations are provided in Electrostatics module; however, the last equation (charge density continuity equation), which calculates for the charge density is not included. The reason is that Electrostatic module assumes the material to be a perfect dielectric and therefore considers volumetric charge density () to be zero. However, in my application, the material is not a perfect dielectric and so the corresponding paremeter is not zero.

Can anyone help how I can couple this equation and Electrostatics physics in COMSOL?

Thanks,

Nazanin

3 Replies Last Post May 20, 2020, 9:59 p.m. EDT
Robert Koslover Certified Consultant
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Posted: 4 years ago May 20, 2020, 1:13 p.m. EDT

Actually, you can specify a non-zero charge density in an electrostatics problem. Your real problem here is dealing with the time dependence. Time dependent charge densities imply currents. If you want to model those currents correctly, don't try to do it with a strict electrostatics formalism. Use one of the other formalisms (several are available) that supports non-zero current densities.

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Scientific Applications & Research Associates (SARA) Inc.
www.comsol.com/partners-consultants/certified-consultants/sara
Actually, you can specify a non-zero charge density in an electrostatics problem. Your real problem here is dealing with the *time dependence*. Time dependent charge densities imply *currents*. If you want to model those currents correctly, don't try to do it with a strict electrostatics formalism. Use one of the other formalisms (several are available) that supports non-zero current densities.
Nazanin Farjam
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Posted: 4 years ago May 20, 2020, 9:05 p.m. EDT

Hello Robert,

Thanks for the reply. I have actually looked into different COMSOL modules, but I couldn't find one that includes the last equation. Could you kindly clarify what are the available formalisms that I can use?

Thanks,

Nazanin

Hello Robert, Thanks for the reply. I have actually looked into different COMSOL modules, but I couldn't find one that includes the last equation. Could you kindly clarify what are the available formalisms that I can use? Thanks, Nazanin
Robert Koslover Certified Consultant
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Posted: 4 years ago May 20, 2020, 9:59 p.m. EDT
Updated: 4 years ago May 20, 2020, 10:01 p.m. EDT

The EC formulation in the AC/DC module, with a time-dependent study, would be one of the options to consider. See screenshot attached.

-------------------
Scientific Applications & Research Associates (SARA) Inc.
www.comsol.com/partners-consultants/certified-consultants/sara
The EC formulation in the AC/DC module, with a time-dependent study, would be one of the options to consider. See screenshot attached.

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