Orthogonal Field Components Research Articles

Evaluation of errors in estimating the azimuth of powerful lightning discharges from measurements of Q-burstst

In this work, we study the variability of errors in determining the azimuth of Q-bursts’ sources on a daily time scale. Qbursts are electromagnetic pulse radiation in the extremely low frequency (ELF) range, excited by powerful lightning discharges, and they are used to locate lightnings over the world. We estimated the errors from data collected for two horizontal orthogonal magnetic field components of Q-bursts. Experimental records of Q-bursts were made at Akademik Vernadsky station from March to April 2019, which covers the vernal equinox day. We determined the azimuth of a Q-bursts’ source by digital rotation of the coordinate system until the signal in one magnetic component would drop to its minimum value. The absolute value of the azimuth error was estimated from the ratio of the Q-burst’s amplitude to the standard deviation of the residual signal. With an automated processing procedure, we analyzed over 800 thousand Q-bursts with amplitude over 10 picotesla. A characteristic diurnal pattern has been discovered in the estimated azimuth errors variations. The night level of the azimuth error exceeded the day level by about two degrees on average. The decrease-rise-decrease И-shaped swing during transition from night to day and mirror-symmetric Nshaped swing during transition from day to night were identified. Each of those transitional swings takes about four hours. A comparison of the daily variations in the total intensity of ELF background noise with the estimated daily azimuth error diagrams demonstrates the opposite character: maximal level of the ELF background noise was observed during the daytime while the estimated azimuth errors take minimal values at this time. This contradicts the generally accepted notion that increasing the noise increases the error. Thus, we suppose that the residual magnetic component in a Q-burst occurs not only from the background noise but can also result from nonlinear polarization of the incident wave due to gyrotropy of the nighttime lower ionosphere. Coherent waves resulting from diffraction of the incident field on the day-night interface in the Earth-ionosphere cavity could explain the И- and N-shaped swings of the azimuth error during the passage of the solar terminator.

High-Efficiency All-Dielectric Metasurfaces for the Generation and Detection of Focused Optical Vortex for the Ultraviolet Domain

The optical vortex (OV) has drawn considerable attention owing to its tremendous advanced applications, such as optical communication, quantum entanglement, and on-chip detectors. However, traditional OV generators suffer from a bulky configuration and limited performance, especially in the ultraviolet range. In this paper, we utilize a large bandgap dielectric material, niobium pentoxide (Nb2O5), to construct ultra-thin and compact transmission-type metasurfaces to generate and detect the OV at a wavelength of 355 nm. The meta-atom, which operates as a miniature half-wave plate and demonstrates a large tolerance to fabrication error, manipulates the phase of an incident right-handed circular polarized wave with high cross-polarized conversion efficiency (around 86.9%). The phase delay of π between the orthogonal electric field component is attributed to the anti-parallel magnetic dipoles induced in the nanobar. Besides, focused vortex generation (topological charge l from 1 to 3) and multichannel detection (l from −2 to 2) are demonstrated with high efficiency, up to 79.2%. We envision that our devices of high flexibility may have potential applications in high-performance micron-scale integrated ultraviolet nanophotonics and meta-optics.

Metasurface supporting broadband circular dichroism for reflected and transmitted fields simultaneously

We demonstrate significant optical activity in the near-infrared spectrum of a chiral metasurface which is designed using an array of L-shaped silver nanostructures. The far-field radiation from the plasmon-polariton surface wave currents produces combination of strong and highly dispersive orthogonal electric field components leading to the observation of broadband circular and elliptical polarization states (dichroism) for reflected and transmitted fields. Full-wave electromagnetic simulations show a linear to left hand and right hand circular polarization conversion between 200–261 THz frequency (1.15 µm–1.5 µm wavelength) range for reflected and transmitted fields. The structural chirality can be further enhanced by engraving another smaller L-dipole in nested configuration reaching near perfect polarization conversion efficiency. The nested L-dipole configuration supports circular polarization conversion between 262–306 THz frequency (980 nm–1.14 µm wavelength) range. Full-wave simulations suggest clear enhancement of the surface currents with helical orientation leading to increased optical activity. The proposed optical waveplate may be utilized in polarization control applications such as optical imaging, sensing, and display components.

Enhanced-Performance Circularly Polarized MIMO Antenna With Polarization/Pattern Diversity

Design of a compact wideband circularly polarized (CP) multiple-input multiple-output (MIMO) antenna with polarization diversity is proposed and characterized for off-body communication. The antenna is based on a simple coplanar waveguide (CPW)-fed monopole extension of the microstrip line. The orthogonal field components required by CP are induced using a simply modified right/left side ground plane. In particular, a stub extending from the ground plane along the length of the microstrip line generates the vertical component, whereas the current along the width of the ground plane contributes to the horizontal components. To obtain a unidirectional radiation pattern in the off-body direction and to reduce the sensitivity to the human body loading effects, a flat reflector printed on a high permittivity flexible substrate is applied. The simple topology of the antenna can be described by a few adjustable parameters, which facilitates its EM design closure. Prior to the experimental validation in the free space and on the body, the antenna is optimized at the full-wave level of description for all major performance figures. The overall footprint of the antenna radiator is only $L_{s}\,\,\times $ $W_{s} =0.24\lambda _{0} \times 0.64\,\,\lambda _{0} = 0.15\,\,\lambda _{0}^{2}$ . The proposed MIMO antenna features $\vert S_{11}\vert \le -10$ dB, average isolation $\vert S_{21}\vert \le -22$ dB, and axial ratio (AR) ≤3 dB from 5.2 GHz to 6.3 GHz with 100% bandwidth overlap between the impedance and axial ratio bandwidths. The envelope correlation coefficient (ECC) is less than 0.004 with the maximum diversity gain (DG) of approximately 9.99 dB. Moreover, the antenna maintains a high efficiency of up to 90% when loaded on the body, and a low specific absorption rate (SAR).

Low-Profile Circularly Polarized Patch Antenna With Wide 3 dB Beamwidth

In this letter, a low-profile circularly polarized (CP) narrow-slots slotted-patch antenna for wide 3 dB axial-ratio beamwidth (ARBW) performance is presented. It consists of two pairs of narrow slots along the diagonal lines of a square patch with a single feed. These pairs of narrow slots are conceived and placed to serve as magnetic dipoles with quarter-wavelength separation, forcing the amplitude of the orthogonal electric field components to be equal across a wide angle. The 3 dB ARBW of the CP antenna is a strong function of the mutual magnetic field, which is feasible to alter with different parameters of the slot. The location, dimensions, and gap between the slots are tuned to achieve wide 3 dB ARBW. Measured results of the fabricated prototype exhibit 3 dB ARBW of 226° with ARmin of 0.52 dB and 198° with ARmin of 1.61 dB in two principal planes at $\boldsymbol{\varphi } = \text{0}^\circ $ and $\boldsymbol{\varphi } = \text{90}^\circ $ , respectively. The antenna offers impedance bandwidth of 85 MHz (2.448–2.533 GHz) and CP bandwidth (CPBW) of 23 MHz (2.474–2.497 GHz). The minimum peak gain is 3.87 dBic in the broadside direction.

Quantification of Sq parameters in 2008 based on geomagnetic observatory data

The paper presents an investigation of the time-dependent parameters of the solar quiet daily (Sq) variation for the minimum of the solar cycle 23/24 in 2008. We apply “Measure of Anomalousness” algorithm to detection of the magnetically quiet days. Global distribution of Sq amplitudes of the three orthogonal magnetic field components is analyzed using one-year data from 75 INTERMAGNET geomagnetic observatories and 46 SuperMAG stations. The study reveals strong latitudinal dependence of the Sq(X) amplitudes, which is approximated by the sixth-order polynomial trend curve. Sq(Y) amplitudes also suggest latitudinal dependence, while no significant difference is found in the Sq(Z) amplitudes across all latitudes. In the equatorial region, Sq(X) amplitudes are strongly affected by the equatorial electrojet (EEJ), having maxima during equinoctial seasons in the region of the South Atlantic magnetic anomaly (SAA). Sq(Y) demonstrates clear dependence on solar activity and amount of solar illumination, as the Sq(Y) amplitudes are typically greater in the summer-hemisphere and smaller in the winter-hemisphere. We analyze equivalent Sq current system using observatory data from the Australian mainland and narrow European-African latitudinal segment. Sq current system also strongly depends on solar activity, as the current vortices in the winter-hemisphere disintegrate showing no trace of Sq current loops’ formation, while the current vortices become evident in the summer-hemisphere.

Characterization and Performance of an Ultra-Wideband Wide-Coverage Multimode MIMO Antenna

A new ultra-wideband multimode (MM) antenna design that enables the detection/transmission of two orthogonal field components over a nearly hemispherical coverage area is presented in this paper. It integrates and colocates two perpendicularly oriented bow-tie dipole elements, a short convex monopole and four horizontally oriented tapered slot antenna (TSA) elements (formed by the dipoles) in order to produce four decoupled and complementary gain patterns. The antenna feeding structure includes four single-ended transmission lines supporting the desired set of individual excitation modes. Experimental verification confirms the predicted negligible coupling between the antenna operating modes and orthogonality of the corresponding radiated field patterns. These unique features can be exploited in applications where pattern and polarization diversity are of importance. In this study, we have evaluated the proposed antenna as a MIMO base station antenna and characterized it in two different propagation scenarios. For this example, it has been shown that the utilization of the additional monopole and TSA modes plays an important role in maximizing MIMO efficiency in line-of-sight (LOS) scenarios and at the same time provides additional independent data streams in rich scattering scenarios. In both considered scenarios, the antenna is shown to have a MIMO frequency bandwidth of 85%.

Broadband linear-to-circular polarization converter based on phosphorene metamaterial

We propose a broadband reflective linear-to-circular (LTC) polarization converter in a mid-infrared regime based on monolayer black phosphorus (phosphorene) metamaterial. The proposed converter consists of periodic unit cells, each cell of which is formed by multiple phosphorene layers, a dielectric layer, and a fully reflective gold mirror. In the frequency range of 14.20 and 23.10 THz, the magnitudes of the reflection coefficients are approximately equal and the phase difference value between the two orthogonal electric field components of the reflected wave is close to π/2 or −3π/2, which indicates the reflective wave can be deemed the circular polarization with the incidence of linearly polarized wave. The simulation results show that the relative bandwidth of LTC polarization conversion reaches 58% and 47.8%, respectively, when the pucker ridge alignment of the phosphorene is perpendicular to the y-direction and x-direction. Finally, the physical mechanism is revealed via the field decomposition and current distribution. This polarization converter has great potential for future applications in electronic measurement, photonic design, and in some other optoelectronic systems.

Ultrafast pulse phase shifts in a charged-quantum-dot–micropillar system

We employ a quantum master equations approach based on a vectorial Maxwell-pseudospin model to compute the quantum evolution of the spin populations and coherences in the fundamental singlet trion transition of a negatively charged quantum dot embedded in a micropillar cavity. Excitation of the system is achieved through an ultrashort, either circularly or linearly polarised resonant pulse. By implementing a realistic micropillar cavity geometry, we numerically demonstrate a giant optical phase shift ($\sim \pm \pi/2$) of a resonant circularly polarised pulse in the weak-coupling regime. The phase shift that we predict considerably exceeds the experimentally observed Kerr rotation angle $(\sim{6 ^{\circ}})$ under a continuous-wave, linearly polarised excitation. By contrast, we show that a linearly polarised pulse is rotated to a much lesser extent of a few degrees. Depending on the initial boundary conditions, this is due to either retardation or advancement in the amplitude build-up in time of the orthogonal electric field component. Unlike previous published work, the dominant spin relaxation and decoherence processes are fully accounted for in the system dynamics. Our dynamical model can be used for optimisation of the optical polarisation rotation angle for realisation of spin-photon entanglement and ultrafast polarisation switching on a chip.

Polarization state of second harmonic generation in split ring resonator based meta-molecule

In this paper, we study the second harmonic generation (SHG) from the stero-stacked meta-molecules consisting of two vertically stacked split ring resonators (SRRs) that resonate at the fundamental wavelength. When pumped by the linearly polarized incident wave with the electric field direction along one of the SRRs’ arms, the meta-molecules emit the SHG that can have two non-zero orthogonal electric field components, provided that the top SRR and the bottom SRR are not arranged in mutually parallel or anti-parallel manner. Due to the strong coupling between the two SRRs, the plasmonic properties of the stero-stacked meta-molecules could be tuned by varying the twist angle between the two SRRs. In this process, we demonstrate that the amplitudes of the two orthogonal SHG field components, and the phase difference between these two components can be varied with changing the twist angle between two SRRs. Based on the concept of the light polarization, different polarization states can be achieved by changing the differences in phase and amplitude between the orthogonal field components. Therefore, the twist angle dependent amplitudes of and phase difference between two orthogonal SHG field components can be used to manipulate the polarization states of the emitted SHG. For the stero-stacked meta-molecules with a fixed twist angle of 60°, elliptically, near-circularly andnear-linearly polarized SHG emission can be obtained at different fundamental wavelengths. In addition, for the fundamental wave with a fixed wavelength of 1500 nm, the stero-stacked meta-molecules with different twist angles are demonstrated to be able to emit SHG with elliptical andnear-linear polarization states.

Low-Cost Polarization Sensing System for Self-Oscillating Circularly-Polarized Active Integrated Antenna

A simple, low-cost yet efficient polarization sensing system, capable of determining the polarization state of a self-oscillating circularly-polarized active integrated antenna (CPAIA), is proposed and demonstrated. The newly developed sensing system is capable of retrieving the phase difference information between the orthogonal field components of a CPAIA without the need of a common synchronous reference signal as that in a conventional pattern measuring system. The two orthogonal electrical fields are captured and mixed to retrieve the relative phase difference information as dc voltages. As a proof of concept, the polarization sensing system has been successfully developed on a printed circuit board, while a typical passive circularly-polarized antenna and a self-oscillating CPAIA were fabricated as a pair of antennas under test (AUTs). On one hand, the passive AUT characterized by the sensing system was supported by data from a commercial measuring setup to validating the accuracy of the newly developed system. On the other hand, the proposed sensing system is believed to be the first demonstration dedicated to retrieving the polarization information of a self-oscillating CPAIA, and hence pave a new way to fully characterize this special sort of active antennas.

Experimental observation of the polarization coherence theorem.

For light fields, the manifestation of correlations between fluctuating electric field components at different space-time points is referred to as coherence, whereas these correlations appearing between orthogonal electric field components at a single space-time point are referred to as polarization. In this context, a natural question is as follows: how are coherence and polarization interconnected? Very recently, a tight equality P2=V2+D2, namely, the "polarization coherence theorem" (PCT) connecting polarization P with interference visibility V (measure of coherence) and distinguishability D (measure of which-path information) has been proposed [Optica4, 1113 (2017)OPTIC82334-253610.1364/OPTICA.4.001113]. We here report a direct observation of the PCT for classical light fields using a Mach-Zehnder interferometer along with a synthesized source producing a complete gamut of degrees of polarizations. Our experimental demonstration could motivate ongoing experimental efforts toward probing the hidden coherences and complementarity features.

Twisted EM beams with structured correlations

The possibility of restructuring the spectral density of a random light beam up to three times along the propagation path in free space is demonstrated. This can be achieved by prescribing special correlations and different twist factors (by magnitude and/or direction) in the two mutually orthogonal electric field components in the source plane. We also show that the degree of polarization of such a light beam can rotate or not on propagation.

Millimeter-Wave Wideband Circularly Polarized Planar Complementary Source Antenna With Endfire Radiation

A novel circularly polarized (CP) complementary source antenna with endfire radiation is proposed in Ka-band. With the existence of two antipodal notches etched at the edges of the two broad walls of an open-ended substrate-integrated waveguide, two orthogonal electric field components radiated from the equivalent magnetic current, and the electric currents separately can be excited simultaneously. The magnitude and phase differences between the two filed components can be controlled effectively by properly tuning the dimensions of the notches. The operating mechanism and the design procedure of the antenna are analyzed in detail. Wide −10 dB impedance and 3 dB axial ratio bandwidths of 64% and 51%, a gain varying from 3.1 to 6.4 dBic, and the symmetrical radiation pattern are obtained. In order to further increase the gain and front-to-back ratio (FTBR) of the antenna, a dielectric rod structure is then integrated with the antenna. An overlapped operating bandwidth of 41%, an improved gain up to 12 dBic and the stable radiation pattern with an FTBR close to 20 dB are verified by a fabricated prototype. The antenna presented in this paper provides a new mean to design the wideband endfire CP antenna with a simple configuration, which would be attractive for future millimeter-wave wireless systems.

Sensitive and stable vector magnetometer for operation in zero and finite fields.

We report on an optically pumped magnetometer that uses multiple laser beams to pump and probe spin-polarized Cs atoms. The selected sensor geometry allows for operation in finite magnetic fields as well as close to zero field. In finite fields the magnetometer employs free spin precession signals to determine the field modulus and direction as described in a separate publication. This publication focuses on the magnetometer operation close to zero field, which is based on a ground state Hanle resonance. The four laser beams permit the simultaneous measurement of two orthogonal magnetic field components in a differential detection scheme that greatly suppresses technical laser power noise. Sensitivities better than 54 fT/Hz1/2 could be demonstrated simultaneously for both measurement channels in a well shielded environment. A minimum Allan deviation, limited by residual field fluctuations, of better than 40 fT was observed for integration times of 2s. The magnetometer achieves high sensitivity and stability in offset fields as well as close to zero field and is, thus, a universal tool for low frequency magnetic field measurements.

Mathematical and diffractive modeling of self-healing

To analyze the self-healing of a partially obstructed optical beam, we represent it by two orthogonal field components. The first component is an exact copy of the unobstructed beam, attenuated by a factor that is computed by a simple formula. The second component represents a pure distortion field, due to its orthogonality respect to the first one. This approach provides a natural measure of the beam damage, due to the obstruction, and the degree of self-healing, during propagation of the obstructed beam. As interesting results, derived in our approach, we obtain that the self-healing reaches a limit degree at the far field propagation domain, and that certain relatively small phase obstructions may produce a total damage on the beam. The theory is illustrated considering a Gaussian beam, distorted by different amplitude and phase obstructions. In the case of a soft Gaussian obstruction we obtain simple formulas for the far field limit values of the beam damage and the self-healing degree.

Numerical Simulations of Air Breakdown by Microwave With Two Orthogonal Electric Fields

In the near-field zone of an antenna or a microwave device, high-power microwave that may contain two orthogonal electric field components frequently causes air breakdown. The electric field power of microwave for heating electrons is deduced from the equation of electron momentum, and is introduced into a model coupling the equations of electron number density and electron energy to investigate air breakdown. Breakdown prediction obtained from the model considerably matches with that of the particle-in-cell Monte Carlo collision model. The amplitude of the mean electron energy changes periodically with the phase difference between the two electric field components with the same amplitude. At a high air pressure, breakdown formation time depends strongly on phase difference, but this dependence decreases as air pressure decreases. The dependence of air breakdown on the amplitude difference between the two electric field components is also unveiled under a fixed electric filed power. The approximate analytical solution of the mean electron energy is presented to analyze our numerical results.

Miniature Tri-Axis Magnetometer With In-Plane GMR Sensors

A miniature tri-axis magnetometer with in-plane giant magnetoresistance (GMR) sensors and a fluxguide was designed, implemented, and characterized in this paper. Three GMR sensor dies were aligned on a printed circuit board with their sensing directions in the same plane. By using the flux bending effect of a fluxguide, the magnetic field components in the mounting plane of GMR sensors were generated, and hence, the effective sensing directions are not in the same plane. The tilt of effective sensing direction from the mounting plane allows the device to detect the out-of-plane field component. When the device was used as an electronic compass, the digitally demodulated sensor outputs were converted into the orthogonal geomagnetic field components by using a real-time conversion process with the voltage-to-field transfer matrix. The result shows that the device is suitable for compass application. Further works to implement the similar design on a CMOS chip with integrated GMR elements and a planar modulation coil will realize a compact and easy-to-fabricate tri-axis magnetic field sensor.

Ultra-wideband high-efficiency reflective linear-to-circular polarization converter based on metasurface at terahertz frequencies.

The polarization conversion of electromagnetic (EM) waves, especially linear-to-circular (LTC) polarization conversion, is of great significance in practical applications. In this study, we propose an ultra-wideband high-efficiency reflective LTC polarization converter based on a metasurface in the terahertz regime. It consists of periodic unit cells, each cell of which is formed by a double split resonant square ring, dielectric layer, and fully reflective gold mirror. In the frequency range of 0.60 - 1.41 THz, the magnitudes of the reflection coefficients reach approximately 0.7, and the phase difference between the two orthogonal electric field components of the reflected wave is close to 90° or -270°. The results indicate that the relative bandwidth reaches 80% and the efficiency is greater than 88%, thus, ultra-wideband high-efficiency LTC polarization conversion has been realized. Finally, the physical mechanism of the polarization conversion is revealed. This converter has potential applications in antenna design, EM measurement, and stealth technology.

Air breakdown induced by the microwave with two mutually orthogonal and heterophase electric field components**Project supported by the National Natural Science Foundation of China (Grant Nos. 61501358, 61431010, and 61627901) and the Fundamental Research Funds for the Central Universities, China.

The air breakdown is easily caused by the high-power microwave, which can have two mutually orthogonal and heterophase electric field components. For this case, the electron momentum conservation equation is employed to deduce the electric field power and effective electric field for heating electrons. Then the formula of the electric field power is introduced into the global model to simulate the air breakdown. The breakdown prediction from the global model agrees well with the experimental data. Simulation results show that the electron temperature is sensitive to the phase difference between the two electron field components, while the latter can affect obviously the growth of the electron density at low electron temperature amplitudes. The ionization of nitrogen and oxygen induces the growth of electron density, and the density loss due to the dissociative attachment and dissociative recombination is obvious only at low electron temperatures.