Electromagnetic Interference
Electromagnetic interference (EMI) is a phenomenon that may occur when an electronic device is exposed to an electromagnetic (EM) field. Any device that has electronic circuitry can be susceptible to EMI. With the ever-increasing use of the electromagnetic spectrum and the more complex and sophisticated electronic devices, issues of EMI are attracting attention. When addressing EMI issues, consider a source, a path, and a receptor. The electromagnetic energy from the source propagates through the path and interferes with the operation of the receptor. All three must exist to have an EMI problem. The path can be conducted, radiated, inductive, or coupled with a capacitor or with electrostatic discharges, or a combination of any of the above. Therefore, to understand the effects of EMI, consider two factors: Emissions and immunity (also known as susceptibility).
What are Emission?
Emissions are a measure of electromagnetic energy from a radiofrequency source. Immunity concerns the degree of interference from an external electromagnetic energy source on the operation of the electronic device. The device will be immune below a certain level of EMI and become susceptible above that level. The three most common EMI problems are radio frequency interference, electrostatic discharge, and power disturbances. This chapter will focus on radiated interference from various radiofrequency sources.
What is EMC?
The threat of EMI is controlled by adopting the practices of electromagnetic compatibility (EMC). This is defined as, “The ability of a device, unit of equipment, or system to function satisfactorily in its electromagnetic environment without introducing intolerable electromagnetic disturbances to anything in that environment.” The term EMC has two complementary aspects: it describes the ability of electrical and electronic systems to operate without interfering with other systems, and it describes the ability of such systems to operate as intended within a specified electromagnetic environment.
References:
1.- Electromagnetic Interference with Medical Devices: In Vitro Laboratory Studies and Electromagnetic Compatibility Standards; Kok-Swang Tan, Irwin Hinberg, in Clinical Engineering Handbook, 2004.
2.- EMC; T. Williams, in Instrumentation Reference Book (Fourth Edition), 2010