To protect against electromagnetic interference (EMI), plastics can be equipped as shielding materials in the MHz and GHz range with electrically conductive and magnetic additive components or also with special filler mixtures of these components.
Suitable electrically conductive fillers are metal fibers, metal flakes, metallised fibers, intrinsically conductive polymers and special carbon additives (e.g. carbon fibers, carbon nanotubes and carbon blacks) which, when incorporated into the plastics, form a network of conductive paths with a specific volume conductivity > 0.1 S cm-1.
Magnetic materials of high magnetic permeability (e.g. ferrites µr > 1000 and nano-crystalline iron alloys with µr output values of 105 to 106 ) reach maximum µr values between 10 to 100 after extrusion and injection molding, depending on the degree of filling in the polymer composites. Magnetically filled polymer composites can be used for the absorption of radio and microwaves or, in the case of polymer hybrids of magnetic particles and electrically conductive fillers, also for the production of higher shielding semi-finished products or housings.
