Using electrically lossy transmission systems to reduce computer rf emissions

Abstract

A computer system employs electrically lossy transmission systems to dissipate RF energy, and thus reduce RF emissions near the source. An electrically lossy dielectric includes a colloidal dispersion of lossy material, e.g., graphite, in a polymer matrix. A layer of this material can be placed in contact with a conductor or with its surrounding dielectric. A metal layer contacts the other side of the lossy dielectric so that an electrically lossy transmission system is defined. Such transmission systems are defined with respect to signal conductors, shields for coaxial cables, PCB boards, and structural metal, such as heat sinks and vent openings, etc. In some cases, impedance mismatches are used to reflect unwanted energy back through or back and forth through the lossy transmission system. The lossy transmission systems dissipate RF energy so that there is less RF energy to radiate to the computer's exterior. When used in conjunction with known RF shielding techniques, the lossy transmission systems provide for reduced RF emissions, especially for frequencies above 100 MHz.