Evaluation of a missile body EMI gasket

A small missile body is being constructed from a series of interlocking sections made from aluminium alloys. Between each section an EMI gasket is fitted to ensure continuity of screening for the whole missile. The author describes how the electrical performance of this gasket has been determined both before and after exposure to a severe corrosive environment. A test method based on a measurement of gasket transfer impedance, using a triaxial test fixture, was developed. A significant factor was that the test jig was a full scale model of one of the joints between the sections, enabling precise design data to be obtained. The gasket used was of a novel design consisting of a conformable knitted circular monel metal mesh which is impregnated with a silicone gel. This silicone gel provided the environmental seal for the electrical contact points in the joint so preventing corrosion within the gasket area. This is essential to maintaining very low values of the joints transfer impedance to be maintained even after prolonged exposure to a severely corrosive environment