Measuring shielding induced attenuation

While shielding attenuation measurements are relatively straightforward in principle, experience shows that their physical interpretation requires a certain amount of understanding. Likewise, carrying out a shielding attenuation measurement leading to a physically acceptable result requires certain precautions to be taken. Against this backdrop, the first paragraph of the dossier focuses on a theoretical description of the behavior of electromagnetic waves in conductors. After a brief reminder of the properties of plane waves, the text addresses the question of propagation in homogeneous media described as "good conductors" where electrical conductivity can vary from 5.8 × 10 ⁷ S/m to 10 ⁴ S/m. In order to gain a better understanding of the primary mechanisms accompanying the reflection and transmission of waves on the air-conductor interface, the study first concerns infinitely extended planar structures whose thickness and the presence of apertures are then brought into play.

As the frequency range considered is between 100 kHz and 10 GHz, the term "radio waves" has sometimes been preferred to "electromagnetic waves".

Given that test benches and measurement protocols for shielding attenuation are widely described in international standards and specialized scientific articles, an exhaustive analysis of these measurement methods is of little interest. For these reasons, the second paragraph is confined to the selection of two procedures adopting a test specimen consisting of a flat shielding sample of finite transverse dimensions. The analysis focuses in particular on the uncertainties generated by the presence of the specimen, depending on whether the plane wave is generated in a coaxial cell or inside a TEM cell.

The third paragraph represents a natural continuation of the previous one. The first part deals with characterizing and then measuring the attenuation of shielded enclosures with or without openings. The text then turns to the use of mode-shuffling reverberation chambers, whose physical properties seem perfectly suited to this field of application. The final section looks at the attenuation provided by the shielding of coaxial cables, and more specifically at the detailed description of a bench for measuring the transfer impedance of a cable, the most appropriate parameter for characterizing the shielding efficiency of a cable.

It is important to note that the dossier has been written to complement the