Range Of Incident Angles Research Articles

Viscoelastic material enhancement of underwater sound absorption in higher-order resonators: from low-frequency to ultra-broadband

Underwater noise control is crucial for improving the marine acoustic environment. This study introduces a novel underwater acoustic absorber design that integrates viscoelastic materials with higher-order resonance structures to enhance the absorption efficiency of low-frequency sound waves. By embedding a thin layer of rubber within a conventional second-order Helmholtz resonator, the rubber's viscoelastic and damping properties significantly improve this structure's underwater low-frequency acoustic performance. Theoretical and simulation calculations have shown that the structure has two perfect absorption peaks in the low-frequency range. The simulation results show that in the frequency range of 415-1848 Hz (Simulation), only four units are needed to effectively absorb up to 90% of noise energy, and the total volume is only. Moreover, the absorber maintains excellent absorption performance over a wide range of incidence angles from 0 to 60 degrees. This work is helpful to design ultra-thin low-frequency underwater absorbers.

Flexible substrate based wideband polarization converter with extremely high polarization conversion ratio

In this article an anticipated reflection-mode cross-polarization converters (CPCs) are designed on a polydimethylsiloxane (PDMS) based flexible substrate operating in the GHz region. The proposed CPC metasurface comprises three layers where a flexible substrate is endwise between the resonating layer and ground layers. The converter can convert linear to circular and circular to cross-polarized waves at the frequency range of 5–8 GHz, as evidenced by the identical amplitude of Rxx and Ryx and a phase difference of 90°. More than 99 % of the polarization conversion ratio (PCR) was performed between the 6.75 and 9.07 GHz frequency range, while more than 80 % of the PCR was performed between the 6.0 and 10.73 GHz frequency range. The highest PCR values show nearly flawless energy conversion from an x-polarized incident wave to a y-polarized reflected wave. The PCR ratio of 80 % is achieved by this ultra-wideband linear-to-cross- and circular-to-cross-polarization converter. The anticipated converter's spectrum for all incidence angles between 0◦ and 60°. The PCR remained higher than 99 % over a wide incidence angle range to 60° without much performance degradation. The bending stability of the PDMS-based flexible substrate is also investigated up to 60°. The structure is fabricated on a flexible substrate, and the measured performance is compared with simulated results. Radar, antenna, and communications systems, as well as other cross-polarization converters, can utilize the transmitted wave's very high polarization purity result.

Dynamic tunable triple-band terahertz perfect absorber based on graphene metamaterial

This work developed a graphene-based perfect absorber with dynamic tuning capabilities. This absorber consists of a metal substrate, a layer of graphene square rings, a layer of graphene disks, and two layers of SiO2 dielectric sandwiched between them. Simulation results demonstrate absorption peaks at 1.23 THz, 4.2 THz, and 6.38 THz, with respective absorption rates of 99.9 %, 99.8 %, and 98.3 %. By analyzing the distributions of the electric field and surface current at the central frequencies of the three absorption peaks, the excitation mechanism of each absorption peak was discussed. It was found that by adjusting graphene's chemical potential, the absorption spectrum can be actively controlled. Furthermore, the absorber is insensitive to polarization and can sustain the stability of the absorption spectrum within an incident angle range of 0∼35°. This work has the potential to advance the research of multi-band terahertz absorbers, dynamically tunable devices, and other graphene-based photonic devices.

Photonic-Enhanced Perovskite Solar Cells: Tailoring Color and Light Capture.

The current exponential growth of solar electricity technologies toward consumer-oriented applications, as in building- or vehicle-integrated photovoltaics (B/VIPV), is calling for improved solar cells, not only in cost-effectiveness, but also with better adaptability and aesthetics. Here, using perovskite solar cells (PSCs) as test bed, we demonstrate an unprecedented photonic method to generate any color on a cell layout, while also increasing PV efficiency. To this end, photonic surface features were designed for PSCs, which filled the dual purpose of light-trapping (LT) and modulation of reflected light interference. A variety of geometries, from simple gratings to complex semispheroids, were optically optimized for two of the most challenging colors, magenta and green, while assuring the generation of their maximum feasible photocurrent. The best results corresponded to a current density of 22.07 mA/cm2, obtained for the magenta solar cell with top domes, exhibiting an increase of 6.68%, relative to an optimized planar reference cell. In turn, the same type of geometry was able to generate the leading green cell, with up to 21.40 mA/cm2 (a relative increase of 3.44%). Additionally, the uniformity of the optical output of the optimal solar cells was tested under a range of incident light angles, between 0◦ and 60◦, where the current density suffered relative losses only down to 6.65%.

Design and performance of a dual-band plasmonic perfect absorber for infrared refractive index sensing

In this study, we introduce what we believe is an innovative design for a plasmonic perfect absorber (PPA) that is based on half-cut disk resonator metamaterials. This design exhibits remarkable stability and versatility, demonstrating effective functionality across a wide range of incident angles for both transverse electric (TE) and transverse magnetic (TM) polarization. The distinct operational characteristics of the PPA are highlighted by the presence of two corresponding absorption peaks at wavelengths of 870 and 1599 nm, where it achieves outstanding maximum absorption rates of 98.99% and 97.5%, respectively. The design’s ultra-narrow resonance peaks are indicative of its high-quality factors, which are vital for enhancing sensitivity in plasmonic sensory applications. This characteristic renders our PPA an exceptional candidate for refractive index (RI) sensing, where precision is critical. The dual-band perfect absorber (PA)-based sensor demonstrates significant RI sensitivity, with values approximately equal to 365 nm/RIU at the first absorption peak and 733 nm/RIU at the second. Our findings elucidate the exceptional potential inherent in this novel dual-band perfect absorber design. The versatility and efficiency across varied applications not only contribute to the existing body of knowledge but also pave the way for future advancements in plasmonic sensor technologies and metamaterial research.

Life-cycle seismic performance of bridges with thin-walled steel piers under bi-directional excitations

In corrosive environments, steel bridges demonstrate time-dependent seismic performance and varied directional responses to bi-directional excitation at different life-cycle stages. However, current seismic assessment methods for bridges have not adequately addressed the time-dependent effects of bi-directional excitation directionality on seismic responses throughout their entire life cycle. Thus, this study aims to investigate the time-varying directional effects of bi-directional seismic excitations on steel bridges with multiple parameters and to propose a method for predicting the range of critical incident angles while considering the aging effects of bridges. Initially, time-dependent functions that characterize steel corrosion are integrated into multiscale finite element models of the steel bridges to simulate corrosion progression across their life-cycle stages. Subsequently, a quantitative analysis of the bi-directional seismic response of steel bridges is conducted throughout their life cycle, accounting for the directionality of seismic excitation. Finally, a method and process for predicting the range of time-varying bi-directional critical incident angles with 95 % probability are derived by fitting the statistical probability distribution boundary values of the critical incident angle deviation index. The study's findings indicate that the aging effects of steel bridges amplify the displacement response under bi-directional seismic excitation, with the maximum displacement response difference exceeds 40 %. The service time may increase the sensitivity of steel bridges to changes in incident angles, potentially amplifying the displacement response by a factor of 1.69. The study's findings highlight the importance of considering aging effects and bi-directional excitation directionality in bridge seismic assessments.

Measurement of turbid media by total internal reflection with Goos-Hänchen angle displacement

Based on the Goos-Hänchen effect and the intensity attenuation of the evanescent wave penetrating and traveling, a new theoretical model of total internal reflection from the interface of turbid media is proposed and an analytical reflectance expression in a wide incident angle range is developed. The Goos-Hänchen angle displacement between the critical reflectance and the saturated reflectance is discovered. A sensor, for measuring the complex refractive index of turbid media in real-time, with divergent light source is designed. The captured images show that the light distribution reflected from the transparent medium has a sharp boundary, but for turbid media, the reflected light intensity attenuates during the transition from total to non-total internal reflection regions. It is successful and accurate that the new model fits the experimental data of the reflectance and the complex refractive index of turbid media is measured by our sensor. The results show that measuring has advantages in real-time, in situ, and with high accuracy.

A novel micro non-imaging concentrating solar module for building façade integration

Owing to the limited installation space and relative low energy density of solar radiation, how to fully utilize the solar energy potential on the building south façade is always an important issue. In this regard, this paper proposed a faced embedded solar thermal module with mini asymmetric parabolic concentrator, which could capture solar radiation within a wide range of incidence angles with relatively high thermal conversion efficiency. The optical efficiency of the proposed solar module maintains over 0.7 with the solar projection angle increasing from 0° to 90°, which covers the annual altitude angle variation of beam solar radiation incidence on the south façade. Corresponding photo-thermal model was developed and validated with 5 days continues outdoor measurement data. The predicted values were in good consistence with the experimental data with a R2 value of 0.975. Experimental results showed a daily thermal efficiency of 0.66 during the clear sky weather. The average daily thermal efficiency of the ACPC module throughout the year was 0.47 with a constant working temperature of 60 °C. The proposed device is expected to help the building integration design towards zero carbon emission building.

DeepCSNet: a deep learning method for predicting electron-impact doubly differential ionization cross sections

Abstract Electron-impact ionization cross sections of atoms and molecules are essential for plasma modelling. However, experimentally determining the absolute cross sections is not easy, and ab initio calculations become computationally prohibitive as molecular complexity increases. Existing AI-based prediction methods suffer from limited data availability and poor generalization. To address these issues, we propose DeepCSNet, a deep learning approach designed to predict electron-impact ionization cross sections using limited training data. We present two configurations of DeepCSNet: one tailored for specific molecules and another for various molecules. Both configurations can typically achieve a relative L2 error less than 5%. The present numerical results, focusing on electron-impact doubly differential ionization cross sections, demonstrate DeepCSNet's generalization ability, predicting cross sections across a wide range of energies and incident angles. Additionally, DeepCSNet shows promising results in predicting cross sections for molecules not included in the training set, even large molecules with more than 10 constituent atoms, highlighting its potential for practical applications.

Particle swarm optimization for performance enhancement of cadmium telluride thin film solar cells by embedded nano-grating structures with a plasmonic metal coating layer

As the demand for energy in world is increasing rapidly and there is pursuit for renewable energy sources which is cheap, easy to generate and requires low maintenance, solar energy is a top contender. The world is in dire need of photovoltaic solar cells that can aid in keeping up with the hiking energy demands. However, thin film solar cells (TFSCs) which are developed for cost effectivity, suffer in performance due to reduced thickness. Therefore, this computational study uses Finite-Difference Time-Domain (FDTD) and delves into the scope of using a 1-D nano-grating structure embedded into absorbing layer of cadmium telluride TFSC to enhance the optoelectronic performance. A unique nano-grating structure with SiO2 at its core and aluminium coating aims to enhance the performance of CdTe TFSC with cost effectivity and ease of fabricability as the main motifs. Additionally, an evolutionary computational technique, Particle Swarm Optimization (PSO), was used to determine the optimal parameters of nano-gratings on CdTe TFSCs, i.e., nano-grating height, angle, duty cycle, aluminium coating thickness and grating substrate thickness. The PSO algorithm resulted in a nano-grating structure that yielded an efficiency increase of 52.86% and increase in short-circuit current density of 25.45% with respect to bare CdTe TFSCs. Subsequently, the performance of the optimal nano-grating structure was also observed to be insensitive to variation of wide range of incidence angle of light, a key feature preferred for versatile application of TFSCs.

Ion incidence angle-dependent pattern formation on AZ® 4562 photoresist by reactive ion beam etching

Reactive ion beam etching is a key technology in the field of ultra-precise surface engineering. In this process nanopatterns can emerge and alter the functional properties of the surfaces. Therefore, it is necessary to understand which reactive ion beam parameters influence the emergence of these nanopatterns. In this study the influence of reactive ion beam etching on the commercially available photoresist AZ® 4562 is investigated. Atomic force microscopy and scanning electron microscopy reveal the formation of nanopatterns (ripples, triangular features, protrusions, facets) depending on a wide range of ion incidence angles (0°–75°) as well as the etch time. The emerged nanopatterns resemble those known from inorganic materials and therefore, lead to the assumption that local redeposition, surface viscous flow and dispersion plays an important role for the pattern formation on polymer surfaces. Major difference from ion beam erosion with inert species is the absence of nanoholes. Spectroscopic ellipsometry shows that the thickness of the modified surface layer depends on the ion incidence angle but not on the fluence in the investigated range. Using X-ray photoelectron spectroscopy, trends of the chemical composition of the surface/near-surface region were detected, which depend on ion incidence angle and etch time.

The high-Q THz stereo metasurface sensor based on double toroidal dipole with wide operating angle bandwidth

A highly sensitive terahertz stereo metasurface sensor, characterized by a high quality factor (Q-factor) and based on dual toroidal dipole (TD) resonance, has been proposed. The optimal structural parameters are ascertained by comparing the pertinent parameters of the stereo and planar structures in relation to TD modal excitation. The effective excitation of the TD mode is demonstrated using the calculations of multipole scattered power, reflection spectra, surface currents, electric fields, and magnetic field distributions. It is crucial that the stereo metasurface exhibits simplicity and that the dual TD resonance can be readily excited through simple adjustments in the distance and height of the intermediate gap. It also demonstrates exceptionally high sensitivity and Q-factor, both of which are essential for sensing applications. Moreover, the proposed stereo terahertz metasurface sensor still shows excellent sensing performance in a wide range of incidence angles (±40°), which is of great significance for practical applications. In conclusion, this structure offers a novel design framework for high-performance terahertz sensors based on the TD mode.

An Efficient Hybrid Method for Calculating the Focal Field of a Cassegrain Antenna

The evaluation of the focal field of Cassegrain antennas is crucial for the design and optimization of the complex feeds in quasi-optical systems. However, employing traditional physical optics methods generates high computational complexity and is inefficient. An accurate and efficient calculation method of Cassegrain antennas’ focal fields that involves a range of incidence angles is proposed, which integrates ray tracing and vector diffraction integration (RT-VDI) theories. It can calculate the focal field in any given or predefined incident direction, not limited to the case of axial incidence. In addition, the use of the equivalent parabolic theory greatly simplifies the process of integral calculation. Moreover, ray tracing and integration operations are executed upon the calculation of the reflector to further improve efficiency. Numerical examples are presented to demonstrate the accuracy and efficiency of the proposed method.

Experimental study on flow field and performance of bionic-wavy leading edge in an axial compressor with positive bowed blades

To enhance the aerodynamic performance of compressors in advanced aeroengines, a compound flow control method combining positively bowed blades and bionic-wavy leading edges is proposed for improving the aerodynamic performance of compressor cascades with controlled diffusion airfoils. This study verified the effectiveness of the compound control method through low-speed wind tunnel experiments using five-hole probe measurements and surface oil-flow visualization techniques. Additionally, the flow field structure was analyzed, and vortex models were established to thoroughly discuss the mechanism of the compound flow control method. The results show that within the incidence angle range of 0°–4° studied in this paper, the composite control method achieved significantly effective control, with a maximum reduction in overall total pressure loss of 25.8% compared to straight blade cascades. Three vortex models were established. The positive bowed blade cascade induced a complex vortex structure in the concentrated shedding vortex region, increasing losses in the concentrated shedding vortex (CSV) region but reducing profile losses. The coupled method further reduced profile losses and optimized the flow field in the CSV region. This study not only validates the feasibility of the compound method but also provides guidance for applying flow control methods to bowed blade cascades.

Polarization-selective terahertz absorber based on square cyclic graphene surface

Graphene-based absorbers are highly valued in terahertz technology due to their efficient performance. In this study, we theoretically propose a tunable, high sensitivity, single-band terahertz perfect absorber with polarization coherence that exhibits stable performance across a broad range of incidence angles. Simulation results show that the absorber's sensitivity to both TM and TE waves can be maintained at about 2 THz/RIU, with optimal values above 13.3 RIU−1 for TM waves and 12.9 RIU−1 for TE waves, and all Q-factors above 52. Furthermore, the impedance matching approach is utilized to explain the mechanism underlying its efficient absorption, and the electric field distribution is used to analyze the polarization coherence phenomena. We also propose a polarization-insensitive hetero-geometric structure based on the original structure, which allows for the separation of the absorption peaks by adjusting the geometrical parameters. These results show that the structure has a wide range of applications in aerospace, communication engineering, and image processing.

Toward high-lift low-solidity design for incidence tolerant gas turbine blade profile

Gas turbines operating under wide operational conditions require minimizing losses across a wide range of incidences. This study employed a blade profile efficient within a 50° incidence range to assess the effect of solidity on performance across wide incidences. The aim was to evaluate the feasibility of adopting high-lift, low-solidity designs for incidence-tolerant blade profiles. The results showed that solidity has both positive and negative effects on loss across a wide range of incidence angles. Increasing the pitch-to-axis chord ratio (the inverse of solidity) from 0.8 to 1.1 not only reduces the blade count by 37.5 % but also enhances performance at negative incidences, reducing the total pressure loss coefficient by up to 17.5 %. However, at positive incidences, the losses increased significantly as the solidity decreased. To expand the operational range of the low-solidity blade profile at positive incidences, strategic integration of leading-edge refinement and maximum deflection adjustment was applied to precisely control losses. This enabled the low-solidity blade profile to maintain lower loss levels compared to conventional high-solidity profiles up to an incidence of 7°, at which point the losses become comparable. The findings indicate that employing high-lift designs with optimized leading-edge and maximum deflection for incidence-tolerant blade profiles is feasible.

Dual-polarized transmissive metasurfaces for near-unitary-NA analog spatial computing empowered by impedance matching and mismatching.

In recent years, due to the increasing requirement for real-time and massive data processing, optical analog computation has arisen as a promising alternative to digital computation. Optical spatial differentiation plays a fundamentally important role in various emerging technologies, including augmented reality, autonomous driving, and object recognition. However, previous demonstrations encountered several limitations, such as the dependence on polarization states and a typically limited numerical aperture (NA) of about 0.5, especially in the transmission mode. Here, a new, to our knowledge, design strategy based on the evolution between impedance matching and mismatching in a metasurface is proposed to fill this gap, which can perform dual-polarized second-order derivative for image processing. Our scheme enables high transmission under dual polarization over an 85° incident angle range (NA = 0.996), resulting in more than twofold spatial resolution. Our work paves the way for polarization-insensitive high-resolution signal and image processing in the terahertz region.

Optimization of the inverted "T"-shaped double-layer subwavelength grating design integrated on an InSb detector

Polarization detectors have significant applications in fields such as target background contrast enhancement and free-space optical communication. While the technology for polarization detection using polarizers and waveplates added to detector lenses is well-established, there is still limited research on on-chip integrated polarization detection based on hypersurface technology. In this paper, we present a novel inverted "T"-shaped double-layer subwavelength grating structure, integrated into an InSb detector for polarization detection in the mid-infrared wavelength region (3–5 μm). This structure primarily consists of a high refractive index dielectric layer and a subwavelength grating layer, which together improve the grating's transmittance and extinction ratio. Using the finite-difference time-domain (FDTD) method, we simulate and optimize the effects of various grating parameters on polarization performance. The results show that the optimized grating achieves a TM wave transmittance of nearly 80% within the 3–5 μm wavelength range, with an extinction ratio exceeding 45 dB, and is suitable for a wide range of incidence angles from 0° to 70°.

How Phenology Shapes Crop-Specific Sentinel-1 PolSAR Features and InSAR Coherence across Multiple Years and Orbits

Spatial information about plant health and productivity are essential when assessing the progress towards Sustainable Development Goals such as life on land and zero hunger. Plant health and productivity are strongly linked to a plant’s phenological progress. Remote sensing, and since the launch of Sentinel-1 (S1), specifically, radar-based frameworks have been studied for the purpose of monitoring phenological development. This study produces insights into how crop phenology shapes S1 signatures of PolSAR features and InSAR coherence of wheat, canola, sugar beet. and potato across multiple years and orbits. Hereby, differently smoothed time series and a base line of growing degree days are stacked to estimate the patterns of occurrence of extreme values and break points. These patterns are then linked to in situ observations of phenological developments. The comparison of patterns across multiple orbits and years reveals that a single optimized fit hampers the tracking capacities of an entire season monitoring framework, as does the sole reliance on extreme values. VV and VH backscatter intensities outperform all other features, but certain combinations of phenological stage and crop type are better covered by a complementary set of PolSAR features and coherence. With regard to PolSAR features, alpha and entropy can be replaced by the cross-polarization ratio for tracking certain stages. Moreover, a range of moderate incidence angles is better suited for monitoring crop phenology. Also, wheat and canola are favored by a late afternoon overpass. In sum, this study provides insights into phenological developments at the landscape level that can be of further use when investigating spatial and temporal variations within the landscape.

A Highly Efficient Plasmonic Polarization Conversion Metasurface Supporting a Large Angle of Incidence

The angle of incidence of the compact polarization conversion device is crucial for practical use in integrated miniaturized optical systems. However, this index is often ignored in the design of quarter-wave plate based on metasurface. Herein, it is shown that a thick metallic cross-shaped hole array supports extraordinary optical transmission peaks controlled by a Fabry–Pérot (FP) resonator mode. The positions of these peaks have been proven to be independent over a large range of incidence angles. We numerically design a miniatured quarter-wave plate (QWP) with an 80 nm bandwidth (840~920 nm) and approximately 80% average efficiency capable of effectively functioning as a linear-to-circular (LTC) polarization converter at an incidence inclination angle of less than 30°. This angle-insensitive compact polarization conversion device may be significant in a new generation of integrated metasurface-based photonics devices.