Different Angles Of Incidence Research Articles

ILD silicon tungsten electromagnetic calorimeter first full scale electronic prototype

The “long slab” is a new prototype for the SiW-Ecal, a silicon tungsten electromagnetic calorimeter for the International Large Detector (ILD) at the future International Linear Collider (ILC). The new prototype has been evaluated with cosmics, radioactive sources and with 3 GeV electrons in beam tests at the DESY facility, Hamburg. A channel-wise calibration has been achieved, at different angles of incidence of the beam on the sensors. Using data collected at non-normal incidence, the signal of particles traversing adjacent pixels were used to estimate the absolute value of the trigger threshold in units of mips. This new prototype provides us many hints on how to improve the design of the front-end electronics. It is also a convenient tool to estimate the critical characteristics of ILD SiW-Ecal (like power consumption, cooling, readout time, etc.) and to optimise the future design of the detector.

Investigating the predictive capacity of Eulerian CFD to model long-duration blast loads on finite cross-section geometries

Typically defined by positive pressure durations over 100ms, long-duration blasts can generate dynamic pressures (blast winds) capable of exerting damaging drag loads on slender structural elements such as columns. With limited availability of appropriate drag coefficients for specific structural geometries or different section orientations, Computational Fluid Dynamics (CFD) can provide a valuable tool for calculating blast interaction and loading on user-specified geometries. Commercially available CFD programs or ‘hydrocodes’ with shock wave modelling capabilities remain based on solving the inviscid Euler equations. The ability to analyse long-duration blasts is still not confidently offered however, with no prior studies examining the accuracy of modelling interaction with relatively much smaller, finite geometries. This remains particularly challenging due to large wavelengths and time durations inherent to long-duration blasts, usually limited by impractical solution domains and computing resource. This paper presents a comparative investigation between numerical simulations and experimental results to assess the predictive capability of Eulerian CFD as a tool for calculating long-duration blast drag loading on an intricate I-section geometry from different angles of incidence. Calculated pressure-time histories on exposed geometry surfaces demonstrated good agreement although reduced accuracy and under-prediction occurred for shielded surfaces manifesting as overestimated net translational loading. Numerical discrepancies were attributed to the inviscid Euler equations underpinning the CFD solver, limiting accuracy when resolving complex aerodynamic flows at bluff I-section orientations. Results of this study provide new understanding and awareness of the numerical capability and limitations of using CFD to calculate long-duration blast loads on intricate geometries.

Interaction of an Electromagnetic H Wave with a Thin Metal Film on a Dielectric Substrate in the Case of an Anisotropic Fermi Metal Surface

The interaction of an electromagnetic H wave with a thin metal film has been calculated with allowance for the ellipsoidal Fermi surface and constancy of the electron mean free path for different angles of incidence of the electromagnetic wave θ and different coefficients of specular reflection q1 and q2 at reflection of electrons from the film surfaces. The metal film is between two media with permittivities e1 and e2. The dependences of reflectance R, transmission T, and absorption A on the effective mass of conduction electrons have been analyzed.

Realization of Epsilon-Near-Zero Metamaterial Stack Based on Dielectric-Semiconductor-Metal Multilayers

The epsilon-near-zero (ENZ) metamaterials are designed theoretically based on multilayer nanostructure stack with three sublayers (in each period) in the visible range for transverse magnetic mode at normal and transverse electric mode at oblique incident lights. The sublayers can be either metal, dielectric, or semiconductor materials. The effective permittivities of the multilayer metamaterial stacks are derived based on the optical nonlocality analysis that expand via the Bloch theory and transfer matrix method. Multilayer metamaterials based on dielectric-semiconductor-metal (DSM) including Al2O3 − Ge − Ag triple layers are considered to study their unique optical properties and determine the ENZ wavelengths at visible frequencies. Furthermore, the propagation properties of terahertz (THz) waves passing through the DSM multilayer stacks have been theoretically investigated by calculating transmission, reflection, and absorption spectra at different angles of incidence. The electric field distribution and absorption results show that the optical loss can be reduced and kept under control in multilayer metamaterial stacks. The result of reflection and transmission indicate that the DSM multilayer stacks can be introduced as a band-pass filter, and various conditions are considered for optimal filtering. In addition, it is shown that the number of depth in reflection spectra (peak in transmission spectra) increases by increasing the number of triple layers in the structures which perfectly matches with the frequencies that satisfy the Bragg’s law. All analytical results are in good agreement with the results obtained from numerical simulations.

An ultrathin and broadband radar absorber using metamaterials

In this article, the design, simulation, fabrication and measurement of an ultrathin and wide band radar metamaterial absorber (MMA) are introduced. The unit of the MMA consists of two different sizes of L-shaped structure and a perfect electric conductor separated by 2 mm dielectric layer (only 0.074 to 0.156 at lowest and highest frequencies, respectively). The simulation results show that the proposed MMA has more than 90% good absorption (below −10 dB) in the frequency range of 11.07–23.36 GHz. By adjusting the scale of the unit, the absorption characteristics of the proposed absorber can be adjusted and moved to the frequency range which we are interested in. The absorption mechanism of the proposed absorber is also analyzed by field and surface current distributions. The proposed absorber has been fabricated and experimentally tested for absorbing properties at different angles of incidence and different polarizations. The experimental results show the absorption rates are consistent with the simulation results. The proposed absorber has potential applications in stealth technology.

Response of box-type structure and effect of structural parameters on reflected pressure under blast load

The study presented herein includes finite element analysis of a box type structure subjected to blast loading using the coupled Eulerian-Lagrangian methodology to investigate the structural response. A comparative assessment of structural response observed from coupled Eulerian-Lagrangian and Unified Facility Criteria guidelines is presented. Furthermore, the effect of the structural parameters on reflected overpressure for different angle of incidence has been investigated and compared with that given in the Unified Facility Criteria. It is observed that the structural parameters significantly affect the reflected overpressure. The Unified Facility Criteria overestimates the response of structure in a certain region of angle of incidence while it underestimates the reflected pressure in the rest region of the angle of incidence.

Generalized Brewster Angle Effect in Thin-Film Optical Absorbers and Its Application for Graphene Hydrogen Sensing.

The generalized Brewster angle (GBA) is the incidence angle at polarization by reflection for p- or s-polarized light. Realizing an s-polarization Brewster effect requires a material with magnetic response, which is challenging at optical frequencies since the magnetic response of materials at these frequencies is extremely weak. Here, we experimentally realize the GBA effect in the visible using a thin-film absorber system consisting of a dielectric film on an absorbing substrate. Polarization by reflection is realized for both p- and s-polarized light at different angles of incidence and multiple wavelengths. We provide a theoretical framework for the generalized Brewster effect in thin-film light absorbers. We demonstrate hydrogen gas sensing using a single-layer graphene film transferred on a thin-film absorber at the GBA with ∼1 fg/mm2 aerial mass sensitivity. The ultrahigh sensitivity stems from the strong phase sensitivity near the point of darkness, particularly at the GBA, and the strong light–matter interaction in planar nanocavities. These findings depart from the traditional domain of thin films as mere interference optical coatings and highlight its many potential applications including gas sensing and biosensing.

Seismic analysis of offshore platforms subjected to pulse-type ground motions compatible with European Standards

Offshore platforms used for petroleum and natural gas exploration and production are important structures which are subjected to different types of environmental loadings. Wave and wind loads generally control the design of these special structures worldwide, while earthquake loads seem to play a secondary role. However, many offshore platforms have been constructed in seismic-prone areas and in this case their seismic performance should be examined in depth. In the past, various studies have examined the seismic response of offshore platforms but these investigations are usually focused on far-field earthquakes and much less on near-fault pulse-like ground motions. Furthermore, most of the aforementioned published works adopted two-dimensional structural models neglecting not only the three-dimensional character of these important structures but also the effect of incidence angle of seismic waves. Additionally, only a few studies have investigated the nonlinear behavior of offshore platform either examining material nonlinearities or geometric ones but the simultaneous consideration of these two discrete nonlinearities has rarely been applied. Finally, most of the previous studies have ignored the flexibility of soil and its effect on platforms’ dynamic response without considering soil-structure or soil-pile-structure interaction phenomena. Even in the case where the aforementioned interactions were taken into account, the soil behavior was usually assumed as linear. In order to exceed all the above-mentioned limitations and restrictions, this paper examines the seismic response of three dimensional offshore platforms subjected to near-fault ground motions with distinct pulses, taking also into account the pile-soil-structure interaction effects. Two models of offshore platforms, one with completely fixed supports and one corresponding to pile foundations, are investigated taking into account the material and geometric nonlinearities for soil and superstructures. It is worth-noticing that the design of these platforms satisfies the provisions of Eurocode 8 as well as the 5% damped linear acceleration response spectra of the aforementioned seismic pulses are closely follows the design spectrum of Eurocode 8. This study also examines the impact of different angles of incidence of seismic records on the maximum response of platforms. Finally, the role of fault mechanism on the response of the platform is investigated for the first time, examining reverse/oblique-reverse as well as strike-slip seismic faults.

POSIBILITY OF CREATING A PRINTED SINGLE-LAYER TRANSREFLECTOR WITH INCREASED PHASE EFFICIENCY

A new type of single‑layer transrefleсtor structure based on microstrip reflective antenna array is described. The developed device is a single‑layer printed circuit board on one side of which a system of printed reflectors is located, and on the other is a polarization structure consisting of parallel metal conductors, in contrast to a microstrip reflectarray antenna. The shape and geometrical dimensions of printed reflectors arranged in a rectangular or hexagonal (triangular) pattern are chosen in such a way that they transform a spherical front of an incident vertically polarized electromagnetic wave into a flat front of reflected wave. In the case of irradiation of the developed transreflector with a horizontal polarization wave, the printed structure makes minimal electromagnetic energy loss during its passage. The results of characteristics modeling (including phase curves) of an element of the reflective lattice in the W‑band for different angles of incidence of the wave on the planar structure under study are given. Based on the results obtained, the sizes of the reflective elements of the transreflector, which provide for the correction of the incident wave with the necessary phase discrete, are determined and an electrodynamic model of the transreflector antenna is built. The simulation of the main radiation characteristics of the antenna with the developed single‑layer transreflector was carried out.

Multi-Criteria Assessment of Physical Properties of Nanostructured Decorative Protective Coatings

One of the most efficient methods of improving the durability of a product is applying different coatings to the working surface. The quality of decorative and protective coatings is determined by the quality of workpiece surface (roughness, texture, etc.), preparation of workpiece surface (contamination, presence of oxide films, degree of surface activation by ion etching), and the production methods. The article presents the results of a series of experiments in creating multi-component ion-plasma coatings by vacuum deposition on Ti-Al basis. A series of experiments aimed at obtaining single-layer coatings have been carried out using a certain pattern of sputtering in argon and nitrogen environment. The obtained coatings can have a wide variety of colors. Different properties of the created coatings including spectral characteristics, reflection coefficient at different angles of incidence of light as well as chemical composition have been studied. The energy-dispersive electron microprobe analysis revealed the dependence of coating reflection coefficient and spectral characteristics on the chemical composition.

Assessing light absorption contributions in thin periodically-textured silicon absorbers under oblique illumination

Periodic texturing is one of the main techniques to enhance light absorption in thin-film solar cells. The presence of periodicity, such as grating, allows the excitation of guided modes in the structure, thus enhancing absorption. However, grating efficiency in exciting guided modes is highly dependent on the wavelength and incident angle of light. This is relevant especially in solar cells application, where the light source – the sun – is broadband and largely angle-dependent. Nevertheless, most of literature only focuses on the frequency response of periodic texturing, thus neglecting the effect of angular movement of the sun. In this work we use Fourier expansion to calculate the absorption of each type of mode (guided and non-guided) in an absorptive periodic waveguide. The structure is illuminated with TM and TE polarized light and under three different incident angles. Using this method, we are able to calculate the contribution of a guided resonance to total absorption for different angles of incidence. The work here developed and supported by rigorous numerical calculations can be used to better understand light propagation in a periodic waveguide structure, such as thin-film solar cells.

Angular dependence in light propagation through silver material based ultra-compact photonic crystal

This paper presents the light propagation efficiency in ultra-compact photonic crystal (UCPC) of silver (Ag) material filled with square air background in periodical lattice structure. In different angles of incidence θ, we extremely investigate the effect exerted by the angular selective in modifying the optical properties of reflection, transmission and absorption spectra. To this aim, we applied the finite-differential time-domain (FDTD) simulations under Lumerical FDTD Solutions; the broadband fixed angle source technique (BFAST) which is based on the split-field FDTD algorithm was selected for the plane wave source injection. This allows to standardize all the interested wavelengths by having the same incident angle and therefore avoided the wavelength dependence issues. It revealed that the increase of reflection is satisfied by incidence angle θ<π/4 rad and wavelength λ > 550 nm. In this spectral range, similar trends of reflection are seen in lower angles of incidence. The transmission is approximately 50% far to the unity due to the high reflection backed and describes divergent features to those of reflection. Addition in layers avoids high reflection, optimizes the field transmitted and enhances significantly the absorption over the Ag UCPC. The optimization of transmission is either occurs with increase in angle of incidence. Consequently, these characteristics opening the way to ensure that such structure may act as filter in electromagnetic light propagation with respect to the position of the angle of incidence and the size of the thickness.

Phase sensitive measurement of the wavelength dependence of the complex permittivity of a thin gold film using surface plasmon resonance

We report on a new method for measuring the wavelength dependence of the complex permittivity of a thin gold film of a surface plasmon resonance (SPR) structure comprising a gold-coated SF10 slide with an adhesion film of chromium attached to an SF10 glass prism. The method is based on spectral interferometry and utilizes a setup with a birefringent crystal and the SPR structure in the Kretschmann configuration, in which channeled spectra are recorded and from them, the phase functions of the SPR for air at different angles of incidence are retrieved. The SPR phenomenon is manifested as an abrupt phase change with respect to the reference phase difference for the interference resolved with the SF10 glass prism alone. The phase changes for different angles of incidence are processed in the vicinity of the resonance wavelengths to obtain the real and imaginary parts of the complex permittivity in a wavelength range from 530 to 850 nm or equivalently, the parameters of a modified Drude-Lorentz model. This research, to the best of the authors’ knowledge, is the first demonstration of spectral interferometry-based measurement of the complex permittivity function of a thin metal film, which is important from the point of view of material characterization directly performed in the Kretschmann configuration.

Optical Properties of New Type of Glazing Unit Modified By Phase Change Material (Theoretical Approach)

Abstract The paper presents the use of phase change material (PCM) in window application that was studied in the framework of the ERA-NET-LAC Project “Solar Hybrid Translucent Component for Thermal Energy Storage in Buildings” (SOLTREN). Increase of energy savings in buildings is the main aim of this study. To achieve the aim, it has been decided to create a theoretical model of the impact of the PCM on the characteristics of the window and, at the next stage, to experimentally test the model. Paraffin has been chosen as the most suitable and available material as PCM. Pure paraffin has high transparency in liquid phase, and dull white colour in solid phase. The paper shows results of total transmittance and absorption spectra for different thicknesses of paraffin with a melting temperature of 35°C, as well as absorption of the glass sample with PCM at different angles of incidence of light.

Investigating the predictive capacity of Eulerian CFD to model long-duration blast loads on finite cross-section geometries

Typically defined by positive pressure durations over 100ms, long-duration blasts can generate dynamic pressures (blast winds) capable of exerting damaging drag loads on slender structural elements such as columns. With limited availability of appropriate drag coefficients for specific structural geometries or different section orientations, Computational Fluid Dynamics (CFD) can provide a valuable tool for calculating blast interaction and loading on user-specified geometries. Commercially available CFD programs or ‘hydrocodes’ with shock wave modelling capabilities remain based on solving the inviscid Euler equations. The ability to analyse long-duration blasts is still not confidently offered however, with no prior studies examining the accuracy of modelling interaction with relatively much smaller, finite geometries. This remains particularly challenging due to large wavelengths and time durations inherent to long-duration blasts, usually limited by impractical solution domains and computing resource. This paper presents a comparative investigation between numerical simulations and experimental results to assess the predictive capability of Eulerian CFD as a tool for calculating long-duration blast drag loading on an intricate I-section geometry from different angles of incidence. Calculated pressure-time histories on exposed geometry surfaces demonstrated good agreement although reduced accuracy and under-prediction occurred for shielded surfaces manifesting as overestimated net translational loading. Numerical discrepancies were attributed to the inviscid Euler equations underpinning the CFD solver, limiting accuracy when resolving complex aerodynamic flows at bluff I-section orientations. Results of this study provide new understanding and awareness of the numerical capability and limitations of using CFD to calculate long-duration blast loads on intricate geometries.

Development of Composite Propeller Blade Model for High Velocity Impacts on Aircraft Fuselage using Finite Element Analysis

An open rotor blade failure and release event can result in a high energy impact on an aircraft fuselage that can reduce the strength of the structure and challenge the safe continuation of the flight and landing. This work highlights the development of a numerical approach and methodology in order to improve the assessment of the damage predictions of a composite propeller blade impact against the fuselage of an aircraft to be able to estimate a minimum thickness of shielding for the full protection of the airframe. A number of dynamic simulations were carried out, from rigid up to deformable and frangible projectiles at different angles of incidence, varying the material and the thicknesses using Abaqus/Explicit. The finite element (FE) models for blade and target were calibrated and validated separately allowing to capture the right behavior and failure modes. Impact tests of partial blade fragments against stiffened composite panels were correlated with simulations and the obtained results show a good agreement regarding deformations and delaminated area. Finally, a full blade FE model was generated and used for the fuselage impact numerical analysis. This was done within the frame of the Open Rotor project funded by Clean Sky European research programme.

Effect of the cascade neutralization energy on the surface modification by the impact of slow highly charged ions

We consider the neutralization dynamics of slow highly charged ions in the interaction with a metal surface covered with a thin dielectric film from the standpoint of the surface modification. The quasi-resonant two-state vector model and the micro staircase model are used for the calculation of cascade neutralization energy for the ArZ+, KrZ+ and XeZ+ ions. The population of several ionic Rydberg states at each step of the neutralization cascade is demonstrated. The correlation between the neutralization and the potential energy is presented for moderate and very low ionic velocities and the relevance of this relation for the surface nanostructure formation is briefly discussed for a different angle of incidence and different dielectric materials.

Analytical theory on electromagnetic shielding effectiveness of infinite conductor plate with periodic aperture array under plane wave illumination

Penetration of a plane electromagnetic wave through the apertures on a perfectly conducting flat plate is a classical electromagnetic problem. In some practical applications like electromagnetic shielding, where only the fields far from the apertures are concerned and the aperture sizes are small compared with a wavelength, the role of apertures can be represented by the equivalent electric and magnetic dipoles located in the centers of the apertures. In principle, the penetration field can be expressed as the superposition of the radiation fields of the dipoles. However, the direct superposition leads to a double series with complex form and poor convergence. On the other hand, this problem may also be solved by full wave numerical simulations. Even so, finding analytical solutions is still desirable considering that it is clear in physical significance and easy to implement. In this paper, the analytical formula of the penetration fields are derived for both TE and TM polarization mode with different angles of incidence. The derivation is carried out firstly by averagely distributing each dipole moment within each periodic unit. As a result, the dipole array is replaced with a flat sheet with uniform magnetization and polarization intensity. Then, the equivalent surface current and charge distributions are obtained directly from the polarization intensity. Finally, the penetration fields are treated as the radiation fields of the surface sources. It is shown that the amplitude of the penetration field is proportional to aperture magnetic polarization coefficient and wave frequency, and it is inversely proportional to the area of a periodic unit. In regard to the effect of the incidence angle, the amplitude of the penetration field is proportional to the cosine of the incidence angle for TE polarization. However, for the TM polarization, the relationship is a little complicated due to the coexistence of electric and magnetic dipoles: the field is not rigorously inversely proportional to the cosine of the incidence angle due to the existence of a correction term involving both the polarization coefficient and the sine of the angle. The formula is used to calculate the shielding effectiveness for several different aperture shapes and different incidence angles. The results are in good agreement with those from the full wave simulation software.

Polarization independent quad‐bandpass frequency selective surfaces with wide‐band ratio

A single layer polarization independent quad-bandpass frequency selective surface (FSS) with wide-band ratio is demonstrated theoretically as well as experimentally. The proposed structure passes four frequency bands with wide band ratio. The proposed FSS design is implemented by incorporating alternate arrangement of four units which are rotated 90° clockwise to form a unit cell of metal over a FR4 substrate. The geometrical dimensions of proposed unit cell are optimized and arranged in such a way that the structure possesses the quad bandpass characteristic and aspect dimensions of one unit is 0.11λ × 0.11λ with respect to first resonant frequency. This FSS provides stable response for different angle of incidence in transverse electric (TE) mode and transverse magnetic (TM) mode. To validate the results proposed FSS array has been fabricated and measured in free space environment. The measured results are in good agreement with the simulated results. Excellent stability is also observed for different incident angle.

An accelerometer balance for aerodynamic force measurements over Hypervelocity Ballistic models in shock tunnel

A force balance to measure drag, lift and pitching moment over Hypervelocity Ballistic (HB) models 1 and 2 has been developed and assessed in an impulse test facility, hypersonic shock tunnel. The experiments were carried out at different angles of incidence of the models with the freestream at nominal Mach numbers of 5.78 and 8.31. The force balance is provided with rubber supports to ensure unrestrained motion of the model during the hypersonic freestream flow. Three dimensional finite element simulations are carried out to assess the performance of the force balance system in measuring the acceleration within the short test duration available in the shock tunnel. The force balance is mounted inside the model and is equipped with accelerometers to sense the model’s acceleration in the desired direction. The aerodynamic force and moment coefficients are then deduced from the measured acceleration signals based on theories in aerodynamics. The measured values of force and moment coefficients match well with the theoretical values estimated using modified Newtonian theory for HB 1 and HB 2 models. In addition, CFD simulations are carried out for the experimental test cases using viscous, laminar models and the numerically computed force coefficients are validated by comparing against the experimental values. The present study demonstrates the use of accelerometer based force balance for measuring aerodynamic forces and moments over realistic long missile configurations.