Dielectric characterization of electromagnetic composite barrier materials with plasma layers on nonwoven fabrics

Composite materials are becoming more widely used in the technique of shielding electromagnetic field. Among these materials, textile materials with modified surfaces are of growing importance. Among them we can distinguish nonwoven fabrics coated with conductive plasma layers which are responsible for the phenomenon of reflection and attenuation of electromagnetic wave. These phenomena are related to the dielectric properties of composite material and its structure, in particular with the phenomena on the surfaces of interphase. In the paper, dielectric properties of plasma layer-polypropylene nonwoven fabric composite is reported. To determine these properties, measurements of transient and conduction currents were used. Dielectric response of the composite to an electric field is complicated, and is a function of both the physical structure of nonwoven and applied layer. Current measurements indicate the existence of build-in charge. Electrical conductivity is nonohmic but is controlled by several mechanisms, which include ion hopping, Schottky emission, space charge limited current, and Poole-Frenkel mechanism. The dielectric parameters vary depending on the morphology of substrate surface and on parameters of the plasma generating process