Microwave permittivity and permeability of ferrite-polymer thick films

Nickel-zinc ferrite-epoxy composites with different ferrite/epoxy ratios, 50/50, 60/40, 70/30 and 80/20, have been prepared as thick films of thickness 100 mum. Different compositions of nickel-zinc ferrite, Ni1-xZnxFe2O4, where x = 0.2, 0.4 and 0.5 have been used to prepare the composite films. The complex permittivity (epsilon' - jepsilon) and the complex permeability (mu' - jmu) of the films as well as of the sintered ferrites have been measured, at X-band (8-12 GHz) microwave frequencies using the cavity perturbation technique. The dielectric constant and the permeability of the films are found to be different from those of the sintered ferrites. epsilon' of films is found to increase with increase in the ferrite content of the composites as well as with frequency while the permeability, mu', is observed to decrease with increase in ferrite content as well as frequency. The high permeability losses exhibited by the films at X-band frequencies, shows their potentiality for applications like suppression of electromagnetic interference in microwave circuits. The composites with the ferrite composition x = 0.5 are observed to exhibit higher losses compared to the composites with other compositions. Also the ferrite/epoxy ratio 80/20 is observed to give comparatively higher losses. (C) 2003 Elsevier Science B.V. All rights reserved.