Electromagnetic Shielding Analysis of Planar Materials Using ASTM D4935 Standard Fixture

In this article, analytic models are proposed for electromagnetic shielding analysis of planar materials using the ASTM D4935 standard fixture typically employed to measure far-field shielding effectiveness (SE). The fixture with an inserted planar material is divided into two coaxial line sections and one material section that are modeled as lossless and lossy transmission lines (TLs), respectively. Using the ABCD parameters of TLs, the far-field SEs of planar materials are analytically derived and calculated. In order to analyze the case where the conductive materials are coated on insulating substrates, contact impedances are considered at the inner and outer conductors of the flanged coaxial fixture. The proposed high-frequency model can accurately predict the absorption loss especially in the high-frequency where the skin depth of the material becomes smaller than its thickness. Low-frequency and lumped models are also derived by approximation of the high-frequency model. In addition, correction factors are introduced to remove the SE error in the low-frequency range due to the attached insulating substrates of the conducting materials. For verification, the proposed models are compared with the theoretical plane-wave SE and the measurement results presented in other literatures. They show a good agreement with each other. Lastly, an influence of the errors in the thicknesses and electrical parameters of actual materials on the analytic SE models is analyzed.