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Single-turn coil gap feed problem
Posted 26.01.2015, 16:35 GMT-5 Low-Frequency Electromagnetics, Studies & Solvers Version 5.0 11 Replies
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I am trying to model gradient coils for use in MRI. I created a saddle coil geometry and I tried to run a study with the current direction specified by gap feed, but it fails to find a solution. I've attached my model to the thread, I would appreciate any insight into this.
Thanks in advance!
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Hi,
you have to close the current path some way inside the modeling volume, or you have to extend the coil to the outer boundaries. Terminals and ports are an option too.
Current cannot just appear and disappear inside the model.
Cheers
Edgar
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Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
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Hi,
you have to close the current path some way inside the modeling volume, or you have to extend the coil to the outer boundaries. Terminals and ports are an option too.
Current cannot just appear and disappear inside the model.
Cheers
Edgar
--
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
Thanks for the reply. But I am looking at single_coil_gap_feed.mph at www.comsol.com/model/single-turn-and-multi-turn-coil-domains-in-3d-14067, and this model works without doing things you prescribed. My saddle coil is just a loop like this torus, so intuitively, I expect same modeling technique to work for both geometries. What am I missing?
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The way I understand a saddle coil is a current that flows along the edges of the saddle or in a domain close to the edges. Something like this: www.ewh.ieee.org/tc/csc/News/Image12.jpg
In such a coil you can add a gap feed similar to the torus example. You may want to study the COMSOL documentation about coil domains and the way to excite them.
Cheers
Edgar
--
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
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I corrected your model and now it solves. Two more remarks. In mf the non-conductive domains mostly need a small conductivity and you have to add a 'Gauge Fixing for A-field' node to achieve convergence.
Also I would advise to assign a material or realistic conductivity to the coil domain to get meaningful coil parameters in the post processing.
I am attaching the rectified model.
Cheers
Edgar
--
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
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thanks in advance
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Well, that's what the thread is about. Have you checked the postings above?
--
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
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Best regards
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Multiply with -1 ? This will also change the sign of the flux, nothing more.
--
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
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