Electric Vector Research Articles

Implementing the single/multiport tunable terahertz circularly polarized dielectric resonator antenna

A tunable terahertz circularly-polarized dielectric resonator antenna is implemented and numerically studied. An aperture coupled terahertz rectangular dielectric resonator antenna operating with the fundamental magnetic dipole is designed. The modal field distribution is perturbed using the material-perturbation technique and the electric field vectors are aligned in the horizontal plane with their orthogonal components having quadrature phase difference between them. Consequently, the circular polarization is obtained in the operating passband. The proposed antenna provides the 10-dB impedance bandwidth of 12.94% (4.27–4.86 THz) and 3 dB axial ratio bandwidth of 3.77% (4.43–4.60 THz). Moreover, tunability is achieved by modulation in the chemical potential of graphene layer coated at the top of the dielectric resonator by applying an electrostatic bias voltage. In addition, antenna provides the gain of 6.45 dBic along with 98% radiation efficiency. The proposed antenna can also be used for the implementation of multi-port wireless THz communication systems with the advantage of tunable CP response with impeccably high radiation performance parameters. A two-port multi input, multi output (MIMO) antenna is implemented with the usage of the proposed metal strip coated DR. This antenna provides high isolation between both the ports along with polarization response and pattern diversity with the acceptable value of MIMO performance parameters like envelop correlation coefficient and diversity gain.

Cold Carrier Injection Mechanism for Gate Oxide Integrity of High Voltage NDMOS

This article studies a reliability mechanism for field-plate-assisted reduced surface field (RESURF) effect 225-V NDMOS devices based on anode hole oxide injection for carriers that are in thermal equilibrium with the surrounding lattice. The injection mechanism is facilitated by a unique combination of layout and application biases that result in electric field vectors pulling low-energy minority hole carriers into oxide traps that overlap the drain potential. The effect of this positive charge trapping along the field oxide is to inhibit the RESURF mechanism, while also weakening the gate oxide where it overlaps the drain that ultimately results in a rupture. To quantify the process, a new accelerated aging technique is described that uses the parasitic n-p-n bipolar parallel of the nMOS channel to significantly increase the number of holes while still maintaining the MOS application voltages needed to enable the mechanism. This provides a cost-effective way to accurately accelerate this reliability mechanism with significantly smaller lead times relative to using higher biases and temperatures. This technique is then used with technical computer-aided design (TCAD) analysis to determine the impact of different manufacturing variables, where process controls are introduced for targeted manufacturing limits that can eliminate this mechanism from occurring.

Сравнительный анализ методов калибровки каналов сигналов антенн моноимпульсной радиолокации

Today, antenna arrays (ARs) are increasingly used as antennas in modern radio engineering systems. With the help of AR, you can control the shape of the radiation pattern (DN) and the position of its main lobe, called the beam of such an antenna system. Each AA channel contains microwave components for controlling the amplitude and phase of the signal passing through it. These components are characterized by errors in setting the amplitude and phase, which negatively affects the shape of the pattern and its characteristics. Therefore, to compensate for these errors, it is necessary to use the AP calibration at the production stage, and also during its operation. The paper presents various calibration methods; the most suitable and promising methods for AA calibration were determined; the principles of operation of these methods are considered, the advantages and disadvantages of the methods are identified, a comparative analysis of all methods is carried out, as well as the conditions under which it is more expedient to use one or another method. The following calibration methods are considered: Phaseless methods: (Rotating-Element Electric Field Vector method - REV method, Measurement of Two Elements method - MTE method, Sorace algorithm, Levita (Leavitt), Correlation algorithm Adaptive methods: (Music method, Capon method, SMI (Sample Matrix Inversion algorithm), least mean square error (LMS) algorithm, Quasi-Newton algorithm); Autocalibration methods: (Friedlander-Weiss method, Wang-Kedzou method, Estelie-Swindleharst-Otterson method), as well as the proposed two-phase AR calibration method. These methods are the most attractive from a practical point of view, since they can be used not only for factory calibration of the AA, but also during operation.

Unraveling the Innermost Jet Structure of OJ 287 with the First GMVA + ALMA Observations

We present the first very long baseline interferometric (VLBI) observations of the blazar OJ 287 carried out jointly with the Global Millimeter VLBI Array (GMVA) and the phased Atacama Large Millimeter/submillimeter Array (ALMA) at 3.5 mm on 2017 April 2. The participation of phased ALMA has not only improved the GMVA north–south resolution by a factor of ∼3, but has also enabled fringe detections with signal-to-noise ratios up to 300 at baselines longer than 2 Gλ. The high sensitivity has motivated us to image the data with newly developed regularized maximum likelihood imaging methods, revealing the innermost jet structure with unprecedentedly high angular resolution. Our images reveal a compact and twisted jet extending along the northwest direction, with two bends within the inner 200 μas, resembling a precessing jet in projection. The component at the southeastern end shows a compact morphology and high brightness temperature, and is identified as the VLBI core. An extended jet feature that lies at ∼200 μas northwest of the core shows a conical shape, in both total and linearly polarized intensity, and a bimodal distribution of the linear polarization electric vector position angle. We discuss the nature of this feature by comparing our observations with models and simulations of oblique and recollimation shocks with various magnetic field configurations. Our high-fidelity images also enabled us to search for possible jet features from the secondary supermassive black hole (SMBH) and test the SMBH binary hypothesis proposed for this source.

Unconventional Landau level transitions in Weyl semimetal NbP

Weyl semimetals were experimentally discovered as a new quantum phase of matter that exhibits topologically protected states characterized by separated Weyl points. Similar to other topological materials, the research of Landau level transitions can provide abundant information on Fermi surfaces. Extensive experimental efforts on low-temperature transport and optical properties have been dedicated to investigating the nontrivial topology structure. However, there are some theoretically predicted unconventional Landau level transitions in Weyl semimetals that have not been observed experimentally. And, their contribution to the electromagnetic response of Weyl semimetal remains elusive. Here, we report the magneto-optical study of Landau quantization and selection rules in Weyl semimetal NbP under Voigt geometry. By changing the direction of the electric vector of the incoming light under Voigt and Faraday geometry, abundant Landau level transition modes which contain $\mathrm{\ensuremath{\Delta}}=0$, \ifmmode\pm\else\textpm\fi{}1, \ifmmode\pm\else\textpm\fi{}2 selection rules are obtained. The richness of the optical spectra, particularly the ones from the Voigt geometry, allows us to determine the location of Fermi energy and its evolution with magnetic fields. We further extract the transitions between Landau levels and Fermi energy and deduce the Landau index. Our results reveal the track of Fermi energy under varying magnetic fields based on the Landau level transitions under Voigt geometry and suggest that a combination of the magneto-optical spectra under Voigt and Faraday geometry can effectively determine the key properties of topological materials that are otherwise inaccessible.

GRACE Accelerometers Sensitive to Ionosphere Plasma Waves: Similarities between Twangs and Whistlers

Electrostatic space accelerometers are high-precision instruments used in gravity and magnetic fields and in fundamental physics missions. From their first use in space, these instruments show disturbances around the read-out frequency. In recent missions like Swarm and GRACE-FO, these instruments are seriously compromised. Their capability cannot be fully exploited or, in the worst case, not used for science data processing at all. We currently neither understand the mechanism nor the cause of the disturbance. For that reason, every correlation, direct or indirect, between signatures in the accelerometer data and other phenomena in the satellite environment is very important to study. In the GRACE mission, some of the disturbances relate to onboard current switching processes, such as switching of heater and torquer currents. In this paper, we examine the phenomena called twangs. The shape of these disturbances is responsible for their name, because they look like a decaying tone. Some of these twangs seem to relate to changing currents, too. They occur when sunlight hits surfaces of the satellite. This can cause the discharging of satellite parts. Here, we focus on special twangs, which we call cloud-related twangs, as recent investigations related them to cloud coverage. How can clouds in the troposphere influence a satellite, orbiting in the ionosphere? We investigated the troposphere–ionosphere coupling and found that the only coupling which can be responsible for disturbances on satellites and which may affect the accelerometers, are electromagnetic waves traveling in the so-called whistler mode at frequencies in the very-low-frequency (VLF) domain. This special propagation mode is a coupled electromagnetic and electrostatic mode. There, the electric field vector has a component in the direction of propagation due to the interaction with ions and the magnetic field in the ionosphere and magnetosphere. This led us to investigate the similarities between whistlers and twangs. The hypothesis that they are related is very important in our further understanding of disturbances on satellite instruments sensible to electromagnetic pulses in the range of very low frequencies and below.

The COMIX polarimeter: a compact device for XUV polarization analysis.

We report on the characterization of a novel extreme-ultraviolet polarimeter based on conical mirrors to simultaneously detect all the components of the electric field vector for extreme-ultraviolet radiation in the 45-90 eV energy range. The device has been characterized using a variable polarization source at the Elettra synchrotron, showing good performance in the ability to determine the radiation polarization. Furthermore, as a possible application of the device, Faraday spectroscopy and time-resolved experiments have been performed atthe Fe M2,3-edge on an FeGd ferrimagnetic thin film using the FERMI free-electron laser source. The instrument is shown to be able to detect the small angular variation induced by an optical external stimulus on the polarization state of the light after interaction with magnetic thin film, making the device an appealing tool for magnetization dynamics research.

High temperature phase transitions in NaNbO3 epitaxial films grown under tensile lattice strain

We have investigated high temperature phase transitions in NaNbO3 thin films epitaxially grown under tensile lattice strain on (110) DyScO3 substrates using metal-organic vapor phase epitaxy. At room temperature, a very regular stripe domain pattern consisting of the monoclinic a1a2 ferroelectric phase was observed. Temperature-dependent studies of the refractive index and the optical bandgap as well as in situ high-resolution x-ray diffraction measurements prove a ferroelectric–ferroelectric phase transition in the range between 250 and 300 °C. The experimental results strongly suggest that the high-temperature phase exhibits a distorted orthorhombic a1/a2 crystal symmetry, with the electric polarization vector lying exclusively in the plane. A second phase transition was observed at about 500 °C, which presumably signifies the transition to the paraelectric phase. Both phase transitions show a pronounced temperature-dependent hysteresis, indicating first-order phase transitions.

Evolving electromagnetic chirality of a focused field from the Poincaré sphere perspective

Chirality, which describes not only the three-dimensional mirror-symmetry violation of objects but also the local handedness and spatial geometrical structure of electromagnetic fields, has gained enormous interest recently because of its fundamental features as well as practical and potential applications in chiral light–matter interactions. Analytical forms of the electric and magnetic field strength vectors as well as optical chirality density and flow of strongly focused full Poincaré sphere beams are presented. The evolution of nonparaxial electromagnetic chirality of input fields from the Poincaré sphere view is explored; in addition its roles in relation to ellipticity, handedness, and orientation are revealed based on the analytical model. Ellipticity affects the localization and magnitude of both chirality density and flow. In contrast, handedness mainly affects the magnitude of the optical chirality density and longitudinal component of flow, whereas both density and flow are independent of the input orientation. Moreover, the structure and appearance of the optical chirality density are dominated by the longitudinal component of its flow. These findings may be of help in chiral particle trapping, nanoscale chiral detection, and sensing.

Studies of porous silicon aging by ellipsometry

Polarization characteristics of the film formed on porous silicon sample surface after its fabrication by electrochemical monocrystalline silicon etching have been studied by the method of multiple-angle-of-incidence ellipsometry which allows, in a number of cases, to determine the parameters of those parts of the reflecting system, which forms the reflected wave. Consequently, of the film existence, a strong ellipsometric parameter tanψ maximum appearing at a certain angle of light incidence on the sample was found. This means that the p-component of the electric field vector in the reflected beam significantly exceeds the s-component and as a result, the reflected light is predominantly p-polarized. Over a long period of observation the maximum gradually decreases in amplitude and a minimum appears instead it. It is assumed that the ellipsometric phenomena observed are due to time changes in characteristics of the film formed as a result of silicon and electrochemical reactions products interaction with atmospheric oxygen. Dependences of ellipsometric parameters on the angle of incidence are approximately described by two-layer model of the film investigated. It was found that the outer film layer has a refractive index of approximately 1.1 that is noticeable lower than natural silicon dioxide refractive index (1.45). This indicates a significant porosity of the near-surface layer of the film.

Phase distributions accompanying the conical diffraction through a Pasteur acentric biaxial crystal, displayed with Bi2ZnOB2O6

The conical diffraction of an optical wave through a biaxial crystal leads to an electric vector field with a specific polarization and phases distributions assessable from a unitary operator. The optical activity, if the crystal is a Pasteur acentric one, modifies deeply the phenomenon and two phases are required instead of one for pure birefringence. These modifications in a Bi2ZnOB2O6 crystal were characterized using a polarimetric method and an interferential conoscope equipped with a liquid crystal retarder allowing the measurement of the Pancharatman phase difference between the electric field under study and a vertically or horizontally polarized reference beam. The orbital angular momentum is linked with this phase. All the experimental data and their theoretical description are in reasonably good agreement without adjusting any optical parameters.

Chiral structures of electric polarization vectors quantified by X-ray resonant scattering

Resonant elastic X-ray scattering (REXS) offers a unique tool to investigate solid-state systems providing spatial knowledge from diffraction combined with electronic information through the enhanced absorption process, allowing the probing of magnetic, charge, spin, and orbital degrees of spatial order together with electronic structure. A new promising application of REXS is to elucidate the chiral structure of electrical polarization emergent in a ferroelectric oxide superlattice in which the polarization vectors in the REXS amplitude are implicitly described through an anisotropic tensor corresponding to the quadrupole moment. Here, we present a detailed theoretical framework and analysis to quantitatively analyze the experimental results of Ti L-edge REXS of a polar vortex array formed in a PbTiO3/SrTiO3 superlattice. Based on this theoretical framework, REXS for polar chiral structures can become a useful tool similar to x-ray resonant magnetic scattering (XRMS), enabling a comprehensive study of both electric and magnetic REXS on the chiral structures.

Photon Ring Symmetries in Simulated Linear Polarization Images of Messier 87*

Abstract The Event Horizon Telescope (EHT) recently released the first linearly polarized images of the accretion flow around the supermassive black hole Messier 87*, hereafter M87*. The spiraling polarization pattern found in the EHT images favored magnetically arrested disks as the explanation for the EHT image. With next-generation improvements to very long baseline interferometry on the horizon, understanding similar polarized features in the highly lensed structure known as the “photon ring,” where photons make multiple half orbits about the black hole before reaching the observer, will be critical to the analysis of future images. Recent work has indicated that this image region may be depolarized relative to more direct emission. We expand this observation by decomposing photon half orbits in the EHT library of simulated images of the M 87* accretion system and find that images of magnetically arrested disk simulations show a relative depolarization of the photon ring attributable to destructive interference of oppositely spiraling electric field vectors; this antisymmetry, which arises purely from strong gravitational lensing, can produce up to ∼50% depolarization in the photon ring region with respect to the direct image. In systems that are not magnetically arrested and with the exception of systems with high spin and ions and electrons of equal temperature, we find that highly lensed indirect subimages are almost completely depolarized, causing a modest depolarization of the photon ring region in the complete image. We predict that next-generation EHT observations of M 87* polarization should jointly constrain the black hole spin and the underlying emission and magnetic field geometry.

Coupled Electrohydrodynamic and Thermocapillary Instability of Multi-Phase Flows Using an Incompressible Smoothed Particle Hydrodynamics Method

This paper concerns the study of coupled effects of electrohydrodynamic (EHD) and thermocapillary (TC) on the dynamic behaviour of a single liquid droplet. An incompressible Smoothed Particle Hydrodynamic (ISPH) multiphase model is used to simulate EHD-TC driven flows. The complex hydrodynamic interactions are modeled using the continuum surface force (CSF) method, in which the gradient of the interfacial tension and the Marangoni forces are calculated with an approximated error or 0.014% in the calculation of Marangoni force compared to the analytical solutions which is a significant improvement in comparison with previous SPH simulation studies, under the assumption that the thermocapillarity generates sufficiently large stress to allow droplet migration, while the electrohydrodynamic phenomena influences the droplet morphology depending on the electrical and thermal ratios of the droplet and the ambient fluid. This study shows that, when applying a vertical electric field and thermal gradient, the droplet starts to stretch horizontally towards a break-up condition at a high rate of electrical permitivity. The combined effect of thermal gradient and electric field tends to push further the droplet towards the break-up regime. When the thermal gradient and the electric field vector are orthogonal, results show that the droplet deformation would take place more slowly and the Marangoni forces cause the droplet to migrate, while the stretching in the direction of the electric field is not seen to be as strong as in the first case.

Symmetry‐Protected Spoof Localized Surface Plasmonic Skyrmion

AbstractElectromagnetic (EM) skyrmions are an EM analogue of the skyrmions in condensed matter physics, offering new degrees of freedom to structure light and manipulate light–matter interactions and thus promising various groundbreaking applications in optics and photonics. Recently, there is a growing interest in composing EM skyrmions based on different field vectors of EM waves. Here, an EM skyrmion is realized, i.e., a spoof plasmonic skyrmion (SPS), using the electric field vectors of spoof localized surface plasmons (LSPs) in a planar microwave resonator with rotational and mirroring symmetries. The SPS is constructed by synthesizing a scalar vortex (a topological charge 0) and a polarization vortex (a topological charge 1) in the in‐plane and the out‐of‐plane component of the fields, respectively. Besides an experimental demonstration, group theory is employed and pinpoints the symmetry origin of the skyrmion. This investigation demonstrates the ubiquity of the existence of the skyrmion in any planar EM resonator holding rotational and mirroring symmetries, regardless the dimensions and the operating frequencies. This skyrmion design not only promises novel microwave applications for sensing and transferring information, but also lays down a general guideline for devising skyrmions operating over a broad range in the EM spectra.

Theoretical study of the molecular-frame photoemission time delay for K -shell photoionization of N2

Photoelectron emission Wigner time delay for $K$-shell ionization of a nitrogen molecule is studied theoretically in the frame of a molecular reference for parallel and perpendicular orientations of the molecule with respect to the electric field vector of linearly polarized ionizing light. Electronic structure calculations are performed by the single center method for photoelectron kinetic energies from 5 to 20 eV and at different levels of approximation. Thereby, the influence of core relaxation effects and interchannel coupling on the $1s$-photoemission time delays, computed across the ${\ensuremath{\sigma}}^{*}$-shape resonance, is investigated in detail. The present theoretical results can be considered as reliable predictions for future experiments.

Stringent axion constraints with Event Horizon Telescope polarimetric measurements of M87⋆

The hitherto unprecedented angular resolution of the Event Horizon Telescope has created exciting opportunities in the search for new physics. Recently, the linear polarization of radiation emitted near the supermassive black hole M87⋆ was measured on four separate days, precisely enabling tests of the existence of a dense axion cloud produced by a spinning black hole. The presence of an axion cloud leads to a frequency-independent oscillation in the electric vector position angle of this linear polarization. For the nearly face-on M87⋆, this oscillation in the electric vector position angle appears as a propagating wave along the photon ring. In this paper, we leverage the azimuthal distribution of electric vector position angle measured by the Event Horizon Telescope to study the axion–photon coupling. We propose a novel differential analysis procedure to reduce the astrophysical background, and derive stringent constraints on the existence of axions in the previously unexplored mass window of ~(10−21–10−20) eV. An axion cloud surrounding a spinning black hole would rotate the electric vector position angles of linearly polarized emissions. Tight constraints on the axion–photon coupling can therefore be obtained from polarization information in the Event Horizon Telescope’s images of M87⋆.

Electromagnetic attenuation distribution in a three-dimensional amorphous carbon matrix with highly dispersed Fe/Fe3C@graphite-C nanoparticles

The dielectric-magnetic synergistic effect can be achieved by dielectric relaxation and magnetic resonances in composites of carbon materials and magnetic particles. However, there is no direct evidence demonstrating the distribution of electromagnetic energy attenuation in the microstructure of composites. Herein, an amorphous carbon matrix with dispersed Fe/Fe3C@graphite-C was fabricated via a facile route. The distribution of the magnetic vector loss and electric vector loss in the hierarchical structures was revealed by numerical simulation. The content and dispersion of magnetic particles as well as the morphology of the amorphous carbon can be tuned. The 3D amorphous carbon matrix with highly dispersed Fe/Fe3C@graphite-C nanoparticles provided the strongest absorption of −69.0 dB and an effective response bandwidth (RL ≤ −10 dB) of 7.06 GHz. The numerical simulation revealed that the magnetic vector loss originated only from the core of Fe/Fe3C, and the electric vector loss was distributed throughout the structure, especially in the graphite-C shell, the interface between graphite-C and carbon nanoflakes, and the junction of different carbon nanoflakes. This work not only reveals the distribution of electromagnetic loss but also supports the theoretical analysis of the electromagnetic wave attenuation mechanism in composites, which provides direction for the future design of composites.

Design, application and investigation of the system for generation of fast changing, rotating magnetic field causing hyperthermic effect in magnetic liquids

The paper presents and discusses the results of research aimed at developing the optimal System for Generation of the fast-changing Rotating Magnetic Field (SGRMF) that causes the hyperthermic effect in magnetic liquids. In the calculations and design of the SGRMF, the three-dimensional (3D), original approach of the Finite Element Method (FEM) has been used. The FEM software prepared by the authors is based on the Ω-T0 formulation with nodal values of the scalar potential Ω to describe the magnetic field, and edge values of the electric vector potential T0 to define currents in windings. In the prepared model of the SGRMF, the relations describing the conversion of electromagnetic energy into thermal energy in magnetic fluids have been taken into consideration. The results of the proposed FEM model and elaborated software are presented and compared with the results obtained from the measurements on the specialized test stand. The prototype of the SGRMF system has been designed and built. Finally, the application of this prototype in the investigations of the hyper-thermal effect in a selected magnetic fluid of APG 513 type is given and discussed.

Local Direction of Optomechanical Stress in Azobenzene Containing Polymers During Surface Relief Grating Formation

AbstractIn this work, it is revealed how the photoinduced deformation of azobenzene containing polymers relates to the local direction of optomechanical stresses generated during irradiation with interference patterns (IPs). It can be substantiated by the modeling approach proposed by Saphiannikova et al., which describes the directional photodeformations in glassy side‐chain azobenzene polymers, and proves that these deformations arise from the reorientation of rigid backbone segments along the light polarization direction. In experiments and modeling, surface relief gratings in pre‐elongated photosensitive colloids of few micrometers length are inscribed using different IPs such as SS, PP, ±45, SP, RL, and LR. The deformation of colloidal particles is studied in situ, whereby the local variation of polymer topography is assigned to the local distribution of the electrical field vector for all IPs. Experimentally observed shapes are reproduced exactly with modeling azopolymer samples as visco‐plastic bodies in the finite element software ANSYS. Orientation approach correctly predicts local variations of the main axis of light‐induced stress in each interference pattern for both initially isotropic and highly oriented materials. With this work, it is suggested that the orientation approach implements a self‐sufficient and convincing mechanism to describe photoinduced deformation in azopolymer films that in principle does not require auxiliary assumptions.