Effect of Ti on the Structure and Mechanical Properties of TixZr2.5-xTa Alloys

To determine the effects of Ti and mixing entropy (ΔSmix) on the structure and mechanical proper-ties of Zr-Ta alloys and then find a new potential energetic structural material with good me-chanical properties and more reactive elements, TixZr2.5−xTa (x = 0, 0.5, 1.0, 1.5, 2.0) alloys were investigated. The XRD experimental results showed that the phase transformation of TixZr2.5−xTa nonequal-ratio ternary alloys depended not on the value of ΔSmix, but on the amount of Ti atoms. With the addition of Ti, the content of the HCP phase decreased gradually. SEM analyses revealed that dendrite morphology and component segregation increasingly developed and then weakened gradually. When x increases to 2.0, TixZr2.5−xTa with the best mechanical properties can be ob-tained. The yield strength, compressive strength and fracture strain of Ti2.0Zr0.5Ta reached 883 MPa, 1568 MPa and 34.58%, respectively. The dependence of the phase transformation and me-chanical properties confirms that improving the properties of Zr-Ta alloys by doping Ti is feasible.

BEHAVIOR OF LED LIGHT SOURCES IN PULSE POWER

The researches results of the energy and dynamic characteristics for FYL-3014 and ARPL-1W LEDs with different spectral radiation when voltage rectangular pulses feds to LEDs are presented in the paper. On the basis of obtained oscilograms it is established that electrical circuits of pulsed supply of the LEDs contain hidden reactive elements of inductive and capacitive nature. The substitution schemes are proposed for these circuits and their parameters have been determined. In substitution schemes that are proposed for these circuits the LED is represented by a parallel RC link, the active component of which is determined by the heterojunction's active region resistance, and the reactive one by a capacity that is equal diffuse capacity of transition. On the basis of analysis of obtained transient processes equations for these circles it established the attenuation coefficient's dependence on the resistance of the heterojunction's active region. The influence of pulse frequency on the LEDs energy efficiency has been investigated. It is established that the maximum pulse frequency of the FYL-3014 and ARPL-1W LEDs is equal 700 kHz. References 12, figures 6.

Low-loss bidirectional buck-boost DC-DC converter

For DC energy systems there is reversible buck/boost pulse converter (RPC) in the classic converter circuit. The maximum efficiency of the RPC without additional mechanisms to reduce the dynamic energy losses in the power semiconductor keys (PSK) during their commutation is about 92%. Improved efficiency is achieved by providing «soft switching» of the transistors RPC, i.e. in zero current/voltage switching. These methods require the introduction of supporting links in the RPC, which have a negative impact on the performance of reversible buck/boost pulse converter. Due to the increase in the number of components, this leads to degradation of mass-size characteristics of the product and decrease in its reliability. New RPC transistors control algorithm RPC provides an opportunity to use transistors at zero voltage without additional elements. Because of the relative novelty of this technical solution, the energy exchange processes in the reactive elements of power semiconductor devices (PSD) are poorly studied. By reason of insufficient studying of power exchange processes in reactive elements of converter, it seems important to study these processes and use the received results for recommendations about reversible buck/boost pulse converter designing. As a result of research it was found out that the recuperation of energy stored in parasitic capacitance of drain-source transistors acting as PSD. At designing of RPC the account of the revealed phenomenon of energy, recovery will allow additionally to raise its efficiency at the expense of decrease in losses of energy on PSK in shutdown state. For this purpose, it is necessary to use transistors with high value of parasitic capacitance of drain-source or include additional capacitors in parallel with PSK.

Extension of Antenna Matching Frequency Band Using Reactive Elements

Системно рассмотрены традиционные подходы к расширению частотных полос согласования антенн с помощью реактивных цепей. Обсуждены критерии эффективности и особенности синтеза согласующих контуров. Проанализирована оценка предельного расширения частотной полосы пассивного согласования антенн контурами на реактивных элементах. Независимо от сложности и количества согласующих контуров получаемая полоса пассивного согласования ограничивается некоторой областью, размер которой обратно пропорционален добротности согласуемой антенны. Показано, что несколько расширить ее для высокодобротных антенн можно с помощью введения резистивных элементов в дополнительные одноконтурные согласующие модули.Рассмотрен синтез активно настраиваемых тюнеров на реактивных элементах для согласования широкополосных радиотерминалов, и выполнен анализ процессов автоматического регулирования в нем. Показано, что их структурная сложность и эффективность работы тоже зависят от добротности антенн.Приведена методика синтеза согласующей цепи для пассивного узкополосного согласования на нескольких частотах для многодиапазонных антенн. Сначала выбирается основная структура согласующей цепи, и для требуемых частот находятся ее реактивные сопротивления и реактивные проводимости. Далее наборы этих реактивных сопротивлений и проводимостей реализуются через синтез реактивных структур в виде первой и второй форм Фостера.Выполнено моделирование влияния выбора структуры согласующего устройства на расширение частотной полосы согласования высокодобротных антенн. При синтезе многоконтурных согласующих структур методом пробного моделирования небольшие преимущества получены у структур с параллельным соединением последовательных контуров.