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How setup a current density in RF module

Posted 14 mars 2014, 23:35 UTC−4 RF & Microwave Engineering, Modeling Tools & Definitions, Parameters, Variables, & Functions 2 Replies

JohnZK
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I am calculating the Lorentz force in a sheet metal near spiral coils. Transient current thru the coils have short period. So I am using the RF module instead of the AC/DC module.

In one example, I learned that I can setup a current density on the cross section of the coil. But for RF module, when I choose the cross section, which is a circle, there is only subdomain settings like electric parameters, magnetic parameters, initial values of A and E. I just can not find anywhere for current density.

I found out one option: to model the coil as lines without no cross section, which means I just need to model the coil as a point in a 2d axisymmetric model. But in this case how should I define the distance from sheet metal and coil considering the radius of the coil?

I am using V3.4. I searched thru the forum without answers about this.
Hope anyone can give me some advice.

Thank you very much, experts!
2 Replies Last Post 25 mars 2014, 18:08 UTC−4
Robert Koslover Certified Consultant
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Posted: 1 decade ago 20 mars 2014, 11:03 UTC−4
First of all, I think your mental picture of the RF module may be too much like a higher-frequency version of the AC/DC module. But that it is not the right perspective. When working with the AC/DC module, one normally thinks about currents and charges as being the fundamental things, with the fields considered to arise from them. In contrast, when working with the RF module, you need to reverse that; think about the fields as the fundamental quantities, with any charges and currents as arising from the fields. Although you can indeed set certain current or charge boundary conditions, it is generally a better idea to set explicitly field-related boundary conditions. At perfect conducting surfaces, this is fairly straightforward, since (for example) the tangential H field (which is in units of Amps/meter) corresponds directly to the surface current density. Just remember your right-hand rules when specifying tangent field vectors at surfaces to correspond to the actual surface currents you want. And of course, always remember that with RF, there are no volumetric currents inside perfect conductors, only surface currents.
First of all, I think your mental picture of the RF module may be too much like a higher-frequency version of the AC/DC module. But that it is not the right perspective. When working with the AC/DC module, one normally thinks about currents and charges as being the fundamental things, with the fields considered to arise from them. In contrast, when working with the RF module, you need to reverse that; think about the fields as the fundamental quantities, with any charges and currents as arising from the fields. Although you can indeed set certain current or charge boundary conditions, it is generally a better idea to set explicitly field-related boundary conditions. At perfect conducting surfaces, this is fairly straightforward, since (for example) the tangential H field (which is in units of Amps/meter) corresponds directly to the surface current density. Just remember your right-hand rules when specifying tangent field vectors at surfaces to correspond to the actual surface currents you want. And of course, always remember that with RF, there are no volumetric currents inside perfect conductors, only surface currents.
JohnZK
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Posted: 1 decade ago 25 mars 2014, 18:08 UTC−4
Thank you so much for the reply. That is wonderful help for me.

Before you answer my question, I have tried with modeling the coil as a point in a 2D axisymmetric model. The result value (electromagnetic force on the blank surface) showed good accordance with literature,but the distribution is different.

Then I tried your advice, modeling the coils with cross section areas and assign a surface current on the interior boundaries ( Jsphi, unit is A/m). But the result is much less than results in literature. I have checked other boundary conditions (the outer boundaries are scattering, and the center is symmetric), the surface current and material properties. They are all fine.

Would you help figure out where the problem could be?
Thank you so much for the reply. That is wonderful help for me. Before you answer my question, I have tried with modeling the coil as a point in a 2D axisymmetric model. The result value (electromagnetic force on the blank surface) showed good accordance with literature,but the distribution is different. Then I tried your advice, modeling the coils with cross section areas and assign a surface current on the interior boundaries ( Jsphi, unit is A/m). But the result is much less than results in literature. I have checked other boundary conditions (the outer boundaries are scattering, and the center is symmetric), the surface current and material properties. They are all fine. Would you help figure out where the problem could be?

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