Re: Shielding Effectivness

[Ken Javor]

For all practical purposes the SE of commonly used metals is infinite except
at audio frequencies where skin depth becomes a problem.  The intrinsic SE
of the material is always dominated by seams and apertures that are inherent
in any enclosure design.  If you think that steel is less conductive than Cu
or Al and therefore should give lower SE, consider that almost all shield
rooms are made of steel and depending on construction meet SE requirements
of 100 dB or better.  Steel actually gives better magnetic performance at
low frequencies, again because of skin depth considerations.  The absolute
best doors for SE are not CU or brass knife edge into Cu or brass
fingerstock but rather the sliding steel doors in a pocket with internal
bladders which force the sides of the door against the inside of the pocket
much like the brake cylinder forces drum brakes against the brake housing.
This is steel on steel with tin flashing to provide a soft, deformable
mating surface.

--
From: "John Harrington" 
To: 
Subject: Shielding Effectivness
List-Post: emc-pstc@listserv.ieee.org
Date: Fri, Sep 28, 2001, 3:11 PM


Would somebody please be kind enough to point me in the direction of some
information on the shielding effectiveness of such metals as copper,
aluminium and steel.

Thank you

John Harrington
RF Group Manager
Nemko Canada
jharring...@nemkoca.com 
Tel: +(1) 613 737 9680 ext 229
Fax: +(1) 613 737 9691

RE: Shielding Effectivness

[WOODS]

You can find it in Vol. 3 of The EMC Handbook published by Don White
Consultants, Germantown Maryland, (301) 948-0028  (verify that the area code
has not changed).
 
Richard Woods
 
 -Original Message-
From: John Harrington [mailto:jharring...@ktlcanada.com]
Sent: Friday, September 28, 2001 4:12 PM
To: emc-p...@ieee.org
Subject: Shielding Effectivness



Would somebody please be kind enough to point me in the direction of some
information on the shielding effectiveness of such metals as copper,
aluminium and steel.
 
Thank you
 
John Harrington
RF Group Manager
Nemko Canada
jharring...@nemkoca.com  
Tel: +(1) 613 737 9680 ext 229
Fax: +(1) 613 737 9691

Re: Shielding Effectivness Question

[Neven Pischl]

I thank all off you who answered my question.

Neven

> -Original Message-
> From: Neven Pischl [mailto:npis...@cisco.com]
> Sent: Tuesday, June 05, 2001 12:16 PM
> To: emc-p...@majordomo.ieee.org; si-l...@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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Re: Shielding Effectivness Question

[Leslie Bai]

 Neven,
There are quite a number of books addressing the shielding effectiveness 
analysis. Personally, I will recommend two of them:
1. White: EMC Handbook, Volume 3: Shielding
2. Ott: Noise Reduction Techniques in Electronic Systems, Chapter 6: Shielding
Hope this helps
Leslie
 
  Neven Pischl  wrote: 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 interst!
ed 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 Pischluite


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RE: Shielding Effectivness Question

[George Tang]

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-p...@majordomo.ieee.org
[mailto:owner-emc-p...@majordomo.ieee.org]On Behalf Of Neven Pischl
  Sent: Tuesday, June 05, 2001 9:16 AM
  To: emc-p...@majordomo.ieee.org; si-l...@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

Re: Shielding Effectivness Question

[Hans Mellberg]

Neven;

In the near field one must know whether the offending emmiter is mostly 
generated
from a magnetic loop or electric field antenna structure. Once that is known, 
the
eventual transmitted portion can be computed. If your shielding is non Fe, Ni 
or Co
and the source is of a magnetic loop nature then there will be minimal 
attenuation.
If the source resembles an electric field antenna (less likely at lower 
frequencies)
then the usual shielding formulae may apply since they are primarily based on
E-fields to some extent and you will have attenuation.  




=
Best Regards
Hans Mellberg
Regulatory Compliance & EMC Design Services Consultant
By the Pacific Coast next to Silicon Valley,
Santa Cruz, CA, USA
408-507-9694

__
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RE: Shielding Effectivness Question

[mkelson]

Here's an informal guideline that I use.  If memory serves, I got it off the
Futurebus specification years ago.  I imagine this guideline was based on
slower frequencies than we have nowdays. 
 
1. Enclosure should have 20 dB of RFI attentuation at 5 Ghz.
2. Maximum gap shall be less than 3 mm in any direction.
3. Holes for indicators, switches, or connectors that are not shielded shall
be limited to the following:
A. No source of high frequency within one diameter distance of the hole.
B. The thickness of the hole wall shall be more than:
0 for a 3 mm hole
2.5 mm for a 7.5 mm hole
10 mm for a 15 mm hole
4. Larger holes shall have back-shielding behind the light, switch, or
connector, and tied to chassis ground through low-impedance gasketing.
 
I would be interested also in any cook-book or analystical information
anyone else might have.
 
Max Kelson
Evans & Sutherland

-Original Message-
From: Neven Pischl [mailto:npis...@cisco.com]
Sent: Tuesday, June 05, 2001 10:16 AM
To: emc-p...@majordomo.ieee.org; si-l...@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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All emc-pstc postings are archived and searchable on the web at:
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