A new error reduction technique for reflection coefficient measurements for use in quick laboratory tests

ABSTRACT

Reflection coefficient measurement is one of those fundamental methods for determining the performance of radar absorber materials, and reflections due to these measurements are originated from the discontinuities in the measurement system and they result in error. In this paper, a new technique for the calibration of the scalar reflection coefficient measurements in the frequency range of 3–18 GHz in a portable two-sectioned metallic chamber is being proposed for use in quick laboratory tests with reasonable error (redacted error). Calibration measurements are performed by two calibration standards in frequency domain and transformed to time domain for further calculation. Proposed technique exhibits a good agreement with the theoretical values for especially in compact chambers where plane-wave conditions are not fully satisfied, and it is not in need of any complex time gating process. Furthermore, it does not require considering the phase differences which occurs at the measurement plane, providing a cheap and faster solution, reducing time and complexity in characterization of radar absorber materials. This technique with the mentioned test set-up could supply scalar reflection coefficient measurements with overall 0.55 dB error level and useful for practical applications where high level of accuracy is not required.     

Exact analysis of hydrogen induced stress in metal solid sphere

The effect of hydrogen in metals requires a detailed study involving an analysis of the stress-strain tensor field, stemming from the introduction of hydrogen atoms to the system. A model is created, utilizing the strain-stress state generated by the hydrogen atom and the coupling effect between the hydrogen and metal atom. A set of equations are established for a spherical body in the context of theory of elasticity and stress components within the system are determined. The effect of hydrogen concentration along with hydrogenation and dehydrogenation are investigated involving theoretical analysis and analytical ratios. Calculations are obtained for spherical solid systems. The effects of hydrogenation was resulted in intensive compressive stresses near the surface of the sphere, whereas tensile stresses were occurred near its surface during dehydrogenation.     

Development of gold-bronze metallic glazes in a clay-based system for stoneware bodies

In this study, a triaxial glaze system consisting of red clay, kaoline, quartz, MnO, CuO and CoO is systematically developed to produce gold-bronze raw metallic glazes for stoneware bodies. At first, all of the glazed samples in the developed system were fired in an electrically-heated kiln at 1160 °C. Then, the selected successful gold-bronze metallic glazes were applied onto 3-D forms of stoneware bodies and fired at the same conditions. Microstructural characterizations of the glazes are done with scanning electron microscopy (SEM) and energy dispersive x-ray analyses (EDS). This study revealed that triaxial blending of the ceramic raw materials is a beneficial method for glaze production and gold-bronze surfaces are obtained in glazes G 9, G 26, and G 34. It is observed that chemical composition of the glazes directly influence the color and the amount of CuO is more significative than MnO for achieving gold-bronze effect.