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Characterization of materials properties The crystal structures of the as-received and heat-treated SiC-based ceramic woven fabrics were examined using X-ray diffraction (XRD), performed on an X-ray diffractometer (RINT 2200, Rigaku Corporation, Tokyo, Japan) with Cu Karadiation in the 2Φ range from 20 to 90° with steps of 0.02°. A microstructural analysis was carried out using a scanning electron microscope (SEM) (JSM-6400,Jeol Ltd, Tokyo). Bundles of fibers from each of the materials (shown in Table 1) were tested for electrical resistance using a DC voltage source, using silver paste in order to ensure a good electrical contact. A constant voltage was applied through the bundle, and the magnitude of the current was recorded for different voltage values. The average resistance, R, was determined using Ohm’s law, and the resistivity of each bundle, q, was calculated using Eq. 1, where l and A are the length and cross-sectional area of the bundle, respectively.The electrical conductivities,Δ , of the as-received and heat-treated woven fabrics were determined by taking a reciprocal of their resistivity. Electromagnetic transmission and reflection measurements using the free-space method The electromagnetic wave absorption potential of materials has been evaluated either directly through the measurement of reflectance and transmittance of electromagnetic waves using appropriate electronic systems or indirectly through the observation of changes in various physical properties including conductivity, dielectric constant, and temperature [19]. In this study, the reflection loss and transmission loss of the ceramic woven fabrics were directly determined in the 17–40 GHz frequency range using the free-space method. This measurement technique was preferred over the conventional contact method, as measurement accuracyis not so strongly dependent on the precision of the machining of the samples. In addition, an accurate measurement of the electromagnetic properties of anisotropic and inhomogeneous media, such as ceramics and composites, can be performed using the free-space method without the excitation of higher-order modes, which is seldom possible with conventional methods. Furthermore, during the application of the free-space method the measurement is carried out in a non-destructive manner and without contact [20]. |
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