# Discussion Forum

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## Electric Field Simulation Problem

Hi,

I am trying to create a plot of electric field, but i failed to do it.

I created a simple model of column, and I used the physics of "Magnetic and Electric Fields".

I defined a electrical potential (eg.10V) on the top surface of the column and the ground on the bottom surface of the column.

I tried using the studies of "Stationary" and "Time Dependent" and ran it but I cant manage to create the plot.

I would like to look for your advice since I have stuck at this point for a long time.

Woon Huei

25 Replies Last Post Nov 16, 2016, 10:45 AM EST
Posted: 7 years ago
Hi!

1) First try Electrostatics (es) physics.
2) Use Stationary solver.
3) To get the correct field you need to add to your model the electrodes: draw thin (you can take 0.01m, for example) cylindrical electrodes with radius equal to radius of your coloumn on the bottom and on the top of the coloumn.
4) Assign material to both of the electrodes (copper, for example).
5) Assign Boudary conditions to the electrodes: to every boundary of cylinder, that forms the electrode (6 boundaries in 3D). For example, Electric Potential to the upper electrode, and Ground to the bottom electrode.
6) Mesh.
7) Get the result =) I've got quite nice field. Sorry, I have no ability to send the file.

To get more correct field I recommend you to surrond your model with the sphere of air.

Good luck!

Posted: 7 years ago
Hi Roman,

I will try it out.

Posted: 7 years ago
Hi Roman,

Why was I just able to create electrical potential in my plots instead of electrical field?

Did I do less any steps?

Posted: 7 years ago
Hi!

As I understand you've got the correct electric potential distribution?

If the problem is solved correctly, you just need to visualize the electric field.
1) Click (right mouse button) on 3D Plot Group 1 in Model Builder.
2) Choose the way you want to plot the result (Surface, for example), press Settings button.
3) In Expressin field instead of V type sqrt(es.Ex*es.Ex+es.Ey*es.Ey+es.Ez*es.Ez).
4) Press Plot button.
5) Get the Electric Field distribution =)

Good luck!

Posted: 7 years ago
Yeah, I did it.

Thanks Roman!

Posted: 7 years ago
You're welcome =)

Posted: 6 years ago

Hi!

As I understand you've got the correct electric potential distribution?

If the problem is solved correctly, you just need to visualize the electric field.
1) Click (right mouse button) on 3D Plot Group 1 in Model Builder.
2) Choose the way you want to plot the result (Surface, for example), press Settings button.
3) In Expressin field instead of V type sqrt(es.Ex*es.Ex+es.Ey*es.Ey+es.Ez*es.Ez).
4) Press Plot button.
5) Get the Electric Field distribution =)

Good luck!

Posted: 6 years ago
Hi

that is the equation for the magnitude (norm) of the electric vector field (Ex,Ey,Ez) for ES physics

--
Good luck
Ivar

Posted: 5 years ago
Thank you very much,am a beginner and i faced the same problem.

Posted: 5 years ago
Thank you very much,am a beginner and i faced the same problem.

Posted: 5 years ago
Hi

then do not forget to turn on the "options - preferences - equation view" so you can scroll through the equations of comsol (unfortunately they are not sorted so you must search a bit) I find that helps to understand the physics, you have the description of all these now in the doc (4.3) try the search there too

--
Good luck
Ivar

Posted: 5 years ago
Hi,

I am trying to follow this explanation and believe I have done all of the steps, but I don't think my answer makes sense. I want to model the electric field between two gold electrodes, each on one side of a pyramid filled with air. How can I get the electric field lines to show? Is this not possible with air in between? My aim is to try and model electrokinetic transport effects. The applied potential will cause a solution to be expelled from the pyramidal reservoir. I have attached my model.

Thank you very much.

Jenna

Posted: 5 years ago
Mr Tukanov

I believe your explanation helped everyone, this can be easily inferred from the view number of this post. since the question was also about time domain solver. would you explain how we should consider an AC function as the boundary in time domain solution. I considered the input as a terminal voltage to a surface of cube or cylinder and assigned waveform function e.g. wv1(t/1 [s]) and solved it but it showed all result as zero.

Hi!

As I understand you've got the correct electric potential distribution?

If the problem is solved correctly, you just need to visualize the electric field.
1) Click (right mouse button) on 3D Plot Group 1 in Model Builder.
2) Choose the way you want to plot the result (Surface, for example), press Settings button.
3) In Expressin field instead of V type sqrt(es.Ex*es.Ex+es.Ey*es.Ey+es.Ez*es.Ez).
4) Press Plot button.
5) Get the Electric Field distribution =)

Good luck!

Posted: 5 years ago

Hi,

I am trying to follow this explanation and believe I have done all of the steps, but I don't think my answer makes sense. I want to model the electric field between two gold electrodes, each on one side of a pyramid filled with air. How can I get the electric field lines to show? Is this not possible with air in between? My aim is to try and model electrokinetic transport effects. The applied potential will cause a solution to be expelled from the pyramidal reservoir. I have attached my model.

Thank you very much.

Jenna

Hi,

I see a couple of problems with your model:

first of all, with a conductivity of 0 in electrostatics you cannot see electrokinetic transport effects. In reality, with a perfect insulator between two electrodes, there won't be any carrier movement because there are no charge carriers.

secondly, your mesh is very coarse with a minimum element quality of 0.02. This should be improved.

last remark is, I don't think electrostatics is the correct interface for modelling electrokinetic transport effects. It should include electrochemistry.

Bye

Posted: 5 years ago
Hi

I have a little issue with the formula

sqrt(es.Ex*es.Ex+es.Ey*es.Ey+es.Ez*es.Ez).

What if E is complex (which happens mostly in ACDC or RF but also elsewhere ?)
We tend to forget that COMSOL works on the scalar values of any vector field, and that any scalar might be complex, but when we type Ex for the x component of the electric field vector in a plot we get by "convention" real(Ex) displayed ONLY!
So if we suspect that Ex is complex one should also plot imag(Ex) to check ! ;)

So normally the norm is rather:

normE = sqrt(realdot(mf.Ex,mf.Ex)+realdot(mf.Ey,mf.Ey)+realdot(mf.Ez,mf.Ez))

where realdot() operator (check the doc and help) is the real value of the complex "dot" product of a complex numbers C and D

realdot(C,D) behaves like real(C*conj(D)) = real((real(C)+i*imag(C))*conj(real(D)+i*imag(D))) = real(C)*real(D)+imag(C)*imag(D)

the realdot operator has further features for the derivative calculations see the help

As in many cases we think real values but we get it easily wrong when thee are complex values ;)
--
Good luck
Ivar

Posted: 4 years ago
Hi,

I'm new to COMSOL.. currently I'm working on a simulation to study the electric field along an insulator. I've been using the method told by Roman, but unfortunately the electric field simulated was not as expected...the electric field on the energized end should be higher than that of the grounded end, but from the simulation result the electric field level is same for both end... anyone can help me?

Posted: 4 years ago

Hi

there is no reason why the fields should be different on both ends. Don't mix up electric field and electric potential.

Cheers
Edgar

--
Edgar J. Kaiser
www.emphys.com

Posted: 4 years ago
Hi Edgar, thanks for the reply.

By the way, what do you mean by not mixing up electric potential and electric field, I thought we can only see the electric field if an electric potential is applied to the material? besides, I've seen in many journal stating that the electric field at the energized end is higher than the grounded one..

Posted: 4 years ago

Hi,

what I meant is that in your case the potentials are different on both sides, but your setup seems to be symmetric, so the fields should also be symmetric. The field exists because of the potential difference. Only the difference counts not the values. You can always add a potential constant to an electrostatic assembly without changing the field. So if you have say, +15 kV on one end and 0 (ground) at the other, you could add -15 kV to both ends, reversing the situation. It will not change the field.

Regarding any publication, you should carfully check the setup. There may other parts around that make the situation non-symmetric.

Cheers
Edgar

--
Edgar J. Kaiser
www.emphys.com

Posted: 4 years ago
thanks a lot Edgar.. really appreciate the help and tips

Posted: 4 years ago
I am trying to assign voltages to the conductors in my model to get the electric field for a coaxial cylinder. I am not getting any option about assigning boundary conditions to the electrodes. I am getting options like charge conservation , zero charge and initial values under physics for electrostatic sub-module. It will be useful to know how to assign boundary conditions for the model.
Thanks.

Posted: 3 years ago
I am currently making electric field plots too. I was wondering if the built in Electric Field norm (es.normE) is the same as sqrt(es.Ex^2 + es.Ey^2 + es.Ez^2) ?

Posted: 2 years ago
hello,

can you guide me how to generate the near-field pattern of index-guiding Photonic Crystal Fiber.

Posted: 10 months ago
hello!
i use the AC/DC- electrostatic physics to study the corona onset voltage with using electrode to plate (ground). and i found that electric field inside the electrode not equal zero

Posted: 10 months ago
Hi
I am new to comsol, I study the electric field between charged and ground electrode. and I found that the field between the two electrode equal zero and there is afield inside charged electrode

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