# Discussion Forum

## How to create a toroidal solenoid?

I am trying to create a helically wound toroidal solenoid with 100 windings (from one wire).

How can I accomplish this? i've tried to use the traditional coil option, but there doesn't seem to be an option to get helical windings in a toroidal shape.

Is my only option to hand design a 3D coil in a helical, toroidal shape? I would prefer to design it along the lines of a parametric curve or, ideally, using the built in coil option. I just have no clue how to do this? How can I design my windings and send a current through them?

I've put a lot of thought into this, but haven't gotten very far. I'd be extremely grateful for some help!

4 Replies Last Post Apr 7, 2021, 8:56 AM EDT

Posted: 3 weeks ago

Hi John,

There actually is a geometry tool to create a parametric curve in COMSOL, and it's called "Parametric Curve"! You can then sweep a shape (say, a disc, if that's what the cross section of your wire should be) along that parametric curve to create a solid, should you need to.

Best,

Jeff

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Jeff Hiller

Posted: 3 weeks ago

Another option may be to add a second torus around the core and use it as a coil domain. For the geometry analysis you need a cross section of this outer torus and define it as input. This should result in a ring current in the coil domain. Should be a good approximation to an explicit helical winding.

Cheers Edgar

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Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com

Posted: 2 weeks ago

Jeff Hiller

Hi Jeff,

Thank you for your helpful answer. I have tried that and it does indeed form a toroidal solenoid, but only when the curve is open. I want to model a closed wire so that I can send a current through it.

As far as I can tell, my options here are to model leads that touch my air bounds or model a closed coil and model excitations from the cross-sectional faces. I am unable to extrude the ends of the coil to the face of the air boundary and mesh successfully--it gives me an error about an empty cavity being generated. (I believe the connection is not orthogonal; but I don't know how to make it so.) On the other hand, I am unable to form a closed coil via sweeping along the closed parametric curve, as COMSOL tells me that edges "must form a non-closed chain."

How can I resolve this issue? Would it be possible to sweep along an open parametric curve and then connect the ends? If so, how?

Thank you again for your help. It is greatly appreciated.

Posted: 2 weeks ago

Hi John,

You can sweep a cross section along a series of curves, so it's just a matter of creating the curves you need using the various curve-drawing tools (could be straight segments, parametric curves, arcs of circles, etc). If you have the Design Module on your license (You can check on that through the menu File > Licensed and Used Products), you could also employ the loft command to connect two faces of your currently-open shape to close it.

If those tips are not enough to get you there, I would encourage you to contact COMSOL support through www.comsol.com/support/ : they'd be able to give you more specific ideas based on your work so far and with knowledge of what license components your license includes.

Best regards,

Jeff

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Jeff Hiller