Re: [femm] Calculating Shieldi Effectiveness with Femm

[David Meeker <dmeeker@xxxxxxxxxxxxxxxxx>]

"V.Petoukhov" wrote:

> Hi, I have 2 questions.
>
> 1. In the example sample.fem the "total current" of the aluminum
> shield must be equal zero, but it is not done by "circuit" properties.
> Is it correct? And what a phisical task solved in this example (with
> no "circuit properties" in the aluminum
> shield)?

Well, this isn't the most "physical" example that I've ever put
together. Planar problems in which the current is not explicitly
conserved in the solution domain can be less than intuitive. Anyhow, in
this problem, there's no condition imposed that forces the total current
to be zero in the aluminum shell. You could think of the aluminum shell
as being "grounded at +- infinity, so a big net current actually flows in
the aluminum part in this problem. (If you are twisted, you could think
of this problem as modeling only one section of a bigger domain, where the
"rest of the domain" could be reconstructed by thinking about the image
current distribution that would be required outside the solution domain to
enforce A=0 on the boundary.) I probably should have made a coax cable or
something, constraining the current to be +i in the middle, and -i on the
outside--this would have been a bit more intuitive.

>
> 2. If it's possible, tell me the addres for downloading
> the student version of Quickfield 3.4a
>

You 3.4a is the msdos version of quickfield. I tend to use it, rather
than the win9x/nt version 4.2 because the 3.4a version lets you have a few
more nodes in the student version. You can get both student versions off
of the quickfield website. Specifically, see
http://www.quickfield.com/free_soft.htm There's a drop-list on this page
that lets you pick between the 3.4a and 4.2 versions. Incidentally,
several demo versions of various other commercial programs are linked off
my page at http://members.aol.com/gmagnetics/links.htm

Dave.


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