Physical approach of EMC testing methods - Analysis of phenomena

This second article, devoted to the physical framework of EMC metrology, deals with the phenomenological aspects essential to understanding the emission measurements and immunity tests described in the article [R 932] . This is a difficult subject, which the author has preferred to develop on the basis of simple examples, coordinated by analytical calculations.

With this in mind, the first paragraph will outline two academic problems summarizing the mechanisms involved in the concepts of emission or immunity. The first problem analyzes the radiation from a printed circuit track carrying signals occupying a wide frequency spectrum. We then explore, in a purely qualitative way, the coupling between the near field of the printed circuit and the internal topology of the device. The configuration reduced to a shielded cable will reveal the existence of resonances correlated to the connections made with the various potential references. The second problem addresses the voltage captured at the end of the track subjected to an immunity test produced by the electromagnetic field of a sustained RF wave. Questions relating to the notions of coupling, interference and immunity criterion carried on this simple example will lead to the examination of non-linear effects acting on active components, in this case an integrated amplifier.

The second paragraph deals with a subject independent of the previous one, but just as revealing of the effort required to interpret experiments designed to measure weak or strong fields. By way of illustration, a careful analysis will be made of the protocol adopted to measure the attenuation of an effectively shielded metal enclosure. The analysis will be followed by the approach taken to measure the field strength encountered in the vicinity of a powerful radio-frequency transmitter. What these two examples have in common is the search for methods to localize and reduce uncertainties due to the self-disturbance of measuring instruments.

The text frequently calls on demonstrations or formulas set out in the article [R 931] devoted to antennas encountered in EMC. In addition, articles