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Electrostatics vs. electric currents?

Posted 5 mar 2020, 05:27 GMT-5 Low-Frequency Electromagnetics Version 5.1 3 Replies

Anna Kashkanova
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Hello, I am trying to simulate the electric field inside of a nanochannel filled the water using 2D geometry. The field results from three parallel electrodes (one with applied potential and another two with ground) embedded inside a glass substrate below the channel.

My first idea was to solve a poisson equation using electrostatics in COMSOL. I checked that I get the correct result for a problem I can solve analytically - if the nanochannel was also filled with glass. Then I fill with channel with water and get a resultant electric field.

However, then I realized that water is significantly more conductive than glass, so maybe I should use current conservation equations (electric currents). This gives me a completely different magnitude and shape of electric field, though again for a simple problem of channel filled with glass the results are the same as what I get from electrostatics.

I realize the difference comes from boundary conditions at the water/glass interface, but I am not sure which way gives the correct result.

I attach my simulation file.

Thank you for any advice.

3 Replies Last Post 5 mar 2020, 09:43 GMT-5
Edgar J. Kaiser Certified Consultant
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Posted: 5 years ago 5 mar 2020, 06:03 GMT-5

Anna,

it is not the boundary between water and glass that causes the difference but the different electrical conductivity of the materials. I think the ec-approach is the correct one. Electrical conductivity must be taken into account because it is by orders of magnitude different in the two materials.

Cheers Edgar

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Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
Anna, it is not the boundary between water and glass that causes the difference but the different electrical conductivity of the materials. I think the ec-approach is the correct one. Electrical conductivity must be taken into account because it is by orders of magnitude different in the two materials. Cheers Edgar
Anna Kashkanova
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Posted: 5 years ago 5 mar 2020, 09:23 GMT-5

Dear Edgar, Thank you, that makes sense! Does that mean that I choose between ES and EC approach depending on how much do to permettivities and conductivities vary between materials in the model? What if there is a situation if both vary similarly? Do you know if there is a way to account for both permettivities and conductivities? Best wishes, Anna

Dear Edgar, Thank you, that makes sense! Does that mean that I choose between ES and EC approach depending on how much do to permettivities and conductivities vary between materials in the model? What if there is a situation if both vary similarly? Do you know if there is a way to account for both permettivities and conductivities? Best wishes, Anna
Edgar J. Kaiser Certified Consultant
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Posted: 5 years ago 5 mar 2020, 09:43 GMT-5

EC takes both into account while ES ignores conductivity.

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Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
EC takes both into account while ES ignores conductivity.

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