Various Angles Of Incidence Research Articles

Temperature Distribution and Influence Mechanism on Large Reflector Antennas under Solar Radiation

AbstractThe solar impact on antenna must be lessened for the large reflector antenna operating at high frequencies to have great electromagnetic performances. Therefore, researching the temperature distribution and its influence on large reflector antenna is necessary. The variation of solar incidence angle is first calculated. Then the model is simulated by the I‐DEAS software, with the temperature, thermal stress, and thermal distortion distribution through the day obtained. In view of the important influence of shadow on antenna structure, a newly proposed method makes a comprehensive description of the temperature distribution on the reflector and its influence through the day by dividing a day into three different periods. The sound discussions and beneficial summary serve as the scientific foundation for the engineers to compensate the thermal distortion and optimize the antenna structure.

Refractive Index Imaging of Cells with Variable-Angle Near-Total Internal Reflection (TIR) Microscopy.

The refractive index in the interior of single cells affects the evanescent field depth in quantitative studies using total internal reflection (TIR) fluorescence, but often that index is not well known. We here present method to measure and spatially map the absolute index of refraction in a microscopic sample, by imaging a collimated light beam reflected from the substrate/buffer/cell interference at variable angles of incidence. Above the TIR critical angle (which is a strong function of refractive index), the reflection is 100%, but in the immediate sub-critical angle zone, the reflection intensity is a very strong ascending function of incidence angle. By analyzing the angular position of that edge at each location in the field of view, the local refractive index can be estimated. In addition, by analyzing the steepness of the edge, the distance-to-substrate can be determined. We apply the technique to liquid calibration samples, silica beads, cultured Chinese hamster ovary cells, and primary culture chromaffin cells. The optical technique suffers from decremented lateral resolution, scattering, and interference artifacts. However, it still provides reasonable results for both refractive index (~1.38) and for distance-to-substrate (~150 nm) for the cells, as well as a lateral resolution to about 1 µm.

Design of ultrathin dual-resonant reflective polarization converter with customized bandwidths

In this paper, an ultrathin dual-resonant reflective polarization converter is proposed to obtain customized bandwidths using precise space-filling technique to its top geometry. The unit cell of the dual-resonant prototype consists of conductive square ring with two diagonally arranged slits, supported by metal-backed thin dielectric layer. It offers two narrow bands with fractional bandwidths of 3.98 and 6.65% and polarization conversion ratio (PCR) of 97.16 and 98.87% at 4.52 and 6.97 GHz, respectively. The resonances are brought in proximity to each other by changing the length of surface current paths of the two resonances. By virtue of this mechanism, two polarization converters with two different types of bandwidths are obtained. One polarization converter produces a full-width at half-maxima PCR bandwidth of 34%, whereas another polarization converter produces a 90% PCR bandwidth of 19%. All the proposed polarization converters are insensitive to wide variations of incident angle for both TE- and TM-polarized incident waves. Measured results show good agreement with the numerically simulated results.

PV module current gains due to structured backsheets

We evaluate the optical performance of PV modules with respect to an increase in short circuit current density. Our evaluation is based on the combination of ray tracing simulations and measurements on test modules with four types of backsheets: Two of them are structured, the third is white and diffusively reflecting and the fourth reflects no light. Under normal incidence, structured backsheets reflect incoming light at an angle that causes total internal reflection at the glass/air interface, which guides the light to the solar cell surface. Three different irradiance conditions are studied: a) standard testing conditions (STC) with light incident perpendicular to the module surface, b) variation in the angle of incidence and c) light source with mean annual distribution of angles of incidence. Using the measured refractive index data in ray tracing simulations we find a short circuit current density (Jsc) gain of up to 0.9 mA/cm² (2.3%) for monofacial cells and a structured backsheet, when compared to a white backsheet with diffuse reflection. For bifacial cells we calculate an even larger Jsc increase of 1.4 mA/cm² (3.6%). The Jsc increase is larger for bifacial cells, since some light is transmitted through the cells and thus more light interacts with the backsheet. Our optical loss analysis reveals the best performance in STC for edge-aligned Ag grooves. This structure reduces absorption losses from 1.8 mA/cm² to 0.3 mA/cm² and reflection losses from 0.7 mA/cm² to 0 mA/cm². This trend also holds under various angles of incidence as confirmed consistently by Jsc measurements and ray racing simulations. Simulations using an annual light source emitting a mean annual distribution of angles of incidence reveal grooves in both orientations edge alignment and east-west alignment achieve similar current gains of up to 1.5% for mono- and of 2.5% for bifacial cells compared to modules with white back sheets. This indicates that for modules with light guiding structures such as these backsheets optimization for STC differs from optimization for annul yield.

Fast electro-optical response of a cell with a homeoplanar layer of a nematic liquid crystal

The refraction of light, i.e., the turn of an extraordinary ray in the liquid crystal layer similar to total internal reflection at an interface between two media, has been studied in a cell with the homeoplanar orientation of the director. The rise, τon, and decay, τoff, times of optical responses have been obtained for various angles of incidence of light on a liquid crystal layer subjected to an electric field. The times τon and τoff of optical responses for the angles of incidence much larger than the angle of total internal reflection are 1–2 ms, which is three orders of magnitude smaller than the relaxation time of an optical response in the case of normal incidence of the ray.

Analyzing the Influence of the Angles of Incidence and Rotation on MBU Events Induced by Low LET Heavy Ions in a 28-nm SRAM-Based FPGA

This paper shows the impact of low linear energy transfer heavy ions on the reliability of 28-nm Bulk static random access memory (RAM) cells from Artix-7 field-programmable gate array. Irradiation tests on the ground showed significant differences in the multiple bit upset cross section of configuration RAM and block RAM memory cells under various angles of incidence and rotation of the device. Experimental data are analyzed at transistor level by using the single-event effect prediction tool called multiscale single-event phenomenon prediction platform coupled with SPICE simulations.

Thin Bandstop Frequency-Selective Structures Based on Loop Resonator

Circular and elliptical loop resonators are proposed as the unit cell of 3-D frequency-selective structure aiming to reduce the structure thickness. The structure exhibits a pseudoelliptic response by utilizing the coupling between the two quasi-TEM modes, which are concentrated in air and substrate regions of the unit cell. Using elliptical loop with stepped-impedance resonator (SIR), the thickness of the structure can be reduced by 80% compared to previous structures. A comparison between the response of the structure employing the microstrip line as the resonator and the structure using the proposed loop resonators is performed. Three prototypes are designed, fabricated, and tested. The first structure is designed to have a dual-band bandstop response using two half-circular loops with end via holes; it has center frequencies at 10 and 14.3 GHz with −3 dB fractional bandwidths of 6.7% and 6.6%, respectively. A half-elliptical loop with SIR is employed in the second structure to achieve more thickness reduction. The third structure is designed to exhibit a dual-polarized bandstop response. Stable frequency response under various angles of incidence is obtained.

Influence of laser beam incidence angle on laser lap welding quality of galvanized steels

Based on the characteristics of laser welded structural parts of auto bodies, the influence of variation in laser beam incidence angle on the lap welding performance of galvanized auto-body sheets was studied. Lap welding tests were carried out on the galvanized sheets for auto-body application at different laser beam incidence angles by using the optimal welding parameters obtained through orthogonal experiment. The effects of incidence angle variation on seam appearance, cross-sectional shape, joint mechanical properties and microstructure of weldments were analyzed. In addition, the main factors influencing the value of incidence angle were investigated. According to the results, the weld seams had a good appearance as well as a fine, and uniform microstructure when the laser beam incidence angle was smaller than the critical incidence angle, and thus they could withstand great tensile and shear loads. Moreover, all tensile–shear specimens were fractured in the base material zone. When the laser beam incidence angle was larger than the critical incidence angle, defects like shrinkage and collapse tended to emerge, thereby resulting in the deteriorated weldability of specimens. Meanwhile, factors like the type and thickness of sheet, weld width as well as inter-sheet gap all had a certain effect on the value of laser beam incidence angle. When the sheet thickness was small and the weld width was narrow, the laser beam incidence angle could be increased appropriately. At the same time, small changes in the inter-sheet gap could greatly impact the value of incidence angle. When the inter-sheet gap was small, the laser beam incidence angle should not be too large.

OCT assessment of non-cavitated occlusal carious lesions by variation of incidence angle of probe light and refractive index matching

ObjectivesThis study evaluated (1) the detection and assessment of non-cavitated occlusal carious lesions by spectral domain optical coherence tomography (SD-OCT) and (2) the impact of varying angle of incidence (AI) of probe light and refractive index matching (RIM). MethodsNine extracted human molars with 18 occlusal lesions (ICDAS code 2) were visually selected. 18 regions of interest (ROI) were imaged with SD-OCT under varying AI (0°, ±5°, ±10°, ±15°) and with/without application of glycerine at 0°. X-ray micro computed tomography (μCT) was used as a validation standard. μCT and OCT signals were categorized according to the lesion extent: 1-sound, 2-lesion limited to half of enamel, 3-lesion limited to enamel, 4-lesion into dentin. Agreement between both methods was assessed. Intra- and inter-examiner reproducibility analyses were conducted. Statistics: Cohen’s kappa coefficient (κ), Spearman’s rho correlation (rs) and Wilcoxon test (α=0.05). ResultsSlight to moderate agreement (κ=0.153) between μCT and OCT was obtained at an AI of 0° (Wilcoxon: p=0.02). With variation of Al a substantial agreement (κ=0.607) was observed (p=0.74). Spearman’s correlation between both methods was 0.428 at 0°, 0.75 with varying AI and 0.573 with glycerine. Kappa values for intra-and inter-examiner analysis ranged between 0.81 and 0.88 and between 0.25 and 0.73, respectively. ConclusionVariation of AI improves the detectability of non-cavitated occlusal carious lesions. RIM can enhance signal-to-noise ratio. Clinical relevanceOCT could provide additional diagnostic information in single and longitudinal assessments of occlusal carious lesions.

Simple phase shifting lateral shearing interferometer based on a thick birefringent plate

A simple phase shifting lateral shearing interferometer based on a thick birefringent plate is proposed. The interferometer is composed of a thick birefringent plate and a polarizer. The thick birefringent plate works as the shear generator as well as the phase shifter. The optical path difference and shearing amount between the two sub-beams emerging from the thick birefringent plate change depending on the incident angle. For incident angles in a certain range, the shearing amount stays almost constant while the optical path difference varies linearly. Thus phase shifting can be obtained by rotating the thick birefringent plate. It is a very simple structure for the testing of a small beam, and equidistant phase shifting can be obtained by equal incident angle variation. The validity of the interferometer is verified by both simulation and experiment.

Ballistic resistance of mild steel plates of various thicknesses against 7.62 AP projectiles

The ballistic resistance of mild steel plates has been studied against 7.62 AP projectiles through numerical simulations using ABAQUS/Explicit commercial finite element package. The projectiles were impacted on 4.7, 6, 10, 12, 16, 20 and 25 mm thick target plates at varying incidence angles. The material parameters proposed by authors for the Johnson–Cook model were used to predict the material behavior of target, while the material behavior of projectile was incorporated from the available literature. The numerical results thus obtained have been compared with the experiments available in the literature. The experimental and numerical results with respect to failure mechanism, residual projectile velocity, and maximum angle for perforation and the effect of configurations on spacing and critical angle of ricochet have been compared. A close correlation between the experimental findings and the predicted results has been found. In general, the resistance of target has been found to increase with an increase in target obliquity. The critical angle of the projectile ricochet has been found to decrease with an increase in target thickness. The ballistic limit for all given thicknesses of mild steel targets has also been obtained numerically. The ballistic limit thus obtained has been used to calibrate the Recht–Ipson empirical model for calculating the residual projectile velocity corresponding to a given incidence velocity. Simulations were also done for three-layered target of 4.7- and 6-mm-thick plate and spacing was varied to study its effect on their ballistic resistance. The variation of spacing at normal impact was found to have an influence as long as the spacing was smaller than the projectile length.

Enhanced Goos-Hanchen Shift and Imbert-Fedorov Shift in Three layered Kretschmann-Geometry with Gaussian Beam, Laguerre-Gaussian Beam and Bessel Beam in Silver Nano Layer with Surface Plasmon Resonance

A new theoretical approach towards the exact identification of the output reflected beam position by the effect of spatial Goos-Hanchen (GH) shift and Imbert-Fedorov (IF) shift using Gaussian beam, Laguerre-Gaussian beam and Bessel beam are observed, designed and simulated with the three layered Kretschmann geometry at a free space wavelength of 1550 nm, where the proposed configuration comprising a BK7 prism (n=1.5007) and a 50 nm thin metal layer of silver (n= 0.4096+10.048i). To the best of our knowledge several articles have been discussed, separately considering the Gaussian beam, Laguerre-Gaussian beam and Bessel beam in which without the composite effect of spatial GH shift and IF shift whereas the exact beam position can only be identified with the effect of these shifts. In our proposed configuration by varying incident angle through Bessel beam, the observed spatial GH shift is tuned from 44.267 µm to 0.261 µm and the spatial IF shift is tuned from 39.301 µm to -13.024 µm. With the same variation of incident angle, the spatial GH shift and IF shift are also observed for Gaussian beam and as well as for Laguerre Gaussian beam. This new idea explores the accurate tuning of output beam position with varying incident angle which expedites the path of fine tuning in optical switching within µm ranges.

The interaction of acoustic waves with a three-layer barrier at different angles of incidence

In this paper influence of the bubble layer on the transmission of the acoustic waves through the three-layer barrier placed in the water at various angles of incidence is investigated. Barrier consists of a layer of gel with polydispersed air bubbles limited polycarbonate layers. It is shown that the presence of bubbles in the layer substantially lowers the transmission of the acoustic waves through the multi-layer barrier for frequencies close to the resonant frequency of the bubbles. For these frequencies the values of the reflection and transmission coefficients are almost independent of the angle of incidence and determined by the parameters of the bubble gel.

Out-of-plane orientation alignment and reorientation dynamics of gold nanorods in polymer nanocomposite films.

In this work, we develop a novel, in situ characterization method to measure the orientation order parameter and investigate the reorientation and reshaping dynamics of polymer grafted gold nanorods (AuNRs) in polymer nanocomposite (PNC) thin films. The long aspect-ratio of AuNRs results in two well-defined plasmon resonance modes, allowing the optical properties of the PNC to be tuned over a wide spectral range. The alignment of the AuNRs in a particular direction can also be used to further tune these optical properties. We utilize variable angle spectroscopic ellipsometry as a unique technique to measure the optical properties of PNC films containing AuNRs at various angles of incidence, and use effective index of refraction analysis of the PNC to relate the birefringence in the film due to changes of the plasmon coupling to the orientation order parameter of AuNRs. Polymer thin films (ca. 70 nm) of either polystyrene (PS) or poly(methyl methacrylate) (PMMA) containing PS grafted AuNRs are probed with ellipsometry, and the resulting extinction coefficient spectra compare favorably with more traditional analytical techniques, electron microscopy (EM) and optical absorbance (vis-NIR) spectroscopy. Furthermore, variable angle spectroscopic ellipsometry measures optical birefringence, which allows us to determine the in- and out-of plane order of the AuNRs, a property that is not easily accessible using other measurement techniques. Additionally, this technique is applied in situ to demonstrate that AuNRs undergo a rapid (ca. 1-5 hours) reorientation before undergoing a slower (ca. 24 hours) rod to sphere shape transition. The reorientation behavior is different depending on the polymer matrix used. In the athermal case (i.e. PS matrix), the AuNRs reorient isotropically, while in PMMA the AuNRs do not become isotropic, which we hypothesize is due to PMMA preferentially wetting the silica substrate, leaving less vertical space for the AuNRs to reorient.

Giant Terahertz-Wave Absorption by Monolayer Graphene in a Total Internal Reflection Geometry

We experimentally demonstrated significant enhancement of terahertz-wave absorption in monolayer graphene by simply sandwiching monolayer graphene between two dielectric media in a total internal reflection geometry. In going through this structure, the evanescent wave of the incident terahertz beam interacts with the sandwiched graphene layer multiple (up to four) times at varying incidence angles. We observed extremely large attenuation (up to ∼70% per reflection), especially for s-polarized radiation. The experimental results are quantitatively consistent with our calculations, where we modeled the experiment as an electromagnetic wave reflection process in monolayer graphene. We also derived analytical expressions for the absorptance, showing that the absorptance is proportional to the amount of Joule heating on the graphene surface induced by the terahertz radiation.

Prototype fabrication and experimental investigation of a conjugate refractive reflective homogeniser in a cassegrain concentrator

The conjugate refractive reflective homogeniser (CRRH) is experimentally tested within a cassegrain concentrator of geometrical concentration ratio 500× and its power output compared to the theoretical predictions of a 7.76% increase. I–V traces are taken at various angles of incidence and experimental results showed a maximum of 4.5% increase in power output using the CRRH instead of its purely refractive counterpart. The CRRH utilises both total internal reflection (TIR) within its core refractive medium (sylguard) and an outer reflective film (with an air gap between) to direct more rays towards the receiver. The reflective film captures scattered refracted light which is caused by non-ideal surface finishes of the refractive medium. The CRRH prototype utilises a 3D printed support which is thermally tested, withstanding temperatures of up to 60°C but deforming at >100°C. A maximum temperature of 226.3°C was reached within the closed system at the focal spot of the concentrated light. The material properties are presented, in particular the transmittance of sylguard 184 is shown to be dependent on thickness but not significantly on temperature.Utilising both TIR and standard reflection can be applied to other geometries other than the homogeniser presented here. This could be a simple but effective method to increase the power of many concentrator photovoltaics.

The effect of a metal surface proximity on the Reflection Absorption Spectroscopy (RAS) signal

The objective of this investigation was to learn how the proximity to a reflecting surface influences Absorbance of infrared (IR) radiation by a thin film of molecules. A distribution of the Mean Square Electric Field Strength (MSEFS) for a convergent beam of IR light, reflected from a metal surface was calculated using Fresnel equations. Calculations were done for a 1200cm−1 radiation in a range of distances of up to 99μm at various angles of incidence. It was found that the electric field undergoes dramatic changes within a well-defined “zone of influence” which spans to a distance, approximately twice the wavelength of IR radiation (e.g. 20μm for the optimal angle of incidence of 80° and 1200cm−1 wavenumber). It has already been established that, p-polarised light undergoes enhancement and s-polarised light vanished at the metal surface. This work adds to that knowledge by showing the variation of the MSEFS within the zone of influence in the surface vicinity, emphasizing a “hot spot” (e.g. 10μm for the optimal angle at 1200cm−1) where the antinodes of both polarisations occur resulting in the magnitude of the MSEFS for s-polarised light exceeding that of the p-polarised light. It was concluded that the contribution of absorbing species from this “hot spot” can be avoided by close control of experimental conditions such as the angle of incidence and the deposited film or IR cell thickness. Outside of the zone of influence, the MSEFS of both polarisations tend towards the value of 2, consistent with the expected behavior considering that light travels twice trough a point in front of a mirror due to reflection. This contribution should yield further insight in understanding and design of Reflection Absorption Spectroscopy (RAS) experiments aimed on investigation of potential-induced processes that take place at the metal electrode surface from adsorption of thin organic films to reduction/oxidation reactions taking place in fuel cells during electrocatalysis.

Evaluating Moisture and Geometry Effects on L-Band SAR Classification Performance Over a Tropical Rain Forest Environment

Multitemporal single (HH) and dual-polarization (i.e., HH, HV) L-band spaceborne synthetic aperture radar (SAR) scenes were evaluated under different moisture conditions caused by precipitation prior to data acquisition at varying incidence angles. The changes affecting backscattering intensity, polarimetric decomposition, backscattering mechanism, and land use/land cover classification performance were evaluated. The study area is a shifting-cultivation environment in the eastern Amazon (Brazil). Several data input scenarios were proposed in the classification scheme (i.e., backscattering intensity alone and combined with alpha/entropy decomposition parameters, band ratios, and textural parameters) using a random forest classifier framework. Integration with optical data was also examined. The classification accuracy scores were then compared with accumulated precipitation data. The results showed that the variation in both the vegetation moisture and incidence angle increases the backscattering intensity for pasture, riparian forest and young regenerated forest by at least 1 dB compared with old successional forest stages due to its more uniform vertical structure and the landscape's increased dielectric constant. The overall classification accuracy proved low for each SAR acquisition date compared with the performance of the Landsat data. Based on SAR data, misclassification occurs for the young successional forest stages and increases in scenes with higher moisture conditions. The classification performance benefits from data integration only for one SAR scene acquired in the dry season. The results highlight the importance of selecting proper temporal intervals for the different SAR polarization modes of the forthcoming SAR missions. Further investigations should address both multitemporal at a single frequency as well as multifrequency SAR approaches.

Experimental validation of the partial coherence model in spectroscopic ellipsometry and Mueller matrix polarimetry

In this contribution, a recently advanced analytical approach for addressing partial coherence in spectroscopic polarimetric measurements is experimentally validated. The approach is based on the fundamental representation of the measurement process as the convolution of the polarimetric response of the sample and the instrumental function of the measurement system. Experimentally, the optical responses of two optically thick transparent layers were acquired by using spectroscopic Mueller matrix polarimetry at various angles of incidence over two spectral ranges (visible and infrared). The layers are considered isotropic and the loss of coherence is assumed to originate from the finite spectral resolution of the instrument. In parallel with the analytical approximation, the standard numerical approach implemented in commercial software was likewise used to reproduce the polarimetric responses. Excellent agreement between the analytical approximation, the commercial software one and the polarimetric measurements was found. The experimental validation of the analytical approximation represents a time-saving alternative to the numerical approaches used in commercial software and is of potential interest to real-time process monitoring by using spectroscopic ellipsometry or polarimetry.

Fabrication of Stacked Layers of Fine Particle Assembly Aiming at Wavelength-Selective Reflection

This study aims to demonstrate that dielectric particles can be stacked to produce electromagnetic functions. By drawing up a hydrophilic substrate from an aqueous suspension in which fine particles are dispersed, monolayer closed-packed or ordered structures can be obtained by utilizing the meniscus attraction between the particles during the drying process. By repeating this process, particles of different sizes and materials can be stacked layer by layer. By changing the permittivity and/or diameters of the particles through layers, the reflectance of light at a particular wavelength can be increased or decreased. Aiming at selective reflection of the near infrared light, silica (SiO2) particles of φ200 nm and titanium oxide (TiO2) particles of φ33 nm were chosen and two layers were stacked on a silicon wafer. The reflectivity was measured with an original setup. Monochromatic light was focused on the sample at various angles of incidence, and the reflection intensity was measured at specified angles independent of the angle of incidence. By scanning the wavelength of the light, the reflection spectrum at specific incident and reflection angles was obtained. It was confirmed that reflectivity increased by 1.7 μm when the TiO2 oxide layer covered the SiO2 layer, as derived from theory.