[SI-LIST] : RE: Shielding Effectivness Question

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From: George Tang (gtang@lsil.com)
Date: Tue Jun 05 2001 - 16:34:14 PDT


RE: Product Safety: A Matter of Law or Litigation?Look for a book on RF or
microwave. My favorite is Fields And Waves In Communication Electronics.
Look in the section on "waveguides." Operate the waveguide below "cutoff."
A small aperture in a sheet metal with finite thickness is essentially a
very short waveguide. Calculate the attenuation of a waveguide operating
below cutoff. The radiated emission from one aperture may seem
insignificant, but when you have 100 apertures radiating in phase may cause
you to fail FCC A.

George Tang

  -----Original Message-----
  From: owner-emc-pstc@majordomo.ieee.org
[mailto:owner-emc-pstc@majordomo.ieee.org]On Behalf Of Neven Pischl
  Sent: Tuesday, June 05, 2001 9:16 AM
  To: emc-pstc@majordomo.ieee.org; si-list@silab.eng.sun.com
  Subject: Shielding Effectivness Question

  I would appreciate if anyone could let me know if there are any references
(books, application notes, anythig ..) that deal with shielding efectivness
in cases when a source is close to an (electrically small) opening in a
shield (enclosure). In such a situation, the field will penetrate through
the hole and leak even if the size is much smaller than the wavelength. I am
particularly interested in situation when high-frequency source, such as a
PCB edge or a component operating at (say) 1 GHz and above is in proximity
of the venting holes, "small" gaps in the chassis etc.

  All references that I have deal with uniform plane wave propagating
incident to a metal plane with a slot or hole, in which case it is enought o
have electrically small size of the opening (e.g. lambda/10) to efficiently
block any field propagation through the barrier. I can't find any useful
reference that deals in any analytical way with the situation I am intersted
in.

  I believe I might get some answers using some of the simulation programs,
but at the moment I am more intersted in the analysis of the problem than in
simulating it.

  Thank you,

  Neven Pischl

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