Shielding Effectiveness of Reverberant Enclosures Containing Printed Circuit Boards

Shielded enclosures are a convenient and widely used method of protecting electronic equipment from an undesirable electromagnetic environment. The amount of protection the enclosure provides is known as Shielding Effectiveness (SE). Generally, the SE is given for an empty enclosure. However, the contents of an enclosure, such as Printed Circuit Boards (PCBs), will change the SE. In this thesis, the absorption and transmission of a set of PCBs has been investigated and this information used to predict the SE of populated enclosures. Power balance modelling was used to predict the SE of a number of configurations of a single cavity and two cavity enclosure with and without contents. These results were compared to measurements made in a reverberation chamber (RC). Measurements and analysis were made of the absorption of individual PCBs and the absorption was shown to change when PCBs were stacked together or positioned close to the RC wall. The transmission through a set of PCBs was measured and found to be low enough to ignore in the models. The results presented in this thesis have shown how the absorption of a PCB can change in different situations and how this information can be used in power balance modelling to estimate the SE of an enclosure. Further investigation into the absorption and transmission of PCBs will refine the models for more accurate results. It is important to know the SE of an enclosure and its contents as a whole system as under or over estimating the amount of SE could lead to equipment malfunctions. If the SE is underestimated additional, unnecessary, shielding may be used which will add weight, cost and space to the equipment. Too little shielding and equipment may not be fully protected.