Marko Tuhkala

Method to characterize dielectric properties of powdery substances

An open ended coaxial cavity method for dielectric characterization of powdery substance operating at 4.5 GHz in TEM mode is presented. Classical mixing rules and electromagnetic modeling were utilized with measured effective permittivities and Q factors to determine the relative permittivity and dielectric loss tangent of different powders with er up to 30. The modeling enabled determination of the correction factor for the simplified equation for the relative permittivity of an open ended coaxial resonator and mixing rules having the best correlation with experiments. SiO2, Al2O3, LTCC CT 2000, ZrO2, and La2O3 powders were used in the experiments. Based on the measured properties and Bruggeman symmetric and Looyenga mixing rules, the determined dielectric characteristics of the powders exhibited good correlation with values in the literature. The presented characterization method enabled the determination of dielectric properties of powdery substances within the presented range, and therefore could be a...

An indirectly coupled open-ended resonator applied to characterize dielectric properties of MgTiO3–CaTiO3 powders

The effect of CaTiO3 addition on the complex permittivity of MgTiO3 powder was characterized with an open-ended coaxial cavity resonator in the range of 2.12–3.66 GHz. Permittivities and loss tangents of (1 − x)MgTiO3-xCaTiO3 composite powders with x of 0, 2, 5, and 10 mol. % were measured and compared to theoretical values. Inclusion permittivities and dielectric loss tangents were determined by using Bruggeman symmetric and Looyenga mixing rules and a general mixing model. Additions of CaTiO3 resulted in a clear increase in inclusion permittivities from 13.4 up to 14.9 and in loss tangents from 7.1 × 10−3 up to 8.5 × 10−3. Comparison with the theoretical loss tangent values and quantitative determination of CaTiO3 molar ratios by using measured loss tangents and a general mixing model gave a good correlation. The characterization method was proved to be capable of detecting dielectric changes of MgTiO3–CaTiO3 composite powder and of quantifying the amount of additional substances. This information can b...

Polymer-ceramic composite filler selection using mixing rules

In this work, classical Bruggeman symmetric and Looyenga mixing rules were used together with a general mixing model to estimate the permittivities and loss tangents of polymer composites in order to make rational filler selections. Eight different fillers were used and compared with theoretical polymer composites. Permittivity levels of the composites were between 2.1 and 70 in the frequency range of 2.5−8 GHz. Results showed that rational selections of fillers also provided better properties of composites when using low permittivity instead of high permittivity filler. However, in certain permittivity targets, better properties were achieved with high permittivity filler. The selections were based on the required volume ratios of fillers and total loss tangents of the composites. Theoretical results correlated well with previously reported values.