Why is H pointing the wrong way inside my permanent magnet?
By default, FEMM takes the view that permanent magnets are essentially the same as solenoids. That is, the magnet is modeled as a chunk of low-permeability material. The “source” of the PM’s flux is a current sheet of density Hc*(m n) on the edges of the permanent magnet, where Hc is the magnet’s coercivity, m is a unit vector in the direction of magnetization, and n is an outward unit normal to the edge of the PM. This is a fairly typical way to model permanent magnets in the context of a finite element formulation (because it is any easy way to include PMs), and it is also equivalent to a magnetic charge-based formulation. This issue is also discussed in one of the appendices of the FEMM manual. By changing a preference, it is possible to make FEMM display the demagnetizing field intensity instead of the equivalent coil field intensity. Just select the “Demag. H in PMs” selection on the “Magnetics Output” preferences tab. This selection shifts the magnet’s operating point back to the
