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Floating potentials when solving Laplace equation

Posted Nov 9, 2015, 10:15 a.m. EST Materials, Modeling Tools & Definitions, Parameters, Variables, & Functions Version 4.3 5 Replies

Ari
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Hi,

I have a question about floating potentials and overridden boundary conditions when solving Laplace equation. My system consists of a few metallic surfaces and some dielectric structures and I solve Laplace equation for the surrounding area using Dirichlet Boundary conditions on the metallic surfaces.

Firstly, the Dirichlet Boundary conditions are overridden by a default zero flux. Does it matter?
Secondly, as far as I understand, to get the right solution I have to change the boundary conditions on the dielectric surfaces into a floating potential otherwise a zero flux is applied to them by default .
What is the way around this issue?

Really appreciate any comment or insight!
5 Replies Last Post Nov 9, 2015, 5:01 p.m. EST
Jeff Hiller COMSOL Employee

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Posted: 9 years ago Nov 9, 2015, 10:48 a.m. EST
Hello Ari,
There is a floating potential boundary condition available right out of the box in the AC/DC Module's and the MEMS Module's electrostatic physics interface.
Best regards,
Jeff
Hello Ari, There is a floating potential boundary condition available right out of the box in the AC/DC Module's and the MEMS Module's electrostatic physics interface. Best regards, Jeff
Ari
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Posted: 9 years ago Nov 9, 2015, 11:40 a.m. EST
Hi Jeff,
Thanks a lot for your quick reply.
So, I have to set up the model with more generality instead of using "Laplace Equation (lpeq)". Also, it does mean that leaving the zero flux on the dielectrics is not a good idea since it changes the physics of my actual problem, right?
Best regards,
Ari
Hi Jeff, Thanks a lot for your quick reply. So, I have to set up the model with more generality instead of using "Laplace Equation (lpeq)". Also, it does mean that leaving the zero flux on the dielectrics is not a good idea since it changes the physics of my actual problem, right? Best regards, Ari
Jeff Hiller COMSOL Employee

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Posted: 9 years ago Nov 9, 2015, 11:59 a.m. EST
When you apply the floating potential boundary condition, it automatically overrides the default (which is zero charge) boundary condition.
Jeff
When you apply the floating potential boundary condition, it automatically overrides the default (which is zero charge) boundary condition. Jeff
Ari
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Posted: 9 years ago Nov 9, 2015, 1:11 p.m. EST
Yes, it obviously does, but I'm a bit confused about when these overridden boundaries might become a concern. What do you think?
Best,
Ari
Yes, it obviously does, but I'm a bit confused about when these overridden boundaries might become a concern. What do you think? Best, Ari
Jeff Hiller COMSOL Employee

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Posted: 9 years ago Nov 9, 2015, 5:01 p.m. EST
I am afraid I may not have understood your questions/concerns. I leave it to others to chime in.
Jeff
I am afraid I may not have understood your questions/concerns. I leave it to others to chime in. Jeff

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