REFLECTIVITY OF HYBRID MICROWAVE ABSORBERS BASED ON NIZN FERRITE AND CARBON BLACK DOI 10.5028/jatm.2012.04032512

Abstract

This study had as main objective to show that the adequate combination of magnetic and dielectric particles can improve the radar absorbing materials performance. For this, formulations of polyurethane resin loaded with carbon black and NiZn ferrite, with general composition MFe2O4, where M = Ni, Zn or both elements, homogenized by conventional mechanical mixture, were prepared. Reflectivity measurements of different coating formulations applied on aluminum flat plates (1.0 ± 0.1 mm-thickness) were performed using the Naval Research Laboratory arch technique, in the X-band frequency range. X-ray diffraction and magnetic susceptibility evolution analyses of the tested ferrite showed that this magnetic additive presents different phases. Attenuation values of ~4 dB (~60% of the wave absorption) for the polyurethane/carbon black/ferrite formulation, 49/1/50 in wt.%, respectively, were found. This low attenuation values (~4 dB) is attributed to the presence of different phases in the NiZn ferrite, as shown by both the X-ray pattern and the magnetic susceptibility analyses, and also to the thickness and the additives concentration used. As main result, this study shows that the adequate combination of carbon black and NiZn ferrite improves the processed radar absorbing materials performance due to the adequate adjustment of the impedance matching, which favors the microwave absorber-electromagnetic wave interaction.