Re: [FEMM] About the modelization of small coils

[David Meeker <dmeeker@xxxxxxxxxxxxxxxxx>]

Patrick Rosa wrote:

> My point is that I would like to use FEMM to KNOW the field produced 
> by a given current in the coil. Measuring with a Gaussmeter could 
> prove difficult (fields are in the 0.1-2G range) and more 
> time-expensive than a calculated estimation. But I don't know at this 
> point whether the block model is precise enough, or if I can correct 
> simply by decreasing the current density to have a current integration 
> over the primary corresponding to current per turn * number of turns. 
> In that case what would be the approximation made on the real value of 
> the field?
> Any similar experience would be welcomed. If someone had to draw 
> individual coils and wrote some routine to do it, that would also be 
> welcomed, I don't feel much like drawing one-by-one 800 and plus 
> circular wires...
> Warmest greetings

If you have a wound coil, it is usually OK to idealize the coil as a 
solid region (i.e. defined by a polygon tightly enclosing the coil) with 
a uniformly distributed current density inside that region.  The current 
density is then chosen to be the total amp*turns carried by the coil 
divided by the cross-section area of the total coil region (i.e. the 
area enclosed by the polygon that tightly encloses the coil). Modeling 
of individual turns is usually only necessary if you are interested in 
computing proximity and skin effect losses in a coil with a small number 
of turns.

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