Discussion Forum

Hi


but why 5V AND 1A ? you are overconstrining your model, you can only define ONE of the two, and the geoemtry and material properties, then COMSOL will find the other depenending on frequency and field solution.

Use the lumped ports/terminal approach to find impedances its easier, check the doc

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Good luck
Ivar

Hi Ivar,

Can you suggest me how to start to simulate these two coils in comsol 4. It will be great if you post any example regarding simulation of coil. how to use doc? please help me.





Regards,
Pranith

Hi

but you have a few examples in the model library, the doc, not to say on the model exchage etc (ok many there in 3.5)

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Good luck
Ivar

I am working on pretty much the exactly same topic and I am also very new to Comsol in general. I found the following example of a Helmholtz coil pair as the closest ready-made model available, maybe it is also useful to you:
www.comsol.com/showroom/gallery/15/

I use Comsol 4.0a, but 3.5 is also still available. In the mentioned model you have 2 coils and each of them has a defined current density which in turn yields a magnetic field. Actually these are not real coils but just rings, but I dont mind that for now. Now I tried the following to see some induced current in one of the rings ("coils"):
-> External Current Density 1: Just apply the given current to one of the two rings and leave the other one out.
-> re-calculate and plot everything.
-> 3d Plot Group 1 -> Surface 1: Here I plot the current density norm now. Now one of my rings has some current density (the one which is specified as an input), while the otherone has zero current density. I confirmed the actual zero current density by setting the range e.g. to 0 to e-30. Indeed, there is no current induced in the secondary coil.

Any hints on how to proceed from there? Did I choose the wrong physics (Magnetic Fields (mf)), or do I have to set some sort of boundaries for the second coil that I am not aware of?

off-topic: Are these sort of questions to be posted here or rather support questions?

Thanks for any input!
Seb

Hi

indeed coils are already somewhat tricky, also because they behave quite differently in DC, ac low frequency AC high frequency, do you want to study te magnetic field in the coil, do you have multiturn coils ... It quickly becomes complex.

to start simple I propose always:

1) use a 2D-axi (do not forget that you implicitely work in 3D cut view with a 2*pi*r "loop length" at each point "r" (horizontal usual "x" direction axis)
1a) start with a current density, and not the advanced single or multi turn coils BC's, once you have understood the simple case, change to these and get the full understanding of what they really do, it's not trivial as they add a few internal variables.
2) if you are in higher frequency (even from above some 10kHz) the current is mainly looping around in the skin of your coil, you can mostly forget the coil interiour and you should distribute the current on the edge

3) as last resort go into 3D, then you have different approaches such as cutting your coil in 2 halves, drive with a small skin source, use cylindrical coordinates ... the best is to go to one of the COMSOL courses (or come next year to the COSMOL conference and assist to the ACDC minicours), as it takes a few days to get through all cases

Also I (as well as in the COMSOL courses too) normally propose to start simple, with "resisitive" cases in ACDC, then capacitive somewhat more complex, and only to end coil, inductive studies as these add another dimension to the involved physics and the number of buttons and handles to tweak, for a correct simualtion

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Good luck
Ivar

Hello,

I was also performing the same experiment of Helmholtz coil.

Query:
1. Which plot function do we use to get the graph of "Magnetic Field Density" vs the "axis through the center of the coils".

Thanks
Uttam

Hi

you need to get a slice plot, or you add a Solution Set with a cut plane and plot that, check with your doc and the help

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Good luck
Ivar

hey yah thanks,

we got it,
procedure:
1. In data set - include Cut Line 3D

2. In Results - include 1D plot

Thanks