Microwave reflection characteristics of Co2Z barium ferrite composites with various volume concentration

Abstract

We have measured the complex permeability and permittivity spectra of Co2 Z/epoxy composites for different volume concentrations V c varying from 0.2 to 0.6. The effects of Vc on matching and bandwidth properties have been studied. For Vc ≥ 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) = -∞ can be theoretically achieved. For V c ≤ 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 δm and ε′. In addition, with an increase in Vc, the percentage bandwidth ΔWp increases and the corresponding optimum thickness t o decreases. A Co2Z/epoxy composite with Vc = 0.6 can achieve ΔWp = 90% for reflectivity |R| (dB)< -10 dB at a thickness of 0.30 cm. © 2008 IEEE.