Reflective Polarization Research Articles

In situ formation SiC nanowires on loofah sponge-derived porous carbon for efficient electromagnetic wave absorption

A lightweight, heterogeneous, three-dimensional network-structured composite has been meticulously developed with the specific goal of optimizing impedance matching and elevating electromagnetic wave absorption properties. SiC nanowires-carbon composites were synthesized through a novel process involving combined carbothermal reduction and chemical vapor deposition, utilizing loofah sponge as the foundational material. Accessible and cost-effective organosilane waste was applied as the silicon source. The resulting composites manifest exceptional electromagnetic wave absorption performance with a minimum reflection loss of − 46.34 dB and a wide effective bandwidth of 3.84 GHz at a thin thickness of 1.9 mm. Superior electromagnetic wave absorption is attributed to synergistic interplay of multiple interfacial polarizations, dipole polarization, conductive losses, and multiple reflections and scattering. This work presents an innovative pathway toward fabricating highly efficient electromagnetic wave-absorbing materials while effectively repurposing recycled waste.

MOF composite FeSiB-based nano-amorphous magnetic powder and the influence of porous morphology on dielectric polarization and microwave absorption mechanisms

FeSiB-based nano-amorphous soft magnetic alloy composites have excellent wave-absorbing properties which are among the most promising high-performance wave-absorbing materials. FeSiBNbCu nano-amorphous soft magnetic alloy micropower was used as the matrix. Fe-based (MIL-101(Fe)) porous materials were grown on the lamellar amorphous surface by in situ composite method, which successfully prepared FeSiBNbCu@MIL-101(Fe) magnetic alloy micropower with excellent wave-absorbing properties. The porous nature of the MOF materials, enhanced interfacial polarization and multiple reflections and scatterings of the composites, and thus significantly improved microwave absorption properties of the materials. Furthermore，the introduction of the MOF materials reduced the electrical conductivity of the materials and optimized the impedance matching. The reflection loss minima (RLmin) of the composites reached −71.29 dB (d= 4.4 mm, f=4.74 GHz) and −63.23 dB (d= 2.4 mm, f=10.35 GHz) at 10 wt% and 20 wt% MIL-101(Fe), respectively, and the effective absorption bandwidths, of RL≤ - 20 dB (1.4 GH and 1.3 GHz), are broadened obviously in the range of d=2.5 mm ∼ 3.5 mm.

Single layer vanadium oxide assisted switchable metasurfaces for transmissive and reflective polarization conversion

Polarization control using metasurfaces is highly advantageous; however, most metasurfaces operate exclusively in either transmission or reflection mode. Additionally, achieving both wide bandwidth and high efficiency simultaneously in their design remains a significant challenge. Here, we design a high-efficiency and wideband switchable metasurface that can switch between transmissive and reflective polarization conversion modes by utilizing a single layer of I-shaped resonators and gold-vanadium dioxide (VO2) alternating gratings printed on a quartz substrate. When VO2 transitions to its metallic phase, the continuous metal layers of gold-VO2 eliminate transmission and the designed metasurface operates as a reflective cross-polarization converter with a polarization conversion ratio (PCR) exceeding 0.9 over a broad frequency range of 1.4–3.3 THz. Conversely, when VO2 is in its insulator phase, the THz incoming wave can transmit through the gratings, and the design behaves as a transmissive cross-polarization converter with a PCR above 0.99 in the 0.75-4.0 THz range for a forward y- polarized wave. The working mechanism for both transmissive and reflective polarization conversion modes is explained through theoretical analysis and surface current distributions. With the advantages of facile design, high performance, and dual functionality, our design is expected to be applied in the fields of imaging, sensing, and communication.

Supercooled Water Cloud Detection From Polarized Multi‐Angle Imager Data Using 1.37 μm Water Vapor Polarized Channel

AbstractDetecting supercooled water clouds (SWCs) is essential for enhancing artificial rainfall, preventing aircraft ice accretion, and developing a better understanding of radiative energy balance. The 1.37 μm channel, known as strong water vapor absorbing, was made polarized in the polarized multi‐angle imager (PMAI) onboard FengYun‐3G satellite. The infight data shown that the new 1.37 μm polarized channel could be used to detect SWCs. The cloudbow is observed around the 140° scattering angle in the 1.37 μm polarization image, with a maximum polarization reflectance of approximately 0.04–0.06. The indicated water clouds with spherical particles in the high‐level altitude could be SWCs. Then, the SWCs detected by 1.37 μm polarized channel is verified using polarized reflectance of other channels, the reflectance difference of channels, and thermal infrared bright temperature. The presence of cloudbow in 1.03 and 1.64 μm channels indicate liquid water cloud. The reflectance difference between 1.03 and 1.64 μm of SWCs agree with characteristic of water cloud. The thermal infrared channels from the imager on the same platform indicate cold cloud with the brightness temperature far below 273.16 K. Therefore, the only use of 1.37 μm polarized channel could perform the identification of SWCs. PMAI provides a powerful tool for monitoring supercooled water clouds.

Increased neutron reflectivity and polarization of neutron-optical engineered Fe/B411CTi multilayer optics

The concept of scattering length density tuning for improved polarization is investigated for Fe/B411CTi multilayers and compared to the commonly used Fe/Si system in polarizing multilayer neutron optics. X-ray and neutron reflectivity, magnetization, and neutron polarization were measured on such multilayers, highlighting differences from conventional Fe/Si multilayers. The multilayer systems were deposited with 25 Å period thickness, a layer thickness ratio of 0.35, and 20 periods using ion-assisted dc magnetron sputtering. Replacing Si with B411CTi for these multilayers showed an increase in reflectivity due to a reduction in interface width. Tuning the ratio between B411C and Ti in the nonmagnetic layers enabled a wide range of scattering length density contrasting and matching for spin-down neutrons, which in turn led to an improved polarization. These findings demonstrate the potential of Fe/B411CTi multilayers as a promising option for polarizing neutron optics and highlight the concept of scattering length density tuning in a large range using B411CTi. Published by the American Physical Society 2024

Modeling and characteristic analysis of reflection polarization on coating surface based on Monte Carlo method

Modeling and characteristic analysis of reflection polarization on coating surface based on Monte Carlo method

Multi-material fused deposition modelling of structural–functional integrated absorber with multi-scale structure possessing tunable broadband microwave absorption

Designing and manufacturing advanced structural microwave absorbers is one of the most feasible methods to address the growing electromagnetic stealth and protection challenges in both military and civilian domains. To this end, under the application context of structural–functional integration, a series of nanocomposites with varying ratios were prepared using multi-walled carbon nanotubes (MWCNTs) and inexpensive thermoplastic polypropylene as raw materials. The dispersion of nanofillers, rheological properties, thermal properties, and mechanical properties were evaluated. The research found that the impedance matching factor of the electromagnetic wave absorbers plays a more critical role in determining the material’s absorption capacity compared to the loss factor. Simple structural layering by changing the composition and design can effectively increase the effective absorption bandwidth (EAB) of the absorbers, with microwave attenuation primarily arising from conductive loss, interfacial polarization, dipole polarization, and multiple reflections. Finally, a multi-scale quasi-honeycomb absorber was fabricated using multi-material 3D printing with a structured design. Both simulation and experimental results showed consistent trends, demonstrating low sensitivity to the incident azimuth angle. This research features simplicity, low cost, and strong design capability, providing a new strategy for the preparation of functionally graded materials with potential applications in electromagnetic wave absorption.

C/Co3O4/Diatomite Composite for Microwave Absorption.

Transition metal oxides have been widely used in microwave-absorbing materials, but how to improve impedance matching is still an urgent problem. Therefore, we introduced urea as a polymer carbon source into a three-dimensional porous structure modified by Co3O4 nanoparticles and explored the influence of different heat treatment temperatures on the wave absorption properties of the composite. The nanomaterials, when calcined at a temperature of 450 °C, exhibited excellent microwave absorption capabilities. Specifically, at an optimized thickness of 9 mm, they achieved a minimum reflection loss (RLmin) of -97.3 dB, accompanied by an effective absorption bandwidth (EAB) of 9.83 GHz that comprehensively covered both the S and Ku frequency bands. On the other hand, with a thickness of 3 mm, the RLmin was recorded as -17.9 dB, with an EAB of 5.53 GHz. This excellent performance is attributed to the multi-facial polarization and multiple reflections induced by the magnetic loss capability of Co3O4 nanoparticles, the electrical conductivity of C, and the unique three-dimensional structure of diatomite. For the future development of bio-based microwave absorption, this work provides a methodology and strategy.

Switchable terahertz polarization converter with dual-functional reflective conversion and asymmetric transmission based on vanadium dioxide

A dual-functional polarization converter designed for both reflective polarization conversion and asymmetric transmission in the terahertz band is proposed, leveraging the phase transition of vanadium dioxide. In its metallic state, vanadium dioxide facilitates reflective mode operation. Simulation results demonstrate that the polarization conversion rate exceeds 90%, converting linearly polarized or circularly polarized waves into cross-polarized waves, with relative bandwidths of 100.6% and 100.8%, respectively. Experimental validation confirms the polarization conversion capabilities of the device. In the insulating state of vanadium dioxide, the converter demonstrates a notable asymmetric transmission effect for wide-angle incident circularly polarized waves. The proposal of this converter fills the gap of switchable polarization conversion and asymmetric transmission functions, and has broad application prospects in multifunctional polarization devices and multi-channel polarization detection.

Broadband metamaterial linear polarization converter designed by a hybrid neural network with data augmentation

Deep learning techniques provide a new approach to the design and optimization of electromagnetic metamaterials. This study used a convolutional neural network and long short-term memory (CNN–LSTM) hybrid network to design and optimize a broadband metamaterial reflective linear polarization converter. The data augmentation method was also employed in few-shot learning to reduce optimization costs and improve model prediction performance. With the inverse prediction, a linear polarization converter that perfectly covers the Ku-band was obtained and fabricated with flexible printed circuit technology. Both simulation and experimental results indicate that this network can accurately predict the structural parameters. The polarization converter not only achieves remarkable broadband polarization conversion efficiency spanning the 2.2–18 GHz range but also maintains precise cross-polarization control across the entire Ku-band. The mean polarization conversion ratio in the Ku-band was calculated to be an impressive 99.69%. Finally, the mechanism of polarization conversion and the influence of each structural parameter on its performance further verify the optimality of the inverse design model. The use of CNN–LSTM deep learning methods significantly simplified the design process of electromagnetic metamaterials, reducing design costs while ensuring high design precision and excellent performance.

Archaeological investigation of burials preluded by ground penetrating radar and geospatial technologies

Ground penetrating radar (GPR) is a non-invasive and efficient scientific tool in burial analysis that can 'see the unseen,' answering both simple questions such as the existence and boundaries of burials, as well as more difficult questions like whether burials are intact or decayed. This paper reviews common reflection signatures associated with burials and applies the three fundamental GPR principles (dielectric contrast, scattering and polarity of reflections) to two distinct caseworks involving historical graves and civilian burials, which serve as benchmarks with known ground truth. It encompasses a third test case involving family tree research in a civilian cemetery, drawing upon the benchmarked results obtained from the first two caseworks. In adherence to geophysical signal reflection principles, our study discerns distinct hyperbolic traits associated with three burial types including intact shroud-wrapped, coffin burials, and decayed or mass-grave burials. A GPR-geospatial integration workflow incorporating GPR, aerial photogrammetry and global navigation satellite system - real time kinetics (GNSS-RTK), is derived to enhance the identification and investigation of burials using GPR. Our workflow encompasses a range of indicators for survey methods and burial classification, presenting a general framework for the systematic contextualization of tailored workflows to individual contexts. This work exemplifies the efficacy of GPR in the detection of burials that have been undisturbed for over a century in the soils of Hong Kong and how geophysics and geospatial science can address the limitations inherent in conventional desktop-based archaeological investigation. Its implications extend to professionals in diverse fields including historians, archaeologists, cemetery management officials, and even family members searching for their lost loved ones.

Multifunctional heterostructured composite foam with 3D hierarchical network for efficient electromagnetic interference shielding

The development of multifunctional electromagnetic interference (EMI) shielding materials represents an important research direction. However, the challenge remains to develop multifunctional and high-performance electromagnetic waves (EMW) shielding materials through the effective integration of multiple functions into the materials through appropriate multicomponent strategies and ingenious microstructural design. In this study, magnetic Fe3O4 nanoparticles with polypyrrole (PPy) encapsulation were successfully assembled on melamine foam (MF) with a hierarchical structure combined with a highly conductive silver layer by in situ polymerization and cyclic immersion processes to achieve absorption-dominated electromagnetic shielding and multifunctionality. The composite benefits from good impedance matching, dielectric/magnetic losses, interfacial/dipole polarization, and internal multiple reflections and scattering due to the three-dimensional conductive network. Moreover, the high concentration of modified Fe3O4@PPy particles assembled on the MF skeleton ensures that the multifunctional heterostructured composite foams remain stable and superhydrophobic even when the surface is repeatedly abraded. At the same time, MHCF exhibits excellent thermal insulation and infrared stealth properties. This work offers new insights into the design and development of lightweight and multifunctional high-performance EMW shielding materials, while simultaneously opening up new prospects for their practical applications.

Effective Visualization of Radar Data for Users Impacted by Color Vision Deficiency

Abstract Color vision deficiency (CVD) is a decreased ability to discern between particular colors. Eight percent of genetic males and half a percent of genetic females have some form of CVD, with many in the radar community falling into this group. When presenting data on a two-dimensional plane, it is common to use colors to represent values via a colormap. Colormap choice in the radar community is influenced by the ability to highlight scientifically interesting features in data, institutional choices, and domain dominance of legacy colormaps. The problem with these current colormaps is that many do not project well for those with CVD (i.e., green next to red). In working with the CVD community to address this problem, multiple colormaps for moments such as equivalent reflectivity factor and Doppler velocity were created for users with forms of CVD such as deuteranomaly, protanomaly, protanopia, and deuteranopia using Python tools such as colorspacious and viscm. We show how these colormaps can improve interpretability for four cases: a mesoscale convective system, a pyrocumulonimbus storm, a wintertime midlatitude cyclone, and widespread storms with a large bird migration. These new radar equivalent reflectivity factor, Doppler velocity, and polarization colormaps are designed to highlight rain, frozen precipitation, nonmeteorological targets, and velocity-based items, are perceptually uniform, and are visually friendly for those with CVD.

Reflection–Polarization Characteristics of Greenhouses Studied by Drone-Polarimetry Focusing on Polarized Light Pollution of Glass Surfaces

Drone-based imaging polarimetry is a valuable new tool for the remote sensing of the polarization characteristics of the Earth’s surface. After briefly reviewing two earlier drone-polarimetric studies, we present here the results of our drone-polarimetric campaigns, in which we measured the reflection–polarization patterns of greenhouses. From the measured patterns of the degree and angle of linear polarization of reflected light, we calculated the measure (plp) of polarized light pollution of glass surfaces. The knowledge of polarized light pollution is important for aquatic insect ecology, since polarotactic aquatic insects are the endangered victims of artificial horizontally polarized light sources. We found that the so-called Palm House of a botanical garden has only a low polarized light pollution, 3.6% ≤ plp ≤ 13.7%, while the greenhouses with tilted roofs are strongly polarized-light-polluting, with 24.8% ≤ plp ≤ 40.4%. Similarly, other tilted-roofed greenhouses contain very high polarized light pollution, plp ≤ 76.7%. Under overcast skies, the polarization patterns and plp values of greenhouses practically only depend on the direction of view relative to the glass surfaces, as the rotationally invariant diffuse cloud light is the only light source. However, under cloudless skies, the polarization patterns of glass surfaces significantly depend on the azimuth direction of view and its angle relative to the solar meridian because, in this case, sunlight is the dominant light source, rather than the sky. In the case of a given direction of view, those glass surfaces are the strongest polarized-light-polluting, from which sunlight and/or skylight is reflected at or near Brewster’s angle in a nearly vertical plane, i.e., with directions of polarization close to horizontal. Therefore, the plp value is usually greatest when the sun shines directly or from behind. The plp value of greenhouses is always the smallest in the green spectral range due to the green plants under the glass.

Parameter Optimization Method for Metal Surface pBRDF Model Based on Improved Strawberry Algorithm

To study the polarization reflection characteristics of metal surfaces, a parameter optimization method for the polarization bidirectional reflection distribution function (pBRDF) model of metal surfaces based on the improved strawberry algorithm has been proposed. Firstly, the light scattering characteristics of metal surfaces were analyzed and a multi-parameter pBRDF model was constructed. Then, the working mechanism of the strawberry optimization algorithm was investigated and improved by introducing the chaotic mapping and Levy flight strategy to overcome the shortcomings, such as low convergence rate and easily falling into local optimum. Finally, the method proposed in this paper was validated by simulating open-source data from references and the obtained ones with a self-built experimental platform. The results show that the proposed method outperforms those by nonlinear least squares, particle swarm optimization and the original strawberry algorithm in fitting the detected degree of polarization (DOP) data, indicating the modeling accuracy was significantly improved and better suited to characterize the polarized reflection properties of metal surfaces.

Ultra-broadband and wide-angle reflective terahertz polarization conversion metasurface based on topological optimization

Abstract Terahertz polarization conversion devices have significant potential applications in various fields such as terahertz imaging and spectroscopy. In this paper, we utilize genetic algorithms to topologically optimize the metasurface unit cells and design a reflective linear polarization conversion metasurface with ultra-broadband and wide-angle characteristics. By partitioning the metallic pattern layer into quadrants, the encoding length is effectively reduced, resulting in a shorter optimization time. The research results indicate that the converter possesses a polarization conversion efficiency ratio higher than 90% and a relative bandwidth ratio of 125% in a range of 0.231–0.995 THz. Meanwhile, it can maintain excellent polarization conversion properties when the incident angle of terahertz waves is less than 45° and the polarization angle is less than 15°, demonstrating excellent practicality. New insights are provided for the design of terahertz wide-angle ultra-wideband polarization conversion devices, and the proposed metasurfce has potential applications in terahertz polarization imaging, spectroscopy and communication fields.

Reflective Surface for Linear-to-Linear and Linear-to-Circular Polarization Conversion at Multiple Frequencies

In this paper, a thin multiband reflective polarization converter surface is proposed that can reflect a circularly polarized (CP) wave in the following frequency bands: 7.8-8.10 GHz, 8.32-10.04 GHz, 10.80-13.75 GHz, 14.19-14.53 GHz, 16.22-16.52 GHz, and 16.77-17.18 GHz. It can also convert a linearly polarized (LP) incident electromagnetic wave into its orthogonal LP reflection wave in these bands: 8.14-8.25 GHz, 10.23-10.60 GHz, 13.90-14.08 GHz, and 16.59-16.71 GHz. With slotted semicircles supported by a metallic ground plane, the suggested unit cell of the periodic structure has significant stability in all frequency ranges, even at oblique incidence within a 75° angle limit. Furthermore, the suggested polarizer has an easy-to-manufacture construction that only needs one substrate layer and does not include any via holes. A sample prototype consisting of 30×30 unit cells was fabricated and tested, validating our design and simulations.

New types of reflective periodical structures in the material with bulk photoalignment of LC polymer using UV polarization holography

Two types of new periodical polarization structures generated by UV polarization holography in thin solid films of LC photosensitive polymer (LCP) due to bulk photo-alignment were experimentally demonstrated. The first type of the structures is similar to cholesteric ones. However, these structures fabricated just by means of optical exposure without chiral dopants. Such technique overcomes some restrictions of alternative known methods of chiral structures fabrications using chiral dopant (e.g., arbitrary orientation of the LC planes). The second type is a new one, which can be realized only using the developed material approach with bulk photo-alignment. This structure is similar to known transmission circular polarization gratings, but the axis is rotated by 90°. The fringes (the planes of equal orientation of LC) in such structures are almost parallel to the layer, and the LC orientation is changing periodically across the layer from in-plane to the perpendicular position. Both new regular periodical structures can be used as volume reflective polarization gratings with several unique properties suitable for the numerous optical applications, including display ones. Specific suggestions for improving the quality of new holographic LC-structures are offered.

Bidirectional vortex beam and reflective polarization conversion terahertz metasurfaces

We design a terahertz metasurface with the functions of bidirectional vortex beams and reflection polarization conversion. The unit cell of the proposed metasurface consists of a vanadium dioxide metal mixed layer, a dielectric layer, a vanadium dioxide thin film, a dielectric layer, and a metal open ring. At room temperature, when a left-handed circularly polarized wave is incident, the metasurface generates a reflected mode vortex beam with topological charges of l=−1 and l=−2 at frequencies of 0.33 and 0.34 THz. Simultaneously, the metasurface produces transmitted mode vortex beams with topological charges of l=−1 and l=−2 at frequencies of 0.33 and 0.36 THz. When the temperature changes to 68°C and y-polarized waves are incident, the metasurface generates a reflected left-handed circularly polarized wave in the frequency bands of 0.6–0.65 THz and 1.75–1.93 THz, and a right-handed circularly polarized wave in the frequency band of 0.86–0.9 THz, achieving the function of converting linearly polarized waves into circularly polarized waves. This metasurface provides a new method for designing a single metasurface structure to achieve bidirectional multifunctional terahertz devices for transmission and reflection modes. In addition, the designed metasurface achieves a perfect polarization conversion function that can convert linearly polarized waves into circularly polarized waves.

27‐1: Flat‐based Double Path Pancake Optics to Improve Productivity

We proposed highly light efficient pancake Head Mounted Display (HMD) optics named “Double path pancake optics” last year, which has 1.8 times higher light efficiency than conventional one.While maintaining such high optical efficiency, this year, we have improved its productivity by replacing curved Reflective Polarizer (RP) with flat one. To realize a structure with flat RP, we have simulated optical concepts and finally found appropriate design. According to our optimized optical design, 25.5 mm thickness with 90 deg Field Of View (FOV) was realized and we have successfully made the prototype and confirmed that the high image quality can be displayed and optical properties are almost the same as our previous one with curved RP.