Electromagnetic shielding of structural foams by using internal conductive materials

This report summarizes the analysis performed during the program to assess the RF shielding effectiveness obtainable by using internal conductive materials in structural foams. The major emphasis was on the use of carbon/graphite fibers as the conductive material although consideration was given to metalized glass fibers and to metal particles. Several mathematical analysis techniques were considered for assessing shielding effectiveness including the method of moments, wire grid analysis, meteorological, and plane wave analysis. The plane wave analysis technique was deemed the most applicable. Calculations of shielding effectiveness are presented in the HF through UHF frequency range for various material characteristics. Test panels were fabricated and tested from 10-1,000 MHz. Carbon, graphite fibers and aluminum coated glass fibers were used as the filler material in the foam panels. Measured data are presented for different concentrations as well as for different types of filler material. Two of the materials tested provided adequate shielding for civilian radio frequency equipment application in the UHF (300-3,000 MHz) region.