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Question about induced electric field

Posted 27 juin 2018, 18:57 UTC−4 Electromagnetics, Low-Frequency Electromagnetics, Studies & Solvers Version 5.3 4 Replies

Henry Froland
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Dear All,

I'm trying to calculate the induced electric field from an external time varying current density. For simplicity just imagine a cylinder with a homogenous current density in the longitudinal direction (z-direction, if you will), that varies sinusoidally with time, say j=cos(t). Solving Maxwell's equations by hand would tell you that there is a magnetic field in the phi (polar angle) direction that varies solely on the radius to the center of the cylinder. Furthermore, this will induce an electric field the longitudinal direction that should be out of phase with the magnetic field, i.e. E~E(r) x sin(t).

I am trying to replicate this behaviour in COMSOL using the AC/DC module (mf physics) in a transient study, but the behaviour COMSOL predicts is not what one would expect, that is sinusoidal. I have attached a picture of the EField vs time plot at some fixed radius. Is this discrepency a possible machine precision error or something of the like? Does anyone have a recommendation or tips on how to implement an induced electric field from some external current density?

Thanks in Advance, Henry

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4 Replies Last Post 28 juin 2018, 17:21 UTC−4
Sergei Yushanov Certified Consultant
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Posted: 6 years ago 28 juin 2018, 08:20 UTC−4

Henry,

Not sure I understand your plot but attached is a toy model showing phase shift between current, electric, and magnetic fields.

Regards

Sergei

Henry, Not sure I understand your plot but attached is a toy model showing phase shift between current, electric, and magnetic fields. Regards Sergei
Henry Froland
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Posted: 6 years ago 28 juin 2018, 11:46 UTC−4

Hi Sergei,

The plot is one I've made in python after importing the data from COMSOL (I do this to run steps to analyze the COMSOL data outside of COMSOL). I'll attach the program I've been running, but I'm just confused why the electric field my COMSOL program gives me is not sinusoidal, and instead just horizontal lines. It reproduces the magnetic field well, but not the electric for some reason.

As some background (I know this looks like a very weird current density), this is trying to replicate the EM properties of a form of exotic matter, that is represented by a field that is uniform on the length scales of the geometry on which the program is running, and it varies sinusoidally in time.

Please let me know if you have any other questions.

Thanks, Henry

Hi Sergei, The plot is one I've made in python after importing the data from COMSOL (I do this to run steps to analyze the COMSOL data outside of COMSOL). I'll attach the program I've been running, but I'm just confused why the electric field my COMSOL program gives me is not sinusoidal, and instead just horizontal lines. It reproduces the magnetic field well, but not the electric for some reason. As some background (I know this looks like a very weird current density), this is trying to replicate the EM properties of a form of exotic matter, that is represented by a field that is uniform on the length scales of the geometry on which the program is running, and it varies sinusoidally in time. Please let me know if you have any other questions. Thanks, Henry

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Sergei Yushanov Certified Consultant
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Posted: 6 years ago 28 juin 2018, 12:54 UTC−4

Henry,

Step Time Stepping to "Intermediate" and you will get harmonic response, as shown in the attached images.

Regards

Sergei

Henry, Step Time Stepping to "Intermediate" and you will get harmonic response, as shown in the attached images. Regards Sergei
Henry Froland
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Posted: 6 years ago 28 juin 2018, 17:21 UTC−4

Hi Sergei,

Your instructions fixed this. Thank you very much.

  • Best Henry
Hi Sergei, Your instructions fixed this. Thank you very much. - Best Henry

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