emc

Aerospace equipment and systems are required to meet electromagnetic compatibility requirements to ensure proper operation and minimize risk to space programs. A standard has been established for electromagnetic compatibility for space related equipment and systems, SMC Standard SMC-S-008. The purpose of the standard is to minimize the risk to space programs with respect to electromagnetic phenomena and compatibility. A series of specific tests have been identified to confirm compliance.

In the past EMC Engineers have relied on metallic enclosures to contain electromagnetic fields and meet radiated emissions limits in military and consumer products. Modern commercial electronics products typically use molded plastic enclosures since they are considered to be aesthetically more pleasing than a metal enclosure, but also to save weight and cost.

The science of electromagnetic compatibility has been in exis­tence for several decades. As an art, it goes back much further, perhaps to the time of Edison when he was just beginning to experiment with practical electrical devices. I am sure that with some of his more sophisticated devices undesired interac­tions took place because of inadequate shielding or filtering. Certainly, with the advent of radio, incompatibility problems occurred as a result of the poor quality of transmitters and receivers. Perhaps the first formal recognition of electromag­netic compatibility problems occurred when the telephone and power companies found they had mutual coupling problems when their lines were carried on the same utility poles. Later on, the increasing use of the radio spectrum called for formal controls administered by departments in the post, telephone, and telegraph offices in many countries, or through the Feder­al Communications Commission in the United States.

A discussion topic between designers, namely those who only do circuit design and have no interest in the field of EMC, and compliance engineers attempting to meet regulatory compliance requirements, is the use of FR-4 as the core material for printed circuit board construction. Fiberglass Resin (FR) is low cost and has been used in almost every electrical product for decades, with exceptions such as military and satellite applications, harsh environmental conditions, and other unique uses. The disagreement lies with the extent that we can use FR-4 in high frequency applications and should we be concerned more with electrical performance or manufacturing and assembly.

The railway environment is generally regarded as a “severe” electromagnetic environment. For an electrified railway, Megawatts of power are required to be converted into the propulsion of trains in order to transport passengers or freight from one destination to another. The railway presents a complex electromagnetic environment made up of many systems including signalling, traction, telecommunications and radiocommunications.