The rapid coating of composites with absorbing paints yields materials that can absorb microwave radiation and still have approximately the same specific mass of the original composites. The use of paints with specific electromagnetic properties together with carbon- nanotube-based materials allows the production of structural materials of interest to the aeronautical industry. Thus, the objective of this study was to produce and characterize the electromagnetic properties of a material consisting of a microwave absorbing coating (carbon nanotubes and polyurethane) applied to a laminated composite made with polyphenylene sulfide and glass fiber. The attenuation of microwaves (8 to 12 GHz) incident on this material was evaluated using the waveguide technique to determine whether this material can be used as an absorbing structural material. The results show that the material absorbs up to 90% of the energy of the incident microwave, indicating that the material is an efficient absorber of microwave radiation.

Foi sintetizada uma ferrita espinélio de NiZnFe2O4 dopada com magnésio e cobre pelo método dos citratos precursores, para pesquisar a influência desses íons na refletividade do pó. Os pós calcinados a 350, 500 e 900 ºC foram caracterizados por difração de raios X, microscopia eletrônica de varredura, magnetômetro de amostra vibrante e refletividade do pó. O pó obtido a 350 ºC é nanométrico e apresentou baixa magnetização e menos de 10% de absorção de radiação. A magnetização e a absorção de radiação aumentaram com o aumento do tamanho de partículas (> 0,4 μm), que causou aumento do volume dos domínios magnéticos. O pó calcinado a 900 ºC/3 h obteve atenuação máxima de -6,4 dB (77 % de absorção de radiação) abrangendo a região de microondas de 8,2 GHz e diminuindo na faixa da banda X. Esses materiais magnéticos que absorvem acima de 35% de radiação na faixa de microondas podem ser aplicados no desenvolvimento de antenas para telefonia celular.

A NiZnFe2O4 spinel ferrite doped with magnesium and copper was synthesized by the citrate precursor method to explore the influence of these ions in the reflectivity of the powder. The powders calcined at 350, 500 and 900 °C were characterized by X-ray diffraction, scanning electron microscopy, vibrating sample magnetometer and reflectivity. The powder obtained at 350 °C is nanosized and showed low magnetization and less than 10% absorption of radiation. The magnetization and radiation absorption increase with increasing particle size (> 0.4 μm), causing an increase in volume of the magnetic domains. The powder calcined at 900 °C/3 h reached maximum attenuation of -6.4 dB (77% absorption of radiation) covering the region of 8.2 GHz microwave and decreasing in the range of the X band. These magnetic materials that absorb over 35% of radiation in the microwave range can be applied to the development of antennas for cellular telephony.

Morphological and microstructure properties of reticulated vitreous carbon (RVC) were analyzed by scanning electron microscopy (SEM), micro-Raman spectroscopy and x-ray diffraction (XRD) techniques as a function of heat treatment temperature (HTT). Samples produced in the HTT range of 1000 to 2400 K have demonstrated a strong dependence of HTT in their structural order mainly attributed to the presence of hydrogen and oxygen (heteroatoms), originated from precursor. In this range, the material is changed from pyropolymer to carbon. The polyfurfuryl alcohol precursor has furanic groups and its cure originates methylenical bonds and sulphur atoms. At HTT higher than 1300 K, these atoms are gradually liberated from the material generating a discrete structure ordering.