OSHA REPORT

PROPAGATION OF ELECTROMAGNETIC ENERGY

Most people, including most electrical engineers, think of electricity as electrons flowing in a wire, much like water flowing in a hose. The idea of electrical energy moving through free space in a wave is a completely foreign concept. Yet, electromagnetic radiation is exactly that, electrical energy moving through space as a wave, and electrical energy in a wire is a special case in which the energy is guided by a wire. Some of the energy is internal to the wire, and some of the energy is external to the wire. When we plug an appliance into the receptacle, the power delivered to the appliance does not actually "go through the cord", but is electromagnetic energy being "guided" by the electron activity in the power cord. The electromagnetic energy delivered to the load is external to the wire. The electron activity oscillating back and forth in the wire is a result of the external electromagnetic energy and in turn serves as a way of telling the electromagnetic wave to follow the wire. The electron movement in the wire is proportional to the strength of the wave being guided. Don't be disturbed if you have difficulty grasping this concept. Even engineering students have difficulty understanding it.

Fortunately, to analyze and solve most problems in DC and low frequency AC circuits, it is sufficient to apply the simple Ohm's law equation. Normally it does not require thinking in terms of electromagnetic fields. Low frequency electromagnetic field theory is typically applied only when analyzing the coils of relays, inductors, transformers, and motors. Electromagnetic wave theory becomes more important as frequency climbs into the Megahertz range, such as in analyzing wireless electromagnetic energy transmission, radio frequency circuits, light wave analysis, etc.

EM waves can travel without the guiding action of wires. The points where EM waves leave the guiding influence of wires and move to free and unbounded travel are called antennas. Antennas act as coupling points for electromagnetic energy to leave the guidance of wires for free space, and visa versa. The area near this coupling activity is exactly where compliance officers have to deal with electromagnetic fields, as in the case of RF heat sealers.

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