In industrial applications, efficient shields are often required to prevent
electromagnetic interference. In the past, several formulae for the evalua
tion of the shielding efficiency were proposed. This paper is aimed at the
comparison of their results with the Finite Element Method, in order to ass
ess their range of applicability. Evidence is given that expressions determ
ined for planar and cylindrical shields of infinite structure can be suitab
ly used to estimate the shielding efficiency of more realistic shaped shiel
ds.