Effect Of Incidence Angle Research Articles

Effect of laser beam incidence angle on cladding morphology in laser cladding process

The change of angle θ between laser cladding powder plane and substrate plane will lead to changes in cladding layer's geometric morphology. Therefore, we established a quantitative numerical prediction model for cladding layer geometry. In this model, we consider the variation of θ, the laser energy attenuation rate and the temperature rise of the powder particles. At the same time, the simulation results were verified by experiments. The results show that when θ is in the range of 50°~90°, the initial temperature is 298 K, the scanning speed is 3.75 mm/s, and the laser spot diameter is 4.5 mm, the Fe#1 powder cladding can achieve better forming effect on Q235. In general, with the decrease of θ, the height of the cladding layer decreases and the width of the layer increases. However, when θ is less than 50°, the quality of the formed morphology significantly deteriorated. The experimental results are in good agreement with the simulation results, which verifies the validity and reliability of the model. This work provides a theoretical reference for further understanding the relationship between the laser cladding morphology and the incident angle.

Analysis of water wave interaction with a submerged quarter-circular breakwater using multipole method

This article studies water wave interaction with a submerged quarter-circular breakwater based on potential theory and multipole expansion method. The obliquely and normally incident waves are independently considered. The series solution of velocity potential in the external fluid domain is expressed through the multipole expansions, while the series solution of velocity potential in the quarter-circular internal fluid domain is obtained through the separation of variables. Then, the unknown coefficients in the series solutions are determined by matching the boundary conditions between external and internal fluid domains. The calculation methods for the reflection and transmission coefficients of the submerged quarter-circular breakwater as well as the horizontal and vertical wave forces on the breakwater are presented. The wave forces acting on the submerged breakwater with a seaside quarter-circular-arc and that with a leeside quarter-circular-arc are compared. The hydrodynamic quantities of the submerged quarter-circular breakwater are also compared with those of the submerged semi-circular breakwater. In addition, the effects of breakwater radius, incident frequency, and incident angle on the hydrodynamic quantities of the quarter-circular breakwater are clarified. Valuable results for practical engineering application are drawn.

A Tunable Terahertz Metamaterial Absorber Composed of Hourglass-Shaped Graphene Arrays.

In this paper, we demonstrate a tunable periodic hourglass-shaped graphene arrays absorber in the infrared (IR) and terahertz (THz) frequency bands. The effects of graphene geometric parameters, chemical potentials, periods, and incident angles on the pure absorption characteristics are studied by using the Finite Difference Time Domain (FDTD) method. In addition, this paper also analyzes the pure absorption characteristics of bilayer graphene arrays. The simulation results show that the maximum absorption reaches 38.2% for the monolayer graphene structure. Furthermore, comparing the bilayer graphene structure with the monolayer structure under the same conditions shows that the bilayer structure has a tunable dual-band selective absorption effect and has a higher maximum absorption of 41.7%. Moreover, it was found that there are dual-band tunable absorption peaks at and with the maximum absorption of 41.7% and 11%. The proposed structure is a convenient method which could be used in the design of graphene-based optoelectronic devices, biosensors, and environmental monitors.

Analyzing the Angle Effect of Leaf Reflectance Measured by Indoor Hyperspectral Light Detection and Ranging (LiDAR)

Hyperspectral light detection and ranging (LiDAR) (HSL) combines the characteristics of hyperspectral imaging and LiDAR techniques into a single instrument without any data registration. It provides more information than hyperspectral imaging or LiDAR alone in the extraction of vegetation physiological and biochemical parameters. However, the laser pulse intensity is affected by the incident angle, and its effect on HSL has not yet been fully explored. It is important for employing HSL to investigate vegetation properties. The aim of this paper is to study the incident angle effect of leaf reflectance with HSL and build a model about this impact. In this paper, we studied the angle effect of leaf reflectance from indoor HSL measurements of individual leaves from four typical tree species in Beijing. We observed that (a) the increasing of incident angle decreases the leaf reflectance; (b) the leaf spectrum observed by HSL from 650 to 1000 nm with 10 nm spectral resolution (36 channels) are consistent with those that measured by Analytica Spectra Devices (ASD) spectrometer (R2 = 0.9472 ~ 0.9897); (c) the specular reflection is significant in the red bands, and clear non-Lambertian characteristics are observed. In the near-infrared, there is little specular reflection, but it follows the Lambert-scattering law. We divided the whole band (650–1000 nm) into six bands and established an empirical model to correct the influence of angle effect on the reflectance of the leaf for HSL applications. In the future, the calibration of HSL measurements applied for other targets will be studied by rigorous experiments and modelling.

Effect of incidence angle on the seismic performance of skewed bridges retrofitted with buckling-restrained braces

This study examines the effect of ground motion (GM) incidence angles on the seismic response of skewed bridges retrofitted with buckling-restrained braces (BRBs) under far-field and near-field ground motions (FFGMs and NFGMs). Bridge models for a three-span reinforced concrete bridge with skew angles of 0°, 18°, 36°, and 54° are used as a case study. Three-dimensional nonlinear dynamic analyses are performed with scaled GMs under 11 incidence angles (from 0° to 180°) to obtain the maximum bridge response parameters on the maximum considered earthquake hazard level. This study demonstrates the effectiveness of a BRB retrofit to reduce the influence of GM incidence angle. The results indicate that skewed bridges are less sensitive to the GM incidence angle and BRBs further decrease the incidence effect. Also, the seismic response under different GM incidence angles is more predictable when the bridge is subjected to FFGMs. In general, the maximum response of skewed bridges could be estimated by applying the scaled principal GMs along the bridge’s longitudinal axis and its orthogonal direction (i.e., 0° and 90°), regardless of GM characteristics, skewed angle, and BRB retrofit.

Colorful and superhydrophobic titanium surfaces textured by obliquely incident femtosecond laser induced micro/nano structures

Multiscale micro/nano structures (e.g. large period ripples and sputtered particles) on titanium surfaces by obliquely incident femtosecond laser texturing. The effects of laser incident angle on surface structures, wettability and structural color were studied. As a result, sputtered particles are formed on the titanium surface for all incident angle. Fine ripples are appeared on the large period ripples, when the incident angle is greater than 50°. However, there is no fine ripples structure when the incident angle is less than 50°. Meanwhile, the structured surfaces appear structural color and superhydrophobicity for all laser angle. The formation mechanism of hybrid micro/nano structures on the titanium surface is also discussed.

Polarization beam splitter based on extremely anisotropic black phosphorus ribbons.

Properly designed black phosphorus (BP) ribbons exhibit extreme anisotropic properties, which can be used to fabricate a high-efficiency transmitter or reflector depending on the linear polarization of excitation. In this study, we design a highly efficient and broad-angle polarization beam splitter (PBS) based on extremely anisotropic BP ribbons around the mid-infrared frequency region with an ultra-thin structure, and study its performance by using transfer matrix calculation and finite element simulation. In the broad frequency range of 80.4 terahertz - 85.0 terahertz (THz) and an wide angle range of more than 50°, the reflectivity and transmissivity of the designed PBS are both larger than 80% and the polarization extinction ratios are higher than 25.50 dB for s-polarization light and 20.40 dB for p- polarization light, respectively. Furthermore, the effect of incident angle and device parameters on the behavior of the proposed PBS is examined. Finally, we show that the operation frequency of this PBS can be tuned by the electron concentration of BP, which can facilitate some practical applications such as tunable polarization splitters or filters, and mid-infrared sensors.

Effects of Oblique Incidence of SV Waves on Nonlinear Seismic Response of a Lined Arched Tunnel

The incident direction of earthquake motion is an important factor affecting the seismic response of underground structures. In this study, a three-dimensional (3D) oblique incidence method of SV waves is proposed and the effects of incident angles of SV waves on the seismic response of a lined arched tunnel are evaluated. Based on wave field decomposition principle and equivalent node force method and together with viscous-spring artificial boundary, the oblique incidence method of SV waves is implemented by transforming seismic wave field into the equivalent nodal forces acting on the artificial boundaries. By deriving the distance of the incident waves and the reflected wave on free surface to artificial boundaries, this method can comprehensively consider the phase difference of the seismic wave propagation and the influence of the damping effect of the rock medium on the seismic wave propagation. The method is programed into a dynamic finite element program and its effectiveness is examined by a numerical example. Consequently, the oblique incidence method is applied to evaluate the seismic behaviors of the tunnel. The numerical results reveal that (1) the oblique incidence of the seismic wave results in a larger seismic response; (2) the response amplitudes of the stress and displacement increase with the increase of incident angles and reaching the maximum in the case of 30° incident angle; (3) the damage extent increases with an increase in the incident angles, and the oblique incidence of the seismic wave is believed to increase the spatial difference of damage distribution.

Tunable strontium titanate terahertz all-dielectric metamaterials

Based on SrTiO3 (STO) elliptical metamaterials (MMs) structures, the tunable propagation properties have been systematically investigated in the THz regime, including the effects of temperatures, incident angles, operation frequencies, and graphene Fermi levels. The results reveal that STO MMs manifest excellent thermally tunable properties, e.g. the amplitude and frequencies modulation depths are larger than 95.3% and 21.8% if temperature varies in the range of 70–320 K. The incident angles affect the resonant curves significantly, the amplitude modulation depth approximates 90% by changing the polarization angles, and the Q-factor reaches more than 20. The tunable Fano resonances can be achieved by utilizing a symmetrical STO-graphene structure. If the graphene Fermi level changes in the range of 0.3–1.0 eV, the amplitude modulation depth of transmission curve is more than 80%. The results are very helpful to understand the resonant mechanisms of ferroelectric MMs and design novel high Q-factor devices in the future, e.g. sensors, modulators, and filters.

The incident electrical field angle effect in localized surface plasmon resonance (LSPR) of bimetallic Ag-Au nanorod using MNPBEM simulation

In this study, we have performed the incident electrical field angle effect in localized surface plasmon resonance (LSPR) spectra of bimetallic Ag–Au nanorod using Metallic Nano-Particle Boundary Element Method (MNPBEM) based on the boundary element method. The diameter and length of nanorod are 40 nm and 100 nm, respectively. The fraction of Ag in bimetallic Agx, Au(100-x) are 0, 20, 40, 60, 80, and 100 within weight percent. The dielectric function of Ag–Au was generated by linear approximation and the incident angle used from 0 to 90 degrees. We found that the intensity of the extinction curve shows decreasing follow logistic type curve as the incident angle increases whereas the resonance peak is constant. For a given silver fraction in bimetallic Ag-Au, the resonance peak of LSPR shifted to higher energy or blue-shift and the intensity increased. Interestingly, the LSPR of bimetallic Ag–Au occurred in the visible range and the transition mode from longitudinal to transverse mode was observed at the angle greater than 60 degrees.

A Finite Element Model for Temperature Prediction in Laser-Assisted Milling of AerMet100 Steel

Laser-assisted milling (LAM) represents an innovative process to enhance productivity in comparison with conventional milling. The workpiece temperature in LAM not only affects the cutting performance of materials, but also the machined surface quality of the part. This paper presents a 3D transient finite element (FE) model for workpiece temperature prediction in LAM. A moving Gaussian laser heat source model is implemented as a user-defined subroutine and linked to ABAQUS. The thermal model is validated by machining AerMet100 steel under different process parameters (laser power, spindle speed and feed per tooth). Good agreement between predicted and measured workpiece temperatures indicates that the FE model is feasible. In addition, the effects of laser spot size and incident angle on workpiece temperature are analyzed based on the proposed model. This work can be further applied to optimize process parameters for controlling the machined surface quality in LAM.

Design of an ultra-thin magnetic radar absorber embedded with double period frequency selective surface for entire L-band microwave absorption

In this paper, a thin, broadband and low frequency with high absorption (more than 90% absorption) radar absorber (RA) consisting of magnetic-type material substrate and double period frequency selective surface (FSS) is demonstrated. The geometric parameters were investigated for its contribution towards absorption by the finite-difference time domain (FDTD) method. The effects of incidence angles of electromagnetic radiation were also discussed. The simulation indicates that the use of the double period FSS makes a remarkable increase of operational bandwidth and moves the resonant frequency to the lower frequency comparison with single magnetic radar absorption materials (SMRA). Due to the excellent symmetric nature of the proposed structure, the reflectivity is insensitive to incident angle from 0° to 30°. The reflectance of RA lower than -10 dB (over 90% absorption) is obtained in the whole frequency range of L-band which is 1.5 times wider than the bandwidth of the same thickness SMRA when the structure thickness is only 2.62 mm. The simulation method is verified by comparison with the experiment in the literature. Thus, the presented RA breaks the limitation of the thickness (λ/4) for the traditional low-frequency band absorbing material and has wide application prospect in electromagnetic shielding and low-frequency stealth.

Temperature-switchable mode selector in superconducting photonic crystals based on the Thue–Morse sequence

In this paper, a novel one-dimensional superconducting photonic crystal based on the quasi-periodic Thue–Morse (ThM) arrangement is theoretically investigated by the transfer matrix method, which can switch two transmission properties by controlling ambient temperature. Its transmission spectrum realizes omnidirectional photonic band gap (OBG) characteristics in low-temperature zones (about 10 K) and wide-angle broadband absorption characteristics in high-temperature zones (about 90 K) as the whole structure remains the same in the terahertz regime. The intrinsic reason for switchable functions can be ascribed to the superconducting negative permittivity that is dependent on both temperature and frequency under the superconducting state, which causes an OBG corresponding to the zero-averaged (volume) refractive index (zero- n ¯ ) and broadband absorption induced by high permittivity dissipation. From the numerical results, the OBG from the Bragg gap or absorption bandwidth can be notably tuned by manipulating the periodicity of the ThM sequence and dielectric or superconducting thicknesses. The effects of incident angle and polarization modes on the proposed structure are also considered. We report that the proposed structure has a preeminent zero- n ¯ OBG ranging from 0.1 to 1.7 THz at 10 K and stable broadband absorption for a wide angle (at most 70 deg) in TM mode at 90 K, which provides theoretical guidance for the design and application of the temperature-switchable mode selector.

A tailored broadband terahertz metamaterial absorber based on the thermal expansion feature of liquid metal

In this paper, a novel temperature field tailored broadband terahertz absorber is proposed, which consists of the metallic mercury resonance units. When the ambient temperature (T) alters, the mercury can be expanded through the vertebral body channel, middle cross glass cavities, cylindrical hole and fill the upper cross glass cavities of such an absorber, which leads to the absorption bands changed. The simulated results indicate that when T = −30 ℃, the wideband absorption (WBA) regions over 90% can be achieved, which are located at 4.53–5.79 THz and 8.15–9.49 THz, and their relative bandwidths (RBs) are 24% and 15.5%, respectively. If T is increased to 300 ℃, such two WBA areas will move to 2.83–3.39 THz and 5.90–7.74 THz, whose RBs are changed to 18% and 13.3%. To investigate the performance of such an absorber, the effects of incident angle, polarization angle and structural parameters on the absorption are discussed. Similarly, the electric and magnetic field intensity distributions, the surface current distributions, power flow and power loss density of the presented absorber are also given to expound the physical mechanism of absorption. The scheme put forward in this paper will provide a new idea for the study of tunable absorbers.

Measuring Surface Moisture on a Sandy Beach based on Corrected Intensity Data of a Mobile Terrestrial LiDAR

Surface moisture plays a key role in limiting the aeolian transport on sandy beaches. However, the existing measurement techniques cannot adequately characterize the spatial and temporal distribution of the beach surface moisture. In this study, a mobile terrestrial LiDAR (MTL) is demonstrated as a promising method to detect the beach surface moisture using a phase-based Z&F/Leica HDS6100 laser scanner mounted on an all-terrain vehicle. Firstly, two sets of indoor calibration experiments were conducted so as to comprehensively investigate the effect of distance, incidence angle and sand moisture contents on the backscattered intensity by means of sand samples with an average grain diameter of 0.12 mm. A moisture estimation model was developed which eliminated the effects of the incidence angle and distance (it only relates to the target surface reflectance). The experimental results reveal both the distance and incidence angle influencing the backscattered intensity of the sand samples. The standard error of the moisture model amounts to 2.0% moisture, which is considerably lower than the results of the photographic method. Moreover, a field measurement was conducted using the MTL system on a sandy beach in Belgium. The accuracy and robustness of the beach surface moisture derived from the MTL data was evaluated. The results show that the MTL is a highly suitable technique to accurately and robustly measure the surface moisture variations on a sandy beach with an ultra-high spatial resolution (centimeter-level) in a short time span (12 × 200 m per minute).

Effect of surface roughness of optical waveguide on imaging quality and a formula of RSE tolerance and incident angle.

The optical waveguide is a lightweight and portable scheme for augmented reality near-eye display devices. However, the surface roughness of the waveguide affects its imaging performance, which has not been studied. In this work, we investigate the light scattering caused by the root-mean-square roughness of the waveguide surface and present two methods to numerically analyze the modulation transfer function (MTF) of the display system. Here, we consider the effects of different surface roughness, incident angle, and incident wavelength on the scattering distribution when other conditions are constant. For a simplified optical waveguide display system, the MTF degradation and the variation of the tolerance is calculated. And when the MTF (@ 40 cycles/mm) is required to be 0.3 and the incident angles of the total reflection surface are 45°, 55°, 65° and 75°, the random surface error (RSE) tolerances are 0.207λ0, 0.255λ0, 0.347λ0 and 0.566λ0 (λ0=0.5461µm), respectively. We find a formula descripting the relationship between RSE tolerance and incident angle. If the RSE tolerance exceeds the value of the formula at an angle, the imaging quality of the system will drop significantly. The formula can predict tolerances and incident angles and provide basic tool for imaging quality analysis and manufacturing for optical waveguide AR/VR display systems.

Effect of incident angle on ultrasonic transmission in steam flow for use with clamp-on ultrasonic flowmeter

Effect of incident angle on ultrasonic transmission in steam flow for use with clamp-on ultrasonic flowmeter

Effect of incidence angle on fluorescence properties of colloidal infrared quantum dots thin film

胶质红外量子点优异的光学性能使其荧光特性具有广泛的应用前景，在实际应用中通常需要封装成薄膜形态以保持稳定的荧光特性。然而，分散形式的改变可能会导致量子点荧光效率降低以及荧光角度特性变化。因此，建立了红外量子点荧光强度探测系统，对胶质红外量子点薄膜在不同角度激发光入射时产生的荧光分布情况进行研究。实验及分析结果表明，激发光与样品表面夹角大小在10°～170°之间的较大范围内入射时，在反射及透射荧光区域均可探测到荧光峰值强度70%～80%以上的荧光出射，在这一范围内的反射荧光与透射荧光强度差异和荧光强度随激发光入射角度的变化规律分别与样品中量子点的浓度以及分布形态有关。同时，随着入射激光能量的增强，样品出射荧光强度对于入射角度变化的“平坦”范围进一步扩大。

Integrating Incidence Angle Dependencies Into the Clustering-Based Segmentation of SAR Images

Synthetic aperture radar systems perform signal acquisition under varying incidence angles and register an implicit intensity decay from near to far range. Owing to the geometrical interaction between microwaves and the imaged targets, the rates at which intensities decay depend on the nature of the targets, thus rendering single-rate image correction approaches only partially successful. The decay, also known as the incidence angle effect, impacts the segmentation of wide-swath images performed on absolute intensity values. We propose to integrate the target-specific intensity decay rates into a nonstationary statistical model, for use in a fully automatic and unsupervised segmentation algorithm. We demonstrate this concept by assuming Gaussian distributed log-intensities and linear decay rates, a fitting approximation for the smooth systematic decay observed for extended flat targets. The segmentation is performed on Sentinel-1, Radarsat-2, and UAVSAR wide-swath scenes containing open water, sea ice, and oil slicks. As a result, we obtain segments connected throughout the entire incidence angle range, thus overcoming the limitations of modeling that does not account for different per-target decays. The model simplicity also allows for short execution times and presents the segmentation approach as a potential operational algorithm. In addition, we estimate the log-linear decay rates and examine their potential for a physical interpretation of the segments.

Optical Properties of Porous Alumina Ceramics with Micron Open Cells

Porous ceramic material is widely used in a great deal of fields. In this work, porous alumina ceramics with micron open cells are modeled by applying the inverse opal structure. The considered porous alumina ceramics are periodic with different size parameters. The diameters of spherical pores are 200, 400, 600, and 800 nm, while the ratios of height to diameter range from 0.1 to 0.9. The absorptivity, transmissivity, and reflectivity for the wavelength range from 0.2 to 2 μm are calculated using the finite difference time domain (FDTD) method. Then the effects of size parameters and incident angle on the optical properties are discussed. The results show that the absorptivity is usually very small. For the transmissivity, a wide dip in the transmission spectrum appears when the diameter and height exceed the critical values, and a red shift of the transmission spectrum's wide dip with increasing height is observed. When the incident wavelength is longer than the critical wavelength, the spectral transmissivities of porous ceramics with a certain diameter reach a stable domain. Moreover, the red shift of the wide dip, the critical incident wavelength, and the critical ratio of height to diameter are visibly affected by the size parameters and the incident angle.