Let's Get to the Bottom of What Those Conductive Gaskets Can Do!

More and more the EMC community has to deal with manufacturers needs for using conductive gaskets well into the GHz region. In the commercial side of the house, there are already PCs running at 2 GHz and above as well as network routers running at speeds approaching 10 GHz. Clearly there is a need to help gasket users with the EMC impact on their product shielding at these frequencies. Making these judgments requires confidence in performing tests to determine such EMC characterizations. This work on P1302 described below will help focus on these needs. I urge you to pitch in to help this committee move this project to completion. Don't wait, sign up now!

Revision/Update of IEEE STD 1302, "Guide for the EM Characterisation of Conductive Gaskets in the Frequency Range of DC to 18 GHz."

IEEE Standard 1302 was originally published in 1998. This standard was the culmination of several years of effort to develop a standardized technique for measuring EMI gaskets. At that time, the working group determined that there were several measurement techniques in use throughout the community, each having its advantages and disadvantages (and "disciples" and "dissenters"). However, there was "no clear winner" and the group decided to issue this guide to assist manufacturers and users of gaskets in either specifying the technique to be used or in evaluating the results provided by a particular technique or to compare the results provided by the different methods. Hence, the work was published as a Guide, not a Standard or Recommended Practice. Since its publication, progress on the characterization of conductive gaskets has been made, and new applications are arising requiring additional measuring techniques. Therefore, an effort to revise and update IEEE STD 1302 by taking out a new Project Authorization Request (PAR) was approved by the EMC Society Standards Development Committee and by the IEEE Standards Association Board in 2000. Professor Johan Catrysse leads the present revision effort.

1. Current Status

The existing document was the first guidance document for the characterisation of conductive gaskets:

• It was a first attempt to compile an overview of available measuring methods;
• Some methods were covered in an extensive way, others just Ômentioned as existing';
• Methods covered include:

  - transfer impedance (as by SAE ARP 1705)

  - relative aperture transmission, derived from the Ôold' MIL STD 285

  - reverberation chamber methods

  - effective power transmission

  - modified ASTM D4935-89 fixture

  - slot aperture

  - TEM-t and H-t fixtures

• The standard concludes with a short discussion on selecting a measurement technique and a discussion on repeatibility.

In the meantime, more work has been done on some methods and some are no longer supported. So, an update of this P1302 is needed in order to make it applicable to current circumstances.

2. Items Not Covered in Original Guide

After a first compilation of the actual guide, looking for its practical use and taking into account the evolution in gasketing techniques, the following issues still need to be addressed:

• The frequency range above 1 GHz, where only small sizes of samples are available (so that the modified MIL STD 285 is not applicable in practice), needs to be more fully addressed
• Correlations (if any) between different methods such as DC resistance, transfer impedance, fixture methods and gaskets applied on enclosures need to be established, if possible
• A test/evaluation method needs to be established for small and thin gaskets which are used under near field conditions for INTRA system use (as in mobile phones)
• All methods should be documented in an equal way based on frequency range, dynamic range, sizes of samples, repeatibility, physical phenomenon that is measured, etc.
• An overview table of all methods, including pro's and con's, needs to be produced.

3. Scope of the PAR Revision

The scope of P1302 is to provide manufacturers of gaskets and designers of (electronic) systems appropriate methods for the characterisation of gaskets, in the way that a test method is used, giving figures which will provide an indication of the shielding that will be obtained in a specific application.

4. Purpose of P1302

This revision of P1302 proposes to provide additional guidance on the strengths and the weaknesses of each method contained in the original guide, and to provide an in-depth documentation for each method.

This document should be the basis for further work at a later date into a standard that will:

• Identify possible additional measuring methods for the characterisation of conductive gaskets
• Identify measuring methods appropriate for small samples of gaskets (and including the frequency range over 1 GHz)
• Correlate between different methods (DC resistance, transfer impedance, shielding, etc.)
• Identify possible measuring methods for near field characterization of gaskets (as to be applied for INTRA system shielding applications)
• Provide a table with pro's and con's of each method, and an in-depth description of each method.

The target date for completion is September 2004. Work must start this year to meet this target date considering not only the textual changes needed, but to do any experimentation to provide data to make decisions in the working group.

5. Development Strategy

It is the intention that most of the work will be done by electronic communication (E-mail). However, some meetings will be scheduled. Where possible, these meetings will be in conjuction with a major EMC symposium.

Are you interested in participating in and contributing to this P1302 Working Group? If so, please contact:

Prof. Johan CATRYSSE
Lab for EMC, KHBO
Zeedijk 101
B 8400 Oostende, Belgium
phone: +32/59/56 90 34 or +32/59/56 90 39
Email: johan.catrysse@khbo.be

I hope to hear from you soon!

Short Curriculum of Prof. J. Catrysse

• Professor at the Electronic Department, KHBO (formerly KIHWV) since 1974.
• Teaches courses on:

  - circuit theory

  - automotive control engineering

  - HF circuit design

  - Electromagnetics and antennas

  - EMC

• Head of Electronic Department, KHBO since 1981.
• Head of EMC laboratory at KHBO, Oostende since 1983.

EMC

NOTICE: IEEE STANDARD 140 WITHDRAWN

At its December 2001 Board Meeting, the IEEE Standards Association withdrew IEEE-STD-140-1990 (R1995) "IEEE Recommended Practice for Minimization of Interference from Radio-Frequency Heating Equipment." Persons wishing to obtain a photocopy of the last version of the standard should go to https://standards.ieee.org or call 1-800-678-IEEE.

COMMENTS WANTED ON IEEE STANDARD 1128

IEEE STANDARD 1128 (Recommended Practice for RF Absorber Performance Evaluation in the Range 30 MHz to 5 GHz) is due for reaffirmation in 2003. If you have any comments, suggestions, or corrections, please send them to jperini@ieee.org prior to the end of August 2002 so that they can be included in the reaffirmation process.