Electromagnetic Shielding
Electromagnetic shielding is a barrier which protects electronic equipment from ambient electromagnetic interference. Electromagnetic interference, or EMI, is the magnetic field which is created by electrical currents; EMI can travel along wires, electrical circuits and conductors, while radio frequency interference (RFI) is radiated electromagnetic "noise" which travels through the air as radio waves. Both EMI and RFI cause similar effects, although EMI typically operates on lower frequencies than RFI. EMI enclosures, EMI coating, EMI gaskets and EMI filters are used as magnetic shielding to guard sensitive electronic equipment. EMI and RFI are created, by widely varying degrees, by everything which conducts electrical energy, including electrical wires, electrical appliances, computers and all electronic equipment. Signal-bearing electronic devices such as mobile phones give off RFI. Normal electrical currents are disrupted when moderate to high levels of EMI or RFI are introduced; un-channeled electromagnetic signals and radio frequency waves can act as "noise", magnetically altering normal flow of electrical currents and impeding the flow of electrical energy. Electromagnetic shielding and EMI filters can be found in medical devices, computers, mobile phones, stereo systems, television sets, windows, vents, fabrics, foils and even walls.
Shielding sensitive electronic equipment from electromagnetic interference and shielding high EMI-emitting equipment from contaminating other equipment can be achieved by enclosing equipment in a conductive EMI absorbing material or by coating equipment or equipment enclosures with EMI coating. Electromagnetic shields are also called magnetic shields and may be made from metals with high magnetic permeability. Metals such as nickel, copper, steel and aluminum are commonly used, although the industry standard magnetic shielding material is Mu-Metal®, an alloy of nickel, iron, copper and molybdenum. Many industries depend on EMI shielding products to protect communication systems, such as hospitals, telecommunication, stage production, sound production and many others. Within circuit boards and CPUs, most problematic EMI comes from electromagnetic cross-talk between different components on the same board as EMI travels across wires and conductive materials.