How does magnetic shielding work?
When magnetic lines of flux encounter high permeability material, the magnetic forces are both absorbed by the material and redirected away from its target, much as a beavers dam absorbs and reroutes water from its den. The most effective shields are constructed as enclosures such as boxes or better yet, cylinders with end caps. Because the field follows the line of the enclosure, an enclosed shape keeps stray fields from finding gaps which could cause unintended interference.
Magnetic fields can only be redirected. They cannot be blocked or reflected. Even to do this requires special shielding alloys with high permeability. All shielding materials work by diverting the magnetic flux to themselves, so although the field from a magnet will be greatly reduced by a shield plate, the shield plate will itself be attracted to the magnet. Closed shapes are the most efficient for magnetic shielding – cylinders with caps, boxes with covers, and similar shapes are the most effective. Magnetic shielding materials offer a very high permeability path for magnetic field lines, directing the electromagnetic energy through the thickness of the alloy, and keeping the electromagnetic field from going where it is not wanted. It is important that the shield offers a complete path for the field lines, so that they do not exit the material in a place where they will cause unintended interference.
