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permanent magnet(cylinder magnet)

Posted 2 févr. 2020, 21:07 UTC−5 Low-Frequency Electromagnetics 5 Replies

Park Mingyu
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Hi, I'm trying to create a cylindrical neodymium magnet.

Why does the magnetic field value from the permanent magnet change each time the size is changed in the air domain?

For example, increasing the horizontal axis increases the value of the permanent magnetic field at the surface center.

In the no-current magnetic field, How do you set up either zero potential or magnetic flux preservation?

5 Replies Last Post 18 mars 2020, 11:24 UTC−4
Lars Dammann COMSOL Employee

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Posted: 5 years ago 3 févr. 2020, 03:29 UTC−5

Hi, the size of the air domain does usually influence the fields everywhere to some degree, as does the boundary condition on the outside of your modeling domain. See this example model for a discussion of the effect in electrostatics: https://www.comsol.com/model/computing-the-effect-of-fringing-fields-on-capacitance-12605 Electrostatics and Magnetic Fields, No Currents are actually quite similar. Zero Charge is equivalent to Magnetic Insulation and Floating Potential is somewhat equivalent to (Zero) Magnetic Scalar Potential. Another way to get accurate results is to use infinite elements, which emulate an infinite simulation domain by stretching the coordinate system. Here is an example of that: https://www.comsol.com/model/magnetically-permeable-sphere-in-a-static-magnetic-field-12735

I'm not totally sure what you mean by setting up zero potential (there is a boundary condition called Magnetic Scalar Potential) and Magnetic Flux Preservation (Magnetic Flux Conservation is the default node and the law of magnetic flux conservation is always fulfilled by default).

I hope this helps. Best regards, Lars

Hi, the size of the air domain does usually influence the fields everywhere to some degree, as does the boundary condition on the outside of your modeling domain. See this example model for a discussion of the effect in electrostatics: https://www.comsol.com/model/computing-the-effect-of-fringing-fields-on-capacitance-12605 Electrostatics and Magnetic Fields, No Currents are actually quite similar. *Zero Charge* is equivalent to *Magnetic Insulation* and *Floating Potential* is somewhat equivalent to *(Zero) Magnetic Scalar Potential*. Another way to get accurate results is to use infinite elements, which emulate an infinite simulation domain by stretching the coordinate system. Here is an example of that: https://www.comsol.com/model/magnetically-permeable-sphere-in-a-static-magnetic-field-12735 I'm not totally sure what you mean by setting up zero potential (there is a boundary condition called Magnetic Scalar Potential) and Magnetic Flux Preservation (Magnetic Flux Conservation is the default node and the law of magnetic flux conservation is always fulfilled by default). I hope this helps. Best regards, Lars
Karthikachandra Kabbinahithlu
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Posted: 5 years ago 10 mars 2020, 14:02 UTC−4

Hello! I have gone through the tutorial notes for one sided permanent magnet. If i want to simuilate magnetic field lines for a normal 2 sided cylindrical magnet, what should I do?

Hello! I have gone through the tutorial notes for one sided permanent magnet. If i want to simuilate magnetic field lines for a normal 2 sided cylindrical magnet, what should I do?
Lars Dammann COMSOL Employee

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Posted: 5 years ago 11 mars 2020, 04:49 UTC−4

Hi, I suggest you create a 3D plot and try the Streamline plot type for that.

Hi, I suggest you create a 3D plot and try the **Streamline** plot type for that.
Park Mingyu
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Posted: 5 years ago 17 mars 2020, 21:16 UTC−4
Updated: 5 years ago 17 mars 2020, 21:20 UTC−4

I designed the nd magnet.

In magnetic flux conservation 1 , the z axis was set to 0.5030T.( Nd magnet)

In magnetic flux conservation 2, air domain was set to relative permeability. (Air zone)

Infinite element domain1 is set at the boundary.(5mm edge layer of air zone)

but if the air region size is made different, the magnetic field value coming out of the center of nd magnet surface becomes different.

I set an infinite element area, but why does the value of the magnetic field change?

Is it because the internal meshing has changed?

I designed the nd magnet. In magnetic flux conservation 1 , the z axis was set to 0.5030T.( Nd magnet) In magnetic flux conservation 2, air domain was set to relative permeability. (Air zone) Infinite element domain1 is set at the boundary.(5mm edge layer of air zone) but if the air region size is made different, the magnetic field value coming out of the center of nd magnet surface becomes different. I set an infinite element area, but why does the value of the magnetic field change? Is it because the internal meshing has changed?

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Mark Harradine
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Posted: 5 years ago 18 mars 2020, 11:24 UTC−4
Updated: 5 years ago 18 mars 2020, 11:24 UTC−4

The default external boundary condition (without Infinite Element Domains) is to have the magnetic flux lines tangential to the boundary, artifically containing the field within the confines of the model. An Infinite Element layer, is an effective way to make the effective air domain much much larger, and the far field has virtually no effect on the near field.

See attached doc for images of this. The top image uses default air domain, the second has IE domains outside of the visible air domain...

Mark

The default external boundary condition (without Infinite Element Domains) is to have the magnetic flux lines tangential to the boundary, artifically containing the field within the confines of the model. An Infinite Element layer, is an effective way to make the effective air domain much much larger, and the far field has virtually no effect on the near field. See attached doc for images of this. The top image uses default air domain, the second has IE domains outside of the visible air domain... Mark

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