Volume 62, Nº 10 (2017)
- Ano: 2017
- Artigos: 15
- URL: https://journals.rcsi.science/1064-2269/issue/view/12421
Electrodynamics and Wave Propagation
Electrodynamic acceleration of thin plates at high current densities
Resumo
Processes accompanying the electrodynamic acceleration of a thin plate liner at a high accelerating current density are investigated. In addition to determining the electrical characteristics, shadow filming of the plate profile was carried out during the acceleration and the deformation of the profile in the region of fixed attachment to the current leads was monitored. A new experimentally reproducible effect in which the plate splits into three separate fragments, which is explained by nonuniform overheating by the current of the plate’s cross section and the electrodynamics of the process, was found. It was detected that, on the acceleration of copper liners, the current sheath is separated from the metal body of the liner and diverges in two directions. The nature of this phenomenon has not yet been determined.
Scattering of the electromagnetic wave by a layer with one-dimensional rectangular irregularities
Resumo
Multiple scattering of a plane electromagnetic wave by a layer with random one-dimensional rectangular irregularities of the permittivity is studied. The dependence of the mean scattered intensity on the parameters of the irregularities is obtained. It is established that the mean intensity of the field oscillates as a function of the mean width of irregularities. The conditions for a substantial increases or decrease in the mean intensity of the wave in the layer are determined.
On focusing of a converging spherical wave traveling through the boundary of a material medium
Resumo
It is revealed in the ray approximation that focusing of a converging spherical wave traveling through the boundary of a material medium can be retained if a lens-like pad is used on the medium boundary. Conditions imposed on the parameters of such a pad are presented. Dimensions of the volumetric spot in the region of the wave focusing point are estimated with consideration for the Fraunhofer diffraction at the edge of a round pad.
Antenna and Feeder Systems
A method for the amplitude–phase synthesis of antenna array based on control of the set of nonidentical partial beams
Resumo
An iterative method for the amplitude–phase synthesis of antenna arrays based on control of the set of partial beams is proposed. In this method, two additional partial beams are added to the radiation pattern at each step. The shape of each beam is optimized with consideration for the difference between the synthesized and specified radiation patterns. Parameters specifying the shape of additional partial beams are chosen with the help of the genetic algorithm. The results of numerical studies allowing comparison of the proposed synthesis method to the least-squares method and the method based on control of the set of identical partial beams are presented.
Theory and Methods of Signal Processing
Navigational GBOC signals and their energy spectra
Resumo
The modulation functions (MFs) of generalized binary offset carrier (GBOC) signals of promising satellite radio-navigation systems, such as Galileo (European Union), global positioning system (GPS) (USA), and BeiDou/Compass (China), is estimated. Analytical expressions for the spectral density and energy spectrum of the single component of the GBOC-signal MF are obtained at different pulse multiplicity coefficients NRSO of rectangular subcarrier oscillations and different duty cycles ρ. The spectra characterizing the important particular cases, namely, binary offset carrier and binary phase-shift keying signals are analyzed by means of the derived general formulas for GBOC signals. The Mathcad software package is used to construct graphs and discuss the properties of the energy spectra of single components entering into the GBOC-signal MF for the following types of modulation: GBOC(1, 1, ρ), GBOC(2, 2, ρ), and GBOC(10, 5, ρ).
PAPR effect remedy in OFDM-based wireless systems
Resumo
An enhancement proposition for a Terrestrial Digital Video Broadcasting (DVB-T) systems is discussed in this work. DVB-T physical layer uses a powerful technique namely Orthogonal Frequency Division Multiplexing (OFDM) technique, which has been used to combat the channel’s effect. However, it has a major drawback that degrades its efficiency; namely Peak-to-Average Power Ratio (PAPR). Two criteria have been used for this purpose; BER curves and CCDF curves in order to distinguish the powerfulness of those propositions in reducing the PAPR effect. In fact, a powerful special averaging technique results are compared to previously published propositions, namely based on wavelet transformations and the one that is based on the pulse width modulation. A mathematical model has been drawn in order to check both of the CCDF and the BER curves, and simulated at same channel limitations and specifications. The proposition gives extra 35% noise immunity over our previously published work that is based on entropy wavelet, and an enhancement of over 25% from the CCDF point of view in combatting the PAPR. Furthermore, a complexity reduction has been attained by decreasing the side information transmission in compared with the work in the literature.
Evaluation of energy efficiency of fifth generation mobile systems
Resumo
There has been active research worldwide to develop the next generation, i.e., fifth generation, wireless network. Next generation mobile communication networks are broadening their spectrum to higher frequency bands (above 6 GHz) to support a high data rate up to multigigabits per second. This work examines how to substantially improve energy efficiency for next fifth generation mobile communication systems. It is depicted how by limited exchange of information between neighboring base stations it is possible to maintain quality of service, over a range of traffic loads, while enabling inactive base stations to sleep. Performance of distributed energy efficient topology management schemes are compared against the system without topology management. Performance evaluation is examined using both analytical and simulation based models. Extensive numerical results show that the schemes deliver a significant energy reduction in energy consumption in the mobile network systems.
Dynamics Chaos in Radiophysics and Electronics
Complicated dynamic regimes in phase-controlled self-excited oscillation system
Resumo
Dynamic states and bifurcations in the phase-locked-loop (PLL) system with modified characteristic of phase discriminator and second-order low-pass filter in the control system are studied. The analysis is based on the dynamic model of a system with one and a half degrees of freedom in a cylindrical phase space. Complicated quasi-synchronous and asynchronous regimes are demonstrated for such a multistable system. The regimes are not possible for a conventional PLL system with sine-shaped characteristic of the discriminator.
Radio Phenomena in Solids and Plasma
Theory of acoustooptical filtration of light beams in the inhomogeneous acoustic field
Resumo
The theory of acoustooptical (AO) interaction between light beams in the longitudinally inhomogeneous acoustic field is constructed with allowance for conditions typical of AO filtration. In the case of smooth acoustic inhomogeneities, analytical expressions for the spatially spectral characteristic relating the spatial spectra of incident and diffracted light beams are derived. The situation where a Gaussian light beam undergoes filtration in the acoustic field excited by a rectangular transducer is discussed in detail. The narrowband quasi-collinear AO filter based on a paratellurite crystal is simulated. It is demonstrated that the maximum diffraction efficiency and transmission-function shape distortion (with respect to the plane-wave model) of the given device depend to the greatest extent on the misalignment between the directions of the group velocities of interacting light beams.
Microwave Electronics
Magnetically shielded electron–optical system of a continuous gyrotron with an operating frequency of 24 GHz
Resumo
It is shown that it is possible to use warm solenoids with copper winding screened with ferromagnetic shields in order to reduce the solenoid supply power by a factor of 1.8–2 while retaining the strength of the magnetic field in the working space for continuous gyrotrons operating in a frequency range of 24–30 GHz. The configuration of the shields as well as the shape and location of the correcting solenoids providing an extended (up to 10 wavelengths long) section of a uniform field in the region of the gyrotron cavity have been determined. It has been shown that introduction of an additional cathode coil into the magnetic system reduces the degree of nonadiabaticity of the magnetic field approximately by an order of magnitude and thereby makes it possible to use the magnetron injection gun for formation of a helical electron beam. Optimization of the configuration of the gun electrodes based on the trajectory analysis makes it possible to obtain an electron beam whose parameters are as good as parameters of the electron beams formed in classical adiabatic electron–optical systems of gyrotrons.
Nanoelectronics
Effect of the radius on the resonance properties of carbon nanotube dipole antennas
Resumo
The resonance characteristics of dipole antennas based on armchair carbon nanotube are numerically investigated. The analysis takes into account the interaction of electrons with acoustic phonons which leads to the dependence of the electron relaxation time on the radius of the nanotube. The input impedance of the nanoantena as a function of the frequency of an incident electromagnetic field in the GHz range is obtained by the numerical solution of the Hallén’s integral equation. The dynamic quantum mechanical conductivity of armchair carbon nanotubes is used including the explicit dependence of the relaxation frequency on the radius. In this way, it is adequately described the resonant activity of the nanoantenna depending on the radius and length of the carbon nanotube. Current distributions are presented.
Specific features of the formation of oblique texture in aluminum nitride films
Resumo
Aluminum nitride films with oblique orientation of the texture axis are produced. Modifications of crystal structure depending on the deposition rate are studied. Two effects of the film growth related to the relation of the deposition rate and surface mobility of substance are analyzed.
Novel Radio Systems and Elements
Millimiter-wave stripline bandpass filters
Resumo
The possibility to use thin (1 mm or less) pseudocombline structures of λ/2 resonators made of sections of symmetric transmission strip lines from a dielectric material with εr = 2.2 as millimeter-wave bandpass filters is shown. It is established that the relative bandwidth of such filters can reach FBW = 0.1. Designs of stripline pseudocombline filters with alternating signs of the coupling coefficients, which are characterized by improved selectivity due to the attenuation poles located on both sides of the passband, are proposed; the filters contain stepped-impedance “half-wave” resonators with a new feature. The results of the computer simulation of the frequency characteristics of the filters in the frequency band of 31–122 GHz and the comparison of them with the characteristics of other filters are presented.
Configurable structured array for fabrication of radiation-hardened analog interfaces
Resumo
The design of a new configurable structured array (CSA) is considered. The CSA is intended for development of multichannel (up to eight channels) integrated circuits of the analog interfaces of sensors. An example of operational amplifier is used to show that circuit synthesis with allowance for radiation-induced variations in characteristics of complementary bipolar transistors may provide minor degradation of parameters of the analog ICs after ionizing irradiation. Electrical schemes of the CSA analog components and experimentally measured parameters are presented.