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.
In recent years, because of the rapid progress in wireless technology, microwave absorbers or noise suppressors have become necessary for a safe-electromagnetic-wave-level environment. To design microwave absorbers or noise suppressors, it is necessary to have knowledge of complex permittivity and permeability. To this end, we used the coaxial waveguide method between 500 MHz–18 GHz and the free space method with a dielectric lens in the K-band (18–26.5 GHz). In this report, we show the complex permittivity, εr* and permeability, µr* of lossy dielectric composite materials such as barium titanate oxide (BaTiO3)/rubber and titanium oxide (TiO2)/rubber. The real part of the complex permittivity, ε'r is available for changing the trimming weight ratio of rubber and replacing TiO2 or BaTiO3.
SUMMARYIn recent years, because of rapid progress in wireless technology, microwave absorbers or noise suppressors have become necessary for an environment with safe electromagnetic wave levels. To design microwave absorbers or noise suppressors, it is necessary to have a knowledge of the complex permittivity ε r * and permeability µ r *. In this report, we present the values of the complex permittivity ε r * and permeability µ r * for composite materials including a magnetic component (iron, Fe coated with Fe 3 O 4 ) and a dielectric component (titanium oxide, TiO 2 ) obtained by varying the Fe/TiO 2 volume fraction ratio. By varying this ratio, we can change the values of the complex permeability (µ r * = µ r g − jµ r gg ) and complex permittivity (ε r * = ε r g − jε r gg ). The results are applied to the design of a microwave absorber in order to tailor the reflection loss and the central frequency to particular requirements, for example, the conditions required for ETC (5.8 GHz) use in Japan.
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