Samples composed of a polymer matrix were loaded with different fractions from 0% to 30% of Fe oxide magnetic nanoparticles with an average size ranging from 5 to 25 nm. The permittivity and permeability of the composites were determined upon a very wide frequency range, spanning from DC to 30 GHz using different methods with overlapping frequency intervals. The nanoparticle content was observed to significantly modify the permeability and permittivity behavior of the polymer. The frequency and intensity of both dielectric and ferromagnetic resonances of the composites are clearly affected by the presence of the magnetic nanoparticles, and the composites can be optimized for specific applications requiring absorption of electromagnetic radiation from the MHz to the GHz range.
Abstract. The paper highlights the most important dielectric features for some nanocomposites polymer matrix based on polypropylene (PP) with insertion of carbon nanotubes multi-walled (MWCNTs). The dielectric characteristics analyzed are the real permittivity and dielectric losses of the sample based on PP with 5% insertion of MWCNTs. The measurements are made in a range of frequency between 1 MHz to 3 GHz. The composite form was also analyzed through computer modeling and simulation and electromagnetic properties for EMC shielding applications are also considered. PP/MWCNTs composite with shielding effectiveness of 15-20 dB was investigated through modeling and simulation at about 5% MWCNTs filling. Shielding mechanism was estimated by calculating the total shielding effectiveness (SE) into absorption and reflection loss. PP/MWCNTs composite indicates a shielding mostly by absorption mechanism; therefore it also can be used in other microwave applications or like a radar absorbing material. The effect of MWCNTs affects the electrical conductivity of the nanocomposite. The proposed material shows some interesting electromagnetic compatibility (EMC) properties and promises better performance using different amounts of MWCNT's.
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