Corrosion Resistant Composite Material For EMI/EMP Hardening Protection In Marine (or Similarly Hostile) Environments

In I987 ( I ) and 1989 (2) initial results of the electromagnetic interference (EMI) evaluation of aluminum technology and indium tin oxide (1TO)lNi-flake technology were discussed by Dixon and Masi. This study is a continuation of the effort to develop composite materials composed of conducting particles, fibers, or flakes in a matrix of polymeric material for use in shipboard connector and junction box electromagnetic shielding applications. These materials are designed to satisfy a full range of electromagnetic, chemical, and mechanical properties. Particular emphasis was placed on the material's shielding effectiveness against electromagnetic ( E M ) fields, its corrosion resistance to hostile environments and its electrochemical compatibility with connecting enclosures and devices made from aluminum. The ability of the oxides to vary the oxide stoichiometry in the presence of other electrochemical species makes these materials of great interest to the military designer. For example, utilizing nickel shielding material against aluminum cabinets or bulkheads, without the rrelectrochemical protection" of an oxide material like ITO, will subject these metals to rapid corrosion in the marine environment. Background information and a summary of results is provided on the earlier composite material developmentlevaluation efforts. However, the emphasis of this paper will be to highlight the results of recent electromagnetic pulse (EMP) testing conducted at NUSC on the ITOINi-flake and other selected composite materials. This testing was pelformed using a high level EMP simulator capable of subjecting the cylindrical, lifesaver-shaped composites to a peak current of 150 amperes from a damped cosine waveform generator. The EMP testing has shown that most of the composite materials have their EM performance improved by one to two orders of magnitude (20-40 dB) after proper surface treatment and high level pulsing. This pelformance improvement remains after the removal of the pulsed source, thereby making the phenomenon somewhat analogous to the annealing process used to improve the EM pelformance of various metals.