Re: Voice Coil Motor with Aluminum bobbin

["tano1938" <rgarritano@xxxxxxxxxxx>]

--- In femm@xxxxxxxxxxxxxxx, David Meeker <dmeeker@xxxx> wrote:
>I'd guess that the node at (0.01,-0.325) should really be at (0,-
0.325), but other than than, the solution looks like I'd expect. 
You'll also need to specify a nonzero conductivity for the 1018 steel 
to get the eddy currents induced in those parts.

The result is just the AC part of the field due to the coil. Remember 
that the program isn't solving the combined AC + DC offset problem--
it can only solve one part at a time. Additionally, the AC problem 
considers only major hysteresis loops (i.e. no DC offset). I 
occasionally threaten to write a combined AC + DC offset program, 
because this scenario keeps popping up in the context of a lot of 
practical problems, but I haven't gotten around to it yet. 

Anyhow, since your DC problem has significant nonlinearity, you'll 
have to be careful how you set up the AC problem--you can't just 
superimpose the results in the way that one can for linear problems. 
For AC analyses, you'd want to replace the alnico with a linear 
material where the permeability of the magnet is chosen to be 
representative of the incremental permeability at the nominal 
operating point. You may have to do a similar trick with the 1018 in 
the areas with high fields in the DC problem.

Dave.


Thanks Dave. I should have read the manual closer.

Would it be OK to model the Alnico magnet with a linear material like 
you suggest, and use the published "recoil permeability" of Alnico 5, 
which is about 5.0?

Ron