Oblique Polarization Research Articles

Transverse Oscillations and Kelvin–Helmholtz Instability in Curved Arcade Loops with Siphon Flows

The effect of plasma flow in curved arcade loops on transverse waves and oscillations is examined analytically. The model under study is a semicircular magnetic slab with finite transverse extensions and a mass flow inside, in the zero-β plasma approximation. It is found that in the quasi-perpendicular propagation limit, the model supports two fast surface modes: one with higher (FSW+) and another with lower (FSW−) frequency. For a weak flow, the frequency of the FSW+ (FSW−) increases (decreases) as the flow speed grows in both propagating and quasi-standing wave regimes. We show that the FSW+ and FSW− are subjected to the Kelvin–Helmholtz (KH) instability, and the threshold flow is greater (less than) the internal Alfvén speed for the FSW+ (FSW−). The presence of plasma flow results in modifying the period ratio P 1/2P 2 of the fundamental harmonic to the first overtone with P 1/2P 2 less (more) than 1 for the FSW+ (FSW−), and this effect degenerates in the straight waveguide limit. The sub-Alfvénic flow can prohibit resonant absorption of kink modes when the frequencies of the FSW+ and FSW− become out of the Alfvén continuum. It is also shown that in the static case and for a weak flow case, the FSW+ (FSW−) is interpreted as a vertically (horizontally) polarized kink mode, while for moderate flow, both modes have oblique polarization. We apply the developed theory to interpret the observational cases of kink oscillations in coronal loops with signatures of a siphon flow and the onset of KH instability induced by the blowout jet along a loop-shaped magnetic structure.

Analysis of Reader Orientation on Detection Performance of Hilbert Curve-based Fractal Chipless RFID Tags

The role of the orientation of the radio frequency identification (RFID) reader is vital in the RFID-based communication system. This study presents the design and analysis of the impact of the orientation of the RFID reader (angle of incidence of the plane wave) on the detection and sensitivity characteristics of fractal chipless RFID tags. Four fractal (irregular) shaped tags are developed using four iterations of the Hilbert curve filling algorithm. The full-wave EM analysis of the designed tags in Matlab is performed by exporting them in Computer Simulation Technologies Micro-Wave Studio (CST MWS) in the frequency range of 2 to 20 GHz. Firstly, the performance of the tags is analyzed by observing the radar cross-section (RCS) of the tag for the fixed orientation of the incident plane wave in three different polarizations (horizontal, vertical, and oblique). Later, the variations in the EM spectrum (RCS results) are analyzed for oblique polarization by varying the incidence plane wave in both elevations (for two cases of 0∘ and 90∘) and azimuth planes (sweeping from 0∘ to 180∘ with a step size of 10∘). The analysis of the proposed aggregated RCS response for all cases in oblique polarization produces higher coding capacity (169 bits), coding spatial capacity (16.504 bits/cm2), coding spectral capacity (9.826 bits/GHz), and coding density (0.960 bits/GHz/cm2) for the realized highly irregular tag using fourth-iteration (4T) of Hilbert curve filling algorithm. The proposed procedure of detection based on aggregated response makes the developed RFID communication system more secure and reliable.

Polarization conversion at multiple angles in the terahertz regime via a metasurface with two crossed L-shaped elements

Although remarkable advances have been made over the past decades, more functional devices suitable for practical systems are needed to further facilitate the development and application of terahertz technology. Among them, polarization devices are essential in terahertz systems. In this work, a metasurface with a multi-angle polarization conversion function is proposed. The device is composed of a top metal structure layer, a dielectric spacer, and a bottom metal film. The unit cell in the metal structure layer consists of two L-shaped elements which are symmetric about the −45° axis and rotated clockwise and counterclockwise around the center, respectively. Cross-polarization conversion can be achieved when the metal structure is in its original position. When the structure is rotated counterclockwise at a certain angle around the center, oblique polarization conversion can be realized within the same frequency band. If we keep rotating the structure, more polarization conversion angles can be achieved. Compared with recent reports, the structure proposed here is more flexible in polarization conversion and more suitable for practical applications and has great potential in the terahertz field.

Review of Processing and Interpretation of Self-Potential Anomalies: Transfer of Methodologies Developed in Magnetic Prospecting

The self-potential (SP) method is one of the most inexpensive and unsophisticated geophysical methods. However, its application is limited due to the absence of a reliable interpreting methodology for the complex geological-environmental conditions. To exclude disturbances appearing in the SP method, a few ways for their removal (elimination) before quantitative analysis are presented. A brief review of the available interpretation methods is included. For the magnetic method of geophysical prospecting, special quantitative procedures applicable under complex physical-geological environments (oblique polarization, uneven terrain relief and unknown level of the normal field), have been developed. The detected common peculiarities between the magnetic and SP fields make it possible to apply the advanced procedures developed in magnetic prospecting to the SP method. Besides the reliable determination of the depth of anomalous targets, these methodologies enable the calculation of the corrections for non-horizontal SP observations and to determine the orientation of the polarization vector. For the classification of SP anomalies, is proposed to use a new parameter: the ‘self-potential moment’. The quantitative procedures (improved modifications of characteristic point, tangent techniques and the areal method) including the determination of the SP vector and SP moment, have been successfully tested on models and employed in real situations in mining, archaeological, environmental and technogenic geophysics. The obtained results indicate the effectiveness of the presented methodologies.

Quantitative analysis of self-potential anomalies in archaeological sites of Israel: an overview

Self-potential (SP) method is one of the most non-expensive and unsophisticated geophysical methods. However, its application limits absence of reliable interpreting methodology, first for the complex geological–environmental conditions. The typical disturbances appearing in the SP method and ways for their removing (elimination) are discussed. Some brief review of the available interpretation methods indicates their insufficient effectivity, especially for the complex environments. For the magnetic method of geophysical prospecting, special quantitative procedures applicable under non-trivial environments (oblique polarization, rugged relief and unknown level of the normal field) have been recently developed. Performed analysis allowed to revealing some essential common peculiarities between the magnetic and SP fields. These common aspects make it possible to apply the advanced procedures developed in magnetic prospecting to SP method. Besides the reliable determination of the depth of anomalous target, these methodologies enable to calculate the polarization effect and corrections for the non-horizontal SP observations. For classification of SP anomalies is supposed to employ a new parameter—‘self-potential moment’. These procedures (improved modifications of characteristic point and tangent techniques) have been successfully tested on SP models and employed in the real situations in various archaeological sites in Israel. The present paper generalizes the earlier performed studies. The obtained results indicate the practical importance of the developed methodology.

Mesoscopic hierarchic polarization structure in the relaxor ferroelectrics Pb[(Mg1/3Nb2/3)1−xTix]O3

Mesoscopic polarization structures such as polar nanoregions and polarization domain walls are the key factors connecting microscopic fundamental polarization structures with macroscopic practical dielectric properties. A snapshot observation of the domain in the relaxor ferroelectrics $\mathrm{Pb}[{(\mathrm{M}{\mathrm{g}}_{1/3}\mathrm{N}{\mathrm{b}}_{2/3})}_{1\text{\ensuremath{-}}x}\mathrm{T}{\mathrm{i}}_{x}]{\mathrm{O}}_{3}$ just in the vicinity of morphotropic phase boundary region was performed by use of 7-ps single shot soft x-ray laser pulse. A self-assembled evolution of the oblique polarization domain was observed in $\mathrm{Pb}[{(\mathrm{M}{\mathrm{g}}_{1/3}\mathrm{N}{\mathrm{b}}_{2/3})}_{72.2}\mathrm{T}{\mathrm{i}}_{27.8}]{\mathrm{O}}_{3}$ under the sample temperature decreased with the thermal equilibrium condition. Based on energetic discussion, antiphase shift of domain wall pairs keeping flat boundaries was proposed for the dielectric response. A sharp enhancement in the dielectric response at the vicinity of morphotropic phase boundary region reported previously was recognized as evidence for the hierarchic nature of the present oblique polarization domain wall.

Oblique projection for direction‐of‐arrival estimation of hybrid completely polarised and partially polarised signals with arbitrary polarimetric array configuration

This study deals with the direction-of-arrival (DOA) estimation problem for hybrid completely polarised (CP) and partially polarised (PP) source signals using arbitrary polarimetric antenna arrays. An oblique projection-based polarisation insensitive direction estimation (OPPIDE) algorithm is proposed by exploiting the spatial-sparsity property of the sources. The OP technique is utilised to provide spatial filters, which are insensitive to the state of polarisation of signals, so that the potential source signals in the spatial domain can be separated later. The DOA estimation is finally implemented by identifying the sources’ spatially sparse structure with the separated signals. Theoretical analysis indicates that the OPPIDE is applicable to any hybrid CP and PP signals, and is independent of special polarimetric array configurations. The effectiveness and superiority of the proposed OPPIDE are substantiated through making performance comparison with the present counterpart algorithms.

Experimental and theoretical directional dependence of optical polar phonons in the LiNbO3 single crystal: New and complete assignment of the normal mode frequencies

In this work, the analysis of both experimental and theoretical angular dispersion of the Raman frequencies of the optical polar phonons in LiNbO3 (LN) single crystal has been determined with the emphasis of the determination without ambiguity of a new and complete set of the normal mode assignments that clarify long‐standing debates. The coherency of such couple assignments is assessed by the computed oscillator strengths that are revealed to be in satisfactory agreement with others on the one hand and by the comparison with the oblique frequencies measured from the compilation of the Raman spectra acquired under different geometrical configurations in the 90° scheme on the other hand. Finally, the directional behavior of the quasinormal vectors has been established and discussed with regard to the symmetry mixing of modes or the mode with oblique polarization.

THz Thermal Emission Control Via Electromagnetic Band Engineering

In the following, we report on the design and implementation of an inexpensive thermal source for THz radiation with a highly tunable radiation signature. It consists of five 350- μm-thick Si wafers, each spaced 1 mm apart. The thermal emission of this structure was calculated analytically and numerically. A comprehensive study was performed that included analyzing the oblique incidence, polarization, and design tolerance effects. The thermal emission was calculated using both Kirchhoff's law and directly using a Green's function method. It was measured using a Michelson interferometer. The predicted and measured thermal emission spectra had peaks around 150 GHz apart, with a narrow bandwidth of 50 GHz. The peaks were up to 80% of the expected blackbody levels and the bandgaps had emission levels of about 20% of those blackbody values. We demonstrate that, using these techniques, it is possible to achieve a desired THz thermal emission signature, with narrowband features that can be engineered to have specific angles of emission and polarization states.

Integral Equation Modeling of Doubly Periodic Structures With an Efficient PMCHWT Formulation

A surface integral equation modeling is described for complex doubly periodic structures. To avoid long computations of the slowly convergent pseudoperiodic Green's function, fictitious surfaces between translated unit cells are set in order to bound regions of the structure within the symmetry cell and use the free-space Green's function. The integral operators on top and bottom surfaces are computed with an algorithm originally used for planar frequency-selective surfaces. This approach uses a unique periodic PMCHWT formulation in all the regions, with two different kinds of Green's function. The method and its advantages are illustrated by two cases in the near-IR domain and in the radar domain. A frequency selective structure is studied, that shows a large flat-top bandwidth under oblique incidence and TM polarization.

Archaeological geophysics in arid environments: Examples from Israel

Israel is a country with mostly arid environments where is localized extremely large number of archaeological objects of various age, origin and size. The archaeological remains occur in multi-layered and variable geological–archaeological media. In many cases physical properties of the ancient objects are disturbed by long-term influence of arid conditions. These disturbances strongly complicate interpretation of observed geophysical anomalies since the useful signal/noise ratio is often sufficiently reduced. Another disturbing factors are the influence of uneven topography, oblique polarization (especially, for magnetic field analysis) and industrial-engineering objects of different kinds situating in the vicinity of studied remains. From a rich arsenal of the developed techniques (the most part of them is described in Khesin et al. (1996)) in the paper are presented the methods of advanced quantitative analysis of potential geophysical fields and 3D magnetic field modelling. A brief archaeological-geophysical review indicates that in Israeli archaeological sites were applied practically all near-surface geophysical methods: beginning from the paleomagnetic examination and ending by microwave remote sensing. Such a diversity of applied methods and constant accomplishing of geophysical, archaeological and other data stipulate creating of a multi-linkage as between the various geophysical methods, so also with other archaeologically related databases.

Estimation of polarization parameters using time–frequency representations and its application to waves separation

This paper deals with the detection of polarized seismic waves, the estimation of their polarization parameters, and the use of these parameters to apply waves separation. The data, containing several polarized waves together with some noise, are recorded by two-component sensors. After a review presenting the tools classically used to estimate the polarization parameters of a wave in the time domain and in the time–frequency domain, respectively, we present a new methodology to detect polarized waves, and estimate their polarization parameters automatically. The proposed method is based on the segmentation of a time–frequency representation of the data. In addition, after describing the proposed polarization estimation method, we present the oblique polarization filter (OPF) that enables the separation of two polarized waves using their polarization parameters, even if the corresponding patterns partially overlap in the time–frequency plane. The OPF consists in applying phase shifts, rotations, and amplifications in order to project one wave on one single component and the other wave on the other component. Being more efficient than classical polarization estimation methods, our approach greatly increases the separation performances of the OPF. Results are presented both on synthetic and real seismic data.

Plastic Deformation of MgGeO 3 Post-Perovskite at Lower Mantle Pressures

Polycrystalline MgGeO3 post-perovskite was plastically deformed in the diamond anvil cell between 104 and 130 gigapascals confining pressure and ambient temperature. In contrast with phenomenological considerations suggesting (010) as a slip plane, lattice planes near (100) became aligned perpendicular to the compression direction, suggesting that slip on (100) or (110) dominated plastic deformation. With the assumption that silicate post-perovskite behaves similarly at lower mantle conditions, a numerical model of seismic anisotropy in the D'' region implies a maximum contribution of post-perovskite to shear wave splitting of 3.7% with an oblique polarization.

Diffraction of Plane Waves by a Finite Array of Dielectric-Loaded Cavity-Backed Slots on a Common Ground Plane for Oblique Incidence and Arbitrary Polarization

Plane-wave diffraction by a finite array of two-dimensional dielectric-loaded cavity-backed slots on a common ground plane is investigated for oblique incidence and arbitrary polarization. The governing system of coupled singular integral/integrodifferential equations is discretized using moment-method-oriented direct singular integral equation methods. Treating all singular integrals analytically via rapidly converging algorithms leads to numerically stable and efficient analytical expressions for all matrix elements. As a result, no numerical integration is required to compute these elements. Several numerical examples are presented to validate the algorithm and illustrate its convergence characteristics. Results are also presented that reveal the possibility of controlling the absorption efficiency by suitably selecting several geometrical and physical parameters of the structure.

Polarisation interferometry flying height testing

The in-depth analyses of polarisation interferometry flying height testing are presented. The drawbacks of the oblique incidence polarisation interferometry method are discussed. The application of the dual-beam normal incidence polarisation interferometry method is illustrated. It is shown that with this normal incidence polarisation interferometer, not only the flying height can be measured down to contact without losing accuracy, but the optical parameters of the head-slider can also be determined.

Observation of in plane magnetization reversal using polarization dependent magneto-optic Kerr effect

We present an experimental setup for in plane two axis magnetometry using the polarization dependent magneto–optic Kerr effect (MOKE). A conventional setup to measure longitudinal MOKE with crossed polarizers is extended by a Faraday cell to compensate for the rotation of the polarization vector caused by a magnetized sample. The shape of the hysteresis loops measured on thin FeNi alloy films depends strongly on the angle between the optical axis of the analyzer and the plane of incidence. We derive expressions for the compensation angle which allow for extraction of vectorial magnetic information from loops detected with oblique polarization. For a small deviation from pure s or p polarization the transverse magnetization is found to be proportional to the difference between the loop obtained with oblique polarization and the one obtained with pure s or p polarization. Thus the complete in plane reversal process split up into longitudinal and transverse components can be observed.

Normal incidence polarization interferometry flying height testing

In this paper, a dual-beam normal incidence polarization interferometer is presented to measure the flying height or head-disk spacing. It has the advantages of both the intensity interferometry method and the oblique incidence polarization interferometry method. With this polarization interferometer, not only can the flying height be measured down to contact without losing accuracy, but also the pitch and roll of the head-slider can be detected dynamically. The optical parameters of the head-slider can also be determined. Design details and experimental results are given.

Large effects of CP- and T-violation in K0 decay

The ϵ-impurity of the K L wave-function gives rise to a huge CP-violating effect in the decay K L → π +π −γ which is hidden in the polarization state (Stokes vector) of the photon. One component of the Stokes vector is CP-odd and T-even, and may be identified with circular polarization. Another component is CP-odd and T-odd (“oblique polarization”) and reveals itself as a large asymmetry (14%) in the decay K L → π + π − e + e −. Striking time-dependent effects are predicted in the angular distribution of the π +π − e + e − system emanating from an initial K 0 or K 0 state.

In Search of a Chiral Smectic Liquid-Crystal State with a Macroscopic Spontaneous Ferroelectric Polarization

The possibility of realizing a chiral tilted smectic phase having a nontransverse spontaneous ferroelectric polarization $\stackrel{\ensuremath{\rightarrow}}{P}$ is investigated theoretically. A ferroelectric smectic phase with an oblique polarization $\stackrel{\ensuremath{\rightarrow}}{P}$ is shown to be compatible with the Sm- ${A}^{*}$\char21{}Sm- ${C}^{*}$ order-parameter symmetry, but not with the property of the medium to be invariant against sign reversal of the director. The properties and possible existence of this smectic state, which is termed Sm- ${C}_{P}^{*}$, are discussed.

Comments on "Electromagnetic wave scattering by an infinite plane metallic grating in case of oblique incidence and arbitrary polarization

In a previous paper by K. Uchida et al. (see ibid., vol.36, no.3, p.415-22, 1988) it is claimed that in the case of an arbitrary polarized plane wave incident on a strip grating, it is necessary to investigate the quasi-two-dimensional problem where the separation into transverse magnetic (TM) and transverse electric (TE) waves is, in general, impossible. It is shown here that although in general, arbitrarily polarized incident wave case decomposition into TE and TM waves is impossible, it is possible to divide any electromagnetic field into two orthogonal components; (1) fast polarization where an H-field component parallel to the strips is zero and (2) slow polarization where an E-field component parallel to the strips is zero. >