Magnetic flux direction 1

[BuildingIt]

I would like to have a cylindrical pin (3/16dia x1/4 long)that is magnitized along the axis (length wise). I want to grind the ends of the pin at a 45 degree angle creating an elipse. Will the flux lines come out of the pin normal to the new surface or paralell to the axis as originally magnatized. What type of magnetic material will maintain the orignal flux line the best.

 

[MagMike]

What is your application?

 

[BuildingIt]

I will have two magnets in repulsion. By angleing the magnets I would create a better vector for my force to be applied as long as the flux stays axial and not normal to the new face.

 

[BobM3]

I would say the direction the flux leaves the surface depends on the geometry of the part and the nearby magnetic parts. So I would not count on it (the flux) leaving perpendicular to the surface or along the axis.

You might want to try some FEA modeling. FEMM is free.

 

[BuildingIt]

Thanks for the suggestion, I found 1 FEMM however I have not had the chance to use it or know how coplex the setup is. Do you have any Suggestion for free or trial versions of FEMM that are easy to use?

 

[BobM3]

I use Tera Analysis' Quickfield program. They do have a limited node free download:

http://www.quickfield.com/free_soft.htm

I tried FEMM but I found Quickfield to be a bit easier.

 

[bz2005]

The direction of magnetic flux lines is affected by other magnetic parts or magnets in the pin's vicinity.

If the pin stands alone, the flux lines are unlikely to retain the axial direction when they leave the 45-degree surface. They would take the shortest path, or the path of least resistance, to go back to the unlike pole. Thus, it looks like the flux lines are normal to the new ellipe surface. It's not a problem of magnet material.

 

[dgallup]

I thought all flux lines exited normal to the surface. They will bend after that depending on the surrounding magnetic material.

 

[bz2005]

Hi Dgallup,

I'm not sure if "all flux lines exit normal to the surface". I suppose it goes back to the boundary conditions at the interface between 2 media as:

Bn1 = Bn2
Ht1 = Ht2

when there is no surface current on the boundary.

Then if the permeability of medium 1 is much higher than that of 2, the exit angle in medium 2 is almost at right angle.

In this case, though, some permanent magnets have relative permeability close to unity. For example, some NdFeB material has a relative permeability of 1.0x. Therefore, I don't see how the flux lines should exit normal to the surface.

This has really confused me. I'd like to believe the flux lines exit at right angle, even on a microscopic scale. Is there a theory to support it?

But one thing is for sure, the flux lines exit the 45-degree angle surface are not going to maintain the axial direction.

Bo