Effect Of Incidence Angle Research Articles

Effects of incident angles of earthquake sequences on seismic demands of structures

Numerous aftershocks can be triggered by a strong mainshock and may cause more severe and widespread structural damage with respect to a single seismic event. This study investigates the effect of relative differences between the incident angles of consecutive earthquakes on seismic demands of structures as bi-linear Single-Degree-Of-Freedom (SDOF) systems. To this aim, constant-strength spectra are developed based on different Normalized Engineering Demand Parameters (NEDPs) to identify this impact as a new seismic uncertainty. Several seismic sequences with one aftershock and also two aftershocks are generated considering different directions of both mainshocks and subsequent aftershocks as input excitations in nonlinear dynamic analyses of SDOF systems. The results demonstrate that taking into account the relative differences of the incident angles of sequential earthquakes can affect significantly seismic responses.

Tunable filter based on the 1D photonic crystal within ultraviolet radiations

In the present study, we develop a one-dimensional semiconductor photonic crystal to control ultraviolet radiation. We study the transmittance spectra of incident light on the proposed structure in the ultraviolet regime. A photonic bandgap appears with a width of 95.2 nm. by changing the thickness parameters, it can reach up to 125.6 nm with appearing of new band gaps. The incident angle effect on the band gap’s width is apparent. The bandgap shifted to a lower wavelength region. So the proposed structure could be useful in preventing UV radiation from passing through it.

A New Transient-Based Earth Fault Protection System for Unearthed Meshed Distribution Networks

This paper deals with the protection against earth faults in medium voltage meshed networks with unearthed neutral. A communication-supported protection system is proposed and assessed through numerical simulations. The protection system is based on the use of directional relays installed at both ends of each line of the network. Each relay communicates by sending permissive signals following the so-called directional comparison overreaching transfer trip scheme. Each directional relay implements a new transient fault detection algorithm based on the angle between the zero-sequence voltage and current phasors. The phasors are estimated at the dominant frequency of the network transient-response within the first milliseconds after the fault, which range can be evaluated by means of a simplified circuit equivalent representation. The performances of the protection system and the detection algorithm are evaluated for different network configurations. By using a specifically developed co-simulation tool that interfaces EMTP-RV with Matlab, the influence of the communication latency is also analyzed. A Monte Carlo method is applied to analyze the effects of fault resistance, incidence angle and fault location variations. Results of a real-time simulation obtained in the Opal-RT environment further support the applicability of the algorithm.

Radiometric Calibration for Incidence Angle, Range and Sub-Footprint Effects on Hyperspectral LiDAR Backscatter Intensity

Terrestrial hyperspectral LiDAR (HSL) sensors could provide not only spatial information of the measured targets but also the backscattered spectral intensity signal of the laser pulse. The raw intensity collected by HSL is influenced by several factors, among which the range, incidence angle and sub-footprint play a significant role. Further studies on the influence of the range, incidence angle and sub-footprint are needed to improve the accuracy of backscatter intensity data as it is important for vegetation structural and biochemical information estimation. In this paper, we investigated the effects on the laser backscatter intensity and developed a practical correction method for HSL data. We established a laser ratio calibration method and a reference target-based method for HSL and investigated the calibration procedures for the mixed measurements of the effects of the incident angle, range and sub-footprint. Results showed that the laser ratio at the red-edge and near-infrared laser wavelengths has higher accuracy and simplicity in eliminating range, incident angle and sub-footprint effects and can significantly improve the backscatter intensity discrepancy caused by these effects.

The electromagnetic wave modulation based on single-frequency reflection in absorption with angle stability of hyperbolic metamaterials

In this paper, the hyperbolic metamaterials (HMs) based on the one-dimensional (1D) plasma photonic crystals is proposed, whose dielectric constant and group index can be obtained through the effective medium theory. By adopting an improved Thue–Morse sequence structure and using the transfer matrix method, the tunable single-frequency reflection in absorption (SFRA) with angle stability is achieved. The effects of incident angle, filling rate, and plasma collision frequency on the refractive index of HM and the SFRA are also analyzed respectively. The simulated results show that the incident angle makes no difference in the frequency position of the SFRA. However, a larger filling rate means that SFRA will move quickly to the lower frequencies, and the greater plasma collision frequency indicates that SFRA will appear in the higher frequencies. The better performance of SFRA can be realized in the cases of a smaller filling rate, plasma collision frequency, and θ (less than 60°). When the incident angle is about 60°, a perfect single-frequency reflection in the absorption region can be found for the transverse magnetic wave. These computed results can provide ideas for designing the new angle stability anti-dispersion waveguide structures, single-frequency filter with reflection, and absorber.

LASER RANGING MODELING UNDER GENERALIZED MIXED PIXELS EFFECT

Abstract. When a target lies on discontinuous surfaces, the footprint of a laser rangefinder covering multiple ranges causes mixed pixels effect and significantly distorts the ranging quality. Meanwhile, the ranging error of incidence angle effect is triggered by a deformed footprint containing various ranges as well. Based on the commonality of causing ranging errors within one footprint, this study proposed an approach to tackle “generalized mixed pixels effect” correcting ranging errors involving in deformed footprint cases. Errors caused by generalized mixed pixels effect vary in rangefinders and are difficult to be uniformly treated. A correction model was formulated through integrating individual effects by considering the physical and geometrical aspects of laser ranging. An adjustment procedure was followed to estimate the parameters of the correction equation taking all observation uncertainties into account. To analyze the individual effects and eventually combine them into a complete model, a five-case workflow has been developed. Firstly, a divergence angle estimation method was presented to eliminate the mixed pixels effect by a decentering approach. Incidence angle effect was modeled and parameter was estimated by adjustment techniques. Particularly, since incidence angles are usually unknown in field surveys, an iterative estimation procedure was designed to obtain the optimal incidence angle of target points. Finally, offset correction accounting for generalized mixed pixels effect was formulated. Through the experimental tests on Trimble M3 DR 2” and Topcon GPT-3002LN, it is confirmed that the proposed method effectively resolves the ranging errors and preserves the ranging quality under generalized mixed pixels effect.

INFLUENCE OF RANGING UNCERTAINTY OF TERRESTRIAL LASER SCANNING ON CHANGE DETECTION IN TOPOGRAPHIC 3D POINT CLOUDS

Abstract. Terrestrial laser scanners are commonly used for remotely sensing natural surfaces into 3D point clouds. Time series of such 3D point clouds can be analysed to gain information of surface changes that are induced by Earth surface shaping processes. The atomic unit in time series analysis is a bitemporal change detection and quantification. This should involve an estimation of the minimum quantifiable change, the Level of Detection, to separate signal from noise, e.g. stemming from the measurement. To enable such an estimation through error propagation, a model of the sensing instrument’s measurement uncertainty is required. In this work, we present an investigation on the ranging component of terrestrial laser scanning on this uncertainty and its influence on 3D distances between point clouds of two epochs. Specifically, we analyse the effects of incidence angle, intensity and range for different object materials, and make additional considerations with respect to waveform information returned by the sensor. We estimate a model for the rangefinder uncertainty of a terrestrial laser scanner and apply it on experimental data. The results show that using a sensor-specific model of ranging uncertainty allows an appropriate estimation of the Level of Detection. At a range of 60 m and a rotational displacement of 10°, this Level of Detection ranges between 0.1 mm to 1 mm for a white and a grey surface and up to 5 mm for a black surface. The completeness of the detection of significant change ranges from 60.2 % (black) to 89.8 % (grey) for the proposed method and from 65.5 % to 88.9 % for the baseline, when compared to tachymeter measurements. The similarity between the results is expected and suggests the validity of error propagation for the derivation of the Level of Detection.

Closed-form formulas, zero RCS and Brewster angle conditions for interface of two different chiral media

This paper investigates the behavior of an electromagnetic plane wave when it makes incidence with the interface of two different chiral media. The incident fields are right and left circularly polarized waves. The reflected and transmitted fields have the both co- and cross-polarized (with respect to the incident polarization) components, because of optical activity existence in chiral medium. Analytical closed-form formulas are presented for the reflection and transmission coefficients. Next, conditions that lead to Brewster angles are presented for the right and left circularly polarized excitations. Finally, the effects of incident angle, chirality parameters and permittivity of the chiral media are analyzed; also finite element method is used to validate the investigation.

Study on Propagation Characteristics of Obliquely Incident Terahertz Wave in Non-Magnetized Plasma

A transmission model of THz wave in non-uniform and magnetized plasma is established. Based on the analysis of transmission characteristics in Gaussian and uniform plasma environments, theoretical simulations are performed using the continuity conditions of the electric and magnetic fields at the boundary of each layer. The effects of collision frequency, electron density and incident angle on the attenuation of THz wave energy are mainly discussed. The attenuation of the THz wave by the collision frequency does not change monotonously, and the optimal frequency needs to be selected according to the actual situation. THz wave attenuation increases with increase of electron density. And the THz wave attenuation decreases with the increase of the incident angle. Vertical incidence can be used as a means to alleviate the “communication blackout”. The conclusions of this paper provide a good theoretical basis and relevant parameter references for alleviating the “communication blackout” problem.

Modulation and Control Technology for Generating Movable Super-Diffraction Optical Needle by Oblique Incidence

The movable super-diffraction optical needle (MSON) is a tightly focused beam like a “needle”, which can realize vector scanning on the focusing plane. Not only does it have a long focal depth, but its resolution also exceeds the diffraction limit. The modulation and control technology required for generating MSON by oblique incidence is explored in this manuscript for the purpose of processing high-aspect-ratio, sub-wavelength structures. As the optical needle generated by traditional methods is static and sensitive to variation of the angle information of the incident beam, here we introduce a confocal scanning system by using a two-dimensional galvanometer system, a scan lens, and a tube lens to control the oblique incidence angle. The effects of the oblique incidence angle on the resolution, depth of focus, uniformity, and side lobes of the MSON were analyzed. Further, the voltage-controlled liquid crystal located between the scan lens and the 2D galvanometer system can be used to compensate for the additional phase difference caused by oblique incidence. The aspect ratio is defined as the ratio of depth of focus to resolution. By modulating and controlling the light field, the MSON with high aspect ratio (7.36), sub-diffractive beam size (0.42λ), and long depth of focus (3.09λ) has been obtained with homogeneous intensity, and suppressed side lobes. High speed, high axial positioning tolerance, and high-resolution laser processing can also be achieved, which removes the restrictions presented by traditional laser processing technology, for which high resolution and long depth of focus cannot be achieved simultaneously.

Anderson localization mode selector based on disordered dielectric photonic crystal

In this paper, we investigate numerically the effect of incident angle on Anderson localization of TE and TM modes, in disordered dielectric photonic crystal. The results show that, depending on the wavelength, increment of disorder strength can either increase or decrease the localization length. Moreover, in the case of oblique incidence and especially at Brewster’s angle, for a wavelength at the end of photonic band gap (PBG), a great difference between the localization length of two polarizations can be observed. This property enables construction of polarization mode selector based on Anderson localized photonic crystal.

Analysis of Oil Droplet Deposition Characteristics and Determination of Impact State Criterion in Aero-Engine Bearing Chamber

The research of oil/air two-phase flow and heat transfer is the fundamental work of the design of lubrication and heat transfer in aero-engine bearing chamber. The determination of impact state criterion of the moving oil droplets with the wall and the analysis of oil droplet deposition characteristics are important components. In this paper, the numerical analysis model of the impact between the moving oil droplet and the wall is established by using the finite volume method, and the simulation of oil droplet impingement on the wall is carried out. Then the effects of oil droplet diameter, impact velocity, and incident angle on the characteristic parameters of impact state are discussed. The characteristic parameters include the maximum spreading length, the maximum spreading width, and the number of splashing oil droplets. Lastly the calculation results are verified through comparing with the experimental results in the literature. The results show as follows: (1) The maximum spreading width of oil droplet firstly increases and then slows down with the incident angle and the oil droplet diameter increasing; (2) when the oil droplet diameter becomes small, the influence of the incident angle on the maximum spreading length of oil droplet is obvious and vice versa; (3) with the impact velocity and diameter of oil droplet increasing, the maximum spreading width of oil droplet increases firstly and then slows down, and the maximum spreading length increased gradually; (4) the number of splashing oil droplets increases with the incident angle and impact velocity increasing; and (5) compared with the experimental data in literature, the critical dimensionless splashing coefficient K c proposed in this paper can better distinguish the impact state of oil droplet.

Mapping sea-ice types from Sentinel-1 considering the surface-type dependent effect of incidence angle

AbstractAutomated classification of sea-ice types in Synthetic Aperture Radar (SAR) imagery is complicated by the class-dependent decrease of backscatter intensity with Incidence Angle (IA). In the log-domain, this decrease is approximately linear over the typical range of space-borne SAR instruments. A global correction does not consider that different surface types show different rates of decrease in backscatter intensity. Here, we introduce a supervised classification algorithm that directly incorporates the surface-type dependent effect of IA. We replace the constant mean vector of a Gaussian probability density function in a Bayesian classifier with a linearly variable mean. During training, the classifier first retrieves the slope and intercept of the linear function describing the mean value and then calculates the covariance matrix as the mean squared deviation relative to this function. The IA dependence is no longer treated as an image property but as a class property. Based on training and validation data selected from overlapping SAR and optical images, we evaluate the proposed method in several case studies and compare to other classification algorithms for which a global IA correction is applied during pre-processing. Our results show that the inclusion of the per-class IA sensitivity can significantly improve the performance of the classifier.

Investigation of graphene fractal frequency selective surface loaded terahertz absorber

The voyage of the research in terahertz (THz) technology has an intriguing application in terahertz detection, and the graphene absorbers have dramatically enhanced the effectivity, and the efficiency in its performance. Though, there is a need of wide angle insensible, polarization angle insensible, broadband terahertz metamaterial absorber (TMA) with reduced design complexity. Hence, in this research an effort has been carried out to develop such TMA with equivalent circuit modelling approach. A massive − 10 dB reflection coefficient (RC) bandwidth of 2.66 THz (1.08–3.74 THz) has been obtained by the proposed TMA device with two significant peaks of − 19.48 dB and − 14.5 dB at 1.32 THz and 3.44 THz, respectively. The oblique incidence stability of the device has been verified by investigating the effect of wave incidence angle, and wave polarization angle in RC characteristic. Further, the physics behind the absorption has been systematically illustrated along with three different absorption mechanism, i.e., input-impedance matching mechanism, wave interference phenomena, and induced current model, that attest the Unprecedented absorption results. Moreover, the electrical parameters of the device (i.e., effective electric permittivity, and effective magnetic permeability) have been extracted to analyze the metamaterial behavior of the device. The results are good enough to explore the potential of the TMA for THz sensing applications.

Low-Cost 1-D Beam-Steering Reflectarray With ±70° Scan Coverage

In this communication, a novel low-cost reflectarray mechanism combining feed displacement and reflectarray panel in-plane rotation is introduced to realize 1-D ±70° beam scan coverage. A subwavelength multiresonance reflectarray element is designed to suppress the grating lobe and provide an adequate phase range over 360°. The spatial-domain phase-matching method (PMM) is applied in the wide-scanning reflectarray synthesis process. Meanwhile, effects of both incident and reflection angles are taken into consideration during the optimization. A 640-element mechanical beam-scanning reflectarray operating at 12 GHz has been designed, analyzed, and fabricated. The measured gain of the designed reflectarray is 26.2 dBi at 12 GHz when the main beam scans to the broadside direction, corresponding to an aperture efficiency of 42.5%. Meanwhile, the measured gain variations of the designed reflectarray are 3.1 and 4.9 dB for scan ranges of ±60° and ±70°, respectively. The lost-cost wide-scanning characteristic of the designed reflectarray makes it suitable for many applications, especially commercial tracking platforms.

Experimental study on wind force coefficient of a truss arch tower with multiple skewbacks

A truss arch tower is a large-span arch structure with multiple skewbacks. This tower is made of a large number of members with unique form, and contains more than five kinds of geometric features. The wind forces and the corresponding wind effects on the truss arch tower are notably complicated. In this study, wind tunnel tests were conducted to evaluate the wind forces on the steel latticed structure mentioned above using the high-frequency base balance technique. Four segmental models, including one arch foot of main truss, two arch feet of sub-truss, and one arch crown of main truss were tested in nominally smooth flow. The drag forces were measured and compared with several existing codes, including the British, American, and Chinese codes. The incidence angle effects and the interference effects on the drag coefficient were analyzed. The testing results showed that the direction of the wind forces has a marked effect on the whole truss tower. The solidity ratio and layout of the segmental models, including the cross-section and the centerline of the members, have critical effects on the drag forces.

Seismic collision potential of adjacent base-isolated buildings with corridor bridges subjected to bidirectional near-fault pulse-like ground motions

Adjacent base-isolated buildings with corridor bridges have a large seismic displacement demand in their isolation layer, and therefore are prone to collision. Moreover, seismic wave incidence angles may have a great impact on their seismic collision response, especially for near-fault ground motions that may exhibit strong directionality dependence. This paper studies the impact of seismic wave incidence angle and near-fault pulse effect on seismic collision potential of adjacent buildings connected by corridor bridges, retrofitted with base isolation. Two adjacent-building systems are established in OpenSees to facilitate analyses. One is a base-isolated (BI) building system adopted as the baseline model, each building of which consists of lead-rubber bearings (LRB) and ordinary-rubber bearings (LNR). The other one is a base-isolation-with-damper (BID) system, where two additional groups of viscous dampers were added to the isolation layers of BI system. The first group of dampers is used to connect the buildings in order to reduce their out-of-phase motion. The second group of dampers is placed at the base of individual buildings to dissipate seismic energy. The effectiveness of using the dampers of the BID results against the BI baselines was compared. A collision potential index D was proposed to quantify the collision potential of the adjacent base-isolated buildings. The research shows that, the seismic wave incidence angle has a great influence on the building collision potential, which does not necessarily be greatest in the maximum pulse direction. Using dampers may not be useful for reducing building deformation demands, but can effectively coordinate the asynchronous movement of adjacent buildings, reducing the potential of seismic collision. Finally, the Pseudo-Spectral Acceleration (PSA) based on the isolation periods of the buildings was shown to correlate well with the index D, which can be used as the pair of seismic Intensity Measure (IM) and Engineering Demand Parameter (EDP) to describe the collision potential between adjacent base-isolated buildings with corridor bridges.

Wave motion over stratified porous absorber combined with seaward vertical barrier

The oblique wave reflection by horizontally stratified porous absorber having two horizontal porous bars of different porosities and friction factors placed on step-type bottom is studied using eigenfunction expansion method based on linearised wave theory. The present study examines several structural configurations such as porous absorber consisting of finite and semi-infinite thickness with/without seaward vertical barrier. The present study derived the direct analytical relations to determine wave reflection by each of the structural configuration for plane-wave assumption using potential flow theory. Initially, the porous absorber considering uniform porosity and friction factor is examined and validated with available numerical results, and the direct analytical relations are also validated with available relations of possible structural configurations. In addition, the present study reported wave reflection performance of submerged single-layer and double-layer porous absorbers with/without seaward vertical barrier. The effect of bottom rigid bar, surface porous bar, middle porous bar depth, multiple porosities, friction factors, incident wave angle and porous effect parameter on wave reflection coefficient is presented in detail for various structural configurations. The significance of seaward vertical barrier on wave reflection and wave trapping is reported. The point of wave trapping, critical angle of impinging, resonating peaks and troughs due to various structural configurations are presented against structural thickness.

Exploring the effect on the columnar structure and porosity of the synthesized Be films by oblique angle deposition in magnetron sputtering

A Kinetic Monte Carlo (KMC) simulation regarding the growth mechanism of oblique angle deposited Be film using magnetron sputtering was performed. We have analyzed the columnar nanostructure, layer density and porosity of generated film under the effect of incident angle and working pressure. Our results suggest that the incident angle of 60° is a demarcation point for the film morphology—the particle number captured by the substrate and the film porosity increase as the working pressure increases when the incident angle is below 60°, while the trend is in the opposite direction when the incident angle varies in the range of 60°–90°. Furthermore, we find that the increasing pressure can work on the decrease of the porosity in film under large angle deposition. The findings indicate that it is feasible to obtain Be film with specific columnar structures and porosity, which has theoretical significance on the experimental preparation of Be films.

Design and thermodynamic analysis of a novel solar CPV and thermal combined system utilizing spectral beam splitter

A novel solar concentrating PV and thermal (CPVT) combined system with beam splitter and compact concentrator structure is proposed in this study. The system structure and its design method are provided. The optical filter is designed and the incident light angle effect on the beam splitting performance is investigated. Solar concentrating simulations are conducted and the relevant results reveal that the CPVT combined system can provide a high solar concentration uniformity. The evaluation results of configuration and optical analyses indicate that when all the other parameters are settled, the optimal installation height of the solar receiver tube is 923.0 mm. The influence study of sun tracking accuracy on the system optical performance is launched. It is concluded that when the tracking error increases to 1.0°, the overall optical efficiency is 66.2%. The thermodynamic analysis results indicate that the PV conversion and overall energy efficiencies of the CPVT system are 30.5% and 26.6%, which are both higher than those of the normal CPV system. Moreover, the operating temperature effect investigation of solar thermal receiver tube is conducted. The results show that an optimal solar thermal receiver tube temperature (356.0 °C) exists, which can result in the maximum total output power.