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WHAT IS EMI?

EMI (Electromagnetic Interference) consists of any unwanted, spurious, conducted, and/or radiated signals of electrical origin that can cause unacceptable degradation of system or equipment performance. The effects of EMI can range from minor nuisance to catastrophic consequences. A minor nuisance is judged to result, for example, when someone is watching a television program for entertainment, and interference ("snow") appears momentarily on the screen due to the operation of an electrical appliance such as a hair dryer or electric shaver. On the other hand, a serious consequence could result should an interfering signal disturb the normal operation of medical electronic equipment being used to monitor the condition of a patient under intensive care in a hospital. These examples are indicative of the nature and potential consequences of EMI and the importance of effective control to achieve EMC or Electromagnetic Compatibility.


WHAT IS EMC?

EMC is the ability of systems, subsystems, circuits, and components to function as designed, without malfunction or unacceptable degradation of performance due to electromagnetic interference, within their intended environment.


THE NATURE AND BASIC ELEMENTS OF EMI

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.