Re: [SI-LIST] : Shielding Effectivness Question

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From: Doug McKean ([email protected])
Date: Tue Jun 05 2001 - 12:26:20 PDT

RE: Product Safety: A Matter of Law or Litigation?Neven,

I did some rather intensive analysis of shielding effectiveness
over the course of several weeks a while back. Results were
extremely informative.

I've read a couple of fields and waves books for slot analysis.
Rau is the one I prefer. I'm at work, but I'll get the name of
it and the ISBN as well.

I've done some experiments with "small" stubs and loops with
reference to wavelength. And I was surprised to find a rather
predictable approx -10dB rolloff per several decades from lo
to high frequencies. Results were debatable.

Converting the wire stubs over to slots by way of Babinet
makes me think that the roll-off for slots is similar. And with
this information, I started my little analysis in the chamber
on products.

I haven't seen nor am I really worried about problems with
holes. Unless of course they're big. Slots are your worst
violator. This is because of the mechanism by which apertures
work. It's, in my opinion, more difficult to impose a voltage
differential across a round hole than it is across a slot.

Slots are more directional than wires by a factor of roughly 10.
That makes your product particularly susceptible during emissions.

Anywho, I'll get you the name of the book and specifics for ya.
And if you want, maybe you can pop over here to do some testing.

- Doug McKean

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