Cross-polarization Research Articles

Performance of the cross-polarization experiment in conditions of radiofrequency field inhomogeneity and slow to ultrafast magic angle spinning (MAS).

In this paper, we provide an analytical description of the performance of the cross-polarization (CP) experiment, including linear ramps and adiabatic tangential sweeps, using effective Hamiltonians and simple rotations in 3Dspace. It is shown that radiofrequency field inhomogeneity induces a reduction in the transfer efficiency at increasing magic angle spinning (MAS)frequencies for both the ramp and the adiabatic CPexperiments. The effect depends on the ratio of the dipolar coupling constant and the sample rotation frequency. In particular, our simulations show that for small dipolar couplings (1 ) and ultrafast MAS (above 100 ) the transfer efficiency is below 40 % when extended contact times up to 20 are used and relaxation losses are ignored. New recoupling and magnetization transfer techniques that are designed explicitly to account for inhomogeneous radiofrequencyfields are needed.

A Differential Slot-type Dual-polarization Ultra-wideband Antenna

A differentially fed dual-polarization slotted antenna with an ultra-wide bandwidth and low cross polarization is presented in this paper. The antenna is composed of a radiation patch and a ground plane, both of which are printed on the top of the dielectric substrate. The ground is extended toward the radiation patch to form a slotted coplanar structure. In order to expand the bandwidth, a cross-shape symmetrical slotted structure is loaded into the radiation patch. Differential feed is adopted to realize 0∘/90∘ linear polarizations and suppress the cross polarization. Simulation and measurement results show that the proposed antenna with dimensions of 0.53λ0× 0.53λ0 × 0.0135λ0 (λ0is the wavelength at 4 GHz) has a differential mode impedance bandwidth of 82.25% (2.27-5.56 GHz), a differential feed port isolation of higher than 28 dB, and a cross polarization level of less than −30 dB, which achieves the characteristics of ultra-wideband, high isolation, and low cross polarization level.

Research on a demand design method of a cross polarization converter metasurface based on a depth generation model

As a two-dimensional electromagnetic metamaterial, the cross-polarization conversion (CPC) metasurface is thin, easy to develop, and has attracted wide attention. However, existing CPC cell surface designs still rely on inefficient full-wave numerical simulation. Although some researchers have explored deep learning CPC metasurface structure design methods, the generated metasurface patterns are of poor quality. In this paper, an on-demand design method for cross-polarization conversion metasurface based on depth-generation model is proposed. Firstly, Wasserstein generative adversarial network (WGAN) is used to reverse design CPC metasurface, and Wasserstein distance is introduced to replace JS divergence and KL divergence to optimize the target. The problem of training difficulty caused by gradient elimination of original generative adversarial network (GAN) is fundamentally solved. Secondly, in the WGAN model, U-Net architecture generator is used to generate images, which greatly improves the surface image quality of CPC. In addition, a simulator composed of convolutional neural network (CNN) is also added in this paper to carry out forward prediction of S-parameter spectrum diagram. By inputting the patterns generated by WGAN into the simulator, the corresponding S-parameter spectrum diagram is generated and compared with the real S-parameter spectrum diagram, so as to verify whether the surface patterns of generated elements meet the requirements. The depth generation model proposed in this paper organically combines the forward spectrum prediction model and the reverse CPC metasurface structure design model, so that the CPC metasurface structure satisfying the expected electromagnetic response can be designed quickly on demand. This on-demand design method is expected to promote the rapid design, fabrication and application of electromagnetic devices.

Low energy eta-baryon interaction

The η-baryon interactions at low energies are studied using a model based on effective chiral Lagrangians, which consider baryons with spin 1/2 and spin 3/2 in the intermediate states. The interacting baryons considered in this work are B=N,Λ,Σ,Ξ. We calculate the expected total and differential cross sections, phase shifts, and polarizations in the center-of-mass frame of reference for each reaction.

An automated multi-order phase correction routine for processing ultra-wideline NMR spectra

Efficient acquisition of wideline solid-state nuclear magnetic resonance (NMR) spectra with patterns affected by large inhomogeneous broadening is accomplished with the use of broadband pulse sequences. These specialized pulse sequences often use frequency-swept pulses, which feature time-dependent phase and amplitude modulations that in turn deliver broad and uniform excitation across large spectral bandwidths. However, the resulting NMR spectra are often affected by complex frequency-dependent phase dispersions, owing to the interplay between the frequency-swept excitations and anisotropic resonance frequencies. Such phase distortions necessitate the use of multi-order non-linear corrections in order to obtain absorptive, distortion-free patterns with uniform phasing. Performing such corrections is often challenging due to the complex interdependence of the linear and non-linear phase contributions, and how these may affect the NMR signal. Hence, processing of these data usually involves calculating the spectra in magnitude mode wherein the phase information is discarded. Herein, we present a fully automated phasing routine that is capable of processing and phase correcting such wideline NMR spectra. Its performance is corroborated via processing of NMR data acquired using both the WURST-CPMG (Wideband, Uniform-Rate, Smooth Truncation with Carr-Purcell Meiboom-Gill acquisition) and BRAIN-CP (BRoadband Adiabatic Inversion Cross Polarization) pulse sequences for a variety of nuclei (i.e., 119Sn, 195Pt, 35Cl, 87Rb, and 14N). Based on both simulated and experimental NMR datasets, it is demonstrated that automatic phase corrections up to and including second order can be readily achieved without a priori information regarding the nature of the phase-distorted NMR datasets, and independently of the exact manner in which time-domain NMR data are collected and subsequently processed. In addition, it is shown that NMR spectra acquired at both single and multiple transmitter frequencies that are processed with this automated phasing routine have improved signal-to-noise properties than those processed with conventional magnitude calculations, along with powder patterns that better match those of ideal NMR spectra, even for datasets possessing low signal-to-noise ratios and/or affected by spectral artifacts.

Strategies for acquisition of resonance assignment spectra of highly dynamic membrane proteins: a GPCR case study.

In protein nuclear magnetic resonance (NMR), chemical shift assignment provides a wealth of information. However, acquisition of high-quality solid-state NMR spectra depends on protein-specific dynamics. For membrane proteins, bilayer heterogeneity further complicates this observation. Since the efficiency of cross-polarization transfer is strongly entwined with protein dynamics, optimal temperatures for spectral sensitivity and resolution will depend not only on inherent protein dynamics, but temperature-dependent phase properties of the bilayer environment. We acquired 1-, 2-, and 3D homo- and heteronuclear experiments of the chemokine receptor CCR3 in a 7:3 phosphatidylcholine:cholesterol lipid environment. 1D direct polarization, cross polarization (CP), and T2' experiments indicate sample temperatures below - 25°C facilitate higher CP enhancement and longer-lived transverse relaxation times. T1rho experiments indicate intermediate timescales are minimized below a sample temperature of - 20°C. 2D DCP NCA experiments indicated optimal CP efficiency and resolution at a sample temperature of - 30°C, corroborated by linewidth analysis in 3D NCACX at - 30°C compared to - 5°C. This optimal temperature is concluded to be directly related the lipid phase transition, measured to be between - 20 and 15°C based on rINEPT signal of all-trans and trans-gauche lipid acyl conformations. Our results have critical implications in acquisition of SSNMR membrane protein assignment spectra, as we hypothesize that different lipid compositions with different phase transition properties influence protein dynamics and therefore the optimal acquisition temperature.

Cross-Polarization Schemes for Improved Heteronuclear Transfers Involving Labile Protons in Biomolecular Solution NMR.

INEPT-based experiments are widely used for 1 H→15 N transfers, but often fail when involving labile protons due to solvent exchanges. J-based cross polarization (CP) strategies offer a more efficient alternative to perform such transfers, particularly when leveraging the Hwater HN exchange process to boost the 1 H→15 N transfer process. This leveraging, however, demands the simultaneous spin-locking of both Hwater and HN protons by a strong 1 H RF field, while fulfilling the γH B1,H =γN B1,N Hartmann-Hahn matching condition. Given the low value of γN /γH , however, these demands are often incompatible-particularly when experiments are executed by the power-limited cryogenic probes used in contemporary high field NMR. The present manuscript discusses CP alternatives that can alleviate this limitation, and evaluates their performance on urea, amino acids, and intrinsically disordered proteins. These alternatives include new CP variants based on frequency-swept and phase-modulated pulses, designed to simultaneously fulfill the aforementioned conflicting conditions. Their performances vis-à-vis current options are theoretically analyzed with Liouville-space simulations, and experimentally tested with double and triple resonance transfer experiments.

Cross‐Polarization Schemes for Improved Heteronuclear Transfers Involving Labile Protons in Biomolecular Solution NMR

AbstractINEPT‐based experiments are widely used for 1H→15N transfers, but often fail when involving labile protons due to solvent exchanges. J‐based cross polarization (CP) strategies offer a more efficient alternative to perform such transfers, particularly when leveraging the Hwater HN exchange process to boost the 1H→15N transfer process. This leveraging, however, demands the simultaneous spin‐locking of both Hwater and HN protons by a strong 1H RF field, while fulfilling the γHB1,H=γNB1,N Hartmann‐Hahn matching condition. Given the low value of γN/γH, however, these demands are often incompatible—particularly when experiments are executed by the power‐limited cryogenic probes used in contemporary high field NMR. The present manuscript discusses CP alternatives that can alleviate this limitation, and evaluates their performance on urea, amino acids, and intrinsically disordered proteins. These alternatives include new CP variants based on frequency‐swept and phase‐modulated pulses, designed to simultaneously fulfill the aforementioned conflicting conditions. Their performances vis‐à‐vis current options are theoretically analyzed with Liouville‐space simulations, and experimentally tested with double and triple resonance transfer experiments.

A Frequency Tunable Dielectric Resonator Antenna with Reduction of Cross Polarisation for Wi MAX and Sub 6 GHz 5G Applications

A frequency Tunable (mechanical tuning) Linearly Polarized (TLP) rectangular Dielectric Resonator Antenna(DRA) coupled with a horizontal/vertical-slot and excited with circular-ring type feed is investigated in this article.The frequency tunability (mechanical tuning) is achieved by the rotation of slot at different angles of the proposedstructure. Hence, two linearly polarized antennas have been proposed for different frequency bands such as Wi-MAX and Sub-6 GHz/5G, respectively, using slot variations (named as DRA-1 and DRA-2). TE 11δ mode has been excited in both the DRAs and confirmed by orientation of electric field inside the rectangular DRA. The measured -10 dB input impedance bandwidths of DRA-1 offer 21.60 % being centered at 2.87 GHz and the separation of co-polarized and cross-polarized field levels is above -24 dB in the broadside direction (xz-plane). Whereas DRA-2 offers measured -10 dB input impedance bandwidths of 23.03% being centered at 3.56 GHz having a separation of co-polarized and cross-polarized field levels are above -23 dB in the broadside direction (xz-plane). In addition, the proposed DRA-1 and DRA-2 show a maximum gain of 5.23 dBi and 4.75 dBi in broadside direction, respectively.

A Low-Profile Broadband Dual-Polarized Omnidirectional Antenna for LTE Applications

In this letter, a broadband dual-polarized antenna with a very low profile and omnidirectional gain patterns is designed for 1.7-2.7 GHz Long Term Evolution (LTE) mobile communications. The designed antenna is constituted by a miniaturized tapered monopole for vertical polarization (VP) and four planar dipoles arranged in a ring for horizontal polarization (HP). The HP antenna is used as the metal ground of the VP antenna, which can avoid the feeding intersection and solve the problem of impedance matching degradation when distance between the HP antenna and the metal ground of the VP antenna is close. By sharing the partial structure, the designed antenna achieves a compact size of 110 mm × 110 mm × 13 mm and an extremely low height of 0.07 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</sub> ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</sub> is the free-space wavelength at the minimum operating frequency). The design achieves an overlapping bandwidth of 45% (1.7-2.7 GHz) with an isolation higher than 20 dB. High efficiency, low cross polarization and good omnidirectivity in the horizontal plane are obtained. The designed antenna is fabricated and measured, and it performs a great consistency between the simulation and measurement.

A Survey of Five Generations of MIMO Multiband Base Station Antennas

AbstractAs telecommunication systems evolve, there is an increasing demand for multi‐band MIMO base‐station antennas. Antenna arrays are generally used to support multiple frequencies with multiple ports in a compact size. However, this can result in significant degradation in scattering patterns and return loss/port isolation due to the close proximity of the radiation from the array. Various techniques have been proposed in the literature to address these issues. This paper presents an overview of the challenges faced by base station antennas (BSAs) over time and their general solutions. With the technological advancements of communication systems, accompanied by high data rates, high‐frequency antenna designs and MIMO operations have been introduced at the base station level. Base station antennas encountered design challenges, including broad bandwidth, high isolation levels, stable half‐power beam width, beam squint reduction, high cross polarization discrimination (XPD), gain improvement, beam steering, compact size, and cost reduction. This survey provides information on the solutions adopted by researchers over time for each design challenge, with citations. Additionally, the authors discuss techniques developed to overcome these challenges, demonstrating the evolution of BSAs from the first to the fifth generation of telecommunication systems.

Low-RCS Transmitarray Based on 2.5-D Cross-Polarization Converter

This paper presents a low radar cross section (RCS) transmitarray with absorption-transmission-absorption frequency response. In contrast to conventional transmitarrays based on multi-layer metallic patterns, a 2.5-dimensional cross polarization converter is employed to provide a large phase shifting range of high transmission efficiency. A benchmark transmitarray composed of the polarizer element with an aperture thickness of 2.3 mm (0.08λ) is designed to achieve a focused radiation beam. As a result, its peak gain is 22.1 dB and maximum aperture efficiency is 57.6%. Next, a low-RCS transmitarray is designed by introducing a lossy layer to absorb the out-of-band incident waves. Compared with the benchmark antenna, the radiation performance of the low-RCS transmitarray is maintained with a peak gain of 21.7 dB and maximum aperture efficiency of 53.7%. Meanwhile, dual-polarized significant RCS reduction can be obtained at both lower and higher frequencies.

1-D Wideband Phased Dielectric Resonator Antenna Array With Improved Radiation Performance Using Characteristic Mode Analysis

A 1-D wideband phased array of the rectangular ring dielectric resonator antenna (RRDRA) is presented for millimeter-wave applications. By using the characteristic mode analysis, it is found that the unwanted higher order mode (HOM) of the RRDRA results in severe gain degradation and high cross polarization when the array scans. To remedy the problem, each RRDRA is loaded with a pair of silver strips. They can suppress the unwanted HOM and enable good scanning performance in a wide frequency range. To demonstrate the idea, a 1×4 phased RRDRA array was designed, fabricated and measured for the licensed millimeter-wave bands (24.25–29.5 GHz). Reasonable agreement between the measured and simulated results is observed.

Cross polarization in Gaussian and Bessel light beams

Cross Polarization is explicitly obtained in the two cases Gaussian and Bessel light beams using the elegant Mukunda–Simon–Sudarshan rule for transition from scalar optics to vector wave optics. Unlike other studies, we obtain the results without solving the Maxwell equations.

Aberration of gravitational waveforms by peculiar velocity

ABSTRACT One key prediction of General Relativity is that gravitational waves are emitted with two independent polarizations. Any observation of extra polarization mode, spin-1 or spin-0, is consequently considered a smoking gun for deviations from General Relativity. In this paper, we show that the velocity of merging binaries with respect to the observer gives rise to spin-1 polarization in the observer frame even in the context of General Relativity. These are pure projection effects, proportional to the plus and cross polarizations in the source frame, hence they do not correspond to new degrees of freedom. We demonstrate that the spin-1 modes can always be rewritten as pure spin-2 modes coming from an aberrated direction. Since gravitational waves are not isotropically emitted around binary systems, this aberration modifies the apparent orientation of the binary system with respect to the observer: the system appears slightly rotated due to the source velocity. Fortunately, this bias does not propagate to other parameters of the system (and therefore does not spoil tests of General Relativity), since the impact of the velocity can be fully reabsorbed into new orientation angles.

COMBINING PATTERN PROJECTION AND CROSS POLARIZATION TO ENHANCE 3D RECONSTRUCTION OF FEATURELESS REFLECTIVE SURFACES

Abstract. 3D digitisation is essential to enhance knowledge and conservation processes for Cultural Heritage (CH). However, movable heritage collected in museums, e.g., archeological finds, statues, coins, and musical instruments, often consists of highly reflective surfaces and/or featureless textures. The aim of this work is to stress the Structure from Motion Dense MultiView Reconstruction (SfM-DMVR) of objects, whose optical properties are challenging to this image-based technique. To improve the results obtained by SfM-DMVR standard acquisition workflow, this study exploited the potential of combining Noise Function Pattern (NFP) projection and light Cross Polarization (CP). Moreover, High Dynamic Range (HDR) image reconstruction was tested on images acquired according to different CP angles. The SfM-DMVR of a texture-less shiny ceramic object was then compared to the one obtained by a structured light triangulation scanner, the most reliable tool for such surfaces, but unfortunately quite expensive. The advantages and limitations of the presented method are discussed.

A dual‐layer polarisation rotating element for transmitarray designs

AbstractA transmitarray adopting dual‐layer polarisation rotating (PR) elements is proposed. The element comprises a pair of perpendicularly placed C‐shaped slots etched on the two sides of a single‐layer substrate and orthogonally rotates transmission wave polarisation with regard to the incidence. By adjusting C‐shaped slot's dimension as well as mirroring the bottom layer of the element, a 360° phase shift with a high transmission magnitude is achieved. Based on the proposed unit‐cell, a dual‐layer transmitarray composed of 529 elements is designed and developed. The experimental 1‐dB gain bandwidth and peak aperture efficiency are 13% and 44% respectively. Furthermore, sidelobe level of 20 dB and cross polarisation level of 26 dB are obtained at 10 GHz. These promising properties demonstrate the superiority of the element for transmitarray designs. In addition, this element can be also a good candidate for folded transmitarray designs.

A Low Cross-Polarization Microstrip Antenna Array for Millimeter Wave Applications

A low cross-polarization microstrip antenna array for millimeter wave (mmW) applications is proposed in this paper. The antenna element is composed of symmetric T-shaped patches with vias. The adoption of a double-sided symmetric radiation patch structure can suppress the cross-polarized electric field, and the vias reduces energy leakage during the power transmission along the antenna patches. To verify the concept, a 1 × 8 antenna array is fabricated and measured. The measured −10 dB impedance of the antenna array is 28.4% (31 GHz–41.5 GHz) and the peak gain is 15 dBi. The cross polarization ratio is above 35 dB and the 3 dB beamwidths on E-plane and H-plane are 7.5° and 135°, respectively. The proposed compact size and low cross-polarization antenna array might be a good choice for phased array radar and 5th generation (5G) mobile communication applications.

Molecular composition and possible transformations of labile soil organic matter fractions in Mediterranean arable soils: Relevance and implications

With the increased global interest in sequestering carbon in soil, it is necessary to understand the composition of different pools of soil organic matter (SOM) that cycle over suitably short timeframes. To explore in detail the chemical composition of agroecologically relevant yet distinct fractions of SOM, the light fraction of SOM (LFOM), the 53-μm particulate organic matter (POM), and the mobile humic acid (MHA) fractions were sequentially extracted from agricultural soils and characterized using both 13C cross polarization magic angle spinning nuclear magnetic resonance (CPMAS NMR) spectroscopy and also Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). The NMR results showed a decrease in the O-alkyl C region assigned to carbohydrates (51–110 ppm) and an increase in the aromatic region (111–161 ppm) proceeding from the LFOM to the POM and then to the MHA fraction. Similarly, based on the thousands of molecular formulae assigned to the peaks detected by FT-ICR-MS, condensed hydrocarbons were dominant only in the MHA, while aliphatic formulae were abundant in the POM and LFOM fractions. The molecular formulae of the LFOM and POM were mainly grouped in the high H/C lipid-like and aliphatic space, whereas a portion of the MHA compounds showed an extremely high (17–33, average of 25) double bond equivalent (DBE) values, corresponding to low H/C values of 0.3–0.6, representative of condensed hydrocarbons. The labile components appeared most pronounced in the POM (93% of formulae have H/C ≥ 1.5) similar to the LFOM (89% of formulae have H/C ≥ 1.5) but in contrast to the MHA (74% of formulae have H/C ≥ 1.5). The presence of both labile and recalcitrant components in the MHA fraction suggests that the stability and persistence of soil organic matter is influenced by a complex interaction of physical, chemical, and biological factors in soil. Understanding the composition and distribution of different SOM fractions can provide valuable insights into the processes that govern carbon cycling in soils, which can help inform strategies for sustainable land management and climate change mitigation.

Monitoring lesion activity on primary teeth with CP-OCT and SWIR reflectance imaging.

The purpose of this study was to use cross polarization optical coherence tomography (CP-OCT) and short wavelength infrared imaging (SWIR) reflectance imaging to monitor changes in the structure and activity of early occlusal caries on primary teeth over a period of 6 months during intervention with fluoride. Participants (n = 29) aged 6-10 each with two suspected active occlusal lesions on primary teeth completed the study. Fluoride varnish was applied to tooth surfaces every 3-months and participants were instructed to brush twice daily with a fluoride toothpaste. Images were acquired using CP-OCT every 3 months for 6 months. SWIR reflectance images were acquired during forced air-drying of the lesions for 30 s at 0 and 6-months. Most of the 42 lesions appeared initially active at baseline. Only 6 lesions appeared arrested at baseline based on the presence of a highly mineralized transparent surface layer (TSL) in CP-OCT images. At 6 months, 14 of the lesions appeared arrested including the 6 initially arrested lesions and the TSL thickness increased significantly (p < 0.0001). The mean lesion depth (Ld) and the integrated reflectivity over the lesion depth (ΔR) increased significantly (p < 0.05) after 6 months for the 42 lesions analyzed. SWIR reflectance images showed that there was a significantly higher (p < 0.05) delay before changes in intensity were measured for active lesions versus arrested lesions during lesion drying. CP-OCT was able to monitor changes in lesion structure and activity including the formation of a highly mineralized TSL indicative of lesion arrest during nonsurgical intervention. Time-resolved SWIR reflectance imaging also shows that there are differences in the dehydration kinetics between active and arrested lesions. This study demonstrates two independent imaging methods that can be used to monitor changes in lesion activity over time.