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Parallel plate capacitor 2D vs 3D issue

Posted 19 nov 2014, 11:55 GMT-5 Low-Frequency Electromagnetics, Geometry, Modeling Tools & Definitions Version 4.4 5 Replies

Saliya Kumara
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I'm a beginner COMSOL user. I came across this problem while i'm doing some test simulations. I've simulated a parallel plate capacitor in both 3D and 2D. I wanted to see if I can extract the same results from the 3D if I use a cut plane. So I created a cut plane so the resultant would be similar to a 2D situation. However when I extract the electric field directions, they do not look even remotely close to the results from 2D simualtion. I've attached two images from two simulations. I'm using "Electrostatic (es)" in both cases and all the materials are same in both cases. I would be very grateful if anyone can point out what I'm doing wrong.

Thank You.

Attachments:

5 Replies Last Post 20 nov 2014, 11:23 GMT-5
Edgar J. Kaiser Certified Consultant
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Posted: 10 years ago 19 nov 2014, 16:28 GMT-5
Hi,

something must be wrong with the arrow surface plot. If you upload the model (delete the solution if it is too big) we could have a look.

Cheers
Edgar

--
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
Hi, something must be wrong with the arrow surface plot. If you upload the model (delete the solution if it is too big) we could have a look. Cheers Edgar -- Edgar J. Kaiser emPhys Physical Technology http://www.emphys.com
Saliya Kumara
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Posted: 10 years ago 19 nov 2014, 17:17 GMT-5
Thank you for your reply Edgar. Original file size was about 50MB and it did not change even I deleted the solution and mesh. Therefore I created another file similar to the original file. Please find it attached(3MB).

All I did was simulated the model and created a 2D plot with a potential surface and a arrow surface representing the electric field. (I used a cut plane on the zx plane.)

Thank You.
Thank you for your reply Edgar. Original file size was about 50MB and it did not change even I deleted the solution and mesh. Therefore I created another file similar to the original file. Please find it attached(3MB). All I did was simulated the model and created a 2D plot with a potential surface and a arrow surface representing the electric field. (I used a cut plane on the zx plane.) Thank You.
Edgar J. Kaiser Certified Consultant
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Posted: 10 years ago 20 nov 2014, 06:57 GMT-5
I modified your model according to your description, looks ok to my taste. You didn't send your model so I can't say what is wrong there.
I am trying to attach the modified model, but it doesn't seem to work.

Yes the attachment didn't work. You can send an email address by private message if you want and I will send the model this way.

--
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
I modified your model according to your description, looks ok to my taste. You didn't send your model so I can't say what is wrong there. I am trying to attach the modified model, but it doesn't seem to work. Yes the attachment didn't work. You can send an email address by private message if you want and I will send the model this way. -- Edgar J. Kaiser emPhys Physical Technology http://www.emphys.com
Jeff Hiller COMSOL Employee

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Posted: 10 years ago 20 nov 2014, 08:15 GMT-5
Hello Saliya,
Check whether in the arrrow plot in your 3D cut plane you are plotting the _in-plane_ components of the E field. I suspect you are not.
Best,
Jeff
PS: Usually, with simulations like these, you do not include the electrodes in the model: they are considered perfectly conducting and you know in advance that the potential is going to be constant in each of them, so you remove them from the geometry and only solve for the potential in the dielectric (i.e. you subtract the two blocks from the sphere). As a result you only need air as a material (no copper).
Hello Saliya, Check whether in the arrrow plot in your 3D cut plane you are plotting the _in-plane_ components of the E field. I suspect you are not. Best, Jeff PS: Usually, with simulations like these, you do not include the electrodes in the model: they are considered perfectly conducting and you know in advance that the potential is going to be constant in each of them, so you remove them from the geometry and only solve for the potential in the dielectric (i.e. you subtract the two blocks from the sphere). As a result you only need air as a material (no copper).
Saliya Kumara
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Posted: 10 years ago 20 nov 2014, 11:23 GMT-5
Hello Edgar and Jeff,

Thank You for your responses. Jeff you were spot on. My plane was a xz plane and I was plotting x and y components on the plane(beginner mistake). Now that I corrected it, it looks the way it should be. That was a great tip to subtract the blocks from the sphere.

Thank You.
Saliya

Hello Edgar and Jeff, Thank You for your responses. Jeff you were spot on. My plane was a xz plane and I was plotting x and y components on the plane(beginner mistake). Now that I corrected it, it looks the way it should be. That was a great tip to subtract the blocks from the sphere. Thank You. Saliya

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