A short history and review of shielded cables: Effective shielding prevents interference from entering or emanating from a cable

摘要

The purpose of a shield is to prevent interference from entering or emanating from a cable. The three types of interference are: radio frequency interference (RFI), electromagnetic interference (EMI), and electromagnetic pulse (EMP). RFI was the earliest type of interference that engineers had to deal with. Early radio signals easily found their way into devices. Coaxial cables and shielded twisted pairs using copper eliminated most of this type of interference. Today, EMI has become more problematic because of high power transmission lines; higher magnetic fields, such as MRI machines in hospitals; and other high power applications. Copper may not offer much resistance to higher magnetic fields; therefore, the use of magnetic materials such as high permeable irons may be required.