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Applying AC current to Helmholtz coil

Posted 03.08.2015, 09:57 GMT-4 Low-Frequency Electromagnetics Version 5.0 5 Replies

Thais Braga
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Hey, I am new to COMSOL and have very basic questions, I hope you can help me. I am trying to measure the impedance of a pair of helmholtz coils at high frequencies (200 kHz), I followed the tutorial for the coils (br.comsol.com/model/magnetic-field-of-a-helmholtz-coil-15) but I don't know how to apply AC current to the coils, I guess I should work in the frequency domain, right? And how would I do to measure the impedance?

And just to make sure, when I apply the multi-turn coil domain it is a 1 layer coil, isn't it? Is it possible to build a multi-layer coil?

Thanks a lot
5 Replies Last Post 15.09.2015, 13:56 GMT-4
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 9 years ago 03.08.2015, 14:39 GMT-4
Hi

you are right wen you select a frequency domain and give i.e. only one frequency such as 200[kHz] then you are studying/solving your model for one sinusoidal boundary flux frequency (a current in your case) of amplitude I0 or whatever scalar value you have chosen (check the doc and the theory on frequency domain solver).

The impedance is simply the ratio U[V]/(I[A]), note it will probably be complex ! and it will not work like that if you have I=0 for any reason.

You have several "coil" boundaries, you can define a domain i.e. of copper with a given section and call it a explicitly "single loop coil" of a conductor, but it's far better to use the built-in BC "single coil" or "multiple coil" as these have built-in lumped parameters to directly calculate impedance etc. check the ACDC doc it's al in there. For the multi-turn coil you have additional sub-nodes to even define how the different coils are winded, by layer or columns or ...

--
Good luck
Ivar
Hi you are right wen you select a frequency domain and give i.e. only one frequency such as 200[kHz] then you are studying/solving your model for one sinusoidal boundary flux frequency (a current in your case) of amplitude I0 or whatever scalar value you have chosen (check the doc and the theory on frequency domain solver). The impedance is simply the ratio U[V]/(I[A]), note it will probably be complex ! and it will not work like that if you have I=0 for any reason. You have several "coil" boundaries, you can define a domain i.e. of copper with a given section and call it a explicitly "single loop coil" of a conductor, but it's far better to use the built-in BC "single coil" or "multiple coil" as these have built-in lumped parameters to directly calculate impedance etc. check the ACDC doc it's al in there. For the multi-turn coil you have additional sub-nodes to even define how the different coils are winded, by layer or columns or ... -- Good luck Ivar
Thais Braga
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Posted: 9 years ago 11.08.2015, 13:14 GMT-4
That was very useful, Ivar, thanks a lot. However, I still got a problem with the coil winding, I want to build a helmholtz coil with 15 turns and 3 layers, I am using the built-in BC 'multi-turn coil' but I can't seem to find the winding options. I have looked into the ACDC module and couldn't find anything about multi-layers coils, I will have a look again but I'd be really glad if you could help me with this.

Kind regards
That was very useful, Ivar, thanks a lot. However, I still got a problem with the coil winding, I want to build a helmholtz coil with 15 turns and 3 layers, I am using the built-in BC 'multi-turn coil' but I can't seem to find the winding options. I have looked into the ACDC module and couldn't find anything about multi-layers coils, I will have a look again but I'd be really glad if you could help me with this. Kind regards
Nirmal Paudel COMSOL Employee

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Posted: 9 years ago 12.08.2015, 09:50 GMT-4

Hi

Unfortunately, there is no "automated" way of doing a multi-layered winding in COMSOL in 3D. You do have to explicitly create a layered structure and assigned a Multi-Turn Coil or Single Turn Coil for each of the layer separately. Hope this helps.

Nirmal Paudel
----------------------
COMSOL Employee
USA
Hi Unfortunately, there is no "automated" way of doing a multi-layered winding in COMSOL in 3D. You do have to explicitly create a layered structure and assigned a Multi-Turn Coil or Single Turn Coil for each of the layer separately. Hope this helps. Nirmal Paudel ---------------------- COMSOL Employee USA
Thais Braga
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Posted: 9 years ago 13.08.2015, 11:05 GMT-4
That does help, thanks a lot, Nirmal!

I've got another question now, I am designing these coils to use in a cryostat, can I simulate that setting the temperature of the multi turn coil domain to the cryostat temperature or should I do something else?

Kind regards,

Thais
That does help, thanks a lot, Nirmal! I've got another question now, I am designing these coils to use in a cryostat, can I simulate that setting the temperature of the multi turn coil domain to the cryostat temperature or should I do something else? Kind regards, Thais
Thais Braga
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Posted: 9 years ago 15.09.2015, 13:56 GMT-4

Hi

Unfortunately, there is no "automated" way of doing a multi-layered winding in COMSOL in 3D. You do have to explicitly create a layered structure and assigned a Multi-Turn Coil or Single Turn Coil for each of the layer separately. Hope this helps.

Nirmal Paudel
----------------------
COMSOL Employee
USA


I have done that, I built a structure with 3 layers and set each as a Multi-Turn Coil and I also set the reference edges for each one of them like in the Helmholtz tutorial, but I am getting a weird profile for the Magnetic flux density in the axis of the coils ( www.dropbox.com/s/rjhjmqnc05fpd43/Multi%20layer%20coils.jpeg?dl=0 ).

I was wondering if I should set the reference edges differently.
I couldn't upload the file because it was too big. I hope you can help me with this, you guy have been really helpful so far, thanks for that!

Coils - www.dropbox.com/s/na29ad0w86p6vmo/Magnetic%20flux%20density%20vs%20y-axis.jpeg?dl=0

Kind regards,
Thais


[QUOTE] Hi Unfortunately, there is no "automated" way of doing a multi-layered winding in COMSOL in 3D. You do have to explicitly create a layered structure and assigned a Multi-Turn Coil or Single Turn Coil for each of the layer separately. Hope this helps. Nirmal Paudel ---------------------- COMSOL Employee USA [/QUOTE] I have done that, I built a structure with 3 layers and set each as a Multi-Turn Coil and I also set the reference edges for each one of them like in the Helmholtz tutorial, but I am getting a weird profile for the Magnetic flux density in the axis of the coils ( https://www.dropbox.com/s/rjhjmqnc05fpd43/Multi%20layer%20coils.jpeg?dl=0 ). I was wondering if I should set the reference edges differently. I couldn't upload the file because it was too big. I hope you can help me with this, you guy have been really helpful so far, thanks for that! Coils - https://www.dropbox.com/s/na29ad0w86p6vmo/Magnetic%20flux%20density%20vs%20y-axis.jpeg?dl=0 Kind regards, Thais

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