Models and Methods for Calculating and Measuring the Shielding Effectiveness of Materials Using Dual and Coaxial TEM Cell

Introduction. Electromagnetic shielding is used as an additional design tool to ensure electromagnetic compatibility of electronic devices. The shielding material is selected based on its electrophysical parameters at the design stage of electronic devices, taking its electrical and operational characteristics into account. The shielding effectiveness (SE) of composite, layered, or fabric materials with a high electrical conductivity and relative magnetic permeability in a wide frequency range (10 Hz…10 GHz) is difficult and, in some cases, impossible to assess a priori. At the same time, the number of studies in this direction is currently limited.

Aim. To generalize models and methods for calculating and measuring the insertion losses (IL) and SE of materials using dual and coaxial TEM cells in a wide frequency range.

Materials and methods. A method for calculating IL for the electric (E) and magnetic (H) components of the field based on the measured S parameters in a dual TEM cell is described. Expressions for calculating an unloaded dual TEM cell are proposed. These expressions differ in terms of considering the thickness of the material and the tooling that prevents sagging of thin materials, thus allowing the difference between the measured and calculated values of S parameters to be reduced to 3.2 dB. Methods for measuring and calculating the SE of composite materials are described. The results obtained using these methods are compared with those obtained by a standardized method for SE calculation.

Results. The frequency dependencies of the IL for the E and H fields calculated on the basis of the measured S parameters of a dual TEM cell with a cotton and knitted shielding fabric placed inside are presented. The results obtained by the classic and electrodynamic modeling are compared with experimental results for a composite material in a new patented coaxial TEM cell.

Conclusion. Models and methods for calculating and measuring IL and SE can be effectively used for a relatively rapid control and testing of new and available shielding materials, taking the above assumptions and limitations into account. 

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