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Cylindrical geometry
Posted 21.05.2013, 03:43 GMT-4 RF & Microwave Engineering Version 4.2 3 Replies
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I'm trying to model RF coils for MRI with Comsol, and I'm not finding it terribly easy to create the actual geometry. As can be seen in your example (www.uk.comsol.com/showroom/gallery/4101/), MR coils often end up looking like a flat circuit printed on another geometry -- there the example is a symmetric birdcage coil, but sometimes we want to create something not symmetric wrapped around a cylinder (or another more complicated shape).
My question is this: I'm not so sure how to easily create geometries like that shown in the example. Is it possible to "morph" or "melt" one structure onto another, as you can often do in other 3D modelling programs? I've tried playing around with creating a local coordinate system, but it appears that these are only for the solver's use -- and you can't easily define a workplane at constant r on a cylinder, for example.
Do you have any tips for how to create these sorts of structures? I basically want to draw copper on the sides of cylinders/other shapes!
Thanks for your help.
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COMSOL gives a nice option for building helical 1-D structures that overlay nicely on cylinders (simply set the minor radius to zero). But, if you have something more complicated I would suggest using a CAD software or 3D Direct modeling software with a "Projection" functionality to "draw on the sides of cylinders" and then the COMSOL CAD Import Module to bring the geometry into COMSOL. It looks like that's what was done in the MRI Bird-Cage Coil model you referenced.
Best regards,
Josh Thomas
AltaSim Technologies
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The geometry sequence in the attached file illustrates how you can build the geometry for the MRI bird-cage coil model you were referring to. As you can see in the model, the steps consist of drawing circular sectors, which in subsequent steps are extruded, moved and rotated to create the geometry. You can easily parametrize the geometry by adding global parameters and using those in the settings for the geometry features.
Best regards,
Lorant
Attachments:
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Thanks for some very useful replies! I've found that it's probably going to be easier using another product (i.e. Blender) to generate geometry and then import into Comsol, but I'll have a look at the attached. It's certainly obvious that it's best to do the geometry in Comsol and then be able to change parameters dynamically, although what I actually want is best described as an object 'wrapped around' a cone/cylinder, and other products provide tools to do that in one step.
Thanks hugely for your help!
All the best,
-- Jack