Microwave Reflection Characteristics of Co$_{2}$Z Barium Ferrite Composites With Various Volume Concentration

We have measured the complex permeability and permittivity spectra of Co
₂
Z/epoxy composites for different volume concentrations V
_c
varying from 0.2 to 0.6. The effects of V
_c
on matching and bandwidth properties have been studied. For V
_c
ges 0.5, there exist two matching points. The first matching, occurring away from the magnetic resonance region, has its origin in the quarter-wavelength matching, while the second matching is related to magnetic resonance. Both matchings are perfect, i.e., reflectivity |R| (dB) = -infin can be theoretically achieved. For V
_c
les 0.4, only one matching, the first matching, is found. At the matching point, |R| (dB) is finite. |R| (dB) decreases with decreasing V
_c
, due to the decrease in tan delta
_m
and epsi'. In addition, with an increase in V
_c
, the percentage bandwidth DeltaW
_p
increases and the corresponding optimum thickness t
_o
decreases. A Co
₂
Z/epoxy composite with V
_c
= 0.6 can achieve DeltaW
_p
= 90% for reflectivity |R| (dB)< -10 dB at a thickness of 0.30 cm.