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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 dielectric (titanium oxide, TiO2) and magnetic (carbonyl iron, Fe(CO)5) materials. 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 60°, which satisfy the necessary conditions for ETC use.
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An et al. (2004) studied this question.
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