electric field

[Roberto Brambilla <rlbrambilla@xxxxxxx>]

Dear David and FEMM-friends,

I'd like to stress you that FEMM can be used to
compute electric fields in the case of plane
problems (xy-cartesian or polar problems, NOT axisymmetric),
if you identify elctric potential (scalar) U(x,y) to the
z-component of vector magnetic potential A(x,y).
You will have

Ex = -dU/dx Ey = -dU/dy
Bx = +dA/dy By = -dA/dx

So you have to identify U = A, Ex = By and Ey = -Bx.
Boundary values for A now are simply the boundary values
you will use for U.
In the case of different materials you have to insert
in properties mu = 1/er, where er is the relative 
(adimensional) permittivity of material to satisfy the
boundary discontinuities of electric field (normal component).
The analogy ceases in axysimmetric problems since grad
and rot in cylindrical coordinates (r,z) involve different 
derivatives.

Now a little problem : how can I represent a vertical homogeneous
magnetic field Bz=Bo in plane and in axisymmetric problems?

Yours, Roberto

Roberto Brambilla
CESI
Via Rubattino 54
20134 Milano
tel +39.2.2125.875
fax +39.2.2125.610
rlbrambilla@xxxxxxx