Different Angles Of Incidence Research Articles

Investigation on angle of incidence and light reflectance

Illuminance is a measurement proportional to the intensity of light. When light is incident on a surface, the angle it makes with the normal vector of the surface plane is the angle of incidence. This paper focuses on an investigation of the relationship between the illuminance of reflected light from a glass block and the angle of incidence of the light on the block. By applying Fresnels coefficients, an expression for the illuminance of reflected light is derived in terms of the angle of incidence. The controlled measurements, including the illuminance of s-polarized and p-polarized light of a green laser (532nm), are directly measured to arrive at a set of calculated reflected illuminance at 10 different angles of incidence. The reflected illuminance is also experimentally measured with a light sensor at these angles. Upon the comparison between the two sets of data in this paper, a close resemblance of the shape of their curves is observed, both revealing an increasing reflected illuminance with a growing rate with respect to the increase of the angle of incidence. However, due to some expected systematic errors in the experiment, the calculated data has a generally higher reflected illuminance than the theoretical data at each angle of incidence. Overall, it is confirmed that as the angle of incidence increases, the illuminance of the reflected light increases with a growing rate.

Characterizing vibrations and associated wake structures of tandem square cylinders at different angles of incidence

Finite element computations were conducted to investigate the transverse vibrations of three identical tandem square cylinders and the associated wake patterns at a Reynolds number Re = 150. The reduced velocities ranged from U*=3 to 20, and the angles of incidence were set at α=0°, 22.5°, and 45°. The streamwise gaps for these three α were Lx=5H, 3.8H, and 3.5H, respectively, where H represents the projected dimension of the cylinder normal to the freestream. The mass ratio of the cylinders was fixed at m*=2, and damping was neglected to allow the cylinders to attain maximum amplitudes. In the presence of primary vortices being shed from all three cylinders, the upstream cylinder at α=22.5° and 45° exhibits three distinct vibration regimes: initial excitation and upper and lower response regions. On the other hand, due to interaction with the upstream vortices, the two downstream cylinders display four response regions. In the case of α=0°, the dynamic response of the upstream cylinder appears in only two regimes, but with a higher peak amplitude compared to α=22.5° and 45°. Vibration and shedding frequencies closely synchronize with the natural frequency of the spring-mass system in the second regime, leading to high amplitude oscillations for the most upstream cylinder with α=22.5° and 45°. The third response regime for the two downstream cylinders is associated with the lock-in phenomenon. In α=0° and 22.5° configurations, the shedding mode is 2S in all response regimes, while at α=45°, the shedding mode shifts to P + S during the second regime. Up to the second regime, lift and vortex forces are in-phase with the cylinder's oscillation for α=0° and 22.5°, but they go out of phase beyond that. In the case of α=45°, although lift remains in-phase with the displacement in the second regime, the vortex force is found to be out of phase. This study is expected to enhance the understanding of fluid–structure interaction phenomena involved in multiple structures and can aid in the design of stable structures in civil engineering, offshore engineering, and development of energy harvesting devices.

Reflection of plane waves in a rotating micropolar double porous thermoelastic medium with temperature dependent properties

AbstractThe objective of this empirical investigation is to explore the behavior of different waves reflected in a homogenous isotropic double porous structured micropolar thermoelastic medium with rotation and temperature‐dependent characteristics. Three‐phase‐lag theory of thermoelasticity is adopted to acquire the governing equations of the model. Six coupled plane waves have been found to propagate across the medium at distinct velocities. Derivation for energy and amplitude ratios of reflected waves were carried out by employing appropriate boundary conditions. For different angles of incidence, the outcomes for energy partition were determined numerically and displayed graphically. It is found that amplitude ratios associated with various reflected waves are affected by angular velocity, temperature‐dependent properties, micropolar parameter, and double porosity. Also, it has been discovered that throughout the reflection phenomena there is no dissipation of energy. Furthermore, this study concludes with a summary of the findings and subsequent observations. The current investigation has yielded inferences regarding specific cases that are of particular interest.

Optical and structural characterization of zinc oxide thin films upon ion beam assisted smoothing

Wurtzite zinc oxide (ZnO) has a preferential growth direction along the c-axis of the hexagonal unit cell, which, especially in combination with underlying (amorphous) heterostructures, can lead to a high surface roughness for the ZnO layers. This poses a significant challenge to the construction of e.g. photonic waveguides or gratings. Here, we propose an efficient way for smoothing ZnO surfaces after deposition using a collimated beam of Argon ions. Furthermore, the influence of this treatment at different angles of incidence and fluence of the ions on the morphological, structural and linear optical emission properties is investigated using atomic force microscopy, X-ray diffraction, spectroscopic ellipsometry and photoluminescence (PL) experiments. Our results suggest that using an ion beam incident at an angle of 85° reduces the surface roughness by around 70% while keeping the ZnO crystal structure intact. Though such a treatment leads to a reduced intensity and to a broadening of the PL-emission, excitonic transitions are still prominently observable.

Unsteady Numerical Simulation of Two-Dimensional Airflow over a Square Cross-Section at High Reynolds Numbers as a Reduced Model of Wind Actions on Buildings

Airflow over a square cross-section at high Reynolds numbers and different angles of incidence is investigated with the aim of providing deeper insight into wind actions on elongated structures and, in particular, tall buildings. The flow around bluff bodies is characterized by separation at sharp corners, as well as possible flow reattachment at side surfaces. The alternate shedding of vortices is also generated in the wake of bluff bodies due to the unsteady nature of flow separation. Two-dimensional (2D) URANS numerical simulations were conducted in order to model transient flow and examine wind actions on a square used as a model of a typical cross-section of a tall building far from its roof and the ground. For validation purposes, the study’s numerical results on drag and lift coefficients, Strouhal numbers, as well as pressure coefficient distribution were found to be in good agreement with available experimental and numerical results in the literature for relatively low Reynolds numbers. The numerical study was then extended to higher Reynolds numbers, approaching values that are pertinent for wind flow around buildings, thus addressing the lack of such results in the literature. On the basis of these results, the impact of Reynolds numbers and angles of incidence on drag and lift coefficients, as well as the pressure coefficient distribution along the walls of the cross-section, is highlighted.

Reflection of quasi plasma wave in photo-piezo semiconductor medium with distinct higher order fractional derivative two temperature models

This article investigates the reflection of thermo-photo-piezo-elastic plane waves from a homogeneous, orthotropic, and piezo semiconductor medium during the photo-thermal process. A novel higher-order fractional dual-phase lag hyperbolic two-temperature model is employed to tackle this study. The analytical solution to the problem in the xz plane reveals the existence of five interconnected waves. The derivation of formulas for reflection coefficients and their corresponding energy ratios is performed for an incident quasi-plasma wave. Numerical computations determine the energy ratios for different angles of incidence. These energy ratios are visually represented in graphs, demonstrating the influence of higher-order parameters, two-temperature effects, fractional order derivatives, and various heat conduction models.

NG-DPSM: A neural green-distributed point source method for modelling ultrasonic field emission near fluid-solid interface using physics informed neural network

Distributed point source method (DPSM) is a collocation point-based semi-analytical method to model the scattered ultrasonic fields in isotropic and anisotropic materials. It requires the evaluation of Green's function solutions and its rigorous differentiation for complex geometry problems having a large set of distributed point sources. DPSM is much faster than the finite element method (FEM) however, it is analytically demanding as it requires differentiation of the Green's function. The intricacy associated with differentiation operation hinders the potential application of DPSM in large-scale automation and real-time structural health monitoring. The current paper introduces machine-learning-based strategies within DPSM and yields the proposed Neural Green-DPSM (NG-DPSM) framework. A physics-informed neural network (PINN) is incorporated in the DPSM framework for evaluating the Green's function and its gradients. To train the PINN, displacement Green's function solutions of wave propagation in isotropic solid is used as the governing physics. Once the PINN is trained for displacement Green's function solutions, the NG-DPSM framework leverages the trained network and its automatic differentiation capability to predict displacement and stress fields annihilating the rigorous differentiation of Green's functions. The accuracy and efficacy of NG-DPSM are demonstrated using two numerical experiments. First, the ultrasonic fields are evaluated for the problem geometry of a plate immersed in fluid excited at different angles of incidence. Further, the efficacy of the proposed approach is demonstrated for wave scattering through a circular hole in the plate. The results show a strong agreement between the ultrasonic fields computed using both NG-DPSM and conventional DPSM.

Using Information about Experimental Conditions to Predict Properties of Metamaterials

In this work, a method of increasing the amount of data for training neural networks is proposed using the possibility of using information about the experimental conditions of measuring the properties of metamaterials. It is shown that the method is flexible and effective. The results of predicting the transmission coefficient of the metamaterial for different angles of incidence of radiation and type of polarization are presented. Using the architecture presented in the work, a high rate of learning and generation of new data was obtained with an error that does not exceed 12% for experiments in one frequency range and does not exceed 31% if all experiments are used for training. The architecture of the neural network and the method by which it is possible to easily change the number and types of experimental conditions are presented.

Grain Orientation, Angle of Incidence, and Beam Polarization Effects on Ultraviolet 300 ps‐Laser‐Induced Nanostructures on 316L Stainless Steel

AbstractLaser‐induced periodic surface structures (LIPSS) represent a unique route for functionalizing materials through the fabrication of surface nanostructures. Commercial AISI 316L stainless steel (SS316L) surfaces are laser treated by ultraviolet 300 ps laser pulses in a laser line scanning (LLS) approach. Processing parameters are optimized (pulse energy of 2.08 µJ, pulse repetition frequency of 300 kHz, and suitable laser scan and sample displacement rates) for the generation of low spatial frequency LIPSS over a large 25 × 25 mm2 area. Different angles of incidence of the laser radiation (0°, 30°, and 45°) and different linear laser beam polarizations (s and p) produce a plethora of rippled surface morphologies at distinct grains. Scanning electron microscopy and 2D Fourier transforms, together with calculations of the optical energy deposited at the treated surfaces using Sipe's first‐principles electromagnetic scattering theory, are used to study and analyze in detail these surface morphologies. Combined with electron backscattering diffraction, analyses allow associating site‐selectively various laser‐induced‐surface morphologies with the underlying crystalline grain orientation. Resulting grain orientation maps reveal a strong impact of the grain crystallographic orientation on LIPSS formation and point toward possible strategies, like multi‐step processes, for improving the manufacturing of LIPSS and their areal coverage of polycrystalline technical materials.

Flow-induced vibration and heat transfer in a cluster of three staggered cylinders with different angles of incidence

A two-dimensional numerical study is performed to explore the synergistic effects of the angle of incidence, gap ratio, and reduced velocity on the flow-induced vibration (FIV) and heat transfer characteristics in a cluster of three staggered, unequal-diameter cylinders. Three distinct angles of incidence (θ = 0°, 15°, 30°) and three gap ratios (G* = 2, 4, 6) are meticulously examined to observe the effect of wake interference on the oscillation amplitude and heat transfer of downstream cylinders by considering forced convection. The investigation encompassed a Reynolds number (Re) of 100, a Prandtl number (Pr) of 0.7, reduced velocity (Ur) ranges from 2 to 20, and a fixed mass ratio (m*) of 2. A user-defined function (UDF) is employed in the Fluent solver to model the cylinder vibration. The findings revealed a captivating pattern: as the gap between the cylinders increased, the oscillation amplitude of the downstream cylinders significantly diminished while simultaneously witnessing a surge in the Nusselt number (Nu). Similarly, a remarkable escalation in both amplitude and Nu is observed when the angle of incidence is increased from θ = 0° to θ = 15° across all the gap ratios. However, for G* = 6 and θ = 30° a reverse trend emerged, characterized by a notable decline in oscillation amplitude up to 32.25% and an exponential rise in the Nu up to 53.74%. Intriguingly, it is further discerned that augmenting θ and G* exerted no discernible influence on the oscillation amplitude and Nu of the downstream cylinder, as it functioned autonomously as a single isolated cylinder.

Insight into light‐ and static‐electric‐field‐induced polarization on polaron‐pair dynamics in neat P3HT device: A transient‐absorption‐spectroscopy‐based study

AbstractWe have investigated the polaron‐pair dynamics following the excitation of vibrationally hot exciton states in organic semiconductor‐based optoelectronic devices to better understand the photophysical properties, which can help to improve the device performance. In our earlier work, published at ‘Phys. Chem. Chem. Phys., 2019,21, 21236‐21248’, we have investigated the role of the static electric internal and external fields on the polaron‐pair dynamics in a neat poly(3‐hexylthiophene‐2,5‐diyl) based device. From this, we have concluded that the polaron‐pair dissociates into charge carriers due to the internal field present inside the device and the dissociation process accelerates when an external electric field is also applied in reverse bias. Apart from the electric‐field‐induced dissociation process, we now have also been interested in the light‐ and electric‐field‐induced polarization effect on the polaron‐pair dynamics. For this, in the present study, we have used femtosecond transient absorption spectroscopy to investigate the polaron‐pair dynamics in a neat P3HT‐based device for different angles of incidence of the light with an additional variation of the static electric field. It is well‐known that thin‐film photovoltaics can be designed for improved angle‐dependent responsivity at specific angles and the photon harvesting efficiency depends on the incident angle of light. Internal electric fields together with the electric field of the incident light both influence the charge generation efficiency of the device, which is determined by the photophysical processes happening between electronic excitation and the formation of charge. The change of reflectivity due to the variation of incident angle and the effect of the electric‐field induced polarization make an overall impact on the polaron‐pair dynamics as demonstrated by our investigations.

Solid particle erosion evaluation of automotive paint coatings under the influence of artificial weathering

Solid particle erosion (SPE) is one of the most critical tribological problems causing damage to automotive paint coatings. The correct characterization of SPE and resistance against it makes the possible extended service life of the coating, increasing the resale value of cars. Car manufacturers and paint industries have developed new techniques to apply coatings and coatings that improve the initial and long-term appearance, scratch performance, and durability of coatings. Several works have focused on studying the degradation and performance of paint coatings. However, there needs to be more understanding of wear progress under different environmental degradation conditions. This study investigates the mechanisms and resistance of erosive wear of actual automotive paint coatings before and after exposure to an accelerated weathering process. Steel substrate panels with a typical paint coating system were exposed to weathering degradation by UV and immersion in an artificial acid rain solution. The chemical changes induced in the coatings were analyzed by FT-IR spectroscopy. Then erosive tests were carried out using silica sand particles at two different angles of incidence (30° and 90°) and temperatures (25 °C and 60 °C) for both samples (unexposed and weathering conditions). The SPE rate was determined for each coating by mass loss estimation using an analytical balance; meanwhile, wear mechanisms were analyzed in detail by SEM. The results showed decreased SPE resistance promoted by chemical changes in samples exposed to both weathering processes.

A Theoretical Approach for Detecting the Chikungunya Virus Based on 1D Photonic Crystals

In the current study, it is aimed at using defective 1D photonic crystals (PCs) to detect the chikungunya virus in various healthy and diseased blood samples composed of plasma, platelets, red blood cells, and uric acid. The proposed PC structure has 14 periods and consists of repeating SiC and SiO2 layers with a central cavity layer. When blood samples are injected into the cavity layer, the transmittance spectrum is examined theoretically by using a transfer matrix approach to determine how the wavelength of the defect mode changes. The cavity layer is 540 and 648 nm thick, and the work is carried out at different angles of incidence. The performance of the sensor is quantified by computing the sensitivity, figure of merit, quality factor, and limit of detection values of the sensor for various blood samples. The maximum sensitivity is 1205.5 nm RIU−1 and detection limit of the order is 10−6 in this proposed work. A lower value of sensor resolution of 0.01218 is also achieved. Such a high‐performance sensor is suitable for biosensing applications with better sensing capabilities.

Miniaturized frequency‐selective surface with reduced number of metallic vias for electromagnetic shielding

SummaryA miniaturized frequency‐selective surface (FSS) for radio frequency (RF) filtering applications is reported in this paper. The proposed FSS is designed to operate with band stop property at 1.57 GHz. The FSS element is developed using highly convoluted lines running on either side of the substrate interconnected using via lines. This specific arrangement increases the electrical length of the resonator without increasing the physical size. Furthermore, the stability towards polarization variation and independence to different angles of incidence are other major concerns in the design of FSS. The FSS unit cell has rotational symmetry thereby providing polarization‐independent operation. The angular independence is tested for various incidence angles, and the results are presented. The performance of the FSS is validated in real time, and the results are presented. The maximum realized transmission loss is 27 dB at 1.57 GHz, and the attenuation bandwidth with reference 10 dB shielding level is estimated to be 400 MHz centered around 1.57 GHz. The convolution technique along with shorting vias has offered this extreme miniaturization ranging from 7% to 95.7% with reference to most of the FSS reported for L‐band services such as radio, telecommunications, military, and aircraft surveillance.

Comparative Study of Polarization‐Dependent Conversion Efficiency of GaAs and Si Solar Cells at Oblique Incident Angles Using Surface DLAR Coating of MgF2/ZnSe

AbstractThe aim of this work is to minimize reflection losses in order to increase the efficiency of solar cells by using anti‐reflection coatings (ARCs). Despite extensive research on improving solar cell conversion efficiency at normal incidence, development at angle of incidence has received little attention. Thus, the reflectivity of single‐layer ARC (SLARC) MgF2 and ZnSe, double‐layer ARC (DLARC), MgF2/ZnSe on Si, and GaAs substrates at transverse electric (TE) and transverse magnetic (TM) modes of polarization in the visible and near‐IR regions for different angles of incidence is analyzed. The optical and electrical properties of Si and GaAs solar cells are analyzed by using the reflectance spectra of SLARC and DLARC at various angles of incidence for the TM and TE modes of polarization under the solar power spectrum (AM1.5). The achieved results due to the effect of DLARC are compared for Si and GaAs solar cells. From these analyses, it is concluded that MgF2/ZnSe is an appropriate DLARC for the range of wavelengths 400–800 nm at 10°–30° angles of incidence in TM mode for tuning the optical and electrical properties of Si and GaAs substrates for terrestrial applications.

Vibroacoustic topology optimization for sound transmission minimization through sandwich structures

Recently, metamaterials, sandwich panels, and a combination of both have shown potential for creating lightweight, load-bearing structures with good noise and vibration suppression properties. However, designing these structures is difficult due to the complex vibroacoustic innate physics and the need to balance conflicting requirements. Structural optimization methods can help address this multi-functional, multi-physical design challenge. While much research has been conducted on optimizing the materials and sizes of plates and sandwich cores, the systematic topological design of fully coupled vibroacoustic cores has not yet been explored. To address this gap, this work presents a topology optimization framework for the vibroacoustic design of sandwich structure cores, with the goal of minimizing sound transmission while constraining volume and structural stiffness. The framework is used to conduct a systematic design analysis, focusing on the dynamic behavior of the optimized structures. The versatility of the methodology is demonstrated by analyzing different targeted frequency ranges, different angles of incidence and the trade-off between the acoustic and structural performance. The resulting designs are lightweight, load-bearing, and achieve high sound transmission loss performance, exceeding the mass law by 15–40 dB in targeted frequency ranges of 500Hz in the interval between 1000Hz and 3000Hz.

The strange case of negative reflection

In this paper, we show the phenomenon of negative reflection occurring in a mechanical phononic structure, consisting of a grating of fixed inclusions embedded in a linear elastic matrix. The negative reflection is not due to the introduction of a subwavelength metastructure or materials with negative mechanical properties. Numerical analyses for out-of-plane shear waves demonstrate that there exist frequencies at which most of the incident energy is reflected at negative angles. The effect is symmetric with respect to a line that is not parallel to the normal direction to the grating structure. Simulations at different angles of incidence and computations of the energy fluxes show that negative reflection is achievable in a wide range of loading conditions.

Under bending optical assessment of flexible glass based multilayer structures fabricated on polymeric substrates

We present the results of the spectral transmittance and reflectance of a SiO2/TiO2 1D photonic crystal deposited by Radio Frequency sputtering on a flexible polymeric substrate, which shows a blue-shift in its transmittance stopband proportional to the incidence angle when bent. An adjustable sample holder was designed to regulate the bending and keep the sample in a bent condition. Different angles of incidence were also achieved through variable angle reflectance, where an increase in incidence angle led to the blue-shift and narrowing of the transmittance stopband. We addressed the sample's resistance against bending wear and tear by comparing the transmittance spectra acquired for the flat sample before and after the measurements made in bent configurations. An important stability has been observed.

Quantifying low-energy nitrogen ion channeling in α-titanium by molecular dynamics simulations

Quantification of nitrogen depth distributions resulting from the low-energy ion implantation into titanium nanoparticles allows tunable and controllable modifications of their properties. We have explored the nitrogen ion implantation into α-titanium target at 0.5–4 keV kinetic energies by molecular dynamics simulations, with particular focus on the ion channeling effects for low-index surface orientations ((001), (100), (110), (111)) at different target temperatures (300–1155 K) and different angles of incidence (0–29 °). The results indicate that the channeling significantly alters the depth distributions, being most prominent for (110) orientation, where causes a new distribution maximum to emerge at a significantly deeper position. An increasing target temperature suppresses notably (albeit not fully) the channeling and a tilted ion incident angle from a perpendicular impact allows controllable reduction of the number of channeling ions.

Structured Light Generation Using Angle‐Multiplexed Metasurfaces

AbstractOn the basis of the Jones matrix, independent control over the amplitude and phase of light has been demonstrated by combining several meta‐atoms into the supercell of a metasurface. However, due to the intrinsic limitation of a planar achiral structure, the maximum number of independent, complex elements in one Jones matrix is three, giving rise to up to three‐channel amplitude and phase control. In this work, more Jones matrices corresponding to different angles of incidence are proposed to add, so that the degrees of freedom in the amplitude and phase control can be further increased. The supercell of the designed metasurfaces consists of three dielectric nanoblocks with predefined rotation angles and displacements in the 2D space, which can be inversely determined with the help of the genetic algorithm. Empowered by the ability to realize four‐ or even eight‐channel amplitude and phase control, the generation of multiple structured light, including two independent perfect Poincaré beams, two double‐ring perfect Poincaré beams, two perfect Poincaré beam arrays, and four vector vortex beam arrays, is numerically demonstrated. Such novel designs are expected to benefit the development of modern optical applications, including but not limited to optical communications, quantum information, and signal encryption.