Low-Frequency Relation Between Transfer Impedance and Shielding Effectiveness of Braided Cables and Grid Shields

摘要

Metal textile fabrics used in electromagnetic shielding are often complex structures, and manufacturers need approximate models to predict their performance. In addition, different physical phenomena make their behavior varying according to the frequency bands. We propose to develop a model to determine the response of these materials in different frequency bands, and this article presents the low-frequency part of the model. A simple method of modeling braids and metallic grids at low frequency is proposed. Because of their periodic nature, these textile structures can be reduced to an elementary pattern that constitutes them. The calculus of the shielding effectiveness (SE) is then possible for complex structures. The concept of sheet transfer impedance has been defined to allow the passage of complex cylindrical structures to planar forms through a simple and efficient formula. The industrial qualification tools such as transfer impedance and SE can then be linked to each other. Full-wave three-dimensional simulations of periodic pattern of braids and grids show a very good agreement (around 0.1 dB) with the proposed analytical model in the low-frequency band up to 100 kHz and an acceptable approximation up to 1 MHz.