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

We have measured the complex permeability and permittivity spectra of Co₂Z/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 Co₂Z/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.