Personal COMSOL challenge (EM)

[vis viva]

TL;DR Summary

For the purpose of exploring COMSOL my challenge is to plot E/M-fields of a piece of current carrying wire.

Hi Y'all

For the purpose of exploring COMSOL, I challenged my self to plot the E/M-fields of a piece of current carrying wire in 3D. It's quite a simple task to plot the fields inside the wire, but I fail when plotting the fields outside the wire.

For plotting the outside fields I have enclosed the wire in a sphere. When the material of the sphere is e.g. FR4 (Circuit Board) I can obtain the below plot. Please note the wire is excited with 1A DC by "Lumped Port 1" and I have chosen "Magnetic and Electric Fields (mef)" as Physics because it is supposed to fully couple Magnetic and Electric Fields.

However if the chosen material for the sphere is "Air" then I always get an error:

Failed to find a solution.
Singular matrix.

For mesh case 0 there are 17824 void equations (empty rows in matrix) for the variable comp1.V.
at coordinates: (-0.00754829,-0.00476567,-0.00350686), (-0.00725854,-0.00573252,-0.00280156), (-0.00659457,-0.00684682,-0.00210367), (-0.00447219,-0.00590542,-0.00477199), (-0.00435897,-0.00567258,-0.00598722), ...

and similarly for the degrees of freedom (empty columns in matrix).
Returned solution is not converged.
Not all parameter steps returned.

What am I doing wrong here?

Klaus Z.

 

[vis viva]

I found the error, so just for posterity:

I was using the material "Air" from the built-in material library which I wasn't hesitant about using, as it worked fine in other example simulations.

However the electrical conductivity property was set to 0 (zero) S/m, and that prevented the solver in converging. Then I changed the value to 8e-15 S/m and it found a solution without problems.