Electromagnetic Interference (EMI) is electromagnetic radiation which is also known as Radio Frequency Interference (RFI). This refers to the unwanted frequency signals, interference and noise that are emitted by quickly changing signals in electrical circuits. These unwanted signals will usually interfere with, obstruct, interrupt, degrade or limit the effective performance of the normal signals and slow down their processes. This type of radiation can be intentionally produced, as it is in some forms of electronic warfare or it can be produced unintentionally, as a result of spurious emissions and responses and intermodulation products etc.
EMI often interferes with the reception of AM radio in urban areas and it can sometimes affect FM radio and television reception to a lesser degree. The most important means of reducing EMI are the use of bypass or decoupling capacitors on each active device. These are connected across the power supply, as close to the device as possible. You can also try to cut down on EMI with rise time control of high speed signals using series resistors and VCC filtering.
EMI signals can be absorbed by using capacitor-based circuits or by applying special coatings to them. If those solutions are not sufficient and will not work, then special shields, which can be made of a variety of materials, can be used. The types of materials that are generally used are rubber, elastomers, shielding tapes and various types of metal such as copper, and aluminum, etc.
The shields can various things such as: gaskets, spring coils, meshes, knockout covers, compressed meshes, grounding tabs, adhesives, coatings, inks, foam-based gaskets, laminated tapes, etc. A spring type is commonly used for cable shielding. Beryllium copper and stainless steel are used as the base materials in gasket types of EMI shields.
Many electronic devices such as mobile phones often used to interfere with other instruments such as medical equipment and airplane controls. A lot of countries around the world now have legal requirements that state electronic and electrical hardware must still work correctly even when they are subjected to certain amounts of EMI, and they should not emit any type of radiation which could interfere with other equipment.