Discussion Forum

Dear Sir or Madam,

I already tried to get help for a similar problem in another thread (www.comsol.com/community/forums/general/thread/87301/) but I think more people will see this discussion if I start a new one; especially some new physical impossible effects occured.

I use COMSOL to simulate induced voltages in saddle shaped detection coils (this is the reason why I have to use COMSOL - it is the only real 3D simulation software for which I have a license at the moment). Nirmal Paudel (COMSOL employee) was kind enough to point me to the secret of the electrical conductivity of air which apparently must not be smaller than 1e-1 S/m in my frequency domain study. Otherwise the biconjugate gradient solver does not converge - for whatever reason (I would be very grateful if someone is able to explain me why since the real electrical conductivity of air is in the range of 1e-15 S/m). Like I already described in my referenced post (see above) I was not able to understand the simulation results of my splitted Helmholtz coil model because a symmetric model and a symmetric magnetic field must theoretically end in identical induced voltages in symmetric detection coils - but they're different. I reduced my model to not-splitted Helmholtz coils and at least both induced voltages fit theoretical considerations with respect to the curve trend U = f(freq) but not to the range of values I think. Hereupon I implemented a new (simple and reduced) model (see attached image: coils.png) and the induced voltage in the saddle coils changes its direction over the given frequency range freq = 1kHz up to 25kHz (see the other attached image: induced_voltages_U_freq.png). I will attach my *.mph file and I hope that someone is that kind that she or he will take the time to look into my files. I would be so grateful if someone could show me my big mistakes.

Thank you for your effort in advance,
Sebastian Draack