MEASUREMENTS OF SHIELDING EFFECTIVENESS IN POLYMER COATING AND COMPOSITE SYSTEMS

摘要

Conventional polymer coating and thermosetting composite formulas are known to be highly insulating or resistive in nature. In many aspects this is a positive feature because galvanic corrosion and risk of electrocution can be reduced. A dilemma arises however when the coating or composite system is meant to replace a metal part in many military and commercial applications, especially for shielding electronics. Because of metal's conductivity, parts made from metal are capable of grounding, of electrostatic discharge (ESD), and of electromagnetic interference (EMI) shielding. Consequently, many composites and coatings are modified with conductive fillers and reinforcements in order to improve conductivity. Since metals have been used almost exclusively until recently, significant data exists which allows for easy prediction of shielding effectiveness (SE) through DC and waveguide measurements. These screening methods are not as effective though for anisotropic systems such as conductive paint coated glass reinforced polymer (GRP) panels and composites utilizing embedded carbon or metal fibers. This is due in part to the fact the metal is homogeneous throughout and the methods were designed with this fact in mind. Carbonaceous fiber and nanomaterial containing composite coupons and coatings are compared with control panels with respect to surface resistivity, faying resistance, and EMI shielding potential in order to determine the ability of the screening methods to predict actual radiated field measurement values.