Yurii Viktorovych Didenko

UHF methods of measuring the parameters of the microwave dielectric materials based on composite dielectric resonator

The article analyzes the microwave methods for measuring the material parameters, showing their advantages and disadvantages, discussed the criteria for selecting the measurement method. The authors proposed a modification of the method of the composite dielectric resonator. The proposed method has a high sensitivity in the measurement of dielectric constant and loss. References 4, figures 6, tables 1.

High hydrostatic pressure effect on functional properties of nanopowder La 0.6 Sr 0.3 Mn 1.1 O 3-δ compacts with various dispersion

Nanopowder La<inf>0.6</inf>Sr<inf>0.3</inf>Mn<inf>1.1</inf>O<inf>3−δ</inf> compacts by the oxide-salt, co-precipitation and atomization hydrolysis technologies have been obtained. Structure and its defects, average particle size and functional properties of the nanopowder compacts by X-ray diffraction, thermogravimetric, resistance, magnetic, ⁵⁵Mn NMR, magnetoresistance and BET methods have been investigated. Connections between the dispersion of nanopowders and their structural, magnetic, resistance, magnetoresistance and baroresistance properties have been established. Broad and asymmetric ⁵⁵Mn NMR spectra testify the high-frequency electron double exchange Mn³⁺↔O²⁻↔Mn⁴⁺ and indicate inhomogeneous environment of Mn by other ions and vacancies. The increase in high hydrostatic pressure up to 1.6 GPa leads to decrease in resistivity and activation energy as well as raise in density, coercive force, magnetoresistance and baroresistance effects of the nanopowder compacts.

Paraelectricity and paramagnetism in thermostable microwave dielectrics

High dielectric constant microwave dielectrics are basic materials for dielectric resonators, filters, microwave substrates, etc. These dielectrics can be improved through understanding of their polarization physical nature. High value of permittivity with small dielectric losses in frequency range of 1…100 GHz can be realized only due to quick-response mechanisms of polarization. In the report, firstly, main motive of increased polarizability in paraelectrics is explained. Secondly, it is determined that composition of microwave dielectrics should be based on “hard” paraelectrics, which structure resists to polar phases formation. Thirdly, we proved that addition of rare-earth paramagnetic ions supports high thermal stability.

Thin dielectric resonators in microwaves

With a purpose of microwave equipment frequency range enlargement, and in order to improve quality factor of frequency-selective devices, thin dielectric resonators (DR) are investigated. The principles of microwave filters and phase shifters designs, based on thin dielectric resonators, are presented. Some new constructions of such devices are elaborated. Results of theoretical and experimental studies of thin DRs are described.

Фільтри НВЧ на основі тонких діелектричних резонаторів

In this paper the principle of microwave filters design based on thin dielectric resonators is presented. Variants of construction of such filters are shown. The technique and the results of theoretical and experimental studies are described. Reference 5, figures 4.

Measuring of the microwave materials parameters on the base of the inhomogeneous microstrip resonator method

In this paper the method for measuring the dielectric constant and dielectric loss tangent of the dielec-tric material in the microwave range of wavelengths using the inhomogeneous microstrip resonator is pre-sented. The measurement technique and the design of the measuring cell are described, the theoretical basis of the method and results of experimental studies are given. Reference 9, figures 2, tables 1.In this paper the method for measuring the dielectric constant and dielectric loss tangent of the dielec-tric material in the microwave range of wavelengths using the inhomogeneous microstrip resonator is pre-sented. The measurement technique and the design of the measuring cell are described, the theoretical basis of the method and results of experimental studies are given. Reference 9, figures 2, tables 1.

Structure imperfection and dielectric properties of single-phase multifferoic Bi1-xLaxFeO3-δ

Using the rapid liquid sintering method the samples of multiferroic Bi_1-xLa_xFeO_3-δ (x = 0, 0.1, 0.3 and 0.5) were obtained. Their structure and dielectric properties were investigated. The X-ray diffraction, thermogravimetric, scanning electron microscopy and dielectric spectroscopy methods were used. The molar formulas of defective structure Bi_1-xLa_xFeO_3-δ were defined. An analysis of the frequency dependence of the relative permittivity ε(f) and dielectric loss tangent tanδ (f) at the low frequency (f = 1...10⁶ Hz) and microwave (f = 8...12 GHz) bands was conducted. It was established that the Bi_0.9La_0.1FeO₃ composition has the greatest value of dielectric permittivity.

Microwave dielectrics with unstable electronic spectrum

High dielectric constant microwave dielectrics are basic materials for dielectric resonators and filters, as well as for microwave substrates, dielectric waveguides, etc. These dielectrics are possible to improve only through the understanding of physical nature of their polarization. High value E without significant absorption electrical energy at the frequency range of 10…100 GHz can be realized only at the expense of quick-response mechanisms of polarization. The theoretical possibility to obtain thermal stable dielectrics with high εmw but at very low temperatures exists. One previously unknown possibility to combine high permittivity, low loss factor with thermal stability is discussed. It is based on fast-response electronic-phonon mechanism of polarization in dielectrics with the unstable electronic spectrum (like in the quasi one-dimensional crystals of TTF-TCNQ type).

Composites based on dielectric materials for microwave engineering

Composites provide possibilities to combine the properties of different materials in order to obtain materials with the necessary parameters (low loss, absorbing, reflective materials, etc.). According to their structure, composite materials are conventionally divided into the microtextures and macrotextures. In turn, these materials may be passive or active. The properties of passive composite materials are invariable, and the properties of active ones can be altered using different effects: electric, magnetic, thermal, etc. In this article we present the results of theoretical and experimental investigations of various microwave dielectric-based composite structures. Particular attention is given to high-Q microwave structures with electrical control.