EMC FLEX BLOG A site dedicated to Automotive EMC Testing for Electronic Modules

Shielding Enclosures & Cables

16. December 2020 15:52 by Christian in EMC/EMI, Shielding
Shielded enclosure example: Shielded enclosure connector types: Shielded cable types: Foil provi

Shielded enclosure example:

Shielded enclosure connector types:

See Troubleshooting RF Noise and Fixing Ground Loops

Shielded cable types:

  • Foil provides high-frequency shielding.
  • Drain wire carries most of the low- frequency current.

 

  • Foil provides high-frequency shielding.
  • Braid carries high-currents.

Why Cable Shielding?

  • Serves different purposes in different applications.
  • Sometimes carries intentional signal currents. This is an example of self-shielding.
  • May prevent coupling of external electric or magnetic fields to signals carried by wires in the cable.
  • Beware of transfer impedance data. It should only be used to compare similar cables for a similar application measured with the same test set-up.

Summary of Main Points:

  • Electric field shielding, magnetic field shielding, cable shielding and shielded enclosures are very different concepts requiring different materials and
    approaches.
  • It is important to be understand the coupling mechanism you are attempting to attenuated before coming up with a shielding strategy.
  • Electric field shields terminate or redirect electric fields. Where they are “grounded” is often critical.
  • Magnetic field shields redirect the magnetic field. Magnetic fields cannot be terminated. 
  • Low frequency (<kHz) magnetic fields must be redirected with high permeability materials. 
  • High frequency magnetic fields can be redirected with good conductors of sufficient thickness.
  • Shields and imperfect shielded enclosures can significantly increase radiated emissions. 
  • Shields reduce radiated emissions by disrupting the coupling from near-field sources and the “antennas” in a system. 
  • In the near field, shields are either electric or magnetic field shields that redirect high-frequency current flow.

 

 

Comments are closed