Graphite/Conductive-Epoxy Electromagnetic Shielding

John H. Glenn Research Center, Cleveland, Ohio

Lightweight shields for electromagnetic interference (EMI) can now be fabricated from composites of (1) electrically conductive fibers made of bromine-intercalated graphite in (2) matrices of electrically conductive epoxy. As shown in more detail below, the shielding ability of a given thickness of this composite material equals that of a greater thickness of aluminum.

The EMI-Shielding Performances of a 2-mm thick sheet of aluminum and a 0.36-mm thick sheet of the present composite material made from electrically conductive epoxy were measured at frequencies of 10 and 35 GHz.

Electrical conductivity of surface layers is essential for EMI shielding. Previously, NASA had developed EMI shields made of bromine-intercalated graphite fibers in matrices of electrically insulating epoxy. However, those shields were not as effective as aluminum shields because of the lack of electrical conductivity in the epoxy (especially in surface layers).

The table compares the shielding effectiveness of a sheet of aluminum and a sheet of the present bromine-intercalated-graphite-fiber/electrically-conductive-epoxy composite. On the basis of performance figures like those in this table, it has been estimated that by use of this composite material, it should be possible to make EMI shields thinner than aluminum shields (which are typically about 2 mm) but equally as strong and equally as effective against EMI. It has been further estimated that reductions in weight, relative to aluminum shields, can be expected to lie between 34 and 88 percent.

This work was done by John D. Lennhoff and George G. Harris of Triton Systems, Inc., for Glenn Research Center. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp under the Materials category.

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