You are thinking of a magnetic field as a force.  Stop it.

Think, instead, of a piece of metal which has two ends.  Think of
particles which want to travel from one end to the other.  They travel
slowly in air, and other non magnetic fields, and faster in ferrous
objects.  Thus the lines of travel are longer through air, and shorter
through ferrous things.  Now, the particles desperately want to get from
one end to the other, so when a ferrous object comes near, they tug at
it, trying to make it part of their path.

You cannot block their path.  Magnetic shielding is simply a nice way of
saying 'lets create a path *through* the casing of the device, instead
of through the device itself, or creating a field opposite the one we
want to avoid, thus deflecting the obnoxious field.'   So your 'magnetic
shielding' either creates a path (thus short circuiting the entire
magnet, and no field reaches the disc) or creates a road block which the
'particles' will stream around.  But the particles will always want to
get back to their own magnet, so the amount of prticles going from
magnet A North to magnet B south must be matched by the same number of
particles going from magnet B North to magnet A South.  Thus all
'forces' you are trying to capture must equal out, and, in the end, you
will get no energy from the magnets that you don't give them in the
first place.

PLEASE NOTE:  There are not such particles, a permanent magnet has a
field which is static.  Einstien was trying to create a 'universal
equation' which contained all the forces we experience, but he couldn't
figure out magnetism before he died.  It is not a subject we can easily
discuss with quantum physics, nevermind without them.  So I made up my
own rules for the sake of the argument, and, aside from the words, the
description is how static ('permanent') magnetic fields will react with
your objects.

I hope this helps!

-Adam

Wagner Lipnharski wrote:
>
> What is the most positive way to block magnetic field using a 5mm *any
> material* board?
> Take a look at the picture and tell me why it doesn't work.
> http://www.ustr.net/jpg/moto1.jpg