Increasing Angle Of Incidence Research Articles

Enhanced absorption of TM waves in conductive nanoparticles structure

This paper tackles anti-reflection coating structure for silicon solar cell where conductive nanoparticle (CNP) film is sandwiched between a semi-infinite glass cover and a semi-infinite silicon substrate. The transmission and reflection coefficients are derived by the transfer matrix method and simulated for values of unit cell sizes, gab widths in visible and near-infrared radiation. We also illustrated the dependence of the absorption, transmission and reflection coefficients on several angles of incidence of the transverse magnetic polarized (TM) waves. We found out that reflection decreases by the increase of incident angle to 50[Formula: see text]. If nanoparticles are suitably located and sized at gab width of 3.5 nm, unit cell of 250 nm and CNP layer thickness of 150 nm, the absorptivity of the structure achieves 100%.

Effect of wind direction and incidence angle on polarimetric SAR observations of slicked and unslicked sea surfaces

The objective of this paper is to investigate the dependency of oil spill observations in polarimetric SAR data on imaging geometry, i.e., on incidence angle and look direction relative to the wind. The study is based on quad-polarization data acquired by the Uninhabited Aerial Vehicle Synthetic Aperture Radar over experimental oil slicks under relatively high winds of 10–12 m/s over an 8-hour period. The data is collected over a wide range of incidence angles and alternates between looking upwind (UW) and downwind (DW). The unique time series enables a detailed study of the behavior of multipolarization parameters over clean sea and oil slicks under varying imaging geometry to be carried out for the first time. For clean sea backscatter, our findings are in agreement with previous studies, showing decreasing backscatter as the incidence angle increases and from UW to DW, with the highest sensitivity in the HH channel. We also find similar variations in oil covered areas. The results suggest that the oil slick backscatter is slightly more sensitive to the relative wind direction than the clean sea, and higher oil-sea damping ratios are found in DW than in UW cases, particularly in the HH channel. All multipolarization features investigated have some degree of dependency on imaging geometry. The lowest sensitivities are found in the magnitude of the copolarization correlation coefficient, the standard deviation of the copolarized phase difference, the polarization difference, the mean scattering angle and the entropy. Several features clearly change behavior when the signal approaches the sensor noise floor, and we find that the measurements and derived parameters may be affected at even higher signal-to-noise ratio (SNR) levels than previously proposed, i.e., closer to 7–9 dB above the sensor noise floor. Overall, the polarization difference is clearly identified as the most interesting parameter for oil spill observation, producing high oil-sea contrast in addition to low sensitivity to imaging geometry. The results show that both the relative wind direction and the incidence angle, in combination with the SNR, should be taken into account when developing operational methods based on multipolarization SAR data.

Performance analysis of air-water quantum key distribution with an irregular sea surface

In the air-water quantum key distribution (QKD), the irregular sea surface has some influence on the photon polarization state. The wind is considered as the main factor causing the irregularity, so the model of irregular sea surface based on the wind speed is adopted. The relationships of the quantum bit error rate with the wind speed and the initial incident angle are simulated. Therefore, the maximum secure transmission depth of QKD is confirmed, and the limitation of the wind speed and the initial incident angle is determined. The simulation results show that when the wind speed and the initial incident angle increase, the performance of QKD will fall down. Under the intercept-resend attack condition, the maximum safe transmission depth of QKD is up to 105 m. To realize safe communications in the safe diving depth of submarines (100 m), the initial incident angle is requested to be not exceeding 26°, and with the initial incident angle increased, the limitation of wind speed is decreased.

Dielectric properties of UV-irradiated ultrathin polysulfone films revealed by surface plasmon resonance method

ABSTRACTThe surface plasmon resonance research of manufactured highly homogeneous ultrathin polysulfone films was performed, which were exposed to the short-wave (254 nm) UV irradiation of various durations. Surprisingly, the resonance incident angle and dielectric constant increase after short-term UV irradiation before the ordinary decrease caused by usual polymer degradation. The experimental results are ascribed to the formation of polar groups leading to orientation of chain fragments of intermediate length followed by their breaking and formation of mobile short fragments under longer times of irradiation.

Intensity, phase, and polarization of a vector Bessel vortex beam through multilayered isotropic media.

This paper investigates the characteristics of reflected and transmitted fields of a vector Bessel vortex beam through multilayered isotropic media on the basis of the vector angular spectrum expansion and presents the effects of media on intensity, phase, and polarization. The method is verified by studying the reflection and transmission on a single interface at vertical incidence. For both paraxial and nonparaxial incident beam cases, numerical simulations of the field components and the time-averaged Poynting vector power density of the reflected and transmitted beams for the three-layered media are presented and discussed in detail. It is shown that as the incident angle increases, the magnitude distribution of the reflected beams illustrates significant distortions and no longer represents similar patterns to that of the incident beam, whereas the magnitude distribution of the transmitted beams can maintain similar profiles to the incident beam, apart from the notable distortion of the central ring. For the same incident angle, the effects of media on the magnitude distribution for the nonparaxial case are more evident than those for the paraxial case. The results of phase distribution and polarization of the reflected and transmitted fields show that as the incident angle increases, the distortion of the phase distribution and polarization for the reflected fields are more significant and the topological charge cannot be preserved.

Photonic band gap properties of one-dimensional Thue-Morse all-dielectric photonic quasicrystal

In this paper, the photonic band gap (PBG) properties of one-dimensional (1D) Thue-Morse photonic quasicrystal (PQC) S4 structure are theoretically investigated by using transfer matrix method in Bragg condition. The effects of the center wavelength, relative permittivity and incident angle on PBG properties are elaborately analyzed. Numerical results reveal that, in the case of normal incidence, the symmetry and periodicity properties of the photonic band structure are presented. As the center wavelength increases, the PBG center frequency and PBG width decrease while the photonic band structure is always symmetrical about the central frequency and the photonic band structure repeats periodically in the expanding observation frequency range. With the decrease of relative permittivity contrast, the PBG width and the relative PBG width gradually decreases until PBG disappears while the symmetry of the photonic band structure always exists. In the case of oblique incidence, as the incident angle increases, multiple narrow PBGs gradually merge into a wide PBG for the TE mode while for the TM mode, the number of PBG continuously decreases and eventually disappears, i.e., multiple narrow PBGs become a wide passband for the TM mode. The research results will provide a reference for the choice of the material, the incident angle for the PBG properties and its applications of 1D Thue-Morse PQC.

A mathematical framework to describe the effect of beam incidence angle on metrics derived from airborne LiDAR: The case of forest canopies approaching turbid medium behaviour

Airborne laser scanning (LiDAR) is used in forest inventories to quantify stand structure with three-dimensional point clouds. However, the 3D distribution of the point clouds depends not only on stand structure, but also on scan angle, because the probability for an oblique beam to be reflected by the canopy increases with the distance it must travel through the canopy. Thus, the canopy appears to increase in density as the incidence angle increases, all else being equal. The resulting variation between and within datasets can induce bias in LiDAR metrics derived from the vertical distribution of points. In this study, we modelled the effect of scan angle on the vertical structure of the point clouds to predict the bias of metrics derived from points sampled off-nadir. Comparison with paired observations from different flightlines (off- and at-nadir observations of the same point) demonstrated that the model accurately reproduced the bias of metrics calculated for a northern hardwood forest with relatively continuous canopy. Thus, the model could be used to correct the bias of LiDAR metrics, and provides a mathematical framework that could be used to inform the selection of maximum incidence angle in LiDAR surveys, considering the trade-off between decreasing acquisition costs and obtaining unbiased measurements.

Impact of Reentry Speed on the Transmission of Obliquely Incident THz Waves in Realistic Plasma Sheaths

Nowadays, the terahertz (THz) communication is believed to be a potential solution to the communication blackout for reentry vehicles. In this paper, a numerical hypersonic fluid model was introduced to obtain the realistic plasma sheaths. The onboard antenna which is installed on the wall was assumed to be conformal. The transmission of obliquely incident THz waves in the plasma sheaths was analyzed. According to this paper, the power transmission coefficient decreases with the increase of reentry speed since both the electron density and the electron collision frequency near the onboard antenna increase with the reentry speed. In addition, the relation between the wave transmission and the reentry speed is revealed. The power transmission coefficient decreases with the increase of incident angle, because the conformal antenna cannot receive the field component which is perpendicular to the wall. Two supplemental schemes to enhance the transmission rate for THz signals were discussed based on this paper.

Effects of proton irradiation at different incident angles on InAlAs/InGaAs InP-based HEMTs**Project supported by the National Natural Science Foundation of China (Grant Nos. 11775191, 61404115, 61434006, and 11475256), the Program for Innovative Research Team (in Science and Technology) in University of Henan Province, China (Grant No. 18IRTSTHN016), and the Development Fund for Outstanding Young Teachers in Zhengzhou University of China

InP-based high electron mobility transistors (HEMTs) will be affected by protons from different directions in space radiation applications. The proton irradiation effects on InAlAs/InGaAs hetero-junction structures of InP-based HEMTs are studied at incident angles ranging from 0 to 89.9° by SRIM software. With the increase of proton incident angle, the change trend of induced vacancy defects in the InAlAs/InGaAs hetero-junction region is consistent with the vacancy energy loss trend of incident protons. Namely, they both have shown an initial increase, followed by a decrease after incident angle has reached 30°. Besides, the average range and ultimate stopping positions of incident protons shift gradually from buffer layer to hetero-junction region, and then go up to gate metal. Finally, the electrical characteristics of InP-based HEMTs are investigated after proton irradiation at different incident angles by Sentaurus-TCAD. The induced vacancy defects are considered self-consistently through solving Poisson’s and current continuity equations. Consequently, the extrinsic transconductance, pinch-off voltage and channel current demonstrate the most serious degradation at the incident angle of 30°, which can be accounted for the most severe carrier sheet density reduction under this condition.

Effect of target color and scanning geometry on terrestrial LiDAR point-cloud noise and plane fitting

AbstractPoint-cloud coordinate information derived from terrestrial Light Detection And Ranging (LiDAR) is important for several applications in surveying and civil engineering. Plane fitting and segmentation of target-surfaces is an important step in several applications such as in the monitoring of structures. Reliable parametric modeling and segmentation relies on the underlying quality of the point-cloud. Therefore, understanding how point-cloud errors affect fitting of planes and segmentation is important. Point-cloud intensity, which accompanies the point-cloud data, often goes hand-in-hand with point-cloud noise. This study uses industrial particle boards painted with eight different colors (black, white, grey, red, green, blue, brown, and yellow) and two different sheens (flat and semi-gloss) to explore how noise and plane residuals vary with scanning geometry (i.e., distance and incidence angle) and target-color. Results show that darker colors, such as black and brown, can produce point clouds that are several times noisier than bright targets, such as white. In addition, semi-gloss targets manage to reduce noise in dark targets by about 2–3 times. The study of plane residuals with scanning geometry reveals that, in many of the cases tested, residuals decrease with increasing incidence angles, which can assist in understanding the distribution of plane residuals in a dataset. Finally, a scheme is developed to derive survey guidelines based on the data collected in this experiment. Three examples demonstrate that users should consider instrument specification, required precision of plane residuals, required point-spacing, target-color, and target-sheen, when selecting scanning locations. Outcomes of this study can aid users to select appropriate instrumentation and improve planning of terrestrial LiDAR data-acquisition.

Controlling emissivity in one dimensional photonic crystals using surface truncation

The properties of emissivity in one dimensional photonic crystals are studied using transfer matrix method and Kirchhoff’s second law. It is found that emissivity and its angular distribution can be controlled by truncating the first layer. It is observed that with increase in incident angle, emissivity is shifted towards lower wavelength. From the studies of angular distribution of emissivity with truncation parameter, it is demonstrated that the magnitude of emissivity can be increased with truncation parameter while maintaining the same angular lobe.

Periodical plasma structures controlled by external magnetic field

The plasma of Hall thruster type in external magnetic field is studied in 2D3V kinetic simulations using PIC MCC method. The periodical structure with maxima of electron and ion densities is formed and becomes more pronounced with increase of magnetic field incidence angle in the plasma. These ridges of electron and ion densities are aligned with the magnetic field vector and shifted relative each other. This leads to formation of two-dimensional double-layers structure in cylindrical plasma chamber. Depending on Larmor radius and Debye length up to nineteen potential steps appear across the oblique magnetic field. The electrical current gathered on the wall is associated with the electron and ion density ridges.

Polarization study about a telescope-based transmitter for quantum communication.

We studied the polarization evolution of a reflective telescope designed for the quantum satellite Micius. The change in polarization extinction ratio (PER) of quantum light was derived and calculated. The PER deterioration caused by increase of incidence angle was calculated to determine the boundary conditions for the system design. The performance of the Micius prototype was evaluated both theoretically and experimentally to verify the viability of our optical design. Minimum and maximum PERs of 38 and 55dB, respectively, were recorded, which were mostly in good agreement with the numerical calculations. Our investigations have contributed to the success of Micius, which is a significant milestone for building a global security network.

BRDF of human skin in the visible spectrum

PurposeSignificant research has been carried out in terms of development of new bidirectional reflectance distribution function (BRDF) instruments; however, there is still little research available regarding spectral BRDF measurements of human skin. This study aims to investigate the variation in human skin reflectance using a new fibre optic-based spectral-BRDF measurement device.Design/methodology/approachDesign of this system mainly involves use of multiple fibre optics to illuminate and detect light reflected from a sample, whereas a hemispherical dome was 3D printed to mount the fibres at various slant/tilt angles. To investigate the spectral differences in BRDF of human skin, 3 narrowband filters in the visible spectrum were used, whereas measurements were taken from the back of the hand for Caucasian and Asian skin types.FindingsThe experiments demonstrate that the BRDF of human skin varies with wavelengths in the visible spectrum and it is also different for Caucasian and Asian skin types. Both skin types exhibit off-specular reflection with increase in angle of incidence and show less variation with respect to viewing angles when the angle of incidence is normal to the surface.Research implicationsA database of spectral BRDF measurements of human skin will help not only in creating realistic skin renderings but also in development of novel skin reflectance models for biomedical and machine vision applications. The measurements would also provide means to validate the predictions from existing light transport/spectral simulation models for human skin and will ultimately help in the accurate diagnosis and simulation of various skin disorders.Originality/valueThe proposed system provides fast scatter measurements by utilising multiple fibres to detect light simultaneously at different angles while also allowing easy switching between incident light directions. Due to its flexible design and contact-based measurements, the device is independent of errors due to sample movements and does not require any image registration. Also, measurements taken from the device show that the BRDF of skin varies significantly in the visible spectrum and it is different for Caucasian and Asian skin types.

Characterization of Surface Radar Cross Sections at W-Band at Moderate Incidence Angles

This paper presents the results of a recent flight campaign conducted over the Great Lakes region and reports the first observations of the W-band normalized backscattered cross section ( $\sigma _{0}$ ) for V and H polarization and the linear depolarization ratios (LDRs) from different types of surfaces at moderate incidence angles ( $\sigma _{0}$ behaves as previously reported at small incidence angles, it features a marked decrease with increasing incidence angles between 20° and 50°. There is a strong dependence of normalized backscattered cross sections both on the wind speed and on the wind direction, with larger values found in the presence of higher wind speeds and when the radar antenna is looking upwind. This is in line with theoretical models (though models tend to overpredict the range of variability at a given incidence angle) and with observations at lower frequencies. The LDRs are steadily increasing from values certainly lower than −30 dB, at vertical incidence, to the values of about −10 dB, at the incidence angles of about 60°–70°, with a good matching between observations and theoretical predictions. On the other hand, land surface backscattering properties are not characterized by a strong angular dependence: $\sigma _{0}$ and LDR values typically range between −20 and 0 dB and between −15 and −5 dB, respectively. This paper is relevant for spaceborne concepts of W-band radars, which envisage moderate incidence angles to achieve a broad swath needed for global coverage.

Interferometric control of the absorption in optical patch antennas

Optical patch nano-antennas possess unique absorption, field enhancement and concentration capabilities – but their crosssection, as well as their response outside of normal incidence are not well understood. Here we explain the large cross-section by considering that each patch nanoantenna is a cavity excited from both sides. Such a simple physical picture allows to fully understand the influence of the angle of incidence – that odd resonances have a very high absorption cross-section which decreases when the incidence angle increases, while even resonances cannot be excited in normal incidence. A direct application would be to use these structures as an optical nanometric set-square.

Periodical plasma structures controlled by external magnetic field

The characteristics of two-dimensional periodical structures in a magnetized plasma are studied using kinetic simulations. Ridges (i.e. spikes in electron and ion density) are formed and became more pronounced with an increase of magnetic field incidence angle in the plasma volume in the cylindrical chamber. These ridges are shifted relative to each other, which results in the formation of a two-dimensional double-layer structure. Depending on Larmor radius and Debye length up to 19 potential steps appear across the oblique magnetic field. The electrical current gathered into the channels is associated with the electron and ion density ridges.

Ku-Band Sea Surface Radar Backscatter at Low Incidence Angles under Extreme Wind Conditions

This paper reports Ku-band normalized radar cross section (NRCS) at low incidence angles ranging from 0° to 18° and in the wind speed range from 6 to 70 m/s. The precipitation radar onboard the tropical rainfall measuring mission and Jason-1 and 2 have provided 152 hurricanes observations between 2008 and 2013 that were collocated with stepped-frequency microwave radiometer measurements. It is found that the NRCS decreases with increasing incidence angle. The decrease is more dramatic in the 40–70 m/s range of wind speeds than in the 6–20 m/s range, indicating that the NRCS is very sensitive to low incidence angles under extreme wind conditions and insensitive to the extreme wind speed. Consequently, the sea surface appears relatively “smooth” to Ku-band electromagnetic microwaves. This phenomenon validates the observed drag coefficient reduction under extreme wind conditions, from a remote sensing viewpoint. Using the NRCS dependence on incidence angle under extreme wind conditions, we also present an empirical linear relationship between NRCS and incidence angles, which may assist future-satellites missions operating at small incidence angles to measure sea surface wind and wave field.

Direct numerical simulations on the flow past an inclined circular disk

The three-dimensional flow past an inclined circular disk is investigated using direct numerical simulations. Various incidence angles of the disk with respect to the inflow are considered from 0° to 60°, where 0° refers to the condition in which the flow is perpendicular to the disk. The aspect ratio (diameter/thickness) of the disk is considered to be 50. The Reynolds number based on the inflow velocity and the diameter of the disk is up to 500. The drag and lift coefficients, pressure coefficients, and three-dimensional vortical structures are analyzed using time-dependent and time-averaged techniques. Detailed comparisons between the results of the disk at different incidence angles are presented. The flow pattern gradually changes from chaotic to a periodic state as the incidence angle increases from 0° to 60°. At incidence angles of 45° and 50°, an evident low-frequency modulation exists whose period is approximately ten times greater than the primary vortex shedding period. For the inclined disks, the wake flow is tilted to the trailing edge side of the disk rather than parallel to the streamwise direction. The distance between two successive vortical rings is observed to decrease as the incidence angle increases. The streamwise length of the mean recirculation bubble decreases as the incidence angle increases.

How crystal configuration affects the position detection accuracy in pixelated molecular SPECT imaging systems?

It is well known that inter-crystal scattering and penetration (ICS–P) are major spatial resolution limiting parameters in dedicated SPECT scanners with pixelated crystal. In this study, the effect of ICS–P on crystal identification in different crystal configurations was evaluated using GATE Monte Carlo simulation. A 99mTc pencil-beam toward central crystal element was utilized. Beam incident angle was assumed to vary from 0° to 45° in 5° steps. The effects of various crystal configurations such as pixel-size, pixel-gap, and crystal material were studied. The influence of photon energy on the crystal identification (CI) was also investigated. Position detection accuracy (PDA) was defined as a factor indicating performance of the crystal. Furthermore, a set of 99mTc point-source simulations was performed in order to calculate peak-to-valley (PVR) ratio for each configuration. The results show that the CsI(Na) manifests higher PDA than NaI(Tl) and YAP(Ce). In addition, as the incident angle increases, the crystal becomes less accurate in positioning of the events. Beyond a crystal-dependent critical angle, the PDA monotonically reduces. The PDA reaches 0.44 for the CsI(Na) at 45° beam angle. The PDAs obtained by the point-source evaluation also behave the same as for the pencil-beam irradiations. In addition, the PVRs derived from flood images linearly correlate their corresponding PDAs. In conclusion, quantitative assessment of ICS–P is mandatory for scanner design and modeling the system matrix during iterative reconstruction algorithms for the purpose of resolution modeling in ultra-high-resolution SPECT.