Re: [FEMM] Origins of the superposition theory.

[David Meeker <dmeeker@xxxxxxxxxxxxxxxxx>]

Thwala Hanana wrote:

> Dear David,
>
> Since it is possible in Femm to model the field as
> a function of distance from magnets. I wonder if is 
> possible for you confirm the basic function used to 
> plot field. I basically need to know the origins of
> the fuction used to plot field/x.
>
> Regards
> Thwala
Although one could obtain magnetic fields by superimposing the 
contributions from magnetization and currents in the solution domain 
(i.e. "Fast Mutipole Method" and so forth), this isn't how FEMM computes 
fields.  FEMM is a finite element program--a good place to look for a 
thorough but comprehensible explanation of the method would be:
P. P. Silvester and R. L Ferrari's "Finite Elements for Electrical 
Engineers" (http://www.amazon.com/o/dt/assoc/handle-buy-box=0521449537)
In FEMM, the entire solution domain is meshed with triangles. Inside 
each triangle, the potential is linearly interpolated from the values at 
the corners of the triangle (i.e. the nodal values).  The nodal values 
are selected by the solver such that the field satisfies the underlying 
Maxwell's equations as closely as possible.  The plotted flux lines are 
the level contours of the computed potential, as linearly interpolated 
from the nodal values.  Flux density is related to the derivatives of 
the potential with respect to position.  These deriviatives are taken by 
differentiating the linear interpolation used inside each element.

Dave.

--
David Meeker
Senior Engineer
Foster-Miller, Inc.
350 Second Avenue
Waltham, MA 02451-1196
781-684-4070
781-890-3489 (fax)
dmeeker@xxxxxxxxxxxxxxxxx 
http://femm.foster-miller.com