Why Can’t I Evaluate Magnetic Flux Density at points Between Coils in COMSOL?

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I am working on a Magnetic Fields (mf) simulation in COMSOL, modeling a triaxial Helmholtz coil system. My goal is to extract the magnetic flux density components (Bx, By, Bz) at a grid of points inside a 25 mm cubic workspace that includes the region between the coils. I attempted to use the Cut Point 3D dataset to define these points and then evaluate the magnetic field components. However, many of these points return NaN (Not a Number) values when I try to extract Bx, By, Bz.

What I Tried

  • The magnetic field visualization works correctly in the 3D plot, meaning Bx, By, Bz are computed somewhere in the solution.
  • Point Evaluation works at mesh nodes, but Grid/Cut Point 3D Evaluation fails with NaN values.
  • I realized that the cut points were being placed in regions between the coils, which do not seem to contain computed field values.
  • The meshed regions include only the coils and a defined workspace, but the air between coils may not be included in the physics calculation.
  • I have assigned materials (Air for the surrounding space), and the coils are current-driven.

Questions:

  • Why does COMSOL return NaN values for Bx, By, Bz in the space between coils?
  • How can I ensure that the magnetic flux density is computed and accessible in these regions?
  • What is the best approach to extract Bx, By, Bz at a grid of points that includes the workspace and space between coils?

I would appreciate any insights or suggestions on how to resolve this issue. Thank you!


1 Reply Last Post 5 feb 2025, 13:55 GMT-5

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Posted: 2 weeks ago 5 feb 2025, 13:55 GMT-5

The meshed regions include only the coils and a defined workspace, but the air between coils may not be included in the physics calculation.

You must mesh, and perform a calculation, for a volume containing the coils, the region of interest, AND anything between. Think of a sphere, or cube, containing all of these regions.

Post the (reduced) model if this does not clarify.

> The meshed regions include only the coils and a defined workspace, but the air between coils may not be included in the physics calculation. You must mesh, and perform a calculation, for a volume containing the coils, the region of interest, AND anything between. Think of a sphere, or cube, containing all of these regions. Post the (reduced) model if this does not clarify.

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