A Multiple Percolation Approach to EMI Shielding Composites Incorporating Conductive Fillers

Abstract

Lightweight composites composed of silver coated hollow microspheres in epoxy for shielding of electromagnetic interference (EMI) address the need for mass reduction in aerospace applications for improvement of economy and payload capability. To achieve the structural integrity of fiber reinforced composites, incorporation of microspheres into a woven fiberglass/epoxy composite is evaluated as a method to retain structural and electrical performance. In this approach, the percolation threshold of conductive filler is reduced by a multiple percolation of the matrix phase. Laminate strength is retained in the 0/90° fiber orientation, and only slightly reduced in the ±45° orientation. Shielding effectiveness in excess of 60 dB is obtained at a microsphere volume fraction of only 19%. Conductive short fibers were also employed, with similar mechanical and electrical performance relative to microspheres. An approach is, therefore, presented to optimize both mechanical and electrical composite properties, at a fraction of the mass of bulk metals, and without the durability issues of thin metallic surface coatings.