| Abstract [eng] |
One of the basic problems in measurements of the electrical properties of materials is finding relations between measured electrical values and characteristics of the material, especially when the field distribution in the device under test with a sample inside is complex. Commercial electromagnetic simulation software was used in unconventional way to calculate materials' electrical properties. Because the software is not adopted for this task, built-in optimisation option was used. In this way dielectric and magnetic properties of materials in very complex shape were calculated. The method was tested by calculation of complex dielectric permittivity of Bi1.5ZnNb1.5O7-xF2 pyrochlore ceramics as well as by calculation of both complex dielectric permittivity and complex dielectric permeability of carbon-coated capsules of Ni embedded into polyurethane matrix from experimental results. Due to the fact that using numerical methods is time consuming, a mathematical model on mode matching approach of rectangular rod in a waveguide and a new model of multimode capacitor were developed. Models were checked by numerical methods. On a high frequency, when electric field in the sample is inhomogeneous, the magnetic field in the sample is much stronger than in the transmission line. Thus, the magnetic permeability of the sample will affect scattering parameters. Based on this circumstance, the method to measure small magnetic permeability using capacitor like in coaxial line when dielectric permittivity is much higher (2-3 orders) than magnetic permeability was suggested. The modified open ended coaxial line method on multimode approach for finite dimensions samples was developed and checked by numerical methods. Lead-free ferroelectric ceramics with a perovskite structure based on (Na0.5Bi0.5)TiO3 and La(Mg0.5Ti0.5)O3 solid solutions were investigated using broadband dielectrics spectroscopy methods. The Meyer-Neldel rule for electric conductivity validation in investigated ceramics group was shown. |
