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Find Potential by using Poisson equation

Posted 7 mag 2019, 13:09 GMT-4 5 Replies

Ali Nawaz Babar
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I want to calculate charge distribution due to the geometry and potential due to geometry of a trap in PDMS. Can you please guide me how can I do this using the poisson equation. I am also new to comsol and have just started using it.

I am attaching the geometry profile with this message.

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5 Replies Last Post 9 mag 2019, 10:09 GMT-4
Alexis Prel
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Posted: 6 years ago 8 mag 2019, 16:37 GMT-4

Hi Ali,

What problem are you struggling with exactly?

Looking at your model, why do you expect any electrical charge to be present?

Hi Ali, What problem are you struggling with exactly? Looking at your model, why do you expect any electrical charge to be present?
Ali Nawaz Babar
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Posted: 6 years ago 8 mag 2019, 18:58 GMT-4

Dear Alexis,

Thank you for your response.

There has to be charges present on the surface of the PDMS if the PDMS is in some liquid. And due to the surface charge density I would like to calculate the potential of the PDMS with the circular shaped trap.

Dear Alexis, Thank you for your response. There has to be charges present on the surface of the PDMS if the PDMS is in some liquid. And due to the surface charge density I would like to calculate the potential of the PDMS with the circular shaped trap.
Alexis Prel
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Posted: 6 years ago 9 mag 2019, 03:40 GMT-4

Dear Ali,

To add a surface charge density, you should right click on the Electrostatics entry of your model builder and select Surface charge density as a boundary condition. In the settings window of the surface charge density that will appear, you need to select the boundaries where this boundary condition applies (presumably all of the PDMS surface in your case). Then you should input the value of the surface charge density that you expect.

Then depending on what you are trying to model, you may want to include a Space Charge Density in the fluid as well, in order to preserve charge neutrality.

Dear Ali, To add a surface charge density, you should right click on the **Electrostatics** entry of your model builder and select **Surface charge density** as a boundary condition. In the settings window of the surface charge density that will appear, you need to select the boundaries where this boundary condition applies (presumably all of the PDMS surface in your case). Then you should input the value of the surface charge density that you expect. Then depending on what you are trying to model, you may want to include a **Space Charge Density** in the fluid as well, in order to preserve charge neutrality.
Alexis Prel
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Posted: 6 years ago 9 mag 2019, 03:42 GMT-4

Also a little tip: for your tests I suggest you first disable your circular trap in the geometry and make sure that the results you get make sense. Then you can enable it again and use the simpler geometry as a reference point to better identify the influence of the trap.

Also a little tip: for your tests I suggest you first disable your circular trap in the geometry and make sure that the results you get make sense. Then you can enable it again and use the simpler geometry as a reference point to better identify the influence of the trap.
Ali Nawaz Babar
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Posted: 6 years ago 9 mag 2019, 10:09 GMT-4

Hi Alexis,

I have tried with your method but there is some error. Can you please go through the attached file and check if I made a mistake somewhere.

Hi Alexis, I have tried with your method but there is some error. Can you please go through the attached file and check if I made a mistake somewhere.

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