Preparation and microwave-absorbing properties of NiFe2O4-polystyrene composites

NiFe2O4 nanoparticles were synthesized by the polyacrylamide gel method with acrylamide as the monomer and N,N'-methylenediacrylamide as lattice agent. The average crystallite sizes of the nickel ferrites annealed at 500, 600 and 800 degrees C are about 10, 30 and 50 nm, respectively. Ferrite-polystyrene composites were made by hot pressing, and microwave-absorbing properties of the composites with different contents of 35, 45, 55 and 65wt% ferrite were investigated by testing complex permeability and complex permittivity in the X-band (8.2-12.4 GHz) frequency range. All the parameters, epsilon', epsilon '', mu' and mu '', increase with increasing ferrite content. The reflection losses were calculated based on a model of a single-layered plane wave absorber backed by a perfect conductor. The composite with 65 wt% ferrite content shows a minimum reflection loss of -13 dB at 11.5 GHz with a -10 dB bandwidth over the extended frequency range of 10.3-13 GHz for an absorber thickness of 2 mm. Crown Copyright (C) 2008 Published by Elsevier B.V. All rights reserved.