Principio

DEFINITION

  • Magnetic shielding is a mechanical solution, most of the time issued from a sheet metal process, done to solve a problem of low frequency  electromagnetic interference. This is called "passive shielding."
     
  • In some cases, you can use "active shielding" that has nothing to do with mechanical manufacturing
     
  • Shielding channels the magnetic lines of the electromagnetic wave at frequencies from 0.1 to 10,000 Hz. Above 10,000 Hz, we use alternative solutions made with different materials (aluminium, copper...) which require other designs.
     
  • The purpose of a shielding is to attract, focus and deflect the magnetic field lines. It prevents them from entering a given volume (Ex: a CRT screen) or prevents a magnetic field from spreading (Ex: shielding a transformer)

 

 

NOTES

  • The area affected by the shield is proportional to the permeability of the material used. However, the risk of saturation becomes more elevated with higher permeability.
         
  • A field line can’t be stored, does not stop and always loops. It will spread into the environment where the permeability is the highest.
         
  • The magnetic field lines are physically inside the thickness of the material.
     
  • For continuous fields, we solely consider the phenomenon of concentration.
       
  • In the case of alternating fields (type 50 Hz), we must consider two factors: the concentration and the eddy currents that oppose the external fields.
         
  • Unlike the electrical shield, magnetic shielding deflects the field lines ; so a single disc is therefore a shield.