Electric Vector Research Articles

Broadband 2D phase-gradient metasurface for linearly-polarized waves by suppressing Lorentz resonance of meta-atoms.

Metasurfaces have exhibited versatile capacities of controlling electromagnetic (EM) waves due to the high degree of freedom of designing artificially engineered meta-atoms. For circular polarization (CP), broadband phase gradient metasurfaces (PGMs) can be realized based on P-B geometric phase by rotating meta-atoms; while for linear polarization (LP), realization of broadband phase gradients has to resort to P-B geometric phase during polarization conversion and polarization purity has to be sacrificed for broadband properties. It is still challenging to obtain broadband PGMs for LP waves without polarization conversion. In this paper, we propose the design of 2D PGMs by combining the inherently wideband geometric phases and non-resonant phases of meta-atom, under the philosophy of suppressing Lorentz resonances that usually bring about abrupt phase changes. To this end, an anisotropic meta-atom is devised which can suppress abrupt Lorentz resonances in 2D for both x- and y-polarized waves. For y-polarized waves, the central straight wire is in perpendicular to electric vector Ein of incident waves, Lorentz resonance cannot be excited although the electrical length approaches or even exceeds half a wavelength. For x-polarized waves, the central straight wire is in parallel with Ein, a split gap is opened on the center of the straight wire so as to avoid Lorentz resonance. In this way, the abrupt Lorentz resonances are suppressed in 2D and the wideband geometric phase and the gradual non-resonant phase are left for broadband PGM design. As a proof of concept, a 2D PGM prototype for LP waves was designed, fabricated and measured in microwave regime. Both simulated and measured results show that the PGM can achieve broadband beam deflection for reflected waves for both x- and y-polarized waves in broadband, without changing the LP state. This work provides a broadband route to 2D PGMs for LP waves and can be readily extended to higher frequencies such as terahertz and infrared regimes.

Exact duality and local dynamics in SU(N) lattice gauge theory

We construct exact duality transformations in pure SU(N) Hamiltonian lattice gauge theory in ($2+1$) dimension. This duality is obtained by making a series of iterative canonical transformations on the SU(N) electric vector fields and their conjugate magnetic vector potentials on the four links around every plaquette. The resulting dual description is in terms of the magnetic scalar fields or plaquette flux loops and their conjugate electric scalar potentials. Under SU(N) gauge transformations they both transform like adjoint matter fields. The dual Hamiltonian describes the nonlocal self-interactions of these plaquette flux loops in terms of the electric scalar potentials and with inverted coupling. We show that these nonlocal loop interactions can be made local and converted into minimal couplings by introducing SU(N) auxiliary gauge fields along with new plaquette constraints. The matter fields can be included through minimal coupling. The techniques can be easily generalized to ($3+1$) dimensions.

A Semianalytical Method for Electromagnetic Scattering by Infinitely Long Arbitrary Shaped Multilayer Cylinders at Oblique Incidence

A simple and fast method for determining the field scattered from an infinite, arbitrary-shaped multilayer cylinder that is obliquely illuminated by a TMz plane wave is presented. The proposed method is a generalization of the meshless method that was previously introduced for the normal incidence case. The main structure of the procedure is similar to the one given for the normal incidence case. However, in the oblique incidence case, the problem cannot be handled as a scalar problem by considering only one field component, namely, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E_{\text {z}}$ </tex-math></inline-formula> for a TMz plane wave. Accordingly, all components of both the electric and magnetic field vectors are involved in the procedure and at each layer, and they are expressed as series of cylindrical functions with unknown coefficients. These coefficients are determined through the solution of a linear system of equations, which is constructed by first enforcing the continuity of the tangential components of the electric and magnetic field vectors on each boundary between the layers, then expressing the cylindrical functions in these continuity relations as Fourier series, and using the orthogonality of complex exponentials. After determining the coefficients, all field components at any point can be easily computed through the series representations.

Lorentz transformation of three dimensional gravitational wave tensor

Recently there has been more and more interest in the gravitational wave (GW) of moving sources. This paper introduces a Lorentz transformation problem of GWs. Although the Bondi-Metzner-Sachs (BMS) theory has in principle already included the Lorentz transformation of GWs, the transformation of the three-dimensional GW tensor has not been explicitly calculated before. Within four-dimensional spacetime, GWs have the properties of ‘boost weight zero’ and ‘spin weight 2’. This fact makes the Lorentz transformation of GWs difficult to understand. In the current paper, we adopt the traditional three-dimensional tensor description of a GW. Such a transverse-traceless tensor describes the GW freedom directly. We derive the explicit Lorentz transformation of the GW tensor. The transformation is similar to the Lorentz transformation for an electric field vector and a magnetic field vector which are three-dimensional vectors. Based on the deduced Lorentz transformation of the GW three-dimensional tensor, we can construct the gravitational waveform of a moving source with high speed if only the waveform of the corresponding rest waveform is given.

Polarisation leakage due to errors in track reconstruction in gas pixel detectors

X-ray polarimetry based on gas pixel detectors (GPDs) has reached a high level of maturity thanks to the Imaging X-ray Polarimeter Explorer (IXPE) providing the first-ever spatially resolved polarimetric measurements. However, as this a new technique, a few unexpected effects have emerged in the course of in-flight operations. In particular, it was almost immediately found that, the unpolarized calibration sources on-board were showing radially polarized halos. The origin of these features was recognized in a correlation between the error in reconstructing the absorption point of the X-ray photon and the direction of its electric field vector. Here, we present and discuss this effect in detail, showing that it is possible to provide a simple and robust mathematical formalism to handle it. We further show its role and relevance for the recent IXPE measures as well as for the use of GPD-based techniques in general. We also illustrate how to model it in the context of studying extended sources.

The Concept and Understanding of Synchronous Stability in Power Electronic-Based Power Systems

Synchronous stability in power systems is of essential importance for system safety and operation. For the phase-locked loop (PLL)-based synchronous stability in power electronic-based power systems, which has recently stimulated interest in researchers in the field of electrical power engineering, but is still controversial, this paper divides the topic into two aspects, including the PLL device stability and the system stability. It is found that the PLL device is always stable and the error between the PLL output angle θpll and the terminal voltage angle θt is always finite. Therefore, the synchronization of power electronic-based power systems should be understood as the output synchronization between the electrical rotation vectors (θt or θpll) from each item of grid-tied equipment, rather than the synchronization of the PLL device itself. In addition, it is found that θpll plays an active role in the system synchronization dynamics not only in electromagnetic timescales but also electromechanical timescales and it could be selected as a dominant observable. In this paper, the concept of synchronous stability is well clarified. These findings are well supported by theoretical analyses and MATLAB/Simulink simulations, and thus could provide insights on the synchronous stability mechanism.

Couple stress-based flexoelectricity of frictionless contact in dielectrics

The presence of flexoelectricity in dielectric materials can affect the mechanics of contact between solid bodies, especially when viewed at the micro/nano-scale. Such an effect can also contribute significantly to contact electrification ─ a charge transfer event that takes place at the contact interface. In particular, the state of deformation and stresses in the vicinity of the contacting area can differ markedly from that anticipated from classical elastic Hertzian contact theory. In the present work, we investigate the flexoelectric effect near the contacting area of an isotropic dielectric material pressed by a frictionless rigid insulator probe, serving as a model problem to reveal the potential role of flexoelectricity in contact mechanics and electrification. The investigation is based on consistent couple stress flexoelectric theory, in which electric polarization may appear due to two-way coupling between the electric field and mean curvature vectors, even for centrosymmetric dielectric materials. To this end, we develop a new boundary element formulation to calculate the displacement, stress, electric potential, and electric displacement for two-dimensional isotropic flexoelectric contact problems. The subsequent computational mechanics investigation highlights several important characteristics of triboelectric phenomena and shows that the state of stress and polarization in contacting isotropic dielectrics is dependent on the effective length scale parameter l of couple stress elasticity and the coupling flexoelectric coefficient f.

Ultrabroadband Multichannel Vector Vortex Beams With Versatile Electrically Induced Functionality

AbstractThe emergence of vector vortex beams (VVBs) has opened new avenues for various applications in optics and photonics. However, owing to the formidable phase aberration ascribed to the chromatic dispersion, the generation of VVBs suffers from a limited working spectrum, thus rendering the massive integration level and functionality challenging. Here, this work proposes a creative paradigm to generate ultrabroadband multichannel VVBs, via programming the electric field vector through the twisted nematic liquid crystals configured by photopatterning. It is experimentally demonstrated the multichannel VVBs propagate along a group of diffraction orders among an unprecedented bandwidth over 1000 nm covering the visible and NIR band, and the working spectrum can be extended into the mid‐IR region even at 10 µm wavelength with a sufficient efficiency of more than 80%. Remarkably, distinct from the usual electrical switching on–off cycle, the multichannel VVBs can be optionally regulated in either a reversible or irreversible manner by conveniently adjusting the applied voltage, thus endowing the versatile functionality for smart control and confidential purposes. The combination of multichannel VVB generation, ultrabroad spectral range, versatile controllability, and simplicity renders the methodology quite promising in photonics, quantum science, and fundamental physics.

Distinguishing Single-Metal Nanoparticles with Subdiffraction Spatial Resolution Using Variable-Polarization Fourier Transform Nonlinear Optical Microscopy.

The development and use of interferometric variable-polarization Fourier transform nonlinear optical (vpFT-NLO) imaging to distinguish colloidal nanoparticles colocated within the optical diffraction limit is described. Using a collinear train of phase-stabilized pulse pairs with orthogonal electric field vectors, the polarization of nonlinear excitation fields are controllably modulated between linear, circular, and various elliptical states. Polarization modulation is achieved by precise control over the time delay separating the orthogonal pulse pairs to within hundreds of attoseconds. The resultant emission from gold nanorods is imaged to a 2D array detector and correlated to the excitation field polarization and plasmon resonance frequency by Fourier transformation. Gold nanorods with length-to-diameter aspect ratios of 2 support a longitudinal surface plasmon resonance at approximately 800 nm, which is resonant with the excitation fundamental carrier wavelength. Differences in the intrinsic linear and circular dichroism resulting from variation in their relative alignment with respect to the laboratory frame enable optical differentiation of nanorods separated within 50 nm, which is an approximate 5-fold improvement over the diffraction limit of the microscope. The experimental results are supported by analytical simulations. In addition to subdiffraction spatial resolution, the vpFT-NLO method intrinsically provides the polarization- and frequency-dependent resonance response of the nanoparticles-providing spectroscopic information content along with super-resolution imaging capabilities.

Fabrication of core-shell Ni@C@PANI nanocomposite-based bionic coating with multi-bands EWM adaptability inspired by porous structure of pachliopta aristolochiae wings

Due to the Planck-Rozanov limit, stealth materials are prevented from realizing ultra-wideband absorption at deep sub-wavelength thickness. Herein, inspired by the absorption model of Pachliopta aristolochiae wings porous structure, a core-shell Ni@C@PANI nanometer powder-based bionic coating with multi-bands EWM adaptability was designed. The synergistic effect of excellent impedance matching, significant attenuation system, conduction loss, dipole polarization, interface polarization and good magnetic loss endow the hierarchical core-shell Ni@C@PANI nanocomposite with excellent EMW absorption properties. Additionally, the absorption of EMW in the low frequency bands mainly originates from the multiple reflection of EMW by the bionic porous structure. At high frequencies, in addition to resonance and reflection, the hole edges convert the linearly polarized electric field vector into a vortex form, thus dissipating the magnetic field energy. Consequently, a minimum reflection loss (RL) of −50.83 dB with a matching frequency of 16.5 GHz is achieved, and the EBA is as wide as 14.75 GHz (3.25–18 GHz), covering all C, X, Ku bands and part of S band. This discovery provides a way for using natural model to break the Plank-Rozanov limit to develop new-type bionic coating with multi-bands EMW adaptability.

Mathematical modeling of electro‐elastic dislocations in piezoelectric materials

AbstractIn this work, based on the theory of linear incompatible piezoelectricity with eigendistortion and eigenelectric field, the concept of electro‐elastic dislocations is presented. Both field variables, the displacement vector u and the electrostatic potential φ, possess a jump discontinuity at the dislocation surface. Electro‐elastic dislocations are described not only by the dislocation density tensor but also by a new introduced field, the so‐called electric dislocation density vector. In addition to electro‐elastic dislocations, inhomogeneities, body forces and body charges are also considered. Within this framework, material balance laws that correspond to the symmetries of translation, scaling and rotation are derived. All fundamental fields of configurational mechanics like the Eshelby stress tensor, the electro‐elastic Peach‐Koehler force, the Cherepanov force, the Eshelby force among others, which take place in the broken (translational, scaling and rotational) conservation laws anymore are given.

Review on Cardiac Arrhythmias with ECG Interpretation on Different Myocardial Regions

Electrocardiogram (ECG) is one of the major diagnostics tools for Cardiac Arrhythmias (CA). ECG interpretation is more important to provide specific treatment of different arrhythmic myocardial regions. In this article the aim is to focus on detailed normal and abnormal ECG interpretation with different myocardial regions. Contraction and Relaxation Process (CRP) during cardiac cycle generates complex ECG with addition of each conduction node electrical vector activity in cardiac conduction system. Epinephrine stimulates Beta1 adrenergic receptors to produce more G stimulation proteins and thus leads to increase calcium level in the cell that provides frequent production of Action Potential (AP) like sinus tachycardia, Early Afterdepolarization (EAD) and Delayed Afterdepolarization (EAD). Myocardial scar regions, AP cannot move because of blockage, in turns moving rapidly around the dead area in a circular way to lead reentrant arrhythmias. On the other hand of respiration cycle, vagus outflow fluctuates (inspiration) the Sinus Node (SN) to increase heart rate (R-R distance will decrease, more P wave and QRS complex will be produced) and to decrease heart rate during expiration (R-R distance will be more). Finally conclude that different myocardial dysfunction regions are the major cause of multi-classified cardiac arrhythmias.

Polarized image of a rotating black hole surrounded by a cold dark matter halo

We have studied the polarized image of an equatorial emitting ring around a rotating black hole surrounded by a cold dark matter (CDM) halo. Results show that the CDM halo density has the similar effects of the halo’s characteristic radius on the polarized image for the black hole. The effects of the CDM halo on the polarized image depend on the magnetic field configuration, the fluid velocity and the observed inclination. With the increase of the CDM halo parameters, the observed polarization intensity decreases when the magnetic field lies in equatorial plane, but in the case where the magnetic field is perpendicular to the equatorial plane, the change of the observed polarization intensity with CDM halo also depends on the position of the emitting point in the ring. The change of the electric vector position angle (EVPA) with the CDM halo becomes more complicated. Our results also show that the influence of the CDM halo on the polarized image is generally small, which are consistent with the effects of dark matter halo on black hole shadows. These results could help to further understand dark matter from black hole images.

Dipolar effects on the work function of an alkali-iodide overlayer (XI, X = Li, Na, K, Rb, and Cs) on tungsten surfaces

A first-principles approach was used to investigate the effects of alkali metal iodide XI (X = Li, Na, K, Rb, and Cs) adsorption on the work functions of (100), (110), and (111) surfaces of W. For the most energetically stable structures, work functions and their corresponding electric dipole moment vectors were calculated. In agreement with available experimental measurements, it was verified that the formation of XI dipoles on the W surface causes the work function to decrease significantly. It was shown that the calculated XI dipoles are tilted with respect to the W surface for all systems. This contradicts earlier published suggestions that the surface electrostatic energy of the dipoles prevented them from being aligned along the surface and were instead normal to the surface. In our work it is shown that the orientations (tilt) and strengths of the dipole moments can be explained in terms of the internal strain caused by the alkali metal’s different atomic sizes and available surface area. What matters for the decrease in the work function is the component of the dipolar moment perpendicular to the surface. For all systems, the work function reduction was shown to be directly proportional to the normal component of the electric field created by these XI dipoles.

Configuration of the global magnetic field in AGN parsec-scale jets

ABSTRACT The magnetic field plays a significant role in the phenomenon of highly collimated jets of active galactic nuclei (AGN). Relativistic effects prevent the direct reconstruction of the magnetic field direction as transverse to electric vectors on radio maps. We determined the topology of the B-field by modelling the transverse distributions of the total and linearly polarized intensity, polarization degree, and deviation of the polarization direction from the local jet axis and by further comparison with observational data. We consider (i) a helical field with a different twist angle and (ii) a toroidal field on the jet axis surrounded by a sheath with a longitudinal field. In the latter scenario, we consider different sheath thickness relative to the spine. We assumed the sheath velocity is equal to or less than that of the spine. The relativistic effects have been considered for a general case, under which the axis and velocity vector of the jet and radial directions do not coincide. Our simulations reproduce the main features of the observed transverse profiles of polarization characteristics in parsec-scale AGN jets. The model transverse distribution shapes of the polarization properties are found to be strongly influenced by kinematic and geometric parameters of an outflow. We demonstrated it for three AGNs having different but typical polarization patterns revealed on radio maps. For each of these objects, we identified the model parameters that provide a qualitative correspondence of theoretical profiles with those obtained from observations, indicating that the B-field is strongly ordered on parsec scales.

MOJAVE – XX. Persistent linear polarization structure in parsec-scale AGN jets

ABSTRACT We analysed the parsec-scale linear polarization properties of 436 active galactic nuclei (AGNs) based on 15 GHz polarimetric Very Long Baseline Array observations. We present polarization and total intensity images averaged over at least five epochs since 1996 January 19 through 2019 August 4. Stacking improves the image sensitivity down to ∼30 μJy beam−1 and effectively fills out the jet cross-section both in total intensity and linear polarization. It delineates the long-term persistent magnetic field configuration and its regularity by restoring spatial distributions of the electric vector position angle (EVPA) and fractional polarization, respectively. On average, about 10 yr of stacking period is needed to reveal the stable and most-complete polarization distribution of a source. We find that the degree of polarization significantly increases down and across the jet towards its edges, typically manifesting U or W-shaped transverse profiles, suggesting a presence of a large-scale helical magnetic field associated with the outflow. In some AGN jets, mainly BL Lacs, we detect quasi-constant fractional polarization profiles across the jet, accompanied by EVPAs that closely follow the outflow. BL Lacs show higher fractional polarization values in their cores and jets than those in quasars up to hectoparsec de-projected scales, while on larger scales, they become comparable. High-synchrotron-peaked BL Lac jets are found to be less polarized than intermediate and low-synchrotron-peaked BL Lacs. The spatial distribution of the EVPAs in BL Lacs tend to align with the local jet direction, while quasars show an excess of orthogonal polarization orientation.

Imaging ferroelectric domains with a single-spin scanning quantum sensor

The ability to sensitively image electric fields is important for understanding many nanoelectronic phenomena, including charge accumulation at surfaces1 and interfaces2 and field distributions in active electronic devices3. A particularly exciting application is the visualization of domain patterns in ferroelectric and nanoferroic materials4,5, owing to their potential in computing and data storage6–8. Here, we use a scanning nitrogen-vacancy (NV) microscope, well known for its use in magnetometry9, to image domain patterns in piezoelectric (Pb[Zr0.2Ti0.8]O3) and improper ferroelectric (YMnO3) materials through their electric fields. Electric field detection is enabled by measuring the Stark shift of the NV spin10,11 using a gradiometric detection scheme12. Analysis of the electric field maps allows us to discriminate between different types of surface charge distributions, as well as to reconstruct maps of the three-dimensional electric field vector and charge density. The ability to measure both stray electric and magnetic fields9,13 under ambient conditions opens opportunities for the study of multiferroic and multifunctional materials and devices8,14.

Short time-scale evolution of the polarized radio jet during V404 Cygni’s 2015 outburst

ABSTRACTWe present a high time resolution, multifrequency linear polarization analysis of very large array (VLA) radio observations during some of the brightest radio flaring (${\sim } 1 \,{\rm Jy}\,$) activity of the 2015 outburst of V404 Cygni. The VLA simultaneously captured the radio evolution in two bands (each with two 1 GHz base-bands), recorded at 5/7 GHz and 21/26 GHz , allowing for a broadband polarimetric analysis. Given the source’s high flux densities, we were able to measure polarization on time-scales of ${\sim }13\,$ min, constituting one of the highest temporal resolution radio polarimetric studies of a black hole X-ray binary outburst to date. Across all base-bands, we detect variable, weakly linearly polarized emission (${\lt } 1{{ \rm per\ cent}}$) with a single, bright peak in the time-resolved polarization fraction, consistent with an origin in an evolving, dynamic jet component. We applied two independent polarimetric methods to extract the intrinsic electric vector position angles and rotation measures from the 5 and 7 GHz base-band data and detected a variable intrinsic polarization angle, indicative of a rapidly evolving local environment or a complex magnetic field geometry. Comparisons to the simultaneous, spatially-resolved observations taken with the Very Long Baseline Array at 15.6 GHz , do not show a significant connection between the jet ejections and the polarization state.

Nonlinear Optical and Magnetic Properties of FeII-SCN-HgII Isomers: Centrosymmetric Layers and Chiral Networks

Research on isomers is highly desirable due to their prospective role in better understanding of physicochemical properties of similar systems and further development of multifunctional molecular materials. Iron(II) and tetra(thiocyanato)mercury(II) ions self-assembled in the presence of 2-acetylpyridine (2-acpy) excess to form two {[Fe(2-acpy)][Hg(μ-SCN)4]}n isomers: two-dimensional (2D) centrosymmetric layers with folded ring structural motifs (1) and three-dimensional (3D) chiral networks with right- or left-handed {···Fe-NCS-Hg-SCN···}∞ helixes (2). New methods of designing and synthesizing functional thiocyanate-bridged materials have been proposed. In addition, the similarity between 1 and 2 allowed for the description of subtle changes in IR and UV-visible spectra. Moreover, 2 shows spontaneous resolution, and it crystallizes in the noncentrosymmetric space group P21, leading to the occurrence of nonlinear optical activity in circular dichroism studies and second harmonic generation (SHG). At room temperature, the SH susceptibility for powder sample 2 reached 6.0 × 10-11 esu. Ab initio calculations indicated the electric polarization vector and the crystallographic twofold screw axis pass through the aromatic ring. Magnetic studies for 1 and 2 revealed high-spin iron(II) with zero-field splitting at low temperatures. Analysis of magnetic data gave |D| = 37.45 cm-1, |E/D| = 5.59 cm-1, and ⟨g⟩ = 2.15 for 1, |D| = 36.78 cm-1, |E/D| = 4.92 cm-1, and ⟨g⟩ = 2.18 for 2, and information about the orientation of magnetic anisotropy vectors for both compounds.

The Event Horizon Telescope Image of the Quasar NRAO 530

We report on the observations of the quasar NRAO 530 with the Event Horizon Telescope (EHT) on 2017 April 5−7, when NRAO 530 was used as a calibrator for the EHT observations of Sagittarius A*. At z = 0.902, this is the most distant object imaged by the EHT so far. We reconstruct the first images of the source at 230 GHz, at an unprecedented angular resolution of ∼20 μas, both in total intensity and in linear polarization (LP). We do not detect source variability, allowing us to represent the whole data set with static images. The images reveal a bright feature located on the southern end of the jet, which we associate with the core. The feature is linearly polarized, with a fractional polarization of ∼5%–8%, and it has a substructure consisting of two components. Their observed brightness temperature suggests that the energy density of the jet is dominated by the magnetic field. The jet extends over 60 μas along a position angle ∼ −28°. It includes two features with orthogonal directions of polarization (electric vector position angle), parallel and perpendicular to the jet axis, consistent with a helical structure of the magnetic field in the jet. The outermost feature has a particularly high degree of LP, suggestive of a nearly uniform magnetic field. Future EHT observations will probe the variability of the jet structure on microarcsecond scales, while simultaneous multiwavelength monitoring will provide insight into the high-energy emission origin.