Electromagnetic Interference (EMI) - Overview

Electromagnetic Interference or EMI, has been defined as the "degradation of the performance of a piece of equipment, transmission channel, or system caused by an electromagnetic disturbance." (ANSI C63.14, 1992; IEC 60050(161), 1990). EMI can occur throughout the EM spectrum from 0 Hz to 20 GHz or higher frequencies. However, EMI problems are most prevalent in the RF frequencies.

For an Electromagnetic Interference or EMI condition to exist, the following conditions must be present:
 

• There must be a source. An interference source is called an "emitter" of electromagnetic energy. The emitter may propagate electromagnetic energy either intentionally, like a hand held radio, or unintentionally, like a power transformer.
• There must be a device sometimes referred to as the "victim", that is susceptible to the electromagnetic energy being emitted by the emitter source. If the susceptible device does not have sufficient immunity to reject the energy it is being exposed to, electromagnetic interference may occur.
• A physical relationship must exist between the two devices wherein they share a common propagated electromagnetic field. The physical distance between devices and their spatial orientation with respect to each other may have a significant role in determining whether the devices will react with each other.

The sensitivity of a device to EMI is described by either susceptibility or immunity. Since susceptibility to EMI varies with many factors, devices can be placed into an active electromagnetic field without user awareness that a potential EMI problem may exist. Adjacent devices may also unintentionally radiate electromagnetic fields that can, in turn, affect other devices.