Dependence of microwave absorbing property on ferrite volume fraction in MnZn ferrite-rubber composites

The effective complex permeability and permittivity spectra in composites with various ferrite volume fractions were calculated using the Bruggeman effective medium theory. The matching conditions for the maximum microwave absorption were determined by substituting the complex permeability and permittivity in the equation for the impedance matching condition. The minimum reflection loss increases from -5 to -40 dB as the ferrite volume fraction increases for /spl nu//sub f/<0.26, where single dip of minimum reflection loss was observed. However, two matching conditions were observed for v/sub f//spl ges/0.26, and two minimum reflection losses shown to be about -40 dB. The results indicate that a microwave absorber with reflection loss of about -40 dB can be designed by controlling the ferrite volume fraction in MnZn ferrite-rubber composites in the frequency range 0.8-12 GHz.