Encapsulation of Ba–Sr hexaferrite nanoparticlesand MWCNTs in conductive polymer matrix for improved dielectric spectroscopy, electromagnetic shielding and microwave absorption applications

Abstract

Ba–Sr hexaferrite nanoparticles were produced using Sol-Gel auto combustion, whereas carrier fluid ultrasonication dispersion and in-situ polymerization were used to synthesize their composites with MWCNTs and conductive polymers. Structural investigations were accomplished using X-rays diffraction, secondary electron microscopy, Infrared and Raman Spectroscopy. The low frequency dielectric measurements revealed increased dielectric losses (304 at 100 Hz for pure nanoparticles, which increases up to 2721 and 7861 for ternary composites within polyaniline and Polythiophene matrix), indicating good energy dissipation behavior. The diminishing magnetism resulted from the weakening of exchange coupling or domain wall pinning at the interface of Ferrite-MWCNTs and Ferrite-Polymer, causing the shifting of magnetic resonance peak towards lower frequency in the shielding effectiveness (Absorption) plots. Increasing DC conductivity adds to the nominal increase of Shielding effectiveness (Reflection) values owing to the rise in charge carrier conduction. The maximum total shielding effectiveness, perceived for the composition of Ba0.5Sr0.5Fe12O19/MWCNTs/Polythiophene, was −34 dB and −33 dB at 8.1 GHz and 16.2 GHz, respectively. The microwave absorption of our samples was evaluated as a function of frequency and thickness, revealing its dependence on the quarter wavelength phenomenon with maximum reflection loss of −39 dB observed for ternary composite with Polythiophene matrix at 7.4 GHz resonance frequency. The resonance bands coincide with the operating frequency of military radars for shipborne and airborne surveillance and navigation in the X band.