Another look at electromagnetic shielding

Electromagnetic shielding is the EMC engineer´s stock in trade and therefore, be well understood. Kunkel (see IEEE International Symposium on EMC, 1991) and Rashid (see IEEE International Symposium on EMC,1992) have expressed doubts about the validity of the popular transmission line method of approaching shielding problems and Rashid suggests that it is only valid when dealing with plane waves. In which case it is not much use for most practical electrically-small enclosures which contain emitters which cannot be regarded as plane wave sources as they are well within the ubiquitous λ/2π of the enclosing shield. In the case of a remote external source which produces plane waves at the outside surface of an effective compact shield the wave emerging inside the shield will not be a plane wave, as will be apparent from the shield geometry. The shield is, in effect, a secondary radiator. In such a case the shielding effect obtained depends on whether the victim receptor responds to the electric (E) or magnetic (H) component of the field