Investigation For Performance And Evaluate Method Of Electromagnetic Shielding Of Material With Medium Conductivity

With the increasing demand of electromagnetic compatibility for all kinds of electronic equipment, how to reduce the electromagnetic radiation, improve the EMC performance of electronic equipment, protect the important target and health effectively deserve more attention and research. In recent years, with the development of material science and technology, nonmetal composite conductive material, such as conductive rubber, conductive fabric and conductive coatings, has the advantage on special occasions on electromagnetic shielding applications. Although their conductivity is relatively poor (conductivity from dozens to thousands S/m), they have adjustable of mechanical properties and physical parameters. Shielding effectiveness calculation model and evaluation method is one of the important academic problems to be solved in the applications of electromagnetic shielding composite materials.Test methods of the power frequency electric and magnetic shielding effectiveness of the materials are proposed respectively. By analyzing the experiment results when adjusting the test scheme, we improved the experiment method. The distributions of the electric field inside and outside of the shielding enclosure are obtained through the experiment. The experiment results can be used to determine the position of the electronic devices under protect in the shielding enclosure and guide the design of electromagnetic shielding enclosures.According to the standard GJB6190-2008, the electromagnetic shielding effectiveness of material of medium conductivity is tested with shielding chamber method and the flange coaxial method. The electromagnetic shielding effectiveness (SE) of a metal cavity using material of medium conductivity is investigated theoretically by using an equivalent circuit method based on transmission line and waveguide theory. The validity of the theoretical model is verified by the comparison with electromagnetic simulation software. The position effect and resonance effect of the SE are calculated. A method for evaluating the SE of materials is suggested. With this method, the influence of the resonance effect and the position effect can be impaired greatly and also the SE of materials against plane wave can be evaluated directly.