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Changing material does not change electric field distribution!

Posted Nov 27, 2017, 8:45 a.m. EST 2 Replies

Hossein Nili
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Hi, I am simulating a 2D domain, wherer there is an electrode as a half-line at bottom of a rectangular domain. I apply a potential (fixed, DC) to the electrode, and the domain is filled with water. I am using the Electric Currents module under AC/DC. The simulation works and I get results. The trouble is that changing the material from water to 'anything' (drastically altering the relative permittivity and the conductivity) does not give the slightest change in the results. It would help a lot if you could please guide me as to where the problem comes from. Many thanks

2 Replies Last Post Feb 20, 2018, 2:59 p.m. EST
Jeff Hiller COMSOL Employee

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Posted: 7 years ago Nov 27, 2017, 9:25 a.m. EST
Updated: 7 years ago Nov 27, 2017, 10:17 a.m. EST

Hello Hossein,

In some cases, the solution of a PDE is independent of the material properties.

In your case, it sounds like you're solving the steady-state electric currents equation with a spatially-independent conductivity , and with your boundary conditions being all Dirichlet or zero flux. In that case, you can see that , the conductivity, is the only material property that appears in the equation and the BCs, and that it can actually be removed from the equation (because is spatially-independent and can therefore be taken out of the divergence and eliminated from the equation by dividing both sides by ) and the BCs (by dividing both sides of those BCs by ).

Best regards,

Jeff

PS: While in your model the voltage and electric potential (which is defined solely in terms of the voltage) do not depend on , some other quantities do, for instance the current density.

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Jeff Hiller
Hello Hossein, In some cases, the solution of a PDE is independent of the material properties. In your case, it sounds like you're solving the steady-state electric currents equation with a spatially-independent conductivity \sigma, and with your boundary conditions being all Dirichlet or zero flux. In that case, you can see that \sigma, the conductivity, is the only material property that appears in the equation and the BCs, and that it can actually be removed from the equation (because \sigma is spatially-independent and can therefore be taken out of the divergence and eliminated from the equation by dividing both sides by \sigma) and the BCs (by dividing both sides of those BCs by \sigma). Best regards, Jeff PS: While in your model the voltage and electric potential (which is defined solely in terms of the voltage) do not depend on \sigma, some other quantities do, for instance the current density.
Shamor
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Posted: 7 years ago Feb 20, 2018, 2:59 p.m. EST
Updated: 7 years ago Feb 21, 2018, 2:05 a.m. EST

Hi, I also have been working on Elictric current intreface. In my model three materials were used. I have attached a schematic diagram, which describes the whole procedure. Where dark circles are copper elctrode. First Result is obtained for perticular dielectric properties (permittivity & conductivity) for material 1 and material 2. Second result is obtained done for different properties of material 2, while other material remain same. Both simulation done under frequency domain. But contribution (current density & electric field) of material 1 is different for 2nd result. What is the reason for that?

Thanks in advance.

Hi, I also have been working on Elictric current intreface. In my model three materials were used. I have attached a schematic diagram, which describes the whole procedure. Where dark circles are copper elctrode. First Result is obtained for perticular dielectric properties (permittivity & conductivity) for material 1 and material 2. Second result is obtained done for different properties of material 2, while other material remain same. Both simulation done under frequency domain. But contribution (current density & electric field) of material 1 is different for 2nd result. What is the reason for that? Thanks in advance.

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