A Lossy Element for EMC Filters

The need and advantages of lossy elements in unconditional EMC filter design are well recognized. This paper describes a lossy device based on the proximity effect using multilayer strip lines. Expressions are derived for the losses in the multilayer strip conductors. Experimental data show good agreement with theoretical expectations when the differences between the theoretical model and actual implementations are taken into account. The formula for an infinite stack provides a theoretical upper limit to the losses as a function of frequency. A modified empirical formula provides a practical design equation. Applications are also discussed.