SAE ARP 1705C-2017

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AEROSPACE

RECOMMENDED PRACTICE

ARP1705™

REV. C

Issued 1981-06

Revised 2017-02

Superseding ARP1705B

Coaxial Test Procedure to Measure the RF Shielding

Characteristics of EMI Gasket Materials

RATIONALE

ARP1705 was revised from Revision B to C to increase the accuracy of the test fixture and increase the frequency range

to 18 GHz.

TABLE OF CONTENTS

1. SCOPE ............................................................................................................................................. 2

1.1 Purpose ............................................................................................................................................ 2

1.2 Background ...................................................................................................................................... 2

2. REFERENCES ................................................................................................................................. 2

2.1 Applicable Documents ..................................................................................................................... 2

2.2 Definitions ......................................................................................................................................... 3

2.2.1 TRANSFER IMPEDANCE................................................................................................................ 3

2.2.2 SHIELDING EFFECTIVENESS (EMC) ............................................................................................ 3

2.2.3 SHIELDING QUALITY...................................................................................................................... 3

3. BASIS FOR TEST METHOD ........................................................................................................... 4

3.1 Electromagnetic (EM) Wave ............................................................................................................ 4

3.2 Induced Currents in Barrier (Surface Current Density) .................................................................... 4

3.3 Seams and Gasketed Joints ............................................................................................................ 4

3.4 Transfer Impedance of a Joint ......................................................................................................... 4

3.5 Measurement of Transfer Impedance .............................................................................................. 4

3.6 Use of Transfer Impedance in Equipment Design ........................................................................... 5

3.7 Penetration of an EM Wave through an EMI Gasketed Joint .......................................................... 5

4. TEST FIXTURES ............................................................................................................................. 6

4.1 Fixture Assemblies ........................................................................................................................... 7

4.1.1 Fixture 1705A ................................................................................................................................... 7

4.1.2 Fixture 1705C ................................................................................................................................... 7

4.1.3 Fixture 1705C assembly notes (see figure C12) .............................................................................. 7

4.2 Maximum Gasket Dimensions ......................................................................................................... 7

4.2.1 Fixture 1705A ................................................................................................................................... 7

4.2.2 Fixture 1705C ................................................................................................................................... 7

4.3 Test Set-Up ...................................................................................................................................... 7

4.4 Dynamic Range ................................................................................................................................ 8

5. NOTES ............................................................................................................................................. 8

5.1 Revision Indicator ............................................................................................................................. 8

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SAE INTERNATIONAL ARP1705™C Page 2 of 32

APPENDIX A TEST PROCEDURE ........................................................................................................................ 9

APPENDIX B TEST FIXTURE 1705A FIGURES ................................................................................................. 13

APPENDIX C TEST FIXTURE 1705C FIGURES ................................................................................................. 21

1. SCOPE

1.1 Purpose

The purpose of this procedure is to establish a technique for reliably and repeatedly measuring the RF shielding

characteristics of EMI gasket materials and EMI gaskets against various joint surfaces. The procedure is also used to test

the reliability of the gasketed joint combinations after being subjected to hostile environments.

1.2 Background

ARP1173 is the existing method for accomplishing the goals expressed in 1.1. This method consists of a small enclosure

with a plate mounted on a metallic wall and gasket around the periphery of the plate. A source is placed within the

enclosure and a receiving antenna located outside the enclosure.

The utility of data from measurements made using this technique is limited, since the results depend upon the dimensions

and construction of the enclosure, the details of the antennae used for the source and receiver, and the dimensions of the

shielded room in which the measurements are made, as well as upon the performance of the gasket under test. Since the

data is so dependent upon the test setup it cannot be accurately used in equipment design analyses. The advantages of

the transfer impedance method are discussed in References 2 and 3.

The transfer impedance method presented in this document offers an attractive alternative to any of the radiated field

methods for evaluating gasket materials, since it yields data which is independent of the test method and test apparatus

and can be used in design analysis.

The tests as described herein are designed to achieve the following: (1) test the relative value of the gasket; (2) test the

relative value of joint surfaces as related to the gasket under test; and (3) test the ability of gaskets and gasketed joint

surfaces to survive hostile environmental conditions.

2. REFERENCES

2.1 Applicable Documents

The following publications form a part of this document to the extent specified herein. The latest issue of SAE publications

shall apply. The applicable issue of other publications shall be the issue in effect on the date of the purchase order. In the

event of conflict between the text of this document and references cited herein, the text of this document takes

precedence. Nothing in this document, however, supersedes applicable laws and regulations unless a specific exemption

has been obtained.

1. ARP1173, Test Procedure to Measure the R.F. Shielding Characteristics of E.M.I. Gaskets, July 1975.

2. “Radiated Field Strength Method for Measurement of the RF Shielding Characteristics of EMI Gaskets”, by D.R.

Awerkamp, IEEE International Symposium on EMC, October 1975.

3. MIL-STD-810G, Environmental Engineering Considerations and Laboratory Tests, October 2008.

4. “Test Procedure to Measure the Transfer Impedance of Gasketed Joints for Shielded Enclosures”, by P.J. Madle,

IEEE International Symposium on EMC, October 1979.

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SAE INTERNATIONAL ARP1705™C Page 3 of 32

2.2 Definitions

2.2.1 TRANSFER IMPEDANCE

“Electromagnetic leakage via seams (and gasketed joints)” in shielded enclosures occurs primarily as a result of currents

which cross the seam.

 Such crossing causes a voltage to be developed on the far side of the seam.

 Electromagnetic leakage through the seam is directly proportional to the (transfer) voltage developed across the seam.

In shielding theory the seam is characterized in terms of its transfer impedance as follows:

ZT = V/JS

ZT = Transfer impedance of seam (-m)

V = Transfer voltage (voltage across seam)

JS = Density of current which crosses the seam (A/m)

2.2.2 SHIELDING EFFECTIVENESS (EMC)

For a given external source, the ratio of the electric or magnetic field strength at a point before and after the placement of

the shield in question.

(IEEE Standard Dictionary of Electrical and Electronic Terms, p. 528. 1972.)

It is noted that this definition must be used with great caution and not in the literal sense of actually placing and removing a

shield. The actual shielding effectiveness of a barrier is a function of many variables which are not accounted for in the

definition above or within the contents of this document.

2.2.3 SHIELDING QUALITY

The shielding effectiveness to the E Field of a gasketed cover is approximately equal to the impedance of the wave divided

by the transfer impedance of the gasketed joint. For the purpose of this document, the definition of shielding quality is:

SQ = 377/ ZT

SQ (dB) = 20 log 377 - ZT (dB)

As an example, using Figure 1 and the subsequent equations and the following:

An incident plane wave of 377 V/m at 2 GHz

Transfer impedance of the gasket = 10-3 -m

Js  1 A/m

e = 10-3 V

2e = 2x10-3 V

l  2 m @ R = 1 m

ET = 10-3 V/m

Shielding Effectiveness (E field)

SE = 377/10-3 = 3.77x105

SQ = 377/10-3 = 3.77x105

 @ R = 1 m

SE  SQ

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