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.

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.