Svirskas Šarūnas, Jablonskas Džiugas, Rudys Saulius, Lapinskas Saulius, Grigalaitis Robertas, Banys Jūras
Faculty of Physics, Vilnius University, Saulėtekio al. 9, 10222 Vilnius, Lithuania.
Rev Sci Instrum. 2020 Mar 1;91(3):035106. doi: 10.1063/1.5136317.
The full-wave analysis was applied for a coaxial line (i.e., transmission line) that has a "short-circuited" discontinuity. The discontinuity has a radius less than or equal to the inner radius of the coaxial line. The "sample region" can be considered as a partially filled circular waveguide. Such a structure is very practical and is of particular interest for the dielectric spectroscopy applications. It takes into account the inhomogeneous field distribution, which is the limiting factor for the determination of high dielectric permittivity values at microwave frequencies. The direct problem was solved by using the mode-matching technique, and the relationship between the complex reflection coefficient and the dielectric permittivity of the cylindrical sample was obtained. By solving the inverse problem, it is possible to obtain the complex dielectric permittivity from the experimental values of the scattering matrix. The results were verified by the finite element modeling of the system and applied for particular materials. The correspondence between these approaches is excellent. This method is very suitable for the determination of permittivity, which exceeds several thousands (it is applicable for any type of material). It extends the frequency range where the permittivity can be determined reliably. There is no necessity to prepare samples with different geometries (i.e., surface area and thickness).
全波分析应用于具有“短路”不连续性的同轴线（即传输线）。该不连续性的半径小于或等于同轴线的内半径。“采样区域”可视为部分填充的圆形波导。这种结构非常实用，在介电谱应用中特别受关注。它考虑了不均匀场分布，这是在微波频率下确定高介电常数的限制因素。通过使用模式匹配技术解决了正问题，并获得了复反射系数与圆柱形样品介电常数之间的关系。通过解决反问题，可以从散射矩阵的实验值中获得复介电常数。结果通过系统的有限元建模得到验证，并应用于特定材料。这些方法之间的对应性非常好。该方法非常适合于确定超过数千的介电常数（适用于任何类型的材料）。它扩展了可以可靠确定介电常数的频率范围。无需制备具有不同几何形状（即表面积和厚度）的样品。
