EM shielding effectiveness of metal sandwiched composites

Thermoset polymer composite materials are finding a wide range of applications in aerospace structural parts, due to many advantageous features. The most important feature is the reduction in weight of the structure compared to other alternatives. Majority of the material systems of this class with the exception of carbon fiber based composites, are also transparent to EM radiation. There are applications where such structural composites should not transmit EM radiation while retaining the weight advantage. The present study investigates the effect of the inclusion of a metallic (Al, Cu) foil, metallized fabric on the EM transparency of such composite material systems. Sample laminated plates following the above scheme were subjected to shielding effectiveness test using EMI/EMC test facilities in accordance with MIL STD 285. Results have indicated effective EM shielding in the frequency range of 20 MHz to 10,000 MHz when metallized fabric, Cu foil and Al foil were used in that order.