Electrical tunability of terahertz nonlinearity in graphene

Graphene is conceivably the most nonlinear optoelectronic material we know. Its nonlinear optical coefficients in the terahertz frequency range surpass those of other materials by many orders of magnitude. Here, we show that the terahertz nonlinearity of graphene, both for ultrashort single-cycle and quasi-monochromatic multicycle input terahertz signals, can be efficiently controlled using electrical gating, with gating voltages as low as a few volts. For example, optimal electrical gating enhances the power conversion efficiency in terahertz third-harmonic generation in graphene by about two orders of magnitude. Our experimental results are in quantitative agreement with a physical model of the graphene nonlinearity, describing the time-dependent thermodynamic balance maintained within the electronic population of graphene during interaction with ultrafast electric fields. Our results can serve as a basis for straightforward and accurate design of devices and applications for efficient electronic signal processing in graphene at ultrahigh frequencies.

DEVELOPMENT OF A METHOD FOR DETERMINING THE MAXIMUM ACHIEVABLE GAIN (TRANSMISSION) KmS

Increasing the level of semiconductor devices, improving their characteristics significantly affects the potential stability in a wide range of frequencies. Classical methods and standard measuring equipment are not designed to measure the parameters of potentially unstable transistors. Measuring systems are excited uncontrollably, which increases the measurement error. Therefore, today there is an urgent task of measuring the parameters of both transistors in particular and quadrupoles in general, in the frequency range of potential instability. The clock frequency at which modern computer equipment works is close to the microwave range (ultrahigh frequencies), which makes the problem of measuring and calculating the various functional units of the computer quite relevant. The development of new methods and means of measuring the parameters of potentially unstable quadrupoles in the microwave range is an important scientific field that can significantly improve the accuracy of their measurement on standard equipment. The conducted researches and the developed technique allow to increase accuracy of measurement of parameters of four-poles and to provide stability of experimental installation at measurement of parameters of any four-pole. The proposed methods are more efficient and solve the problem of measuring the S-parameters of potentially unstable quadrupoles in the microwave range. The parameters of the quadrupole have the dimensions of the elements of standard W-parameters, their measurements are performed in the microwave range with an error of less than 5%, and to a lesser extent depends on the coefficient of stability of the measuring path than when measuring S-parameters. When measuring the parameters of the quadrupole, there is no need to use the modes of short circuit and XX or make measurements with a coordinated measuring path, which allows to increase the measurement accuracy and ensure stability when measuring potentially unstable quadrupoles with Ks> 0.

HYGIENIC ASSESSMENT FOR THE ELECTROMAGNETIC FIELD'S LEVELS OF ELECTRONIC INFORMATION AND EDUCATIONAL SCHOOLS' ENVIRONMENT

Results of the study on hygienic assessment of the electromagnetic field levels of the electronic information-educational schools’ environment showed that the intensity values of the electromagnetic field were within the limits of the permissible levels in conference rooms, in recreation, in canteens, in classrooms and in workplaces of computer and distance-learning rooms. The packages of system units, small servers, microwave ovens, monitors, televisions, laptops, sockets and extension cords were the main sources of electromagnetic radiation in modern comprehensive schools. The values of electromagnetic radiation of ultrahigh frequencies in the general education establishments were within the limits of the maximum permissible levels. We have been developed recommendations for the hygienic safety of the information-communication technology use and the equipment and furniture placement in computer classes of comprehensive schools.

Сравнение радиационной стойкости перспективных биполярных и гетеробиполярных транзисторов

Approaches to solving the problem of the development of efficient bipolar and heterobipolar transistors operating at radio- and ultrahigh frequencies (0.1–10 GHz), which could be used as active elements of modern Si-based and GaAs-based radiation-resistant analog-digital integrated circuits, are discussed. Comparison of the radiation resistance of prospective “lateral” Si-based bipolar and “vertical” AlGaAs/GaAs heterobipolar transistors with a characteristic base thickness of 70–350 nm is performed. The features of the electron transport in active transistor regions are analyzed in detail and the influence of a surge in the velocity and the diffusion of quasi-ballistic electrons on an increase in the radiation resistance of transistors is evaluated.

MODERN TECHNOLOGIES OF RECEIVING DIETARY FIBERS FROM SECONDARY PRODUCTS OF PROCESSING OF VEGETABLE RAW MATERIALS

Рассмотрены перспективы получения пищевых волокон (ПВ) из вторичных продуктов АПК. Приведены результаты анализа опубликованных исследований о перспективах получения ПВ, проявляющих детоксикационную и адсорбционную активность, с целью обогащения ими продуктов питания. Рассмотрены современные технологические решения получения ПВ из продуктов переработки сахарной свеклы и яблок. Признано целесообразным дальнейшее проведение научно-экспериментальных разработок новых технологий получения ПВ из растительного сырья с применением электромагнитного поля крайне низких и сверхвысоких частот. The prospects of obtaining dietary fibers (DF) from secondary products of agriculture are considered. Results of the analysis of sources on the prospects of receiving the DF showing detoxification and adsorption activity for the purpose of enrichment of food by them are given. Modern technology solutions of receiving DF from products of processing of sugar beet and apples are given. Further carrying out scientific and experimental developments of new technologies of receiving DF from vegetable raw materials with application of the electromagnetic field of extremely low and ultrahigh frequencies is perspective.

Calculation of radio engineering characteristics of the radome from the multicomponent material impregnated with water

Using for the solution of a problem of passing of a flat wave through a wall of an antenna radome electrodynamic model and representing wall material as multicomponent mix, assessment of influence of water on frequency radio engineering characteristics of the antenna radome system is carried out. Water, having at ultrahigh frequencies high dielectric permeability and big size of dielectric losses in comparison with radome wall material, considerably distorts the field of the falling wave at hit on a surface or in a radome wall body. As material of a wall of a radome the quartz ceramics with the time filled with air was considered. It is experimentally defined that water is in a material time in liquid state. Water was represented how the additional component which is evenly distributed on thickness in a time to quartz ceramics. The carried-out model calculations showed that introduction of water to material of a wall of a radome leads not only to reduction of level of coefficient of passing of an electromagnetic wave through a wall, but also to noticeable shifts on the frequency of radio engineering characteristics of the antenna-radome system.

Features of the Signal System of Automated Design of Frequency Converters Systems - Ultrahigh Frequencies

The article analyzes and outlines the modern principles of the theory of the signaling system of automated design with frequency transformations on a non-reciprocal electronic device - the transistor of ultrahigh frequencies. In addition, schematic variants of frequency converters on-field and bipolar transistors, Schottky diodes (varicaps) are considered; the signal theory of transistor and diode frequency converters is described: resistive and capacitive. Schematic performances of frequency converters represent variants of the signaling system of automated designing at ultrahigh frequencies.