Research in the past eight years has established the ability of polymer composites made with sufficient electrical conductivity to be suitable as shields against electromagnetic interference (EMI). A number of conductive fillers have been used to produce such composites. These include carbon black, carbon fibers, metal fibers, metal flakes, and metal-coated glass fibers. Each filler offers its own set of advantages and disadvantages. An important aspect of developing polymeric composites for EM1 shielding applications is measuring their shielding ability in a reliable, easy-to-use test facility. Once a reliable test has been developed, basic data relating the bulk conductivity (or surface conductivity of coatings) can be generated. The objective of this article is to discuss the relative utility of the different types of fillers commonly used, present an analysis of the utility of different testing approaches, and show data correlating volume resistivity with shielding effectiveness.small conductive particles can be segregated in a network within the composite, low concentrations can be used to form conductive composites (2). This does not lead to practical mass production techniques, however. The most practical means of producing a conductive network with a low concentration of filler is by utilizing 40

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June equation is, in equilibrium,Substitution of (5) into (6) gives directly the Einstein relationship.Integration of (5) yieldsThe quasi-equilibrium approximaticn requires that (6) be satisfied for small deviations from equilibrium. ThusDefining the applied potential VA as(9) and using ( 7 ) and (8) yields V d = -l n -~ This communication discusses an interesting property of the autocorrelation function c ( k ) for a sequence ( x i ) where xi = (+) or (-).