Discussion Forum

Hi

well what is the difference between your case "2" and the COMSOL "current driven coil case" where

Icoil=((VoltageTotal)/coilResistance)

did you do your measurements with a constant current, or a constant voltage applied ?

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Good luck
Ivar

Hi Ivar,

Thanks for looking into this. The measurements where made at a constant voltage.

Well I guess that, as you say, my case two is quite similar to the current driven coil case. However, in a Multi-Turn Coil Domain the conductivity (sigma) is set to zero, and I set it to the average conductivity of the coil cross-section instead.

And the modelled impedance is calculated as
Impedance = VoltageTotal / CurrentTotal

where CurrentTotal = (external current density + induced current density) integrated over the coil domain.

If the conductivity is set to zero the induced current density is also zero.

Regards,
Johan

Hi

I understood the doc that sigma is set to "0" for the main physics, because it is used in the extra equations introduced by this particular element to couple the induced voltage, check the equations carefully, at equation subnode level (turn them on with Options Preferences Equation on, but I exect you to know this already ;)

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Good luck
Ivar

Hi Johan,

If you are talking about the multi-turn coil domain for the magnetic fields interface, I have faced similar questions too. So I empirically verified the model of an N turn coil, cross-sectional area A, with a current excitation of say I mamps at a freq of f KHz. for Hz (magnetic field z component) at a given z distance from the coil. They matched to within 1 dB, which shows good agreement b/n the model and experimental data.

I then replaced the multi-turn coil domain with an external current density of Je=NI/A in order to obtain similar model results (sigma of coil was obviously zero). However, when sigma of coil is say sigmacopper, I then obtain low values of Hz, indicating that Jiphi is now high because of sigmacopper value and thereby decreasing the value of Jphi and inturn Hz.

Obviously you realize that this applies to the frequency domain regime only and we are solving for

(j*omega*sigma-omega^2*epsilon0)*Avector+curl(curlAvector)/mu0 = Je

I am still playing around and trying to understand different approaches, I guess you are too.

Hi

what I have understood by reading carefully the doc, is that the multiturn coil feature solves for V and if you specify J it adapts the voltage to get the desired current.
Furthermore, it turn off all skin effects as the magetic field is not resolved inside the coil. Check the equations underneath, note that these change dependingon the options of your BC. There isa thread from about a year ago with a good pdf article too, on the forum, relating to simulating multiturn cils, try a search

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Good luck
Ivar

Hi Ivar,

Good observation. I think Je is obtained for the multi-turn module in two different ways depending on if you choose current excitation or voltage excitation, as described in the PDF. It uses this external current density to solve Ampere's law in order to determine A. I have listed some observations below and also attached a couple of simple models herein. It would be great to nail this. I have also started a new thread for this, please feel to reply anywhere.

Please find the attached models Coil_axysmmetric2D_DCandAC.mph, CoilandShield_axysmmetric2D_DCandAC.mph.

My questions are as follows and for the models listed:

Coil_axysmmetric2D_DCandAC.mph
1) For the magnetic fields interface, if we are solving Ampere’s law, (j??-?^2 ?_0 ) A ?+?×((?×A ?)/?_0 )=J^e in the frequency regime, using the multi-turn coil domain, why don’t I get the same value of (say) the magnetic flux density norm when I excite the coil using a current excitation of 28 mA (please see underlined model) as compared to a voltage excitation of Vcoil=0.47516 V (which equals Vcoil = Icoil X Rcoil = 28mA X 16.97ohms). How do both these excitations arrive at different values of A ?phi. If this is because of mf.Vind_1 then how is mf.Vind_1 calculated, i.e. if mf.Vind_1=root.mod1.mf.intmtcd1(-300*mf.Ephi*r*pi/mf.coilDomainArea_1), and mf.Ephi= -Aphit, where Aphit is calculated from Ampere’s law above, is it not the case of the chicken and the egg ? I am trying to understand how the solution works here i.e. the sequence of evaluation. I empirically verified this model of an 150 turn coil, with a current excitation of 28 mA at a freq of 175 KHz. for Hz (magnetic field z component) at a given z distance from the coil. They matched to within 1 dB, which shows good agreement b/n the model and experimental data. However, the question of voltage excitation remains.
2) Can I estimate that Zcoil= mf.Rcoil + j*?* mf.Lc_1 ?


CoilandShield_axysmmetric2D_DCandAC.mph
1) Again, for the magnetic fields interface, if we are solving Ampere’s law, (j??-?^2 ?_0 ) A ?+?×((?×A ?)/?_0 )=J^e in the frequency regime, using the multi-turn coil domain. When I excite the 150 turn coil using a current excitation of 28 mA @ 175 KHz (please see underlined model) and evaluate the inductance of the coil+shield assembly, I obtain a close empirical match. mf.Lc_1 is the exact same value that you would obtain if the real coil+shield assembly were hooked to an impedance analyzer in the lab (the impedance analyzer lumps the value of Zdut into Ldut and Rdut based on the topology that is chosen). Obviously mf.Lc_1 is lower for the coil+shield assembly of this model example as compared to mf.Lc_1 as evaluated by the coil only model example (Coil_axysmmetric2D_DCandAC.mph), indicating that the shield is indeed loading the field of the coil.
2) However I cannot use Zcoil= mf.Rcoil + j*?* mf.Lc_1 now because mf.Rcoil is still the resistance of the coil only. How would I be able to measure the total impedance of the coil + shield assembly (as I would obtain if I were to use an impedance analyzer) ?
3) Constant Current Vs. Constant voltage coil excitation in the multi-turn coil domain:
(a) For a Constant current excitation, progressing from a Coil only model to a Coil+Shield model with all coil parameters, including the coil excitation current remaining the same, would the loading of the shield on the coil field be represented by, say, the difference in Hz(magnetic field component in the z direction) between the two models ? Would I be right in saying that we cannot observe a reflected impedance effect from the shield loading when the coil is excited by a constant current.
(b) For a Constant voltage excitation, progressing from the Coil only model to the Coil+Shield model with all coil parameters, including the coil excitation voltage remaining the same, how would the addition of the shield reflect in the model. Would Vind increase so that Je is now lower and hence generate a lower field ? What is the sequence of evaluation here ?

Thanks for your time. Your replies and advise is greatly appreciated.


Regards,

Venkat Gaddam

Hi
I want to simulate a solenoid in both 2D(not symmetric) and 3D and calculate the resulting force on a nearby plate,
Id be glad if you could help me with both 2D and 3D or either of them

Thank you in advanced