The origins of EMI are basically electrical with the unwanted emissions
being either conducted (voltages and/or currents) or radiated (electric
and/or magnetic fields). In the time domain, EMI can be transient, impulsive,
or steady state. Within the frequency domain, EMI can contain components
with frequencies ranging from the lower power frequencies of 50, 60,
and 400 Hz, on up into the microwave region. The sources of EMI can
be classified as man-made or natural. The classifications of EMI are
designed to facilitate recognition of sources, determine receptor susceptibility,
identify coupling paths between source and receptor, and assist in determining
means of control.
The three essential elements for an EMI situation to exist are: an electrical
noise (EMI) source, a coupling path, and a victim receptor. The noise
source emission can be either a conducted voltage or current, or an
electric or magnetic field propagated through space. It can be seen
that some equipment or systems can serve as both sources and receptors.
Methods of coupling between sources and receptors can be divided into
two basic groups: radiation or field coupling by electromagnetic wave
propagation through space or materials, and coupling via conducted paths
through which current can flow.
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