Comparison of electromagnetic absorber used in anechoic and semi-anechoic chambers for emissions and immunity testing of digital devices

The absorber used in anechoic and semi-anechoic chambers employed for emissions and immunity testing of digital devices is examined. Using reflectivities obtained by the method of homogenization, the advantages and disadvantages of urethane pyramids, twisted-pyramids, wedges, as well as ferrite tiles, ferrite grids, and "hybrid" combinations of urethanes and ferrites, are determined. General reflectivity guidelines are also presented for comparing absorber used for the electromagnetic compatibility (EMC) testing of digital devices from 30 to 1000 MHz.