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Modeling of resistance in a rectangular sheet with COMSOL

  1. Jun 22, 2009 #1
    Hi,

    I have got a simple problem which makes me struggle.
    I have a rectangular thin conductive sheet (2D) of width w, height h
    and conductivity suspended in air.
    I would like to calculate with COMSOL/Femlab the electrical resistance between one of the corners of the conductive sheet and any other point on the sheet?
    I selected the 'conductive media DC' mode in 2D. I am not sure what
    boundary condition I should choose and how to apply a potential to one
    of the corners.
    Since the sheet is suspended in air I thought of putting isolating
    boundary conditions on all 4 sides, but then how will I apply the
    potential to the corner? Somehow it does not give meaningful results.

    Your help is greatly appreciated.

    David
     
  2. jcsd
  3. Jun 22, 2009 #2

    marcusl

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    Science Advisor
    Gold Member

    I don't know COMSOL so I can't help with your numerical simulation. I can tell you that the potential becomes singular at the infinitesimal points where your are introducing/removing current. Suggest using finite-sized electrodes to make the numerical solver better behaved. A small circular electrode on the plate and a semi-circular electrode at the corner, both small compared to the rectangle but enclosing multiple meshes, should do it.
     
  4. Jun 23, 2009 #3
    you should be able to set the potential along the boundaries. Make sure youve got a ground somewhere on ther, and have you tried a point condition?
     
  5. Jun 23, 2009 #4
    @Marcusl: Thanks for the suggestion. makes sense to me.

    @Nick: Yes, it is possible to set the potential along a boundary. I could for example define a small square electrode whose boundary I set to a potential of say 5V. I am also able to set the border of the big rectangle to isolating. Now I still need to get a ground somewhere, but where. I think if I want to calculate the resistance between one corner and a point (X,Y) then I have to set the corner to 5V and this point (X,Y) to ground and then somehow calculate the current. But this calculation I would have to code in a script and repeat 10000 times, if I assume a 100 x 100 grid.
    I am wondering if there is a faster solution.
    I have looked through all Femlab examples and could not find the solution.

    Thanks
     
  6. Jun 23, 2009 #5
    Try and contact Mina with Comsol on their website. shes a big help.
     
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