Electromagnetic Interference (EMI) or Radio Frequency Interference (RFI) is an unwanted signal (interference/noise) which is transmitted or emitted from an electrical device or transmission medium. This energy can be disruptive to another device if it couples into another device or transmission channel. The coupling can be radiated, conducted or both. EMI interrupts, limits obstruct or degrades the transmission
performance. EMI can come from unintentional radiation due to poor design, due to the operation or spurious emissions, or maybe purposefully generated with the intent to disrupt.
Shielding is the most common and effective means of reducing EMI by creating a conductive barrier between the environment and receiving devices or channels. Shielding is typically applied to cables, isolating the internal wires from the environment around the cable, or is applied to enclosures separating electrical content from the outside environment. The amount of reduction depends upon the material used, the method
of connection of the shield (or screen) and the frequency. Typical materials include sheet metal, metal mesh and aluminum foil. Shielded cable is protected by a wire mesh or foil surrounding an inner core. When properly grounded and bonded, the shielding impedes the escape of any signal from the core conductors and prevents
external signals from being introduced to the core.