Various Angles Of Incidence Research Articles

Atomistic modeling of physical vapor deposition on complex topology substrates

Molecular Dynamics simulations of Cu physical vapor deposition are employed to investigate the effects of substrate topology and line of sight on the synthesis of thin films on Cu substrates. The deposition and surface relaxation processes of sputtering Cu ions are simulated considering various angles of incidence (0–60°) and sputtering energies (1, 10, 25, and 50 eV). Cu substrates are constructed with three different surface geometries: i) a flat Cu (111) surface; ii) a sinusoidal shaped substrate with a period of 127.6 Å and amplitude 20 Å; and iii) a combined substrate composed of a flat Cu (111) surface and a cylinder of radius 63.8 Å, floating 50 Å above the flat surface. Results from simulations with low impact energy (1 eV) show a strong effect of the angle of incidence on the roughness of the thin film produced on the flat surface. For non-flat substrates, areas with no line of sight have diminished film coverage, which is offset by increasing the deposition energy. Higher energy atoms have greater adatom mobility enabling the coverage of regions with no line of sight and the reduction of surface roughness. The results show a lower sticking probability for highly energetic deposition at high angles of deposition, effectively promoting film coverage in areas with no line of sight through physical redeposition processes, which is augmented by particle-induced sputtering. These atomistic insights are relevant for the understanding of physical vapor deposition processes on convoluted topology substrates, such as magnetron sputtering on metamaterial lattices.

Nonlinear Cylindrical Markers Using Metamaterials

In this paper, the research of nonlinear cylindrical metastructure was obtained. An algorithm for finding the total field of a nonlinearly loaded perfectly conducting cylinder covered with a metamaterial (MM) layer based on Maxwell’s equations with nonlinear boundary conditions on the surface of nonlinear loads (NL) was developed. A software package implementing this algorithm was created. Based on the results of numerical calculations of the program, the scattering diagrams of a metal cylinder with NL, covered with a layer of MM at the fundamental, second, and third harmonics were obtained. The dependences of the harmonics of the scattered field on the parameters of nonlinear loads were also studied. With the help of numerical simulation using Ansys HFSS, the extract procedure of the effective parameters of cylindrical MM was realized. Based on the results of calculation and numerical simulation, a model of a nonlinear cylindrical structure of two radii was made and an experimental study was carried out. As a result of the experiment, the frequency characteristics of the metastructure were obtained at various angles of incidence of the wave. The results of numerical simulation were confirmed by the results of the experiment. It is shown that the use of the provided nonlinear cylindrical marker with metamaterial makes it possible to obtain the levels of the first and second harmonics in a scattered field of the same order. This structure can be used as a nonlinear marker in both military and civilian areas.

Integrated optical-thermal-electrical modeling of compound parabolic concentrator based photovoltaic-thermal system

The main aim of this work is to propose an integrated optical, thermal and electrical model to obtain the overall performance of a concentrated photovoltaic-thermal system (CPV/T). Monte Carlo ray-tracing (MCRT) simulations are done to obtain the flux profile on the absorber of a compound parabolic concentrator (CPC) for various angles of incidence. The obtained heat flux is mapped onto the solar cell in the finite volume method (FVM) to obtain its temperature profile. The modelling is done for both glazed and unglazed compound parabolic concentrator-photovoltaic/thermal (CPC-PV/T) systems using uniform (average heat flux) and non-uniform heat flux distribution. The obtained numerical results are compared with experimental results available in the literature. The results show that the prediction is accurate, with a maximum deviation in solar cell temperature of less than 3%. The deviations obtained when using non-uniform heat flux are much less than when using average heat flux. The temperature contours show that the temperature profile of the photovoltaic module obtained by using local non-uniform heat flux is different from the temperature profile obtained by using average heat flux, and these results will have a greater impact when designing a cooling system.The absorbed radiation from the optical analysis and average cell temperature from the thermal analysis are given to the five parameter electrical model of a solar photovoltaic cell to obtain the electrical power output. With the results of the integrated optical-thermal and electrical model, the overall useful power from both glazed and unglazed CPC-PV/T systems is calculated. The results show that the performance of the unglazed CPC-PV/T system is superior to the glazed CPC-PV/T system in terms of electrical and overall system output. This work demonstrates the need for a local heat flux profile and a coupled multi-physics model to accurately predict the performance of a concentrated photovoltaic/thermal (CPV/T) system.

The Effect of Arrive Angle of External Magnetic Field on The Shape of Hysteresis Curve Permalloy Ni80Fe20 By Simulation

Magnetic sensor is a type of sensor that utilizes changes in resistance caused by changes in the magnetic field H or B. One of the suitable magnetic materials to be used as a study material for making magnetic sensors is permalloy Ni80Fe20. The reading error of the magnetic sensor of the Ni80Fe20 permalloy material affects hysteresis curve of the material and requires correction of the angle of incidence of the external magnetic field in order to provide accurate results on the storage media. In this our current research using Finite Difference OOMMF, we investigated the effect of the angle of incidence of the external magnetic field (H) on the hysteresis curve was carried out on an application based on. The research was conducted by reviewing the parameter literature of the Ni80Fe20 permalloy material and then compiling it in a script and simulating it on an application based on Finite Difference OOMMF. The data obtained from the simulation are normalized magnetization (m), external magnetic field H and coercivity field (Hc) which have been influenced by the angle of incidence. The results of the hysteresis curve at a size of 5 nm with a variation of the angle of incidence 0o are indicated by the value of the external magnetic field H of 10000 mT to -10000 mT with a coercive field Hc of 5000 mT to -5000 mT. The normalized magnetization value m is 1 to -1. The variation of the angle of incidence of 30o produces a coercive field Hc of -108.3 mT to 108.3 mT and a normalized magnetization of 0.86 to -0.86. The 45o incident angle variation produces a coercive field Hc -88.4 mT to 88.4 mT and a normalized magnetization of -0.7 to 0.7

L-Band SAR Co-Polarized Phase Difference Modeling for Corn Fields

This research aims at modeling the microwave backscatter of corn fields by coupling an incoherent, interaction-based scattering model with a semi-empirical bulk vegetation dielectric model. The scattering model is fitted to co-polarized phase difference measurements over several corn fields imaged with fully polarimetric synthetic aperture radar (SAR) images with incidence angles ranging from 20° to 60°. The dataset comprised two field campaigns, one over Canada with the Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR, 1.258 GHz) and the other one over Argentina with Advanced Land Observing Satellite 2 (ALOS-2) Phased Array type L-band Synthetic Aperture Radar (PALSAR-2) (ALOS-2/PALSAR-2, 1.236 GHz), totaling 60 data measurements over 28 grown corn fields at peak biomass with stalk gravimetric moisture larger than 0.8 g/g. Co-polarized phase differences were computed using a maximum likelihood estimation technique from each field’s measured speckled sample histograms. After minimizing the difference between the model and data measurements for varying incidence angles by a nonlinear least-squares fitting, well agreement was found with a root mean squared error of 24.3° for co-polarized phase difference measurements in the range of −170.3° to −19.13°. Model parameterization by stalk gravimetric moisture instead of its complex dielectric constant is also addressed. Further validation was undertaken for the UAVSAR dataset on earlier corn stages, where overall sensitivity to stalk height, stalk gravimetric moisture, and stalk area density agreed with ground data, with the sensitivity to stalk diameter being the weakest. This study provides a new perspective on the use of co-polarized phase differences in retrieving corn stalk features through inverse modeling techniques from space.

Reflectarray Antenna Concept for a Snow Mass Measurement SAR Mission in Ku-Band on a Nanosatellite Platform

The design of a 1 × 0.33 m dual-polarized reflectarray antenna (RA) operating in Ku-Band (17.2 GHz) for a synthetic aperture radar (SAR) mission using a 12 U CubeSat is presented. The SAR RA has larger electrical size, larger aspect ratio, and smaller focal to aperture length ratio (F/L) compared to existing CubeSat RAs designed for communication payloads. Electrically small unit cells accounting for large incidence angle variations, improving phase resolution, and preventing grating lobes are designed. To illuminate the RA with the desired elliptical beam, a compact aperture-coupled microstrip patch array antenna was designed. Tests done on a CubeSat mockup integrating the dual-polarization feed source and a five-panel reflectarray showed good agreement between the simulated and the measured beamwidths, with low sidelobe and cross polarizations levels.

A Comparison of Top Distributed Bragg Reflector for 1300 nm Vertical Cavity Semiconductor Optical Amplifiers Based on III–V Compound

In this work, the design of GaAs/AlGaAs distributed Bragg reflector (DBR) has been implemented for 1300 nm vertical cavity semiconductor optical amplifiers (VCSOAs) for optical fiber communication applications. The top DBR period and Al concentration are varied, the peak reflectivity of the DBR is increasing from 50% to 97.5% for 13 periods with increasing Al concentration, whereas the reflectivity bandwidth is increased to almost 190 nm. The relation between wavelength and incidence angle variation on DBR reflectivity is increasing with the incident angle (0°, 20°, 30°, and 50°), the resonant wavelength and bandwidth of the measured reflectance spectra shifts to shorter wavelength and wider bandwidth, respectively. In addition, a comparison between the linear, the graded, and the parabolic DBRs has been achieved with transfer matrix method using MATLAB software to show the influence of layer in DBRs and its effect on lasing wavelength. It is shown that using grading DBR mirror is much more beneficial compared to abrupt DBR, whereas it has lower reflectivity of almost 10% due to VCSOAs device which needs less number of top layers until prevent reaching lasing threshold.

Computational analysis of the thermomechanical behavior of lightweight multifunctional photovoltaic sandwich structures

In this study, the thermomechanical behavior of multifunctional (photovoltaic/ aluminum core/ skin) sandwich structures is investigated numerically using the finite element simulation. Parametric studies were performed to determine how the types of boundary conditions and loadings influence the deformed shape (flatness) and temperature of PV sandwich structures with four types of skin materials and three different core structures. High temperature in silicon layer as well as high deviation in flatness are undesirable. The high flatness deviation can lead to high variation in incident angle. Our simulation results show that the CFRP skin provides the smallest flatness deviation followed by steel, aluminum and PLA, respectively. Temperature of silicon layer for the CFRP skin configuration is comparable with that of skin configurations using high thermal conductivity skin materials (aluminum and steel). The reentrant core demonstrates the smallest flatness deviation but approximately the same temperature compared to honeycomb and semi-reentrant cores. Furthermore, introducing a double-skin configuration (PV/ CFRP skin/ aluminum core/ CFRP skin) while maintaining the total thickness of the skin causes no effect on temperature but tends to increase flatness deviation. Therefore, the single-skin configuration (PV/ aluminum reentrant core/ CRFP skin) is a potential candidate for lightweight multifunctional PV sandwich composites.

Charge and excitation state of Na projectiles scattered from Al surfaces

This work addresses the issue of the anomalous neutralization of slow sodium ions at aluminum surfaces by measuring spectra of Auger electrons emitted by collisionally excited sodium projectiles. The anomalous fraction of scattered singly charged ions is due to the Auger decay of singly excited projectiles. Electron emission experiments reveal a sizeable production of doubly charged ions that should be observed in ion fraction measurements. Measurements at varying incidence angles provide a rather detailed description of the successive stages of the inelastic scattering events that determine the charge state of scattered projectiles.

Design of a novel polarization insensitive pentaband THz metamaterial

AbstractThis paper presents the design and characterization of a novel metamaterial with five distinct operating bands for THz applications. The proposed metamaterial is constructed using an ultra‐thin polyimide substrate. The proposed metamaterial has a square geometry with metallic patterns suitably designed to obtain the desired frequency characteristics. The metamaterial operates based on surface plasmon hybridization with stopband characteristics at 0.82, 1.96, 2.77, 3.40 and 4.74 THz. The metamaterial has a small geometry 0.082λo × 0.082λo where λo is wavelength calculated under free‐space conditions at 0.82 THz. The operation of the proposed pentaband metamaterial is described using electric field distributions. The metamaterial reported in this paper has rotational symmetry and hence it is polarization independent. The performance of the metamaterial for various angles of incidence has been evaluated and the results reveal that the proposed metamaterial is stable up to ±70 degrees. The THz metamaterial is appropriate for components like frequency selective surface, sensors and detectors.

Terahertz vortex beam propagation through a magnetized plasma-ferrite structure

Interaction of vortex beams with materials has proven to be a key for controlling and exploiting theirs properties. In this paper, we propose an adjustable stratified structure constructed from plasma and ferrite layers, which greatly manipulates the intensity and phase distributions of incoming terahertz vortex beam (TVB), and demonstrates a considerable amount of Faraday rotation. To obtain the output beam profiles, first using angular spectral expansion technique the incoming TVB is decomposed into a superposition of plane waves, then employing 4×4 matrix formalism total reflection and transmission coefficients are extracted. Numerical analysis reveals that how the variations of external static magnetic field, incident angle, and radial and angular indices of the TVB affect the features of reflected and transmitted beams. It is expected that this investigation will shed new light on the interaction of TVB with anisotropic magnetic materials, and open new possibilities for wavefront engineering and material characterization.

Angular dependence of localized mode of chalcogenide photonic crystal

In this paper, we have designed a one-dimensional chalcogenide photonic crystal using As2Se3/air multilayered structure. A single defect is introduced by replacing As2Se3 layer with As2S3. In the proposed structure, the well-known transfer matrix method is employed to determine the transmission spectra for both TE (transverse Electric) and TM (transverse Magnetic) modes. A theoretical analysis of effect of incidence angle on defect modes is presented. Variation in incidence angle causes the shift in defect modes.

Transformation of laser-induced broadband pulses of longitudinal ultrasonic waves into pulses of shear waves in an isotropic solid plate immersed in a liquid

Transformation of laser-induced broadband pulses of longitudinal ultrasonic waves into pulses of shear waves and back into pulses of longitudinal waves (further called as the “double” transformation) in an isotropic solid plate immersed in a liquid is theoretically studied. It is shown that the time profile of the pulse of shear waves strongly depends on the angle of incidence and only at a certain value of this angle the time profiles of the incident longitudinal-wave pulse and induced shear-wave pulse coincide. For various angles of incidence, the broadband pulses of longitudinal waves experimentally obtained after the double transformation in an aluminum and fused silica plane-parallel plates immersed in distilled water correspond to the theoretically calculated profiles except for the increased duration of experimental pulses. Based on the double transformation scheme, the method of broadband acoustic spectroscopy of longitudinal and shear waves for isotropic solid plates in the spectral range of the blue-green glass laser source of ultrasound (1–40 MHz) was proposed and experimentally realized for the first time. The obtained frequency dependences of the attenuation coefficients of longitudinal and shear ultrasonic waves in stainless steel, cast babbit, and brass can be used for appropriate choice of an operating frequency range by ultrasonic nondestructive testing of these materials.

Effect of Skull Porous Trabecular Structure on Transcranial Ultrasound Imaging in the Presence of Elastic Wave Mode Conversion at Varying Incidence Angle

With the advancement of aberration correction techniques, transcranial ultrasound imaging has exhibited great potential in applications such as imaging neurological function and guiding therapeutic ultrasound. However, the feasibility of transcranial imaging varies among individuals because of the differences in skull acoustic properties. To better understand the fundamental mechanisms underlying the variation in imaging performance, the effect of the structure of the porous trabecular bone on transcranial imaging performance (i.e., target localization errors and resolution) was investigated for the first time through the use of elastic wave simulations and experiments. Simulation studies using high-resolution computed tomography data from ex vivo skull samples revealed that imaging at large incidence angles reduced the target localization error for skulls having low porosity; however, as skull porosity increased, large angles of incidence resulted in degradation of resolution and increased target localization errors. Experimental results indicate that imaging at normal incidence introduced a localization error of 1.85 ± 0.10 mm, while imaging at a large incidence angle (40°) resulted in an increased localization error of 6.54 ± 1.33 mm and caused a single point target to no longer appear as a single, coherent target in the resulting image, which is consistent with simulation results. This first investigation of the effects of skull microstructure on transcranial ultrasound imaging indicates that imaging performance is highly dependent on the porosity of the skull, particularly at non-normal angles of incidence.

Sentinel-1 Backscatter Analysis and Radiative Transfer Modeling of Dense Winter Wheat Time Series

This study evaluates a temporally dense VV-polarized Sentinel-1 C-band backscatter time series (revisit time of 1.5 days) for wheat fields near Munich (Germany). A dense time series consisting of images from different orbits (varying acquisition) is analyzed, and Radiative Transfer (RT)-based model combinations are adapted and evaluated with the use of radar backscatter. The model shortcomings are related to scattering mechanism changes throughout the growth period with the use of polarimetric decomposition. Furthermore, changes in the RT modeled backscatter results with spatial aggregation from the pixel to field scales are quantified and related to the sensitivity of the RT models, and their soil moisture output are quantified and related to changes in backscatter. Therefore, various (sub)sets of the dense Sentinel-1 time series are analyzed to relate and quantify the impact of the abovementioned points on the modeling results. The results indicate that the incidence angle is the main driver for backscatter differences between consecutive acquisitions with various recording scenarios. The influence of changing azimuth angles was found to be negligible. Further analyses of polarimetric entropy and scattering alpha angle using a dual polarimetric eigen-based decomposition show that scattering mechanisms change over time. The patterns analyzed in the entropy-alpha space indicate that scattering mechanism changes are mainly driven by the incidence angle and not by the azimuth angle. Besides the analysis of differences within the Sentinel-1 data, we analyze the capability of RT model approaches to capture the observed Sentinel-1 backscatter changes due to various acquisition geometries. For this, the surface models “Oh92” or “IEM_B” (Baghdadi’s version of the Integral Equation Method) are coupled with the canopy model “SSRT” (Single Scattering Radiative Transfer). To resolve the shortcomings of the RT model setup in handling varying incidence angles and therefore the backscatter changes observed between consecutive time steps of a dense winter wheat time series, an empirical calibration parameter (coef) influencing the transmissivity (T) is introduced. The results show that shortcomings of simplified RT model architectures caused by handling time series consisting of images with varied incidence angles can be at least partially compensated by including a calibration coefficient to parameterize the modeled transmissivity for the varying incidence angle scenarios individually.

Ultra-wideband, wide angle, asymmetric transmission based chiral metasurface for C and X band applications

A multi-layered chiral device manifesting asymmetric transmission (AT) facilitating one-way channeling of electromagnetic (EM) waves, based on the inherent polarization is presented. The designed metasurface depicts a high transmission contrast with an efficiency above 80% for an ultra-wide operational range of 6.3–12.3 GHz, constituting a fractional bandwidth of 64%. As an additional feature, the reported metasurface yields robustness against oblique incidences up to 45^circ while maintaining high transmission efficiency. This report also introduces a unique analogy of the AT based communication system with logic-gates by formulating its truth-table and logic circuit. Furthermore, new insights of AT magnitude’s dependence to oblique incidences are presented on the account of surface impedance mismatch due to TE and TM polarization with varying incidence angle. Moreover, avoidance of grating lobes and the associated transmission deterioration through utilization of electrically small periodic metasurface is presented. The results have been numerically and practically validated yielding state-of-the-art features. Operating within C and X band, the reported work is an ideal candidate for practical AT applications.

Reducing the thermal deformation of InSb crystal by using double-bounce HHRMs in the TPS tender X-ray absorption spectroscopy beamline.

The Taiwan Photon Source (TPS) with high brightness and energy tunability is suitable for applications in spectroscopy. The tender X-ray absorption beamline will be optimized for X-ray absorption spectroscopy measurements using a bending-magnet source in a unique photon energy range (1.7-10 keV) and two crystal pairs [InSb(111) and Si(111)] separated using back-to-back double-crystal monochromators (DCMs). InSb crystals are typically used in the lower photon energy range of 1.7-3.5 keV. However, the poor thermal conductivity of InSb crystals leads to severe deformation. This factor should be considered when the monochromator is installed on a tender X-ray beamline in a storage ring with a high power density. There are many approaches to reducing the thermal load on the first crystal of a DCM. Double-bounce high harmonics rejection mirrors in front of the DCM serve not only to reduce the high-order harmonics but also to absorb considerable quantities of heat. Two coating stripes on the silicon surfaces with a variable incident angle will be key to solving the thermal load on this beamline.

Oblique and Polarization Independent Metasurface-Based Absorber for Bio-Sensing Applications

In this paper, a submillimetric/THz metasurface polarization/oblique independent absorber is designed and characterized. The absorber is designed using a periodic arrangement of a modified split ring resonator unit cell. The symmetric absorber is insensitive to the variation of incident angles and polarization angles. The results confirm that perfect absorption is achieved (close to 100%) for either TM or TE polarization at 300 GHz. Moreover, the absorber is efficient for normal and oblique incident angle (above 90% for 45° angle of incidence). In all the presented cases, the full width half maximum bandwidth is 20 GHz. The absorber unit cell size is only 0.0052 λ 0 × 0.0052 λ 0 and it has a low-profile thickness = 0.0002 λ 0, at the operating frequency. Also, an absorber-based biosensor is presented. The sensing has proved the coating analyte thickness can be detected by shifting the absorption frequency. The maximum sensitivity is 24.9% RIU−1 with a low-profile maximum of 50 µm thickness. Analytical formulas for the frequency shift have been extracted. The presented results are discussed based on 3D full-wave EM simulations.

Optical Constants and Structural Properties of Epitaxial MoS2 Monolayers.

Two-dimensional layers of transition-metal dichalcogenides (TMDs) have been widely studied owing to their exciting potential for applications in advanced electronic and optoelectronic devices. Typically, monolayers of TMDs are produced either by mechanical exfoliation or chemical vapor deposition (CVD). While the former produces high-quality flakes with a size limited to a few micrometers, the latter gives large-area layers but with a nonuniform surface resulting from multiple defects and randomly oriented domains. The use of epitaxy growth can produce continuous, crystalline and uniform films with fewer defects. Here, we present a comprehensive study of the optical and structural properties of a single layer of MoS2 synthesized by molecular beam epitaxy (MBE) on a sapphire substrate. For optical characterization, we performed spectroscopic ellipsometry over a broad spectral range (from 250 to 1700 nm) under variable incident angles. The structural quality was assessed by optical microscopy, atomic force microscopy, scanning electron microscopy, and Raman spectroscopy through which we were able to confirm that our sample contains a single-atomic layer of MoS2 with a low number of defects. Raman and photoluminescence spectroscopies revealed that MBE-synthesized MoS2 layers exhibit a two-times higher quantum yield of photoluminescence along with lower photobleaching compared to CVD-grown MoS2, thus making it an attractive candidate for photonic applications.

PHANTOM COOLING EFFECTS ON ROTOR BLADE SURFACE HEAT FLUX IN A TRANSONIC FULL SCALE 1+1/2 STAGE ROTATING TURBINE

Abstract An experimental and numerical investigation of phantom cooling effects on cooled and uncooled rotating high pressure turbine blades in a full scale 1+1/2 stage turbine test is carried out. Objectives set to capture, separate, and quantify the effects of upstream vane film-cooling and leakage flows on the downstream rotor blade surface heat flux. Multiple series of tests were carried out in the Air Force Research Laboratory, Turbine Research Facility, at Wright-Patterson Air Force Base, Ohio. A non-proprietary research turbine test article is uniquely instrumented with high frequency double-sided thin film heat flux gauges custom made at AFRL. High bandwidth, time resolved surface heat flux is measured on multiple film-cooled and non-film-cooled HPT rotor blades downstream of both film-cooled and non-film-cooled vane sectors. Upstream wake passing and heat flux is characterized on both rotor pressure and suction side surfaces, along with quantifying rotor phantom cooling effects from non-uniform 1st stage vane film cooling and leakage flows. Fast response heat flux measurements quantify how rotor phantom cooling impacts the blade pressure side greatest; increasing along the pressure side towards the trailing edge. It is discovered upstream vane film-cooling alone can account for 50% of the rotor blade cooling effect, and even outweigh the rotor blade film cooling effect far from the blade showerhead holes. Added unsteady numerical simulation demonstrates how variations in inlet total temperature and incidence angle can also contribute to circumferentially non-uniform rotor heat flux.