Cross-polarized Configuration Research Articles

Effects of Polarizer-Analyzer Configurations for FTIR Spectroscopy: Implications for Multiple Polarization Algorithms.

Polarized Fourier transform infrared (p-FTIR) spectroscopy is a widely used technique for determining orientational information in thin organic materials. Conventionally, a single polarizer is placed in the path of the incident light (termed the polarizer). Occasionally, a second polarizer is also placed after the sample (referred to as the analyzer). However, this polarizer-analyzer configuration has the potential to induce polarization-dependent variances in the final spectra beyond those that are expected, i.e., the squared-cosine relationship of absorptance with respect to polarization angle is no longer accurate. These variances are due to changes in the polarization state of the transmitted light induced by the sample and have yet to be explored in the context of p-FTIR. Consequently, this study employs both theoretical and experimental approaches to identify the effects of including a second polarizer in p-FTIR analyses of anisotropic organic samples. For thin samples, the most significant spectral variance arising from only birefringence is observed on the shoulders of the dichroic peaks. By adopting a crossed polarizer configuration, it is shown that there is potential to identify anisotropy of samples that are generally considered too thick for p-FTIR analysis by exploiting this feature. Furthermore, the squared-cosine relationship of absorptance with respect to the polarization angle is also shown to be inapplicable when a second parallel-oriented polarizer is included. Accordingly, a function that accounts for the second polarizer is proposed for multiple polarization techniques.

Mutual coupling effects in 2×2 antenna array for ground penetrating radar on multilayered soil

<span>Caral stands as the Americas’ oldest city, boasting a heritage spanning 5,000 years. Over time, various natural forces have woven a complex geological stratum. To gain a deeper understanding of the Caral civilization, non-intrusive exploration methodologies like ground penetrating radar (GPR) are beginning to be used. This method safeguards the integrity of ancient subterranean remains. A GPR system is in development, tailored to the <br /> [200-500] MHz range, employing a 2×2 antenna array with dual polarization. These features enhance resolution without compromising penetration depth. However, using multiple antennas within complex, multi-layered environments introduce impedance band constraints and exacerbates antenna coupling issues. This study assesses the coupling of two antenna candidates: the Vivaldi with defected ground structures (DGS) and the log periodic dipole array (LPDA). The scattering parameters show that the LPDA antenna performed better considering measured and simulated data. Cross-polarization exhibited a broader bandwidth in the LPDA antenna, evident in both simulated and measured data. Additionally, a comprehensive comparison of GPR simulations for each antenna type within an 11-level multilayer medium, with different electromagnetic properties, further highlights LPDA. This antenna boasts a 209 MHz bandwidth and a coupling better than -23 dB for the cross-polarization configuration, firmly showing its best performance.</span>

Near-Field Spectroscopy of Individual Asymmetric Split-Ring Terahertz Resonators.

Metamaterial resonators have become an efficient and versatile platform in the terahertz frequency range, finding applications in integrated optical devices, such as active modulators and detectors, and in fundamental research, e.g., ultrastrong light-matter investigations. Despite their growing use, characterization of modes supported by these subwavelength elements has proven to be challenging and it still relies on indirect observation of the collective far-field transmission/reflection properties of resonator arrays. Here, we present a broadband time-domain spectroscopic investigation of individual metamaterial resonators via a THz aperture scanning near-field microscope (a-SNOM). The time-domain a-SNOM allows the mapping and quantitative analysis of strongly confined modes supported by the resonators. In particular, a cross-polarized configuration presented here allows an investigation of weakly radiative modes. These results hold great potential to advance future metamaterial-based optoelectronic platforms for fundamental research in THz photonics.

Analysis of the performance of a polarized LiDAR imager in fog.

This paper focuses on exploring ways to improve the performance of LiDAR imagers through fog. One of the known weaknesses of LiDAR technology is the lack of tolerance to adverse environmental conditions, such as the presence of fog, which hampers the future development of LiDAR in several markets. Within this paper, a LiDAR unit is designed and constructed to be able to apply temporal and polarimetric discrimination for detecting the number of signal photons received with detailed control of its temporal and spatial distribution under co-polarized and cross-polarized configurations. The system is evaluated using different experiments in a macro-scale fog chamber under controlled fog conditions. Using the complete digitization of the acquired signals, we analyze the natural light media response, to see that due to its characteristics it could be directly filtered out. Moreover, we confirm that there exists a polarization memory effect, which, by using a polarimetric cross-configuration detector, allows improvement of object detection in point clouds. These results are useful for applications related to computer vision, in fields like autonomous vehicles or outdoor surveillance where many variable types of environmental conditions may be present.

Analysis of 2D and 3D GPR data interpretation using continuous wavelet transforms: Case study from an archaeological test site

Ground-penetrating radar (GPR) is one of the most important techniques for obtaining high-resolution data in archaeological research, and it is becoming increasingly important. The continuous wavelet transform (CWT), which is non-numerical technique, gives an overcomplete representation of a signal by continuously varying the wavelet’s translation and scale parameters in the time series dataset. This paper focuses on the novel technique of integrating CWT and the wavelet transform maxima (WTM) to extract information from an archaeological test site in south-eastern China. For the characterization of archaeological features, we assessed the importance of dense and accurate data collection as well as GPR signal processing. The mathematical formulation and applicability of GPR attributes, particularly amplitude-based attributes, to identify and characterize archaeological buried targets are also discussed. GPR data is acquired using co-polarized and cross-polarized configurations with transverse-electric (TE) and transverse-magnetic (TM) broadside frequency plates at 100 and 200 MHz. Next, CWT was applied using six different wavelet levels, followed by amplitude comparison. The archaeological targets were successfully interpreted using peak amplitude and CWT. The proposed methodology has significantly improved data visualization and interpretation of GPR data, and it also gave us good results in identifying archaeological anomalies.

Single-crystalline transition metal phosphide superconductor WP studied by Raman spectroscopy and first-principles calculations

We present a study of phonon modes and electron-phonon coupling in superconductor WP using angle-resolved polarized Raman spectroscopy. Seven out of twelve Raman-active modes are detected, with frequencies in good accordance by the first-principles calculations. We analyze parallel- and cross-polarized configurations of ${\mathrm{A}}_{\mathrm{g}}$ and ${\mathrm{B}}_{3\mathrm{g}}$ phonon modes with polarization- and angle-resolved Raman measurements. For the observed seven modes, the total electron-phonon coupling parameter $\ensuremath{\lambda}$ is only about 0.07, which is too small to achieve superconductivity. Our results elucidate that the low-frequency phonon modes play a key role in the superconductivity within the Bardeen-Cooper-Schrieffer theory framework.

Dual-Cross-Polarized GPR Measurement Method for Detection and Orientation Estimation of Shallowly Buried Elongated Object

Detecting a shallowly buried and elongated object and estimating its orientation using a commonly adopted co-polarized GPR system is challenging due to the presence of strong ground clutter that masks the target reflection. A cross-polarized configuration can be used to suppress ground clutter and reveal the object reflection, but it suffers from inconsistent detection capability which significantly varies with different object orientations. To address this issue, we propose a dual-cross-polarized detection (DCPD) method which utilizes two cross-polarized antennas with a special arrangement to detect the object. The signals reflected by the object and collected by the two antennas are combined in a rotationally invariant manner to ensure both effective ground clutter suppression and consistent detection irrespective of the object orientation. In addition, we present a dual-cross-polarized orientation estimation (DCPOE) algorithm to estimate the object orientation from the two cross-polarized data. The proposed DCPOE algorithm is less affected by environmental noise and performs robust and accurate azimuth angle estimation. The effectiveness of the proposed techniques in the detection and orientation estimation and their advantages over the existing method have been demonstrated using experimental data. Comparison results show that the maximum and average errors are 22.3{\deg} and 10.9{\deg} for the Alford rotation algorithm, while those are 4.9{\deg} and 1.8{\deg} for the proposed DCPOE algorithm in the demonstrated shallowly buried object cases. The proposed techniques can be unified in a framework to facilitate the investigation and mapping of shallowly buried and elongated targets.

Self-driving dynamic plasmonic colors based on needle steering for simultaneous control of transition direction and time on metallic nanogroove metasurfaces.

Dynamically tunable plasmonic colors hold great promise for a wide range of applications including color displays, colorimetric sensing, and information encryption. However, dynamic control speed of plasmonic colors is still slow to date. Herein, we propose to use a needle to direct the flow of water and gas pressure to drive water, realizing a simultaneous direction-controllable and fast plasmonic color transition. The highly reflected background light of the metallic nanogroove metasurface is suppressed to generate high-purity plasmonic colors through the cross-polarized input and output configuration. When the environment is changed from air to water, a giant color change from cyan to red (a wavelength shift of 156 nm) is experimentally observed. More importantly, by utilizing a needle to steer the flow of water, direction-controllable and fast plasmonic color transition is achieved by controlling gas pressure to drive water. Compared with current state-of-the-art plasmonic color scanning technology, the color transition time via water driven by gas pressure decreases by three orders of magnitude for the same scanning length. The multi-degrees of freedom dynamic structural colors could have potential applications in dynamic displays, anti-counterfeiting, and information security.

MIMO Antenna for IEEE 802.11ac with Cross-Polarized Circular Configuration of Printed Yagi Elements

Antennas characteristics contribute significantly to Multiple Input Multiple Output (MIMO) system performances. IEEE 802.11ac is a wireless technology standard supporting transmission data rate of up to 1 Gbps by implementing the MIMO system. The design of the antenna should be capable to support the achievement of high channel capacity. This paper proposes the design of MIMO antenna for IEEE 802.11ac access point. The proposed MIMO antenna is composed of eight Printed Yagi elements, and each one has a bandwidth covering the frequency band of the IEEE 802.11ac system. In order to ensure a low coupling level between elements, the cross-polarized arrangement is used. In order to achieve good coverage for the area around the access point, the circular arrangement of Printed Yagi elements has been chosen as the solution referring to the problem. Computer simulations and laboratory measurements have been performed in achieving the design of the proposed antenna. Simulation and measurement results show that the proposed MIMO antenna has been able to support channel capacity of up to 1 Gbps at the low Signal to Noise Ratio (SNR) conditions of 10 dB.

A Low Cross-Polarization Configuration Method for Phased Array Radar Antenna

The cross-polarization isolation (CPI) is a key parameter to assess the dual-polarization antenna because the cross-polarization closely affects the antenna application. A polarization state configuration (PSC) approach is proposed to configure the polarization state of the polarimetric phased array radar antenna. Unlike the traditional fixed polarization states such as the linear polarization (LP) and the circular polarization (CP), the PSC method modulates the polarization state of the radiated wave continuously. In addition, the optimal excitation magnitude and phase of the dual-polarization element is calculated, thereby maximizing the CPI. Most of the configured polarization state is the elliptical polarization (EP), and a lower cross-polarization level and higher CPI could be obtained. This method could expand the acceptable angle range when compared with the LP and CP waves. Numerical simulations and comparisons are conducted to manifest the validity of the proposed method.

Cross-polarized VNIR hyperspectral reflectance imaging for non-destructive quality evaluation of dried banana slices, drying process monitoring and control

Banana and its dried products are one of the most common foods consumed all over the world. Quality attributes of dried banana slices are typically evaluated using time-consuming and labor intensive methods which do not allow to evaluate each individual slice. Replacement of the current destructive methods for quality evaluation of dried banana slices by fast, non-destructive methods would provide large added value to the food industry. Therefore, the aim of this study was to monitor the moisture content, texture and color of banana slices during the drying process in a fast and non-destructive way. VNIR hyperspectral reflectance imaging in the 400–1000 nm range was selected for this purpose. Thanks to a cross-polarized configuration the effects of glare or specular reflection on the banana slice surfaces in the hyperspectral diffuse reflectance images was largely reduced. Reference quality attributes for all the slices (moisture content, texture and color (L*, a*, b* values) obtained using conventional destructive methods and colorimeter were predicted from their corresponding average reflectance spectra extracted from the hyperspectral images by means of partial least squares regression (PLSR). The PLSR calibration models were validated on samples which had not been used for model calibration. The results were very good for water content (R2P = 0.97, RMSEP = 0.05 kg water/kg DM), quite good for and b* value (R2P = 0.83, RMSEP = 1.95), and reasonable for texture (R2P = 0.66, RMSEP = 11.8 N), a* value (R2P = 0.53, RMSEP = 1.32) and L* value (R2P = 0.61, RMSEP = 5.92). Subsequently, these calibration models were used to predict those quality attributes at pixel level for the validation slices to visualize the spatial distribution of these quality parameters at different stages during the drying process. The obtained results clearly indicate the potential of cross-polarized hyperspectral reflectance imaging for non-destructive monitoring of the quality attributes of banana slices during drying.

Experiments and simulations of a prototype triaxial electromagnetic induction logging tool for open-hole hydraulic fracture diagnostics

The monitoring and diagnostics of induced fractures are important for the real-time performance evaluation of hydraulic fracturing operations. Previous electromagnetic-based studies show that single backbone triaxial induction logging tools are promising candidates for real-time monitoring and diagnosis of fractures in noncased wells. With a fast-forward solver and reliable parametric inversion techniques, it may be possible to estimate many features of the propped fracture geometry (e.g., area, dip, conductivity) from the measured induced voltages. To support the development of field deployable tools, the concept must be tested in experiments, in a controllable environment, before it is tested under field-like conditions. To this end, we have designed and built a prototype induction tool and performed two sets of tests to compare with numerical simulation results. The experimental setup consists of triaxial transmitter and receiver coils in coaxial, coplanar, and cross-polarized configurations. Thin (highly conductive) metallic targets of various sizes, shapes, and orientations are used to emulate various fracture geometries. The laboratory and shallow earth measurements are shown to be in good agreement with simulations for all examined cases. The average relative and maximum discrepancies of the measured signals from the simulated ones are lower than 3% and 10%, respectively. With the prototype tool, strong signals sensitive to the fracture’s surface area and dip are measured in a coaxial coil configuration, whereas weaker signals sensitive to the fracture’s aspect ratio are observed in a coplanar configuration. Cross-polarized signals are also shown to be strong and sensitive to the fracture’s dip. The results suggest that a tool of similar specifications can be used for the detection and extraction of the parameters of fractures propped with sufficiently electrically conductive proppant.

Structural and dielectric properties of barium doped BFO

Polycrystalline Bi1-xBaxFeO3(x=0.0, 0.1, 0.2and0.3) were prepared by citric acid sol-gel auto-ignition method to study the structural and dielectric propertied in multiferroics. Raman studies revealed that all 13 Raman modes predicted for rhombohedral structure (3Rc) of BFO, have been observed in work. To distinguish A1 and E modes, Raman measurements were carried out in both the parallel and crossed polarization configuration. In addition to E modes, intense peaks corresponding to A1-1, A1-2 and A1-3 modes at 128.8,166 and 211 cm-1 respectively observed in the polycrystalline BFO. The results of Raman studies match with reported literature. As Ba doping concentration was increased the structure of BFO changed from rhombohedral to tetragonal. In dielectric studies, dielectric constant (both ε’ and ε”) and dielectric loss decreases with increases in frequency (100Hz to 1MHz) at room temperature. Dielectric constant and loss dispersion increases with increases in temperature. Leakage current density increases with Ba doping.

Ultrafast nonlinear optical investigation on a dispersed red one derivative: A femtosecond Z-scan and degenerated pump-probe study

Z-scan technology, numerical simulation and degenerated pump-probe experiment under different polarization configurations, were performed to study the ultrafast nonlinear optical properties of a dispersed red one (DR1) derivative (DR1-T, dissolved in THF solution) based on triphenylamine. The ultrafast Z-scan nonlinear optical absorption curve was measured and numerical simulated as well. Different polarization configurations between the pump and probe beams, were set for investigation in degenerated pump-probe measurements. When a parallel polarization configuration was set, the dynamic show two processes: a fast process approximately 0.75ps (was ascribed to the formation of the intramolecular charge transfer state, and mainly vibrational relaxation process), and a long process approximately 175ps (was ascribed to the evolution of the intramolecular charge transfer state), respectively. Obvious excited state dynamic anisotropy was observed under two polarization configurations. When a cross polarization configuration was set, the evolution of the intramolecular charge transfer process slowed down obviously, indicating some other mechanism involved.

Optical anisotropy of cubic photonic crystals under conditions of multiple-mode light propagation

Bragg reflection spectra of light are studied for opal-like photonic crystals made of polystyrene spheres. A resonant enhancement of reflectivity is observed in cross-polarization configuration of the analyzer and polarizer when varying the azimuthal orientation of a sample in respect to the incidence plane. The cross-polarization effect takes place at oblique incidence of light on the lateral (111) crystal plane with the plane of incidence being non-perpendicular to the inclined (11-1) crystal plane. The effect is shown to be due to the multiple Bragg diffraction of light when the resonant Bragg conditions are fulfilled at a certain angle of incidence and azimuth for the lateral and inclined crystal planes simultaneously.

Statistical Modelling and Characterization of Experimental mm-Wave Indoor Channels for Future 5G Wireless Communication Networks.

This paper presents an experimental characterization of millimeter-wave (mm-wave) channels in the 6.5 GHz, 10.5 GHz, 15 GHz, 19 GHz, 28 GHz and 38 GHz frequency bands in an indoor corridor environment. More than 4,000 power delay profiles were measured across the bands using an omnidirectional transmitter antenna and a highly directional horn receiver antenna for both co- and cross-polarized antenna configurations. This paper develops a new path-loss model to account for the frequency attenuation with distance, which we term the frequency attenuation (FA) path-loss model and introduce a frequency-dependent attenuation factor. The large-scale path loss was characterized based on both new and well-known path-loss models. A general and less complex method is also proposed to estimate the cross-polarization discrimination (XPD) factor of close-in reference distance with the XPD (CIX) and ABG with the XPD (ABGX) path-loss models to avoid the computational complexity of minimum mean square error (MMSE) approach. Moreover, small-scale parameters such as root mean square (RMS) delay spread, mean excess (MN-EX) delay, dispersion factors and maximum excess (MAX-EX) delay parameters were used to characterize the multipath channel dispersion. Multiple statistical distributions for RMS delay spread were also investigated. The results show that our proposed models are simpler and more physically-based than other well-known models. The path-loss exponents for all studied models are smaller than that of the free-space model by values in the range of 0.1 to 1.4 for all measured frequencies. The RMS delay spread values varied between 0.2 ns and 13.8 ns, and the dispersion factor values were less than 1 for all measured frequencies. The exponential and Weibull probability distribution models best fit the RMS delay spread empirical distribution for all of the measured frequencies in all scenarios.

Origin of ellipticity of high-order harmonics generated by a two-color laser field in the cross-polarized configuration

Recently several techniques demonstrated the production of elliptically polarized high harmonics. One of these techniques consists of the interaction in a noble gas of two-color laser beams having orthogonal linear polarizations. Here we present the theoretical explanation of such a result observed in Lambert et al. [Nat. Commun. 6, 6167 (2015)]. Numerical calculations based on the nonperturbative light-atom interaction theory reproduce well the experimental data. The degree of polarization is analyzed for different harmonic orders and found to be high. With the help of a simplified theoretical model it is shown that the degree of harmonic ellipticity depends mainly on the population of atomic state sublevels with different angular momentum projections.

Optimized interferometric setup for chiral and achiral ultrafast IR spectroscopy.

We report an actively stabilized interferometer-based set-up for the detection of vibrational circular dichroism (VCD) and optical rotatory dispersion (VORD) with femtosecond laser pulses. Our approach combines and improves elements of several previous measurement strategies, including signal amplification in a crossed polarizer configuration, precise control and modulation of polarization, phase stability, tight focusing, broad-band detection and spectral interferometry. Their importance for static and transient measurements is motivated by a signal analysis based on Jones matrices and response theory. Only depending on the pump-beam polarization, the set-up can selectively detect transient VCD and VORD or transient linear birefringence (LB) and linear dichroism (LD), which usually constitute the dominant artifacts in the chiral measurements. For illustration we present transient LB and LD data of an achiral Rhenium carbonyl complex, detected simultaneously by spectral interferometry, and we analyze residual background signals in the experimental configuration for transient chiral spectroscopy.

Advances in GPR data acquisition and analysis for archaeology

The primary objective of this study is to evaluate the applicability and the effectiveness of ground-penetrating radar (GPR) to identify a thin burnt soil layer, buried more than 2 m below the topographic surface at the Liangzhu Site, in Southeastern China. The site was chosen for its relatively challenging conditions of GPR techniques due to electrical conductivity and to the presence of peach tree roots that produced scattering. We completed the data acquisition by using 100 and 200MHz antennas in TE and TM broadside and cross-polarized configurations. In the data processing and interpretation phase, we used GPR attribute analysis, including instantaneous phase and geometrical attributes. Validation analysis ground-truthing performed after the geophysical surveys, validated the GPR imaging, confirmed the electrical conductivity and relative dielectric permittivity (RDP) measurements performed at different depths, and allowed a reliable quantitative correlation between GPR results and subsurface physical properties. The research demonstrates that multiple antenna configurations in GPR data acquisition combined with attribute analysis can enhance the ability to characterize prehistoric archaeological remains even in complex subsurface conditions.

Indoor Office Wideband Millimeter-Wave Propagation Measurements and Channel Models at 28 and 73 GHz for Ultra-Dense 5G Wireless Networks

Ultra-wideband millimeter-wave (mmWave) propagation measurements were conducted in the 28- and 73-GHz frequency bands in a typical indoor office environment in downtown Brooklyn, New York, on the campus of New York University. The measurements provide large-scale path loss and temporal statistics that will be useful for ultra-dense indoor wireless networks for future mmWave bands. This paper presents the details of measurements that employed a 400 Megachips-per-second broadband sliding correlator channel sounder, using rotatable highly directional horn antennas for both co-polarized and crosspolarized antenna configurations. The measurement environment was a closed-plan in-building scenario that included a line-of-sight and non-line-of-sight corridor, a hallway, a cubicle farm, and adjacent-room communication links. Well-known and new single-frequency and multi-frequency directional and omnidirectional large-scale path loss models are presented and evaluated based on more than 14 000 directional power delay profiles acquired from unique transmitter and receiver antenna pointing angle combinations. Omnidirectional path loss models, synthesized from the directional measurements, are provided for the case of arbitrary polarization coupling, aswell as for the specific cases of co-polarized and cross-polarized antenna orientations. The results show that novel large-scale path loss models provided here are simpler and more physically based compared to previous 3GPP and ITU indoor propagation models that require more model parameters and offer very little additional accuracy and lack a physical basis. Multipath time dispersion statistics formmWave systems using directional antennas are presented for co-polarization, crosspolarization, and combined-polarization scenarios, and show that the multipath root mean square delay spread can be reduced when using transmitter and receiver antenna pointing angles that result in the strongest received power. Raw omnidirectional path loss data and closed-form optimization formulas for all path loss models are given in the Appendices.