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Electric Field of Capacitor

Posted 9 mars 2022, 08:38 UTC−5 4 Replies

Derek M
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Hi there,

I am trying to plot a Line Graph using '1D Plot Tool' of the electric field across a parallel plate capacitor.

I have completed the geometry by creating 2 rectangles, assigned them Copper material and created a larger rectangle around them both and assigned that Air.

I can only seem to plot Electric Potential, can anyone help me with how I can plot the Electric Field?

Kind regards

4 Replies Last Post 14 mars 2022, 08:44 UTC−4
Robert Koslover Certified Consultant
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Posted: 3 years ago 10 mars 2022, 11:50 UTC−5

If you are already successfully plotting the electric potential along a line, then you should be able to very easily replace the expression for the potential with an expression for the electric field, and then plot that. If this perhaps overly-simple advice isn't enough to guide you in solving your problem, then I encourage you to post your .mph file to the forum so that everyone can see the details of your model and can offer you more specific and useful help.

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Scientific Applications & Research Associates (SARA) Inc.
www.comsol.com/partners-consultants/certified-consultants/sara
If you are already successfully plotting the electric *potential* along a line, then you should be able to very easily replace the expression for the potential with an expression for the *electric field*, and then plot that. If this perhaps overly-simple advice isn't enough to guide you in solving your problem, then I encourage you to post your .mph file to the forum so that everyone can see the details of your model and can offer you more specific and useful help.
Jeff Hiller COMSOL Employee

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Posted: 3 years ago 10 mars 2022, 13:28 UTC−5
Updated: 3 years ago 10 mars 2022, 14:55 UTC−5

Hello Derek,

Two quick remarks:

  1. While the potential is a scalar, the electric field is a vector quantity, so you can't plot it with a surface plot (though you could plot its norm, or any other scalar quantity derived from its components); consider using an arrow plot or a streamline plot. You will find the electric field is then one of the ready-to-use quantities for those types of plots. There are training videos on the topic of arrow plots and streamline plots in the Learning Center.
  2. Copper being a vastly better conductor than air, typically you leave the copper electrodes out of the simulation entirely (Their potential being known a priori) and replace them by boundary conditions on the electrostatics problem solved on the air domain only. See this capacitor model for an example.

Best,

Jeff

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Jeff Hiller
Hello Derek, Two quick remarks: 1. While the potential is a scalar, the electric field is a vector quantity, so you can't plot it with a surface plot (though you could plot its norm, or any other scalar quantity derived from its components); consider using an arrow plot or a streamline plot. You will find the electric field is then one of the ready-to-use quantities for those types of plots. There are training videos on the topic of arrow plots and streamline plots in the [Learning Center](https://www.comsol.com/learning-center). 2. Copper being a vastly better conductor than air, typically you leave the copper electrodes out of the simulation entirely (Their potential being known a priori) and replace them by boundary conditions on the electrostatics problem solved on the air domain only. See [this capacitor model](https://www.comsol.com/model/tunable-mems-capacitor-123) for an example. Best, Jeff
Derek M
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Posted: 3 years ago 12 mars 2022, 18:34 UTC−5

Thank you both for the advice. I am trying out your suggestions now, much appreciated.

My only further question is that when I am trying to plot the electric field using 1D Plot Tool, Line Graph, there is no option for distance on the x axis. I would like to plot the electric field on the y axis and the distance on the x axis.

Any further help appreciated.

Regards,

Thank you both for the advice. I am trying out your suggestions now, much appreciated. My only further question is that when I am trying to plot the electric field using 1D Plot Tool, Line Graph, there is no option for distance on the x axis. I would like to plot the electric field on the y axis and the distance on the x axis. Any further help appreciated. Regards,
Jeff Hiller COMSOL Employee

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Posted: 3 years ago 14 mars 2022, 08:44 UTC−4

Hello,

It sounds like you need to add to your model a "Cut Line 2D" dataset, corresponding to the line along which you want to plot the quantity. But remember my earlier remark: the electric field is not a scalar; a line plot will allow you to plot a scalar quantity derived from the electric field (such as its norm for instance), but not the electric field itself.

Best,

Jeff

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Jeff Hiller
Hello, It sounds like you need to add to your model a "Cut Line 2D" dataset, corresponding to the line along which you want to plot the quantity. But remember my earlier remark: the electric field is not a scalar; a line plot will allow you to plot a scalar quantity derived from the electric field (such as its norm for instance), but not the electric field itself. Best, Jeff

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