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.