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MgTiO3 is a material often used in different types of high-frequency capacitors, temperature compensating capacitors, and chip capacitors, so the enhancement of this material is still the focus of many research groups due to its remarkable dielectric properties. Outstanding features can only be achieved when the ceramics are highly dense. Densification of magnesium titanate by Spark Plasma Sintering (SPS) was the aim of this work. Magnesium titanate ceramics were prepared by applying mechanical activation as the first step. Powders prepared in this way were SPS sintered, at 1200 °C with a heating rate of 100 °C/min. After reaching the desired temperature, a uniaxial pressure of 50 MPa was applied. The dwell time at this condition was 5 min, followed by cooling to room temperature at 5°C/min. X-ray diffraction was performed in order to establish the phase composition of milled powders and obtained ceramics. Differences between samples milled in various times intervals, as well as sintered ceramics were examined by means of scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The presence of MgTiz0s phase was detected in XRD and was confirmed by EDS analysis for the non-milled ceramics. In the samples obtained from milled powders, no MgTi2O5 was detected in XRD patterns, but this phase was detected in EDS spectra in a lower amount. Dielectric measurements were performed at a wide range of frequencies, while the hardness of the SPS samples was measured at loads up to 10 N. The highest value of the hardness was obtained from powder milled for 15 min before SPS.

Perovskite ceramic material based on MgTiO3 is used in various types of electronic devices owing to its dielectric properties, high dielectric constant, and low losses. These features can be tailored by setting preparation conditions. Densification of magnesium titanate by Spark Plasma Sintering (SPS) was the aim of this work. First, the mechanical activation in the highenergy ball mill was applied on the powder of MgO-TiO2 mixed in mole ratio 1:1. Prepared powder mixtures, activated for different times, were SPS sintered, at 1200 o C with a heating rate of 100o C/min. After reaching the desired temperature, a uniaxial pressure of 50 MPa was applied, and dwelled at this condition for 5 min, followed by cooling to room temperature at 5o C/min. The starting powders, activated mixtures, and sintered ceramics bodies were investigated by X-ray diffraction, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The presence of the MgTi2O5 phase was noticed for the nonmilled ceramics. In the samples obtained from milled powders, MgTi2O5 was detected in EDS spectra in a lower amount, below the threshold of the XRD method. Dielectric measurements were performed at a wide range of frequencies and temperatures. The highest value of the hardness was obtained from powder milled for 15 min before SPS. X Serbian Ceramic Society Conference - Advanced Ceramics and Application : new frontiers in multifunctional material science and processing : program and the book of abstracts; September 26-27, 2022; Belgrade

The objective of this thesis is to systematically analyze and optimize nonuniformly-wound helical antennas, along with classical (uniform) helical antennas. The optimization of the nonuniform helical antennas has many degrees of freedom. Hence, the optimization space is large and the optimization task is challenging. It is shown that, in most practical cases, the optimal nonuniform helical antennas outperform the uniform helical antennas presented in the literature. It is also shown that the nonuniform helical antennas are the preferable choice when the losses are low or medium, whereas for high losses, the uniform helical antennas should be used. A large database is assembled from the optimization results, wherefrom a complete design procedure is developed for the nonuniform helical antennas. This procedure comprises all necessary equations and graphs for evaluating the optimal antenna parameters and estimating the antenna characteristics. The design procedure is verified experimentally, by measurements of a fabricated prototype. Quad (2 x 2) arrays of nonuniform helical antennas are also investigated. Their design procedure includes the optimization of single antennas along with their positions in the array. The solution of a real engineering problem is presented: a quad array that meets predefined specifications is designed and a prototype is fabricated and measured. Циљ ове тезе је систематична анализа и оптимизација неуниформно мотаних хеликоидалних антена, као и класичних (униформних) хеликоидалних антена. Оптимизација неуниформних хеликоидалних антена има много степени слободе. Стога је оптимизациони простор велики, а оптимизација изазован задатак. Показано је да, у највећем броју практичних случајева, оптималне неуниформне хеликоидалне антене надмашују по перформансама униформне хеликоидалне антене представљене у литератури. Осим тога, показано је да су неуниформне хеликоидалне антене бољи избор када су губици мали или средњи, док би у случају великих губитака требало користити униформне хеликоидалне антене. Резултати оптимизације чине велику базу података, на основу које је развијен поступак пројектовања неуниформних хеликоидалних антена. Овај поступак обухвата све потребне једначине и графике за одређивање оптималних параметара антена и процену карактеристика антена. Поступак дизајна је потврђен експериментално, мерењем карактеристика реализованог прототипа. Такође су испитивани низови од 2 x 2 неуниформне хеликоидалне антене. Процедура за њихов дизајн садржи оптимизацију засебних антена, као и оптимизацију положаја антена у низу. Представљено је и решење реалног инжењерског проблема: дизајниран је низ од 2 x 2 антене који испуњава унапред дефинисане спецификације, а прототип је направљен и измерен.