 Subjects -> ELECTRONICS (Total: 207 journals)
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- Multi-Barrel Gyrotron for DNP/NMR Spectroscopy
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Abstract: We consider an example of implementation of a multi-barrel gyrotron. The simplest scheme of the multi-barrel gyrotron combines the advantages of both the canonical gyrotron and the gyrotron with the near-axis beam as the system of formation of helical electron beams and efficient selection of modes synchronous with high gyrofrequency harmonics, respectively, and is attractive from the viewpoint of applications that require moderate power levels. The design of a multi-barrel gyrotron with the possibility of simultaneous generation at frequencies of 263, 395, and 526 GHz is presented. Additionally, the possibility of generating the radiation at a frequency of 594 GHz is considered. Such frequencies are required for DNP/NMR facilities with proton Larmor frequencies of 400, 600, 800, and 900 MHz, respectively. Along with the conventional scheme of radiation output towards the collector, the features of the scheme with the radiation output toward the electron gun are considered.
PubDate: 2023-10-16
- Correction to: Pulses of the Electromagnetic Field with a Non-Zero
Electric Area-
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PubDate: 2023-10-10
- On the Problem of Inhomogeneous Spatial Distribution of the Redox Index of
Polyvalent Iron Ions in the Volume of Ultrapure Synthetic Quartz Materials
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Abstract: We show that the strong spatial inhomogeneity of absorption (the change from the maximum to the minimum value was more than 50 times on a spatial scale of the order of 200–300 μm), which was observed in our earlier studies of ultrapure synthetic quartz glasses and a synthetic quartz crystal at a wavelength of 1070 nm, can be related to an inhomogeneous spatial distribution of the redox state of iron traces. Using experimental data on absorption of metal impurities in the studied glasses, we present a calculation of the iron ion concentration, which is of the order of a few ppb. This is several times better than the limit of detection of the mass spectrometry method used for certification of ultrapure quartz glasses. Based on the results of the mass spectrometry measurements of concentrations given by manufacturers and the values of the maximum (10−5 cm−1) and minimum (10−7 cm−1) absorption coefficient we have measured, we calculated the maximum possible concentrations of the Fe2+ and Cu2+ ions and OH groups in quartz glasses and hydrothermal synthetic crystalline quartz.
PubDate: 2023-10-10
- Observation of Excitation of Eigenmodes in Surface-Wave Resonators Having
the Cylindrical Geometry-
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Abstract: We present the results of theoretical and experimental studies of the surface-wave Ka-band resonators which are formed by sections of cylindrical waveguides with single-period wall corrugations. The electrodynamic characteristics of such resonance cavities are analyzed within the quasioptical approach and three-dimensional simulation by the finite-difference time-domain method. The results of the theoretical analysis agree quite well with the experimentally measured frequency dependences of the reflection coefficients, which demonstrate the existence of surface modes with different numbers of longitudinal field variations. The measured Q-factors and frequencies of the above-specified modes corresponded well to the calculated values. In order to perform “cold” electrodynamic tests, wideband waveguide converters of the TE mode of the standard rectangular waveguide to the TM mode of an oversized cylindrical waveguide, which have a sufficiently low level of ohmic loss at a conversion efficiency exceeding 95% in the 34–40 GHz frequency range, were manufactured by the the 3D printing method.
PubDate: 2023-10-10
- Bifurcations and Chaos in Open Quantum Systems
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Abstract: A study of open quantum systems and dynamical regimes that emerge in such systems is an actively developing field of the theoretical and experimental physics. Although the bifurcation analysis and the theory of dynamical chaos are very important branches of nonlinear dynamics, their use for describing the processes occurring in open dissipative quantum systems has been restricted until recently. In this work, we present a review of recent results on the generalization of the methods of the oscillation theory for such systems. We present quantum analogs of the classical bifurcations, which are observed in the structural changes of the asymptotic density matrix, namely, the pitchfork bifurcation, saddle-node bifurcation, transition to quantum chaos via a period-doubling cascade, and the Neimark–Sacker bifurcation. We also consider numerical characteristics of dissipative quantum chaos. The largest quantum Lyapunov exponent, which is based on analyzing the divergence rate of the initially close quantum trajectories, allows one to numerically study the structure of the regular and chaotic domains of various open quantum systems. Numerical characteristics of dissipative quantum chaos, which can be observed in a physical experiment, are also considered. It is shown that the qualitatively different statistics of the distribution of times between the successive emissions of individual photons by the system take place for the regular and chaotic regimes in an open quantum cavity.
PubDate: 2023-10-10
- Coulomb and Quantum Interference Effects in the Spectra of High-Order
Harmonics Generated by Aligned Molecules-
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Abstract: We study theoretically the features of the spectra of high-order harmonics of laser radiation generated in an ensemble of aligned diatomic molecules outside the framework of the strong-field approximation. The studies were carried out on the basis of numerical calculations within the framework of a model given by a two-center generalization of the Yukawa potential. Influence of the interference of contributions from different electron trajectories and the ion core potential on the accuracy of extracting spectroscopic information about the state of the nuclear subsystem of a molecule using high temporal resolution nonlinear spectroscopy based on the analysis of multicenter effects in the spectra of high-order harmonics has been explored.
PubDate: 2023-10-10
- Excitation of Electromagnetic Oscillations of a Dielectric Ball by a
Complex Oscillation of a Radial Dipole-
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Abstract: We consider excitation of electromagnetic oscillations of a homogeneous dielectric ball by a radial dipole, oscillations forming a periodic sequence of radio pulses. It is shown that at high frequencies the field distribution is close to the field distribution of the eigenoscillations corresponding to these frequencies, whereas the neighboring harmonics also have an impact at low frequencies. It is also shown that an action at low frequencies characterized by a low Q-factor is needed for exciting short radio pulses in the resonator.
PubDate: 2023-10-10
- Čerenkov Radiation of an Ultrashort Laser Pulse Propagating in a Strongly
Magnetized Plasma at Various Intensities and Directions of the Magnetic
Field-
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Abstract: We study generation of Čerenkov radiation by an ultrashort laser pulse propagating in the magnetized plasma across an external magnetic field basing on the analysis of the dispersion relation and numerical simulation in the case where the cyclotron frequency exceeds the plasma frequency. It is shown that the radiation with a frequency in the range from the plasma frequency to the cyclotron one and with an angle between the wavevector and propagation direction below 45° can escape the plasma. The radiation power increases with the magnetic field before reaching the maximum at the cyclotron frequency being of the order of the inverse of the laser pulse duration and starts decreasing afterwards. It is also observed that, with an increase in the field, the pattern of the radiation escaping from the plasma narrows, the generated pulse is shortened, and the pulse spectrum widens.
PubDate: 2023-09-28
- Adaptive Processing of a Set of Signals in Antenna Arrays with Extended
Reception Band-
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Abstract: We propose a method of multisignal adaptive spatial filtering, which generalizes the classical method of adaptive spatial filtering of a single signal with a known arrival direction. Additionally, the formulas for the modified Capon direction-finding method are found. Reliability of the relationships, which are obtained on the basis of the maximum-likelihood method, is confirmed by the limiting transitions and the results of numerical simulation for typical signal-reception conditions in radio-monitoring and passive radar systems.
PubDate: 2023-09-28
- Absorption of a Narrow-Band Signal in a Dispersive Medium
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Abstract: We consider propagation and absorption of a narrow-band signal in a homogeneous dispersive medium. It is shown that all signals can be divided into two qualitatively different classes, namely, holonomic and piecewise-holonomic signals. When propagating in an absorbing medium, the holonomic signals are attenuated obeying an exponential law and, therefore, almost disappear at a sufficient long path lengths. The piecewise-holonomic signals are attenuated significantly slower (obeying a hyperbolic law) and, therefore, continue to exist even at substantially longer paths.
PubDate: 2023-09-28
- Experimental Study of Terahertz Radiation Generation in the Interaction of
Ultrashort Laser Pulse with Gas Targets-
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Abstract: We present the first experimental results obtained with a setup created on the basis of the PEARL laser facility for studying the processes of generating terahertz radiation from laser wake fields which are formed during the propagation of a high-power femtosecond laser pulse in a rarefied plasma. In particular, the occurrence of terahertz generation in the case where the laser–plasma interaction region is located between a pair of dielectric prisms of total internal reflection is demonstrated. The dependence of the terahertz radiation energy on the energy of a femtosecond laser pulse and on the plasma density is studied.
PubDate: 2023-09-28
- Two Methods of Target Detection in an Automotive Radar Against the
Background of its Own Noise-
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Abstract: We consider the problem of simultaneous detection of close and distant targets in an automotive millimeter-wave radar. Two approaches for solving the problem are proposed. The first approach is based on the subtraction of more powerful signals in the time domain and the subsequent detection of less powerful signals. The second approach is based on the most plausible estimate of the impulse response of the radar channel. The methods have different computational complexity. Numerical simulation of the proposed methods for processing of signals reflected from targets in terms of the false-alarm and missed-detection probabilities has been carried out. Simulations have shown that both close and distant targets can correctly be detected simultaneously with a low predetermined false-alarm probability.
PubDate: 2023-09-28
- Pulses of the Electromagnetic Field with a Non-Zero Electric Area
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Abstract: We analyze the possibility of existence of electromagnetic-field pulses with a non-zero electric area (time integral of the electric field) within the framework of the Maxwell equations. It is demonstrated that in the absence of charges and currents in vacuum, the non-zero electric area of a pulse would lead to its infinite energy. A pulse with the non-zero area is shown to form already in the case of uniform and rectilinear motion of the charge. The conditions for formation of such pulses by a localized charge system are found, and an example of such a system is presented. The asymptotics of the electric area far from the system of charges is obtained.
PubDate: 2023-09-28
- Measurements of the Atmospheric Electric Current Density by a Passive
Horizontal Ring Antenna in the Surface Layer: Quasi-Stationary
Approximation-
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Abstract: We consider a quasi-stationary approximation for turbulent electrical processes in the atmospheric boundary layer and their recording by a passive horizontal ring antenna acting as a collector of atmospheric electric current. On the basis of large eddy simulation, variations in electrical variables are calculated and spatial correlation functions and the spectral density of fluctuations of the atmospheric-current density components are estimated along with the response of the collector current to local turbulent perturbations of the conduction-current density and an instantaneous change in the global potential difference between the ionosphere and the Earth’s surface. Based on the simulation results, we estimate the ratio of the total vertical atmospheric electric current density and the conduction current density at the height of the antenna location, which can be used to extrapolate the results of ground-based measurements beyond the atmospheric boundary layer. The results of direct observations of the atmospheric electric current density by the collector are compared with the results of synchronous observations of the atmospheric electric field and the electrical conductivity in the surface layer. The frequency spectra of the collector-measured and calculated fluctuations of electric current have a power-law decay with increasing frequency with indices that are consistent for measurements and model calculations in the range from −1.0 to −1.5.
PubDate: 2023-09-11
- Plasma-Chemical Facility for Synthesis of Micro- and Nanoparticles Having
Controlled Compositions and Structures on the Basis of a Microwave
Discharge in the Gyrotron Radiation-
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Abstract: We present a description of a plasma-chemical facility designed for synthesis of micro- and nanoparticles using the radiation of a high-power gyrotron. The facility has been developed at the Plasma Physics Division of A.M.Prokhorov General Physics Institute of the Russian Academy of Sciences. The facility includes a plasma-chemical reactor, a gyrotron unit, an in-line calorimeter, a diagnostic system, which ensures video and spectroscopic measurements, balance measurements of the microwave radiation, and thermal imagery measurements, a chemical unit for specimen preparation and analysis of synthesis products, an electronic logging unit, and a specimen labeling system for organization and storage of a large amount of experimental data and specimens.
PubDate: 2023-09-11
- Source Localization in a Channel with a Rough Surface Using a Multi-Rank
Capon Algorithm-
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Abstract: We consider the problem of acoustic source localization in a shallow water channel, in which the prevailing mechanism of sound scattering is developed wind seas. For the given scenario, an adaptive multi-rank Capon algorithm, which is capable of processing in both the conventional and mode space and localizes the source under conditions of incomplete information on a random propagation channel, is constructed. This method of solving the inverse problem uses the worst-case principle and provides greater stability of the estimation procedure to a mismatch caused by the discrepancy between the true coherence matrix of the signal field and its computational model. The results of statistical modeling, which demonstrate the probabilities of correct source localization depending on the input signal-to-noise ratio and the sample size, are presented. The method is validated using the experimental data observed on a stationary path in the Barents Sea. It has been shown that under real conditions, the presented approach is rather efficient and ensures an acceptable source reconstruction quality without using a computationally intense joint search for both the source coordinates and unknown waveguide parameters.
PubDate: 2023-09-11
- Creation of a HF and VHF Radio Communication Channel Through an Artificial
Ionospheric Repeater-
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Abstract: We study experimentally the possibility of creating a HF and VHF radio communication channel at frequencies above the hop-by-hop MUF through an artificial ionospheric repeater, which is formed by as scatterers in the form of magnetic field-aligned small-scale artificial ionospheric irregularities, created at the altitudes of reflection of a high-power O-mode pump wave. The experiments were carried out on the Dymer (Kyiv region)—Sura—Kachalinskaya (Volgograd region) path in the HF sounding regime at fixed frequencies and in the chirp sounding regime on the IZMIRAN—Sura—Rostov-on-Don path. On the Novocherkassk (Rostov region)—Sura— Kachalinskaya path, the measurements were carried out at a frequency of 45.8 MHz. Comparison with simulation results is performed. To ensure stable HF and VHF radio communication through an artificial ionospheric repeater, it is necessary to take into account the state of the ionosphere, the frequency of the communication signal, and the height of the location of scattering irregularities. To adapt communication systems to the current ionospheric environment under conditions of insufficient accuracy in predicting the state of the ionosphere, it is necessary to monitor the ionospheric channel using technical tools for broadband oblique HF and VHF sounding.
PubDate: 2023-09-11
- Mechanically Machined Microwave Multi-Layer Antireflective Coating of a
Dielectric-
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Abstract: We present theoretical and experimental results on mechanically machined multilayer antireflective coating of a dielectric plate. The microwave ouptut window made of fluoroplast with the refractive index n = 1.41, was studied experimentally. Holes of two different diameters were drilled in a honeycomb pattern on the surface of the dielectric to different depths in such a way that two thin quarter-wave layers were formed. The effective dielectric permittivity of the obtained layers with cylindrical inhomogeneities was calculated by the Maxwell–Garnett method. The parameters of the layers were chosen according to the Chebyshev method. This allowed us to achieve a reflection coefficient of −30 dB in the frequency range 65–100 GHz. The experimental results were compared with the theoretical calculation and the numerical analysis performed via the multiple-reflection method.
PubDate: 2023-09-08
- Estimation of the Variance of a Random Signal with an Unknown Frequency
Bandwidth-
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Abstract: We consider the problem of estimating the variance of a Gaussian stationary stochastic signal with a regular spectral density and a priori unknown frequency bandwidth. Two methods for overcoming an a priori uncertainty are proposed, namely, the quasi-likelihood algorithm and the joint maximum-likelihood estimation of all unknown parameters. The structural schemes are developed and the estimation characteristics are found for the synthesized algorithms. The estimation-accuracy loss because of the a priori ignorance of the spectral-density width of a useful signal are determined.
PubDate: 2023-09-08
- Propagation of Pulsed Electromagnetic Signals with the Axisymmetric Field
Structure in a Nonlinear Nondispersive Medium-
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Abstract: We consider the propagation of pulsed electromagnetic signals with the axisymmetric field structure in a nonlinear nondispersive medium. It is also assumed that in the linear limit (for small amplitudes of the field components), an axisymmetric inhomogeneity of dielectric permittivity can be present in the considered model of the medium. A rigorous solution for the problem of the behavior of the pulse field in such a medium is obtained. Based on the found solution, the propagation of electromagnetic signals excited by currents with various time dependences is studied. The influence of the nonlinearity and inhomogeneity parameters of the medium on the spatial distributions of the components of the excited field and on the behavior of the vector of the energy flux density is analyzed.
PubDate: 2023-07-15
DOI: 10.1007/s11141-023-10256-w
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