RESONANT VAVILOV–CHERENKOV RADIATION IN DISPERSE METAMATERIALS
P. N. Melezhik, A. Ye. Poyedinchuk, N. P. Yashina, G. Granet
The present work suggests some investigation into the Vavilov–Cherenkov radiation coming from a beam of charged particles skimming the surface (generally periodic) of a dispersive medium. Depending on frequency, this medium can be right-handed (normal dielectric), mono-negative (either permittivity or permeability can be negative) or left-handed (both permittivity and permeability are negative). The obtained results are provided by rigorous mathematical models and corresponding effective computational algorithms. The present research is focused on qualitatively new resonant phenomena arising after micro- and macroperiodic structures are put together in the context of the given electromagnetic problem. Specifically, the micro- (and even nano-) periodic structure of a metamaterial will be combined with a macro-periodic diffraction grating whose period is comparable with the electron beam radiation wavelength.
CHAOS AND FREQUENCY TRANSFORMATION IN SYSTEMS OF COUPLED OSCILLATORS
V. A. Buts, D. M. Vavriv, D. V. Tarasov
Chaotic instabilities and frequency transformations caused by the interaction of oscillators are important effects for many applications. We review these effects from the point of view of their influence on the dynamics of practical electronic systems. It is demonstrated that the interaction of high-frequency (HF) and low-frequency (LF) oscillations can result in the development of chaotic oscillations even in the quasilinear limit creating a threat for the stability of many electronic devices. This result is illustrated by considering the destruction of both trains of pulses in a nonlinear RLC-circuit and a harmonic oscillation in a two-mode system. In its turn, the LF to HF transformations that occur in multi-mode systems can be used for the development of novel types of generators. We illustrate this approach by considering the dynamics of an ensemble of linear oscillators with controlled coupling. A possible practical realization of such generator by using an antenna array is proposed.
THE FOURIER TRANSFORM APPLICATION TO SEARCH FOR LOCALIZED MODES OF GRADIENT PLANAR WAVEGUIDES
V. M. Fitio, V. V. Romakh, Ya. V. Bobitski
Planar waveguides are important components in construction of various integrated optical devices. At present, science literature describes a number of analytical methods to calculate planar gradient waveguides, which, however, cover only certain types of those structures. In this study a numerical method of finding propagation constants and their corresponding field distributions of planar waveguide localized modes is developed. It is based on the Fourier transform of wave equation. The method is tested on many examples. The influence of numerical process parameters on the values of propagation constants is studied too. During the study numerical stability and high calculation accuracy are provided, confirming the efficiency of the method proposed. It is expected that the study results can be used for design of semiconductor lasers.
EXPERIMENTAL DETERMINATION OF MATERIAL PARAMETERS OF THE CHIRAL MEDIA IN THE MILLIMETER WAVELENGTH RANGE
S. Yu. Polevoy
Chiral structures can be successfully used for the simulation of the interaction of electromagnetic waves with various composite media (from isotropic to bianisotropic). Such structures can be quite promising for compact microwave devices design. However, in the millimeter wavelength range, which is one of the most important today from the practical point of view, the amount of experimental studies of chiral structures is insufficient. The paper presents methods of the experimental determination of the effective constitutive parameters of the chiral media in the millimeter wave range. The focus is on the experimental study of the polarization properties of chiral media. The frequency dependence of the polarization plane rotation angle of the electromagnetic wave transmitted through the investigated bulk chiral structure consisting of the array of two-dimensional chiral structures was analyzed. The frequency dependence of the chirality parameter for several values of its thickness was calculated. The possibility of controlling the angle of the polarization plane of the transmitted electromagnetic wave, and the chirality parameter by changing the thickness of the structure was demonstrated. The frequency dependence of the real part of the chirality parameter by two methods was determined experimentally. The comparison of the obtained characteristics has been carried out. The qualitative agreement between the results of both methods in the vicinity of the frequency of the maximum of the chirality parameter module has been obtained. Results can be used for design of various telecommunication devices: filters, polarizers, directional couplers.
THE INTERMODE SCATTERING AS A SOURCE OF QUANTUM CHAOS IN A MICROWAVE RESONATOR SUBJECTED TO SINGULAR PERTURBATION
E. M. Ganapolskii, Yu. V. Tarasov
The spectra of a microwave cylindrical resonator with the embedded thin metal rod playing the role of a singular perturbation are studied both theoretically and experimentally. The intra- and inter-mode scattering caused by the perturbation are clearly distinguished and recognized to play essentially different parts in the appearance of spectrum chaotic properties. Statistical analysis based on the mode-mixing operator norm shows that the singularity-induced inter-mode scattering results in the essential correlation of resonance frequencies. The results we have obtained in the experiment are in good conformity with our theory. Clear manifestations of quantum chaos are revealed for the resonator with the asymmetrically inserted rod, namely, the Wigner-type distribution of the inter-frequency intervals, the apparent correlation between spectral lines, and the characteristic curve of the spectral rigidity. By comparing the theory and the experiment we succeeded in establishing unequivocally and for the first time that it is just the inter-mode scattering that gives rise to quantum chaos in the spectrum of wave-billiard systems subject to singular perturbation.
FOCUSING OF ELECTOMAGNETIC FIELD OF THE ELEMENTARY ELECTRICAL DIPOLE BY THE INTERFACE BETWEEN ORDINARY AND LEFT-HANDED MEDIA
V. K. Ivanov, O. O. Silin, O. M. Stadnyk
The problem of focusing of wave fields of different physical nature and frequency bands is relevant both for scientific experiments and practical applications in industry, medicine and technology. Unique opportunities for the development of devices focusing electromagnetic fields, which are associated with the emergence of metamaterials (left-handed media), can not be fully realized in the framework of the geometrical optics approach used in most studies, the main advantage of wich is the visibility. Since this approach does not allow an evaluation of the effect of losses, location, orientation and type of the source on the structure of the radiated field, there is a need for a consistent electrodynamic solution to model problems. In the paper the problem of radiation from infinitesimal electric dipole located horizontally above the plane interface between passive and normal left media is strictly solved from the first principles and numerically simulated. It is shown that the electromagnetic field of the dipole, penetrating into the metamaterial half-space, is focused into spatial distribution of the field with a pronounced maximum and complex interference structure. The dependence of the focusing on the position and orientation of the dipole, as well as losses in metamaterials were studied. A hypothesis that the focusing ability is the property of the interface between ordinary and left-handed media, but not of each of them separately is set forth and qualitative arguments are given.
HEMISPHERICAL AND ASPHERIC WGM DIELECTRIC RESONATORS WITH CONDUCTING ENDPLATES: RADIATION AND CONDUCTIVITY LOSSES DEPENDING ON SHAPE OF THE RESONATORS SURFACE
A. A. Barannik, N. T. Cherpak, M. S. Kharchenko, S. A. Vitusevich
The measurement technique based on whispering gallery mode (WGM) dielectric resonators for surface microwave impedance characterization of high-Tc superconducting films is very accurate. However its sensitivity is limited by the radiation loss of these open electrodynamic systems and depends on effectiveness of interaction of microwave fields and the film (coefficient As). The aim of the work is to study the radiation and conductivity losses in WGM resonators of different shape of the body of rotation. In this work, electromagnetic properties of a number of WGM resonators with conducting endplates are studied. Losses are studied in Ka-band for two kinds of dielectric material, namely, isotropic (Teflon) and anisotropic (single-crystal sapphire). For the Teflon hemispherical resonator, the analytical approach is used and its results are compared with the results of experimental measurements. The resonators of other shapes are studied experimentally. Experiments show that aspheric sapphire resonator has maximum coefficient As. however the radiation Q-factor is larger in the hybrid sapphire resonator (aspheric+cylindrical disk). Thus, the hybrid resonator with As 25 % greater than As of the hemispherical resonator with approximately the same radiation loss is a better option for the (super)conductor measurement purpose in microwave range.
MIXED STATE IN A COMBINED ANNULAR BILLIARD
Yu. L. Bolotin, I. Yu. Vakulchik, K. A. Lukin, V. A. Cherkaskiy
Annular billiards are among the most popular models for studying of fundamental properties of quantum and wave chaos in the modern quantum mechanics and microwave electrodynamics, respectively. In the present paper we propose the model suitable for both the areas mentioned above, namely: the compound billiards composed of two annular billiards (the chaotic and the regular ones) connected via a narrow crosspiece (narrow waveguide). By means of numerical methods some distributions of particle energy levels (resonant frequencies) and corresponding spatial distributions of wave function squared (a square of electric field component) are investigated. Chaotization of particle motion in regular billiards has been shown in case of weak influence of almost isolated chaotic annular billiard. Existence of the mixed regular-chaotic states in the investigated billiards has been shown and their possible application in chaos generators is specified.
ORBICTRON-OSCILLATOR: DESCRIPTION OF A MODEL AND COMPUTATIONAL RESULTS OBTAINED IN THE 180 GHz RANGE
V. D. Yeryomka, A. A. Kurayev, A. K. Sinitsyn
At present submm wave sources are in great demand when many engineering issues have to be tackled. Specifically these are: luggage scanning, photography of tumors, radars and coupling between large-size high-speed computers. These sources are bound to generate an output power of 1 to 50 W when using environmentally safe low-voltage electron flows. Among the electromagnetic radiation mm-wave sources the modification of an orotron is an obvious candidate for generating submm-waves. In this oscillator modification the binary comb is used instead of a plane periodical reflecting structure to ensure the wave slowing-down. This type of modification was referred to as an orbictron (open resonator, binary comb, electron). The critical factors that result in diminishing its efficiency, as the operating frequency increases, are sheet electron flow layering (lamination) effect and clipping of the HF-field amplitude in a rectangular channel in which there occurs interaction of electrons and electromagnetic waves. These factors are due to the usage of the open resonator with marginally high load Q. A resonance effect in the binary comb of the orbictron has been detected. It showed that the HF-field amplitude in the electron-wave interaction space surpassed the field amplitude many times over across the space between the operating surfaces of open resonator mirrors. This effect is apt to change radically the estimation of the required Q value of the orbictrons resonance system and eliminates the amplitude clipping problem. Using the channel for the sheet electron flow in the interaction space as the form of the binary comb’s operating tapered-shaped surfaces (klynoorbictron) yields sheet electron flow lamination (layering). The mathematical model that we have devised was applied to carry out an optimization search for promising variants of the orbictron-oscillator design in the 180 GHz range, with a 3.5 kV operating voltage of the electron flow and 0.1 F operating current. We have found the oscillator variants with 10 to 12 % efficiency at quality factors of that do not exceed 1 000. It is shown that the efficiency tends to increase up to 14 % owing to the use in the orbictron-oscillator of klynotron effect (klynoorbictron), whereas the resonator Q-factor shows a three-fold decrease. The obtained results indicate that the orbictron and its modified designs of klynoorbictron hold a great promise as THz-range electromagnetic radiation sources.
DEVELOPMENT OF COMPACT MEDIUM POWER SOURCES OF ELECTROMAGNETIC RADIATION OF MILLIMETER AND SUBMILLIMETER RANGES
A.N. Kuleshov
Compact sources of electromagnetic radiation of both short part of millimeter and sub-millimeter ranges are widely used in spectroscopy. Most powerful devices in these regions are VEDs and the problems of further increase of both VED output power and frequency as well as frequency tuning in wide range are actual. Research results dedicated to the development of compact clinotrons in sub-millimeter range and also simulation results on clinotron output power increase considering the interaction of intense electron beam with hybrid space-surface modes of inhomogeneous SWS have been presented. The second part of the paper is dedicated to research results of low-voltage CRM. Also the research results on the generation of ribbon helical electron beam for planar CRM, which is capable to frequency tuning in wide range by changing the distance between the resonators mirrors such as in diffraction radiation oscillator, are presented.
DEVELOPMENT AND EXPERIMENTAL INVESTIGATIONS OF HIGH POWER PULSED THZ GYROTRONS
M. Glyavin, A. Luchinin, M. Morozkin
The terahertz radiation looks promising for pointer plasma discharge, remote detection of concealed radioactive materials, plasma diagnostics based on collective Thompson scattering, enhancement of spectroscopy methods, new medical technology and so on. The aim of our investigations is development of powerful and relatively compact microwave sources. Powerful THz generation has been demonstrated in pulse gyrotrons. Pulsed coils with field intensity up to 50 T have been developed and tested. This field gives a chance to operate at fundamental cyclotron resonance conditions between electron beam and operating mode and, as result to simplify problem of mode selection. The output power 5 kW at 1 THz and 0.5 kW at 1.3 THz has been obtained with pulse duration 40 µs at the fundamental harmonic with 30 kV/5A electron beam. The power 200 kW at the frequency 0.67 THz has been realized with efficiency about 20 %. Despite the requirement of strong operating magnetic fields, the THz frequency has been achieved by the pulse gyrotrons operating at the fundamental harmonic. Today it is clear that relatively small-size tubes with a high level of output power (from a hundred to several kilowatts) at the frequencies of 0.3–1.5 THz will be available soon for many applications.
B. E. Bekirov, I. V. Ivanchenko, A. A. Lukhanin, N. A. Popenko
The gapless semimagnetic semiconductors with the resonant donor level and mixed-valence are of fundamental and applied interest. The high mobility of the band electrons in them allows one to use almost the entire arsenal of modern methods and means of studying the physical properties of solids. One of the effective methods of studying the magnetoresonance properties of this class of semiconductors is the method of electron paramagnetic resonance. However, due to the high conductivity of semiconductors like those, the requirements applied to the sensitivity of suitable spectrometers are increased. This is largely determined by the electromagnetic properties of the resonance cell that is used there. The problem is exacerbated when carrying out the investigations in the short-wave part of the millimeter range, where the skin depth is a few microns only. The modification of the functional units of the electron paramagnetic resonance spectrometer with the aim to enlarge the operating temperature range has been realized. Furthermore, the original resonant cell as a two-mirror open resonator for the registration of absorption spectra of various substances in the short-wave part of the millimeter range within the temperature limits Т = 1.7…300 K is proposed. The electron paramagnetic resonance spectra for the gapless semimagnetic semiconductor HgSe:Fe measured at a frequency of 123 GHz are shown. These spectra illustrate the benefits of the proposed resonant cell used in the spectrometer while studying high-frequency magnetoresonance properties of substances with high conductivity.
R. V. Golovashchenko, V. N. Derkach, M. K. Zaetz, V. G. Korzh, A. S. Plevako, S. I. Tarapov
The problem of accurate temperature stabilization and its accurate measurement arises during the design of low-temperature radiospectrometers for measurement of dielectric parameters of materials in the millimeter waveband and for wide temperature range. Thermometers for measurement of low and ultralow temperatures are usually based on the temperature dependence of special properties of intrinsic material. Electric resistance thermometers are most widespread for design of the schemes for measurement and stabilization of temperature under the abovementioned conditions. The temperature controller-stabilizer – the precision automated block for measurement and stabilization of temperature of the disk dielectric resonator, is designed for the operation in the 0.8 K¸300 K temperature range. The block is designed for cryodielectrometer of gigahertz band. The four-wire scheme with alternative current is applied. The specialized resistive sensors with different sign of temperature coefficient of resistance were tested. The accuracy of resistance detection about 0.05 % is achieved. The accuracy of stabilization of temperature is higher than ±0.01 K. Results of test experiments devoted to measurement of the material parameters of low loss dielectrics at low temperatures are presented.