Full Polarizations Research Articles

LAGRS-Soil: A Full-Polarization GNSS-Reflectometry Model for Bare Soil Applications in FY-3E GNOS-R Payload

The Land Surface GNSS Reflection Simulator (LAGRS)-Soil model represents a significant advancement in soil moisture detection with the aid of Global Navigation Satellite System (GNSS) Occultation Sounder-Reflectometry (GNOS-R) technology, which is one payload of the Fengyun-3E (FY-3E) satellite that was launched on 5 July 2021. To fully exploit the properties of noncoherent scattering, the LAGRS-Soil model has the capability to calculate DDM information for different observational geometries, which relies on the random surface scattering models employed in LAGRS-Soil. This will provide a comprehensive understanding of soil moisture dynamics across diverse terrains and environments. One of the most notable features of LAGRS-Soil is its ability to obtain DDMs for full polarizations, which enhances soil moisture retrievals compared to current methods that only utilize the commonly used LR polarization (left-hand circular polarization received and right-hand circular polarization transmitted). Meanwhile, the model can also capture frozen soil DDMs which holds immense potential for near-surface Freezing/Thawing (F/T) detection, opening up new research and application opportunities in cold climate regions. LAGRS-Soil is built on microwave scattering models, making it a robust and efficient theoretical model for the FY-3E GNOS-R payload. This model can support ongoing soil moisture retrieval efforts by combining physical models with investigations of diffuse scattering and polarization capabilities for soil moisture detection.

Dual-band metasurface generating multiple OAM beams independently in full polarizations.

In this paper, a dual-band metasurface (MS) generating multiple orbital angular momentum (OAM) beams independently in full polarizations is proposed. First, the design principle of controlling full polarizations independently is analyzed. Second, the frequency selective surface is introduced to the meta-atom design that ensures the meta-atom operates at Ku- and Ka-band independently, while, at each band, sixteen optimized meta-atoms realize the high reflection amplitude and enough phase coverage. Next, the optimized dual-band meta-atom controlling full polarizations independently is utilized to design the MS, which could generate eight independent OAM beams including the x-polarized, y-polarized, left hand circularly polarized, and right hand circularly polarized OAM beams at dual-band. Finally, the MS is designed, fabricated, and measured. Both simulated and measured results verify that the proposed MS could generate multiple OAM beams in full polarizations at dual-band, showing the perspective in the OAM-based area, such as the wireless communication, target detection, and security encryption.

Polarization-Insensitive Metasurface Cloak for Dynamic Illusions with an Electromagnetic Transparent Window.

Artificial camouflage has garnered long-standing interest in both academia and industry. The metasurface-based cloak has attracted much attention due to the powerful capability of manipulating the electromagnetic wave, convenient multifunctional integration design, and easy fabrication. However, existing metasurface-based cloaks tend to be passive and of single function and monopolarization, which cannot meet the requirement of applications in ever-changing environments. So far, it is still challenging to realize a reconfigurable full-polarization metasurface cloak with multifunctional integration. Herein, we proposed an innovative metasurface cloak, which can simultaneously realize dynamic illusion effects at lower frequencies (e.g., 4.35 GHz) and specific microwave transparency at higher frequencies (e.g., X band) for communication with the outside environment. These electromagnetic functionalities are demonstrated by both numerical simulations and experimental measurements. The simulation and measurement results agree well with each other, indicating that our metasurface cloak can generate various electromagnetic illusions for full polarizations as well as a polarization-insensitive transparent window for the signal transmission to enable the communication between the cloaked device and the outside environment. It is believed that our design can offer powerful camouflage tactics to address the stealth problem in ever-changing environments.

Inundated Vegetation Mapping Using SAR Data: A Comparison of Polarization Configurations of UAVSAR L-Band and Sentinel C-Band

Flood events have become intense and more frequent due to heavy rainfall and hurricanes caused by global warming. Accurate floodwater extent maps are essential information sources for emergency management agencies and flood relief programs to direct their resources to the most affected areas. Synthetic Aperture Radar (SAR) data are superior to optical data for floodwater mapping, especially in vegetated areas and in forests that are adjacent to urban areas and critical infrastructures. Investigating floodwater mapping with various available SAR sensors and comparing their performance allows the identification of suitable SAR sensors that can be used to map inundated areas in different land covers, such as forests and vegetated areas. In this study, we investigated the performance of polarization configurations for flood boundary delineation in vegetated and open areas derived from Sentinel1b, C-band, and Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) L-band data collected during flood events resulting from Hurricane Florence in the eastern area of North Carolina. The datasets from the sensors for the flooding event collected on the same day and same study area were processed and classified for five landcover classes using a machine learning method—the Random Forest classification algorithm. We compared the classification results of linear, dual, and full polarizations of the SAR datasets. The L-band fully polarized data classification achieved the highest accuracy for flood mapping as the decomposition of fully polarized SAR data allows land cover features to be identified based on their scattering mechanisms.

Electromagnetic Effective Degree of Freedom of an MIMO System in Free Space

Effective degree of freedom (EDOF) of a multiple-input-multiple-output (MIMO) system represents its equivalent number of independent single-input-single-output (SISO) systems, which directly characterizes the communication performance. Traditional EDOF only considers single polarization, where the full polarized components degrade into two independent transverse components under the far-field approximation. However, the traditional model is not applicable to complex scenarios especially for the near-field region. Based on an electromagnetic (EM) channel model built from the dyadic Green's function, we first calculate the EM EDOF to estimate the performance of an arbitrary MIMO system with full polarizations in free space. Then, we clarify the relations between the limit of EDOF and the optimal number of sources/receivers. Finally, potential benefits of near-field MIMO communications are demonstrated with the EM EDOF, in which the contribution of the longitudinally polarized source is taken into account. This work establishes a fundamental EM framework for MIMO wireless communications.

Independent Wavefront Tailoring in Full Polarization Channels by Helicity‐Decoupled Metasurface

AbstractControlling the polarization and wavefront of light is essential for compact photonic systems in modern science and technology. This may be achieved by metasurfaces, a new platform that has radically changed the way people engineer wave–matter interactions. However, it still remains very challenging to generate versatile beams with independent wavefronts in each polarization channel by a single ultrathin metasurface. By modulating both the geometric and propagation phases of the metasurface, here a method is proposed that can generate an assembly of circularly and linearly polarized beams with simultaneously the capability of independent encoding desired wavefront to each individual polarization channel, which is believed to greatly enhance the information capacities of the metadevices. Two proof‐of‐concept designs are experimentally demonstrated in microwave region. Upon the excitation of an arbitrary linear polarization, the first device can generate distinct vortex beams with the desired two linear and two circular orthogonal polarizations, whereas the second one can generate multifoci containing components of full polarizations. This approach to generate versatile polarizations with tailored wavefront may pave a way to achieve advanced, flat, and multifunctional metadevice for integrated systems.

Smart Doppler Cloak Operating in Broad Band and Full Polarizations

Invisibility cloaks, a class of attractive devices that can hide objects from external observers, have become practical reality owing to the advent of metamaterials. In previous cloaking schemes, almost all demonstrated cloaks are time-invariant and are investigated in the system that is motionless, and hence they are limited to hide stationary objects. In addition, the current cloaks are typically static or require manual operation to achieve dynamic cloaking. Here, a smart Doppler cloak operating in broadband and full polarizations is reported, which consists of a time-modulated reflective metasurface and a sensing-feedback time-varying electronic control system. Experimental results show that the smart Doppler cloak is able to respond self-adaptively and rapidly to the ever-changing velocity of moving objects and then cancel different Doppler shifts in real time, without any human intervention. Moreover, the wideband and polarization-insensitive features enable the cloak to be more robust and practical. To illustrate the capabilities of the proposed approach, the smart Doppler cloak is measured in three scenarios with two different groups of linearly-polarized incidences at 3.3 and 4.9GHz, and one group circularly-polarized incidences at 6.0GHz, respectively.

In-situ measurement of electrode kinetics in porous electrode for vanadium flow batteries using symmetrical cell design

Electrode kinetics are crucial to electrochemical performance of vanadium flow battery. However, existing studies on electrode kinetics are mostly performed in ex-situ conditions based on planar electrodes, so the obtained rate constant can neither reflect the kinetics in practically used porous electrode nor be used to predict the activation polarizations of a real flow cell. To address this limitation, an in-situ measurement of electrode kinetics in porous electrode is conducted in this study by a symmetrical cell design for vanadium flow battery. For both V2+/V3+ and VO2+/VO2+ couples, the activation polarization as a function of current density is firstly acquired on the symmetrical cell through measurements of polarization curve, high frequency resistance and local mass transfer coefficient, followed by Tafel fitting that yields both rate constant and transfer coefficient. Based on kinetic parameters of both V2+/V3+ and VO2+/VO2+, the simulated full cell activation polarizations coincide well with the full cell experimental result. By further comparing to simulation results using reported kinetic parameters determined from planar electrodes, the reliability of the proposed method is further highlighted. The electrode evaluation is much more involved than Tafel polarization and stack design is not treated in this contribution.

First-principles study of the metal-insulator transition in the Ti-substituted rutile CrO2

The effect of Ti-substitution for Cr in CrO2 is extensively studied by employing first-principles electronic structure calculations. The host material is a ferromagnetic half-metal. This material encounters first step transition from half-metal to a metallic phase at 50% Ti-substitution for Cr. The application of Coulomb interaction U significantly changes the electronic and magnetic properties of Cr0.5Ti0.5O2. This material remains in its metallic phase up to U = 2 eV and encounters a second step transition from the metallic to a half-metallic phase at U = 3 eV. Eventually, this system exhibits a metal-insulator transition (MIT) at U = 4 eV with a band gap of 0.15 eV. Nevertheless, Cr0.5Ti0.5O2 preserves its ferromagnetism (FM) in all the metallic, half-metallic and insulating phases. The metal to half-metal transition in Cr0.5Ti0.5O2 is observed due to full spin polarizations accompanied by strong dynamical correlations of Cr-dyz/xz electrons. Besides this, weak static but the strong dynamical correlation of electrons in the bonding and anti-bonding components of Cr-dyz/xz orbitals is accounted for the key element of MIT in Cr0.5Ti0.5O2. The FM in the half-metallic Cr0.5Ti0.5O2 arises from the double exchange interaction of electrons in the partially occupied bonding and anti-bonding components of Cr-dyz/xz orbitals. In addition, the double exchange interaction of electrons in the bonding components of Cr-dyz/xz orbitals triggers FM in the insulating phase of Cr0.5Ti0.5O2. The ferromagnetic Curie temperature increases due to Ti-substitution in CrO2. Finally, a trivial structural distortion is observed due to Ti-substitutions in CrO2.

Modelling of radio frequency sheath and fast wave coupling on the realistic ion cyclotron resonant antenna surroundings and the outer wall

In order to model the sheath rectification in a realistic geometry over the size of ion cyclotron resonant heating (ICRH) antennas, the self-consistent sheaths and waves for ICH (SSWICH) code couples self-consistently the RF wave propagation and the DC SOL biasing via nonlinear RF and DC sheath boundary conditions applied at plasma/wall interfaces. A first version of SSWICH had 2D (toroidal and radial) geometry, rectangular walls either normal or parallel to the confinement magnetic field B0 and only included the evanescent slow wave (SW) excited parasitically by the ICRH antenna. The main wave for plasma heating, the fast wave (FW) plays no role on the sheath excitation in this version. A new version of the code, 2D SSWICH-full wave, was developed based on the COMSOL software, to accommodate full RF field polarization and shaped walls tilted with respect to B0. SSWICH-full wave simulations have shown the mode conversion of FW into SW occurring at the sharp corners where the boundary shape varies rapidly. It has also evidenced ‘far-field’ sheath oscillations appearing at the shaped walls with a relatively long magnetic connection length to the antenna, that are only accessible to the propagating FW. Joint simulation, conducted by SSWICH-full wave within a multi-2D approach excited using the 3D wave coupling code (RAPLICASOL), has recovered the double-hump poloidal structure measured in the experimental temperature and potential maps when only the SW is modelled. The FW contribution on the potential poloidal structure seems to be affected by the 3D effects, which was ignored in the current stage. Finally, SSWICH-full wave simulation revealed the left–right asymmetry that has been observed extensively in the unbalanced strap feeding experiments, suggesting that the spatial proximity effects in RF sheath excitation, studied for SW only previously, is still important in the vicinity of the wave launcher under full wave polarizations.

Full Valley and Spin Polarizations in Strained Graphene with Rashba Spin Orbit Coupling and Magnetic Barrier.

We propose a graphene-based full valley- and spin-polarization device based on strained graphene with Rashba spin orbit coupling and magnetic barrier. The underlying mechanism is the coexistence of the valley and single spin band gaps in a certain Fermi energy. By aligning the Fermi energy in the valley and single spin band gaps, remarkable valley- and spin-polarization currents can be accessed.

Stable Target Detection and Coherence Estimation in Interferometric SAR Stacks

We propose a novel method to select long-term coherent targets from a set of repeated-pass interferometric acquisitions. The major assumption is that targets are so close together to share the same optical path. This leads to an efficient singular-value-decomposition-based estimator of the targets' phase and, then, to PS detection. The estimated phase can be used to define the PS coherence for each image. Being sensitive to acquisition and processing artifacts, the PS coherence is a valuable tool for quality assessment of the interferometric stack. Results are shown with real data sets in both single and full polarizations.

Markov Chain CFAR Detection for Polarimetric Data Using Data Fusion

This paper proposes a new Markov-chain-based constant false alarm rate (CFAR) detector for polarimetric data using low-level data fusion and high-level decision fusion. The Markov-chain-based CFAR detector extends traditional probability density function (pdf) based CFAR detection to first-order Markov chain model by considering both correlation between neighboring pixels and pdf information in CFAR detection. With the additional correlation information, the proposed approach results in advancing the performance of conventional CFAR detectors. Moreover, to take advantage of full polarizations of polarimetric data, various data fusion methods are considered to improve detection performance, including polarimetric transformation, principal component analysis, and decision fusion. Our experimental results confirm the superiority of the new Markov chain polarimetric CFAR detector over conventional pdf-based CFAR detectors.

Tuning the band gap and magnetic properties of BN sheets impregnated with graphene flakes

The BN sheet is a nonmagnetic wide-band-gap semiconductor. Using density functional theory, we show that these properties can be fundamentally altered by embedding graphene flakes. Not only do graphene flakes preserve the two-dimensional (2D) planar structure of the BN sheet, but by controlling their shape and size, unexpected electronic and magnetic properties also emerge. The electronic band structure can be tuned from a direct gap to an indirect gap, the energy gap can be further modulated by changing the bonding patterns, and both hole injecting or electron injecting can be achieved by tailoring the triangular embedding pattern. Furthermore, the Lieb theorem still holds, and the embedded triangular graphene flakes become ferromagnetic with full spin polarizations of the introduced electrons or holes, opening the door to their use as spin filters. The study sheds new light on hybrid single-atomic-layer engineering for unprecedented applications of 2D nanomaterials.

Bistatic radar scattering measurement of sands at different sizes

An equipment set of microwave scattering measurements is presented with full polarizations and a wide frequency from 10 MHz to 40 GHz. The system used for this network analyzer consists of three groups of antenna, in which one group antenna with a range of 1∼18 GHz can be used to measure the scattering coefficients of samples of sand of different sized particles using different azimuths and incidence angles. Using the object-limited measurements and the metal calibration, the scattering coefficients of three samples of sand of different sized particles were accurately obtained by measuring the same area sand samples and metal plates, including both forward-scattering and backscattering measurements. The results show that the scattering coefficients of three samples of sand of different sized particles can be measured using this network analyzer system.

THEORETICAL MODEL OF ELECTROMAGNETIC SCATTERING FROM 3D MULTI-LAYER DIELECTRIC MEDIA WITH SLIGHTLY ROUGH SURFACES

A theoretical model of scattering from three-dimensional arbitrary layered media with 3D inflnite rough surfaces based on the small perturbation method (SPM) is derived in the present paper. The scattering fleld and bistatic scattering coe-cient for linear polarized waves are derived respectively. Firstly, the electric and magnetic flelds in each region of the layered structure are expanded into perturbation series in spectral domain. Secondly, the expansion coe-cients of each order are obtained by applying the boundary conditions. As a result, the expressions of the zeroth-, flrst- and second-order solutions of the scattering problem based on the SPM are obtained, in which the second-order solution is the primary contribution of this work. The theoretical model is helpful to understand the dependence between the scattering fleld and physical properties of the layered structure (such as surface roughness and dielectric constants at difierent depths). The result can be applied to modeling of the received radar signal from nature targets such as layered soil and ice with full polarizations.

Spin filtering implemented through Rashba spin-orbit coupling and weak magnetic modulations

We present two theoretical schemes for spin filters in one-dimensional semiconductor quantum wires with spatially modulated Rashba spin-orbit couplings (SOCs) and weak magnetic potentials. In the first scheme, the SOC is periodic and the weak magnetic potential is applied uniformly along the wire. Full spin polarizations with opposite signs are obtained within two separated energy intervals. In the second scheme, the weak magnetic potential is periodic while the SOC is uniform. An ideal negative/positive switching effect for spin polarization is realized by tuning the strength of SOC. The roles of SOC, magnetic potential, and their joint action on the spin filters are analyzed.

Coupling superconducting-ferromagnetic point contacts by Andreev reflections

The properties of a device made of two point contacts between normal (N) or ferromagnetic (F) tips, and a superconductor (S), are discussed as a function of the spin polarization and the distance L between the contacts. When L is smaller than the superconductor coherence length ξ, nonlocal Andreev reflections occur: for opposite spin polarizations of the contacts, “mixed” Cooper pairs made of electrons coming one from each tip can be injected into the superconductor. This leads to unusual properties, for instance, the parallel resistance of two S/F contacts goes from infinity for full and equal polarizations, to a finite Andreev value for opposite ones.

Polarization of Neutrons and Protons by Scattering

Neutrons and protons can be polarized by scattering provided there is a spin-orbit interaction between the incident particle and the scattering nucleus. The polarization effect has been found for a nucleus of spin zero allowing for the possibility of resonance scattering. Particular attention has been paid to the resonance scattering of neutrons by ${\mathrm{He}}^{4}$ where almost full polarizations can be obtained, together with large cross sections. The polarization can be detected by a double scattering experiment, since the second scattering will be axially asymmetric with respect to the direction of the first scattered neutron. The existence of this effect and a preliminary treatment of it was first pointed out by Schwinger.The scattering of polarized neutrons by protons has been studied for potentials suggested by the symmetrical, charged and neutral meson theories. The polarization effect on the differential cross section is negligible for the symmetrical theory, but is significant for the other two.