Electromagnetic shielding
How RF shielding workshttp://en.wikipedia.org/wiki/Electro...hielding_works
http://en.wikipedia.org/wiki/Faraday_cageFaraday cage
The metal layers are grounded to dissipate any electric currents generated from the external electromagnetic fields, and thus block a large amount of the electromagnetic interference.
http://en.wikipedia.org/wiki/Electro...etic_shieldingMagnetic shielding
Equipment sometimes requires isolation from external magnetic fields. For static or slowly varying magnetic fields (below about 100 kHz) the Faraday shielding described above is ineffective. There exists a limited possibility of passively isolating a volume magnetically by using shields made of high magnetic permeability metal alloys such as Permalloy and Mu-metal[1]. These materials don't block the magnetic field, as with electric shielding, but rather draw the field into themselves, providing a path for the magnetic field lines around the shielded volume. The best shape for magnetic shields is thus a closed container
http://en.wikipedia.org/wiki/Magneti...#ParamagnetismParamagnetism
Paramagnetism is a form of magnetism which occurs only in the presence of an externally applied magnetic field. Paramagnetic materials are attracted to magnetic fields, hence have a relative magnetic permeability greater than one (or, equivalently, a positive magnetic susceptibility). The magnetic moment induced by the applied field is linear in the field strength and rather weak. It typically requires a sensitive analytical balance to detect the effect. Unlike ferromagnets, paramagnets do not retain any magnetization in the absence of an externally applied magnetic field, because thermal motion causes the spins to become randomly oriented without it. Thus the total magnetization will drop to zero when the applied field is removed. Even in the presence of the field there is only a small induced magnetization because only a small fraction of the spins will be oriented by the field. This fraction is proportional to the field strength and this explains the linear dependency.


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