High Reflectivity Research Articles

A double-layer radiative cooling coating that utilizes the refractive index difference between layers to achieve extremely high solar reflectivity

A double-layer radiative cooling coating that utilizes the refractive index difference between layers to achieve extremely high solar reflectivity

Durable hybrid metamaterial with hierarchically porous structure for efficient passive daytime radiative cooling

Passive daytime radiative cooling, which strongly emits heat while minimally absorbing sunlight, constitutes a promising strategy to address the energy density mismatch between solar irradiance and the low infrared radiation flux from material surfaces. However, nanoscale-precision manufacturing and the need for additional metal backing often result in low efficiency and limited applicability. Here, we present a durable hybrid metamaterial (DHM) comprising a randomly distributed inorganic dielectric particle–polymer composite with a hierarchically porous structure created via a simple phase separation method. Despite the absence of a metal backing, the DHM exhibits a broadband, high mid-infrared emissivity of 98.2 % and a high solar reflectivity of 98.0 %, enabling it to strongly radiate heat and scatter sunlight. Outdoor testing demonstrates that the DHM achieves an average cooling temperature of 9.0 °C under an average solar irradiance of 853.4 W·m−2, comparable to recently reported radiative coolers. The high electronegativity of C–F bonds in polyvinylidene fluoride–hexafluoropropylene (PVDF–HFP) and the high thermal and chemical stability of zirconium dioxide microparticles (ZrO2 MPs) endow the DHM with excellent environment durability. Moreover, the DHM provides effective and passive protection for ice and snow under sunlight exposure. Considering its outstanding cooling performance, environmental stability, and scalability, the DHM holds great promise for widespread applications in building and vehicle cooling, as well as glacier preservation efforts.

Electrical and current-carrying tribological properties of CoCrFeNi-(Mo, Ti, W) high-entropy alloy coatings on copper alloys by infrared-blue composite laser cladding

Infrared-blue composite laser cladding technology is used to prepare highly conductive and wear-resistant CoCrFeNi-(Mo, Ti, W) HEA coatings on the surface of the copper alloy to overcome the problem of high reflectivity of copper alloy aiming to enhance the surface performance of copper alloy current-carrying friction part. The microstructure and electrical properties of the high-entropy alloy coating were investigated. The wear resistance of the coatings was tested under high-speed and high-current conditions using a self-made current-carrying friction and wear testing machine. The results show that fine-grain and second-phase strengthening significantly enhances the hardness of the high-entropy alloy coating. The high-entropy alloy coating maintains the excellent electrical conductivity of the copper alloy, with an overall conductivity remaining above 60 % IACS. During the current-carrying friction process, the CoCrFeNi-(Mo, Ti, W) HEA coatings exhibited good wear resistance, with wear rates of 0.84 g/h, 1.08 g/h, and 1.32 g/h, respectively. The wear mechanisms observed included varying degrees of adhesive wear, abrasive wear, fatigue wear, and arc erosion.

A Detailed First‐Principles Study of the Structural, Elastic, Thermomechanical, and Optoelectronic Properties of Binary Rare‐Earth Tritelluride NdTe3

AbstractRare‐earth tritellurides (RTe3) are popular for their charge density wave (CDW) phase, magnetotransport properties, and pressure‐induced superconducting state among other features. In this literature, Density functional theory is exploited to study various properties of NdTe3. The calculated elastic and thermomechanical parameters, which are hitherto untouched for any RTe3, uncover soft, ductile, highly machinable, and damage‐tolerant characteristics, as well as highly anisotropic mechanical behavior of this layered compound. Its thermomechanical properties make it a prospective thermal barrier coating material. Band structure, density of states, Fermi surfaces, and various optical functions of the material are reported. The band structure demonstrates highly directional metallic nature. The highly dispersive bands indicate very low effective charge carrier mass for the in‐plane directions. The Fermi surfaces display symmetric pockets, including signs of nesting, bilayer splitting among others, corroborating previous works. The optical spectra expose high reflectivity across the visible region, while absorption is high in the ultraviolet region. Two plasma frequencies are noticed in the optical loss function. The optical conductivity, reflectivity, and absorption reaffirm its metallic properties. The electronic band structure manifests evidence of CDW phase in the ground state.

Laboratorial investigation on optical, thermal and pavement performance of biomimetic dark reflective coatings with composite structure for pavement cooling

The surface temperature of asphalt pavement in summer can reach up to 70 °C, which leads to poor outdoor thermal comfort and exacerbates the urban heat island effect. Reflective coatings can effectively reduce pavement temperature, but their intrinsic light color with high reflectance causes safety issues such as glaring. In this study, based on the biomimetic idea of chameleon skin structure, composite pavement coatings for cooling and anti-glare were developed. Their optical properties, thermal behavior, adhesion and skid-resistance performances were investigated. The results showed that near-infrared reflectance of black and grey double-layer reflective coatings could reach 0.66 and 0.70, respectively (58 % higher than single-layer coatings). The optimal mass fraction of perylene black in the upper black/grey coating was 2.94 % and 0.74 %, respectively. The double-layer dark coatings could decrease the temperature by 14 °C at the depth of 3 cm below road surface, which achieved cooling effect close to that of white single-layer reflective coatings. The adhesion between coating and stone was generally higher than the cohesion of asphalt, therefore, opening traffic for a period of time or carrying out micro-milling before coating could improve the abrasion resistance. Due to increase in the thickness of the double-layer coating, the microscopic texture of road surface was reduced, thereby reducing skid-resistance. However, it still met the standard requirements. This study intends to provide a reference for developing pavement coatings that balance cooling and visual safety to mitigate the heat island effect, and improve the sustainability of transportation infrastructure.

Laser Powder Bed Fusion of Copper-Tungsten Powders Manufactured by Milling or Co-Injection Atomization Process.

The processing of pure copper (Cu) has been a challenge for laser-based additive manufacturing for many years since copper powders have a high reflectivity of up to 83% of electromagnetic radiation at a wavelength of 1070 nm. In this study, Cu particles were coated with sub-micrometer tungsten (W) particles to increase the laser beam absorptivity. The coated powders were processed by powder bed fusion-laser beam for metals (PBF-LB/M) with a conventional laser system of <300 watts laser power and a wavelength of 1070 nm. Two different powder manufacturing routes were developed. The first manufacturing route was gas atomization combined with a milling process by a planetary mill. The second manufacturing method was gas atomization with particle co-injection, where a separate W particle jet was sprayed into the atomized Cu jet. As part of the investigations, an extensive characterization of powder and additively manufactured test specimens was carried out. The specimens of Cu/W powders manufactured by the milling process have shown superior results. The laser absorptivity of the Cu/W powder was increased from 22.5% (pure Cu powder) to up to 71.6% for powders with 3 vol% W. In addition, a relative density of test specimens up to 98.2% (optically) and 95.6% (Archimedes) was reached. Furthermore, thermal conductivity was measured by laser flash analysis (LFA) and thermo-optical measurement (TOM). By using eddy current measurement, the electrical conductivity was analyzed. In comparison to the Cu reference, a thermal conductivity of 88.9% and an electrical conductivity of 85.8% were determined. Moreover, the Vickers hardness was measured. The effect of porosity on conductivity properties and hardness was investigated and showed a linear correlation. Finally, a demonstrator was built in which a wall thickness of down to 200 µm was achieved. This demonstrates that the Cu/W composite can be used for heat exchangers, heat sinks, and coils.

Numerical simulation of electrically-pumped overgrown III-V microwire lasers on silicon

Electrically-pumped III-V lasers on Si by aspect ratio trapping (ART) techniques have been a promising candidate for Si-based light sources. Although the lasers based on the ART approach enable large-scale integration and are compatible with complementary metal-oxide semiconductor processes, the sub-micron size laser structure suffers from severe metal absorption loss and heat accumulation. In this paper, we propose a novel Si-based III-V multi-quantum well laser by ART methods. The overgrowth of III-V microwires is adopted, with additional {110} quantum wells (QWs) generated during epitaxy. Through numerical simulation, the mode loss of the overgrowth structure is reduced from 3.59 dB/cm to 0.96 dB/cm, the threshold current is decreased by 42.5% and the output power is increased by 91.7% under pulsed conditions. Due to the growth of QWs on {110} planes, the injection efficiency of the device increases, leading to an improvement of performance. The effects of temperature and cavity length on the lasing characteristics of the device under continuous wave (CW) conditions are also analyzed that the proposed structure can realize CW lasing at room temperature. Moreover, the device deterioration caused by growth defects is discussed, which can be improved by high reflection coating. The suggested Si-based overgrowth III-V microwire laser has great potential to integrate high-density electrically-pumped light sources for silicon photonics.

Enhanced Scratch Detection for Textured Materials Based on Optimized Photometric Stereo Vision and Fast Fourier Transform–Gabor Filtering

In the process of scratch defect detection in textured materials, there are often problems of low efficiency in traditional manual detection, large errors in machine vision, and difficulty in distinguishing defective scratches from the background texture. In order to solve these problems, we developed an enhanced scratch defect detection system for textured materials based on optimized photometric stereo vision and FFT-Gabor filtering. We designed and optimized a novel hemispherical image acquisition device that allows for selective lighting angles. This device integrates images captured under multiple light sources to obtain richer surface gradient information for textured materials, overcoming issues caused by high reflections or dark shadows under a single light source angle. At the same time, for the textured material, scratches and a textured background are difficult to distinguish; therefore, we introduced a Gabor filter-based convolution kernel, leveraging the fast Fourier transform (FFT), to perform convolution operations and spatial domain phase subtraction. This process effectively enhances the defect information while suppressing the textured background. The effectiveness and superiority of the proposed method were validated through material applicability experiments and comparative method evaluations using a variety of textured material samples. The results demonstrated a stable scratch capture success rate of 100% and a recognition detection success rate of 98.43% ± 1.0%.

Dual-band millimetre wave MIMO antenna with reduced mutual coupling based on optimized parasitic structure and ground modification

In this study, a high-isolation dual-band (28/38 GHz) multiple-input–multiple-output (MIMO) antenna for 5G millimeter-wave indoor applications is presented. The antenna consists of two interconnected patches. The primary patch is connected to the inset feed, while the secondary patch is arc-shaped and positioned over the main patch, opposite to the feed. Both patches function in the lower 28 GHz band, while the primary patch is accountable for inducing the upper 38 GHz band. An expedited trust-region (TR) algorithm is employed to optimize the dimensions of the antenna components, ensuring the antenna operates efficiently with high reflection at both bands. The antenna demonstrates a gain exceeding 7 dBi at both frequencies. An array of four antennas is configured orthogonally to create a MIMO system with isolation surpassing 19 dB. The isolation is further enhanced through the addition of a circular parasitic patch at the front and modifications made to the ground. The TR method is employed again to optimize their parameters and achieve the desired isolation, exceeding 32 dB at both bands. The MIMO system demonstrates outstanding diversity performance at both frequencies, characterized by low values of the envelope correlation coefficient (ECC) (< 10 − 4), channel capacity loss (CCL) (< 0.03 bit/s/Hz), and total active reflection coefficient (TARC) (< − 10 dB). Additionally, it secures a diversity gain (DG) exceeding 9.99 dB. The MIMO system is manufactured and tested, showing good alignment between simulation and measurement data for all performance metrics.

BN fiber aerogels with high solar reflectivity and thermal insulation for green buildings

There exists more than one-third of the stock of buildings that do not meet energy-saving building standards, so there is an urgent need for breakthroughs in the field of green buildings. Herein, we successfully prepared boron nitride (BN) fiber aerogels by sol-gel, freeze-drying and high-temperature pyrolysis. When the molar ratio of C3N6H6 to H3BO3 was 1:2 and the roasting temperature was 1000 °C, the BN fiber aerogel was produced with high specific surface area (257.690 m2/g) and high porosity (99 %). BN fiber aerogels, with their low thermal conductivity (0.043 W/(m·K)) and stable mechanical properties (no change after 45 cycles at 30 % strain), offered possibilities for thermal insulation in green buildings. Its hydrophobic properties protect the wall from the natural environment. In particular, it had a solar reflectivity of 98.6 %, which exceeds most reflective coating materials, enabling the cooling of green construction on hot summer days. The high-temperature resistance of BN fiber aerogels could be applied in special environments such as blast furnace plants and thermoelectric power plants.

AN INTEGRATING SPHERE SPECTROPHOTOMETER PROTOTYPE

Spectroscopy is essential for research in the qualitative and quantitative analysis of samples. In recent years, the need to develop portable and accessible equipment for sample characterization has reduced real-time analysis. The objective is to design and build a prototype of a portable spectrophotometer with an integrating sphere using tools such as Rhinoceros and Trace-Pro for its theoretical design and radiation simulation. The result is an integrating sphere 3D printed with PLA material and an internal coating with a 95% high reflectance paint. The AS7265 Triad module is the detector, along with signal processing to obtain spectra from control samples. The spectral profiles obtained were comparable with commercial equipment, validating the viability of the measurement system as the first spectroscopic instrument in the field, in complement to other spectroscopic techniques. This breakthrough promises to facilitate research in the field and in environments where mobility and accessibility are priorities. Keywords: Integrating sphere, High reflectance coating, simulation Trace Pro, Manufacturing integrating sphere, spectroscopy.

The development of environmentally friendly Pr/W Co-doped Bi2MoO6 green pigment with high near-infrared reflectivity

In this article, a green pigment Bi1.95-xPrxW0.05MoO6+δ (x = 0.1–0.5) co-doped with Pr and W was developed using high temperature solid-phase synthesis method. The microstructure, color performance, and optical characteristics of the novel pigment was analyzed using x-ray diffraction instrument (XRD), field-emission scanning electron microscopy (FESEM), L∗ a∗ b∗ color date, and ultraviolet–visible–near infrared light spectrophotometer. The results indicate that all the samples possess a monoclinic structure, characterized by the space group P21/c(14). Compared to Bi2-xPrxMoO6+δ doped solely with Pr6O11, the Pr/W co-doped Bi2MoO6 pigment demonstrates superior green coloration. The solar reflectance in the near-infrared region of all pigment samples exceeds 80 %, highest value reaches 92.82 %. In thermal insulation tests, the temperature difference between the Bi1.95-xPrxW0.05MoO6+δ pigment coating and a blank galvanized sheet reaches up to 10.3 °C after 60 min under infrared lamp irradiation. The color difference ΔE∗ of the pigment powder after immersion in acid and alkali solution and high-temperature calcination are less than 5, indicating good chemical stabilities in acidic, alkaline and high-temperature environments. To our knowledge, Bi1.95-xPrxW0.05MoO6+δ has the highest reflectivity among green pigments without toxic metals.

A micro-sandwich-structured membrane with high solar reflectivity for durable radiative cooling

A micro-sandwich-structured membrane with high solar reflectivity for durable radiative cooling

In-Situ Surface Modification of Nickel Mesh for Superior Electromagnetic Interference Shielding

Metal mesh, with its inherent conductivity, transparency, and flexibility, has proven to be an exceptional choice for high-performance reflection-dominated electromagnetic interference (EMI) shielding materials, due to its multifunctionality and wide applicability. However, the development of metal-based absorption-enhanced EMI shielding materials characterized by high absorption and low reflection is crucial but remains challenging. Herein, we introduce a novel surface modification strategy for nickel mesh (NM) aimed at augmenting its surface electromagnetic wave absorption through electrochemical surface microstructure alteration and subsequent wet chemical sulphuration. This approach leverages the multiple reflections within the microporous structure and the impedance matching enhancement provided by the magnetic sulfided nickel layer, resulting in the sulphur-treated porous NM (Ni3S2-PNM) achieving an outstanding average EMI SE of 59.6 dB across a broad frequency range of 4 to 40 GHz. The surface electromagnetic wave absorption rate of Ni3S2-PNM has increased from under 1% for unmodified NM to over 60%, significantly reducing the re-reflection of electromagnetic waves back into free space (the average SER value decreases from about 20 dB to 2.2 dB). Characterized by its simplicity and cost-effectiveness, this in-situ surface modification method on bulk industrial-grade NM, enhancing electromagnetic shielding, presents a promising avenue for wider application in electromagnetic protection.

Why do understorey Licuala palm fruits turn from red to white and then black when ripe?

Licuala ferruginea Becc., a tropical forest understorey palm, is observed to have fruits that appear red in colour when unripe, turning pink, then white, purple and finally black in colour as they ripen. We monitored 13 fruiting palms in rainforest fragments and recorded the consumption of fruits by animals via camera traps. We also documented the fruiting phenology of two palms in the nursery. In the rainforest fragments, a Cream-vented Bulbul (Pycnonotus simplex) was observed plucking a mature purple fruit from a L. ferruginea palm, before flying away with the fruit in its beak. This was the only bird that was observed feeding on the mature fruit. A range of mammals, dominated by edge species such as the Long-tailed Macaque and Wild Boar, were observed to consume L. ferruginea fruits indiscriminately across all five colour stages, thereby limiting the dispersal of the fruits. Forest bulbul gape sizes also matched the fruit size, suggesting that forest bulbuls are the likely dispersers of the palm in the original forest where edge species are not in high densities. We further posit that the initial phase of red fruits, with high contrasting red reflectance against a green foliage background, might be a form of early advertisement to birds. The fruit then turns pink and white, which have high green reflectance and is less contrasting, thereby reducing the conspicuity of the fruit. This allows the fruit to ripen with high fructose and glucose content, and turn purple and black, which are known visual cues for birds. This study provides indicative support for the dispersal syndrome hypothesis and highlights the potential effects of forest fragmentation on plant-frugivore interactions.

Clinical Implications of Ultrasound-Based Morphology in Choroidal Melanoma

ObjectiveTo describe the frequency of different B-scan morphologies and their association with clinical features and outcomes. DesignCohort study of patients enrolled in the Prospective Ocular Tumor Study from January 2000 to January 2024 initially seen at Mayo Clinic Rochester. ParticipantsConsecutive inclusion of patients with posterior uveal melanoma. MethodsB-scan ultrasounds were performed by an experienced technician and treatment modalities were implemented by the attending oncologist. Main outcomes and measuresTumors were classified by shape as observed on B-scan. Enucleation-, metastasis, -and overall survival (EFS, MTS, and OS) rates were analyzed using Cox-regression models and Kaplan-Meier curves. ResultsAmong 1021 cases of uveal melanoma, 739 (72.4%) were dome-shaped, 119 (11.7%) mushroom-shaped, 85 (8.3%) multilobulated, 77 (7.5%) minimally elevated, and 1 (0.1%) diffuse. The median follow-up duration after presentation was 37 months (3-324). The macula was more commonly involved in minimally elevated tumors compared to the other groups (63.6% vs. 13.8%, p<0.001). These tumors also exhibited a larger proportion of high internal reflectivity (13% vs. 2.3%, p<0.001). The multilobulated group exhibited a significantly larger diameter at baseline (median 15 mm, IQR 6.1-30), whereas the mushroom-shaped group had greater thickness (median 7.9 mm, IQR 1.3 - 17.3) compared to the other groups (p<0.001). EFS at 36 months was lower for mushroom-shaped [60.1% (95% CI, 47.7-70.3)] and multilobulated tumors [71.1% (95% CI, 55.7-82.7)]. At 36 months, multilobulated tumors had lower MFS [68.2% (95%, CI 55-78.2)] and OS [73.9% (95%, CI 59.9-83.64)]. On multivariate analysis adjusted for tumor thickness and diameter, multilobulated melanomas had a higher risk of metastasis (HR 2.08, p=0.003) and death (HR 2.38, p<0.001). ConclusionChoroidal melanoma configuration by B-scan can vary from minimally elevated to dome-shaped to mushroom-shaped or multilobulated. Independent of presenting tumor size, multilobulated morphology was identified as a predictor for metastasis and death. Multilobulated melanomas, identified by a readily available tool such as ultrasonography, warrant a vigilant approach and close monitoring due to a potential association with poor prognosis.

Source-independent Q-compensated viscoacoustic least-squares reverse time migration

The strong viscosity of the subsurface introduces amplitude absorption and phase-velocity dispersion. Incorrect compensation of the inherent attenuation (the strength of the seismic attenuation can be quantified by the inverse of the quality factor Q, which is defined as [Formula: see text] times the ratio of the stored energy to the lost energy in a single cycle of deformation) can significantly affect imaging quality. Although Q-least-squares reverse time migration ( Q-LSRTM) allows for the compensation of attenuation effects during the iterations, the traditional [Formula: see text]-norm minimization, which is highly sensitive to the source wavelet, poses a challenge in accurately estimating the source wavelet from the field data. Thus, we develop a source-independent Q-LSRTM, in which a convolutional objective function is introduced to replace the [Formula: see text]-norm constraint to mitigate the source wavelet effect. According to the Born approximation, we first linearize the constant-order decoupled fractional Laplacian viscoacoustic wave equation to derive the demigration operator and then construct the corresponding adjoint equation and gradient based on the convolutional objective function, iteratively estimating the reflectivity images. Our method relaxes the sensitivity to the wavelet compared with the conventional [Formula: see text]-norm scheme due to the convolutional objective function, which has the ability to construct the same new source for simulated and observed data. Numerical tests on a layered model, the Marmousi model, and field data demonstrate that our source-independent Q-LSRTM enables us to obtain high-quality reflectivity images even when using incorrect source wavelets.

Ultraviolet response of ZnO nanorod/Sb-doped ZnO thin film homojunction structure prepared by all-chemically wet process

In this work, ZnO nanorod/Sb-doped ZnO thin film structure was fabricated and its relevant properties were investigated. The device was prepared by Sb-doped ZnO sol-gel spin coating technique onto ITO substrate annealed in nitrogen atmosphere followed by the hydrothermal process to obtain ZnO nanorod. The crystal structure demonstrates (002) plane dominant hexagonal wurtzite ZnO without phase impurity. The deterioration in the crystal structure of Sb-doped ZnO due to the Sb is incorporated in the ZnO lattice. The element component in each layer is confirmed by depth profile measurement. The low transmittance in the visible region is due to high reflection at the surface of the ZnO nanorod. The electrical measurement confirms that ZnO nanorod/Sb-doped ZnO thin film has p-n homojunction properties under dark conditions and 18 times higher photovoltage than the Sb-doped/undoped ZnO double layer device under UV LED irradiation due to enhanced photon harvesting of ZnO nanorod structure.

Automatic Identification of Three-Body Scatter Spike Based on Jensen–Shannon Divergence and Support Vector Machine

Abstract The three-body scatter spike (TBSS), an echo artifact in radar imagery, manifests as a weak, linear echo extending radially from a core of high reflectivity. Adequately, though not indispensably, indicating the presence of large hail in convective storms, the automatic identification of the TBSS proves advantageous in significantly improving the effectiveness of hailstorm detection. This study introduces an algorithm that synergizes Jensen–Shannon divergence (JSD) and support vector machine (SVM) for rapid TBSS detection in two decades’ worth of single-polarization radar data across China. The algorithm, tested on data from 50 S-band China Next Generation Weather Radar (CINRAD) in central and eastern China, utilized reflectivity factor images for sample extraction. An application in Chenzhou, China, demonstrates the algorithm’s efficacy in improving hailstorm detection resolution. Significance Statement In recent years, China’s hail recordkeeping, primarily based on manual observations at national surface meteorological stations, has suffered from limited spatial and temporal detail. However, the advent of the China Next Generation Weather Radar (CINRAD) network offers a new avenue for hailstorm detection. TBSS, a secondary but significant indicator for large hail in S-band radar, presents an opportunity for enhanced hail warning capabilities. By automating TBSS detection in radar archives spanning two decades, this research significantly enhances the resolution of hailstorm climatology, contributing to more effective hail disaster mitigation and management.

Cellulose acetate hierarchical porous coated textile with passive daytime radiative cooling, flexibility and durability

Passive daytime radiative cooling technology is a highly efficient cooling technology with zero energy consumption. When utilized for personal thermal management, radiative cooling textiles are capable of finely regulating the temperature of the human skin microenvironment. This study presents a cellulose acetate (CA) hierarchical porous coated textile that accomplishes high reflectance of sunlight over the full wavelength range, with a low cost and scalability, and a simple preparation procedure. With a high reflectance of 0.91 in the solar wavelength band and a high emissivity of 0.95 in the atmospheric window wavelength band, the CA hierarchical porous coated textile offers exceptional spectrally selective performances. It manifests a subambient cooling temperature of up to 19.0 °C and a skin overheating prevention effect of up to 4.2 °C. Furthermore, the coated textile possesses promising abrasion resistance, acid-alkali corrosion resistance, and mechanical properties. The present work provides a facile path for the development of green-based radiative cooling coated textiles.