ABSTRACT
The effect of electromagnetism on sensitive devices is called electromagnetic interference (EMI) and is a rather complex subject. This chapter discusses some of the essential elements of EMI. One advantage of knowing the frequency bands used by any particular group or agency is that once the offending frequency band is determined, the source of the EMI may be determined with reasonable accuracy. Two important properties of electromagnetism are electrical and magnetic fields. An electrical field is present whenever an electrical charge placed in a dielectric or insulating medium experiences force acting upon it. Magnetic fields exist when two poles of the opposite orientation are present: north pole and south pole. The decibel is used to express the ratio between two quantities. Radiated emission is a measure of the level of EMI propagated in air by the source. Conducted emission is a measure of the level of EMI propagated via a conducting medium such as power, signal, or ground wires.
