A microwave absorber for use in an electronic toll collection(ETC) device, having a central frequency of 5.8 GHz, is fabricated using a composite of magnetic (iron, Fe (coated by Fe3O4), made from Carbonyl Iron, Fe(CO)5) and dielectric (titanium oxide, TiO2) material. The reflection loss in free space, using a circularly polarized wave, was −20 dB or more around a central frequency of 5.8 GHz at incident angles of up to 60o, which satisfies the necessary conditions for ETC use in JAPAN. In this study, we explain the characteristic evaluations of microwave absorbers by changing the weight ratio of Fe/TiO2 composite materials (Fe/TiO2 = 100/0-0/100) and incidence characteristics of the transverse electric wave (TE wave), the transverse magnetic wave (TM wave) and the circularly polarized wave (CP wave) in a free-space without a characteristic deterioration. In addition, we show the experimental results by changing the arrangement of microwave absorber that also satisfied a necessary condition for ETC use.

Keywords: Microwave absorber, Complex permittivity, Complex permeability, Dielectric-magnetic composite material.