Contact Resistance and Porpoising Effects in Braid Shielded Cables

Abstract

Current practice treats braided metal shields as perforated metal pipes. Calculations of diffu­ sion of electromagnetic energy through-the metal thickness and coupling through the apertures satisfactorily explain the performance of some braided shields. This paper explains another coupling mechanism, termed "porpoising," which takes into account details of the braid weave pattern and contact resistance between braid wires as they cross each other in passing from the exterior to the interior of the shield. The porpoising mechanism dominates the shielding performance of some braided shields.