Screening theory of metallic enclosures

The intention of this paper is to study and explain on which conditions different approximations can be used in shielding attenuation calculations of metal boxes or rooms. Maxwell´s equations are recalled as the basis of the screening theory. Both the method using the quasistationary assumption and the method using reflection and absorption loss are shown to be based on Maxwel´s equations and the boundary conditions. The principles of both methods are annexed. Results of both methods are compared with results calculated using Maxwell´s equations directly. This comparison and discussion on the effect of practical details leads to conclusions on the choice of the correct method.