EMI EMC Tutorial:

What is EMI & EMC?
Electromagnetic Interference (EMI):
The process by which disruptive electromagnetic energy is transmitted from one electronic device to another via radiated or conducted paths (or both) is known as Electromagnetic Interference.

Electromagnetic Compatibility:
The capability of electrical and electronic systems, equipment, and devices to operate in their intended electromagnetic environment within a defined margin of safety and at design levels or performance without suffering or causing unacceptable degradation as a result of electromagnetic interference(EMI).

EMI & EMC Terminology:
Radio Frequency:
A frequency range containing coherent EM radiation of energy useful for communication purposes - roughly the range from 9 kHz to 300GHz. This energy may be emitted as a by-product of an electronic device's operation.  Radio frequency is emitted through two basic mechanisms: 

• Radiated Emissions - The component of RF energy that is emitted  through a medium as an EM field. Although RF energy is usually emitted through free space, other modes of field transmission may be present.
• Conducted Emissions - The component of RF energy that is emitted through a medium as a propagating wave generally through a wire or interconnect cables.  Line conducted interference(LCI) refers to RF energy in a power cord or AC mains input cable. Conducted signals propagate as conducted waves.

Immunity - A relative measure of a device or system's ability to withstand EMI exposure while maintaining a predefined performance level.

Radiated Immunity - A product's relative ability to withstand EM energy that arrives via free space propagation.

Conducted Immunity - A product's relative ability to withstand Em energy that penetrates through external cables, power cords, and input-output(I/O) interconnects.

Susceptibility - A relative measure of a device or a system's propensity to be disrupted or damaged by EMI exposure to an incident field. It is due to lack of immunity.

Electrostatic Discharge(ESD): A transfer of electric charge between bodies of different electrostatic potential in proximity or through direct contact.

Line Impedance Stabilization Network(LISN): A network inserted in the supply mains load of an apparatus to be tested that provides, in a given frequency range, a specified load impedance for the measurement of disturbance voltages and which may isolate the apparatus from the supply mains in that frequency range.