The failure of coaxial TEM cells ASTM standards methods in H.F. range

The paper deals with one of the most used and reliable ways to characterize the shielding capability of materials, based on the Schelkunoff isomorphism. This method uses the physical-mathematical equivalence of equations describing SE_dB in the case of infinite plane shield, respectively in the case of material sample introduced in the measuring coaxial TEM cell (IA_dB), and it resulted into the ASTM standards ES7-83 and D4935-89. The paper shows that these standards (and Schelkunoff isomorphism) are not valid for electrically thick samples; there is no identity between shielding effectiveness and insertion attenuation/insertion loss in H.F. range.