Different Angles Of Incidence Research Articles

Dynamical behaviors of aluminum droplets impinging on horizontal and inclined surfaces

Aluminum (Al) droplets collide with the wall of the combustion chamber in a solid rocket motor at different angles of incidence and velocities, which exhibit rebounding, splashing, and other behaviors. It increases the loss of two-phase flow to degrade the performance of the engine and poses a challenge to the thermal protection system. In this study, an experimental system in which molten Al droplets impact the walls of the chamber is designed. The size of the Al droplets produced by the generator ranged from 120 μm to 2000 μm while their speeds of impact ranged from 0.85 m/s to 9 m/s. This was used to examine the process of impact of Al droplets on flat and inclined walls. The residence time and spreading diameter of the droplets were quantified to reveal their mechanism of collision. Their empirical correlations were obtained by regressing the experimental data, and the predictive error of the model was within 20% of the experimental values. Furthermore, a theoretical model was developed to analyze energy distribution during the collision between the droplets and the wall. It showed that the effect of viscous dissipation energy on droplet flow was negligibly small, but the adhesion energy of the droplet increased significantly with its initial energy. In addition, the dimensionless sliding distance was S≈8 when the tangential Weber number was greater than 90, where this was related to the high surface tension of the Al droplets. The results here provide a theoretical basis for the design of thermal protection system of solid rocket motors.

Photonic Topological Insulator Based on Frustrated Total Internal Reflection in Array of Coupled Prism Resonators

Total internal reflection occurs at the interface between two media with different refractive indices during propagation of light rays from a medium with a higher refractive index to a medium with a lower refractive index. If the thickness of the second medium is comparable to a specific light wavelength, then total internal reflection is violated partially or completely. Based on the frustrated total internal reflection, herein we discuss a two-dimensional photonic topological insulator in an array consisting of triangular, quadrangular, or hexagonal transparent prism resonators with a narrow gap between them. An array of prism resonators allows topologically stable edge solutions (eigenwaves) similar to those studied in ring resonators. Moreover, total internal reflection occurs at different angles of incidence of light. This makes it possible to obtain a set of fundamentally new edge solutions. The light is presumably concentrated at the surface; however, in the new solutions it penetrates relatively deep into the photonic topological insulator and excites several layers of prisms positioned beyond the surface. Remarkably, the direction of light propagation is precisely biased, and therefore new solutions exhibit lower symmetry than the resonator array symmetry.

SEE sensitivity of a COTS 28-nm SRAM-based FPGA under thermal neutrons and different incident angles

This paper provides an experimental study of the single-event upset (SEU) susceptibility against thermal neutron radiation of a 28-nm bulk Commercial-Off-The-Shelf (COTS) Xilinx Artix-7 FPGA under different angles of incidence. Experimental results indicating SEUs on configuration RAM (CRAM) cells, Flip-Flops (FFs), and Block RAMs (BRAMs) are presented and discussed. Shapes of multiple events (ranging from 2 to 12-bit) are also analyzed, and their dependency on the incident angle of the particle beam against the device's surface. Possible shapes of 128 and 384-bit multiple events are also investigated, revealing a trend to follow word lines. The results of the front incident angle are compared with 14.2-MeV neutrons, demonstrating a considerable difference in the device's sensitivity against both irradiation sources. Finally, a modeling tool called MUSCA-SEP3 is used to predict the device's sensitivity under the same environmental conditions. The obtained experimental results will show a good agreement with the predicted ones in a very accurate way.

Study on the physical mechanism of water layer on the morphological evolution of transient-pulse high-speed water jet

This research investigates the physical mechanism of a water layer on the morphological evolution of a transient-pulse high-speed water jet. Numerical methods were used to explore the influence of a water layer on an underwater explosive jet to observe the physical processes and streamline distribution during formation of the jet. An experimental system measured velocity and wall pressure, captured the evolution of the jet shape in different modes and determined the formation conditions of a transient-pulse water jet. When the tube is located above the water layer, the top of the jet forms a significant tip. When the tube is located below the water layer, the explosion in the tube produces a transient-pulse water jet. Under the action of the tip edge effect and tip front effect, a ligament is formed. The transient-pulse water jet produces a compression wave, leading to water hammer and necking phenomena and increasing the impact area and speed. With different angles of incidence, similar pulse tower-shaped structures and gravity are the main influencing factors of jet morphology, which can be decomposed into different shapes. It is concluded that the water layer plays a crucial role in the jet morphological evolution and rupture mode.

Flexible and Polarization Independent Miniaturized Double-Band/Broadband Tunable Metamaterial Terahertz Filter.

In this paper, the design of a double-band terahertz metamaterial filter with broadband characteristics using a single conducting layer is presented. The design uses a structured top metallic layer over a polyimide material. The proposed design has achieved broadband band-pass transmission characteristics at the resonances of 0.5 THz and 1.65 THz, respectively. The 3-dB bandwidths for these two resonances are 350 GHz and 700 GHz, respectively, which indicates that dual-band resonance with broadband transmission characteristics was obtained. The design has achieved the same transmission characteristics for two different orthogonal polarizations, which was confirmed using numerical simulation. The design was tested for a different angle of incidences and it was observed that this results in angle-independent transmission behavior. In addition, for obtaining tunable resonant behavior, the top conductor layer was replaced by graphene material and a silicon substrate was added below the polymer layer. By varying the Fermi level of graphene, modulation in amplitude and phase was observed in numerical simulation. The physical mechanism of double-band behavior was further confirmed by surface current distribution. The proposed design is simple to fabricate, compact, i.e., the size is λ0/8, and obtained dual-band/broadband operation.

Ultra-broadband wave-absorbing metamaterials with open-hole effect

In this paper, propose the open-hole effect, which can improve the absorption effect of electromagnetic absorbers in the X- and Ku-band by regularly opening certain shaped through-holes in the dielectric material. Based on this effect, an ultra-wideband metamaterial absorber with a special open-hole structure is designed and successfully prepared by numerical simulation, and the effective wavelength bandwidth (absorption > 90 %) covers X- and Ku-band. By optimizing the dielectric material and structural parameters of the absorber, an ultra-broadband metamaterial absorber with a thickness of 2.2 mm, a maximum absorption rate of 99.35 % and an effective absorption bandwidth of 11.6 GHz was obtained. Simulations of TE and TM waves at different angles show that the absorber has excellent electromagnetic wave absorption at different angles of incidence (θ < 30°).

Aerodynamic noise characteristics of non-circular cylinders in subcritical flow regime

The present study experimentally investigates the aerodynamic noise from the flow around cylinders of square and equilateral triangle cross-sections at different angles of incidence ( α). The cylinder models have a side dimension of 10 mm and a span of 300 mm. The free stream velocity ( U 0) is in the range of 12–36 m/s, and the corresponding Reynolds numbers are 7.8 × 103 to 2.3 × 104, which is in the subcritical flow regime. The characteristic acoustic tones are generated at α = 30° and 45° for square and triangular cylinders. The frequency of acoustic tones linearly increases with the free stream velocity, and the corresponding Strouhal numbers are found to be in the range of 0.13–0.16. Depending on the angle of incidence, the overall sound pressure level is higher than the background noise by 4–24 dB for the square cylinder and 3–15 dB for the triangular cylinder at U 0 = 36 m/s. The highest noise level of the square cylinder is 90 dB at α = 45° and 79 dB at α = 30° for the triangular cylinder. The spectral scaling with the sixth power of the free stream velocity indicates the dipole behaviour of the acoustic tones. The mean and root-mean-square velocity profiles in the wake region characterise the noise emissions at different angles of incidence. The comparative acoustic study of the non-circular cylinders with a circular counterpart showed that the highest noise level is from the square cylinder at α = 45°. The directivity study shows that the noise level of the square cylinder at α = 45° at 90° angular location ( θ) is higher by 6.5 dB than that at θ = 30°.

Optical polarimetry of the May 2022 lunar eclipse

ABSTRACT The sunlight reflected from the Moon during a total lunar eclipse has been transmitted through the Earth’s atmosphere on the way to the Moon. The combination of multiple scattering and inhomogeneous atmospheric characteristics during that transmission can potentially polarize that light. A similar (although much smaller) effect should also be observable from the atmosphere of a transiting exoplanet. We present the results of polarization observations during the first 15 min of totality of the lunar eclipse of 2022 May 16. We find degrees of polarization of 2.1 ± 0.4 per cent in B, 1.2 ± 0.3 per cent in V, 0.5 ± 0.2 per cent in R, and 0.2 ± 0.2 per cent in I. Our polarization values lie in the middle of the range of those reported for previous eclipses, providing further evidence that the induced polarization can change from event to event. We found no significant polarization difference (&amp;lt;0.02 per cent) between a region of dark Mare and nearby bright uplands or between the lunar limb and regions closer to the disc centre due to the different angle of incidence. This further strengthens the interpretation of the polarization’s origin being due to scattering in the Earth’s atmosphere rather than by the lunar regolith.

Metasurface Terahertz Perfect Absorber with Strong Multi-Frequency Selectivity.

In this paper, we design a metasurface terahertz perfect absorber with multi-frequency selectivity and good incident angle compatibility using a double-squared open ring structure. Simulations reveal five selective absorption peaks located at 0–1.2 THz with absorption 94.50% at 0.366 THz, 99.99% at 0.507 THz, 95.65% at 0.836 THz, 98.80% at 0.996 THz, and 86.70% at 1.101 THz, caused by two resonant absorptions within the fundamental unit (fundamental mode of resonance absorption, FRA) and its adjacent unit (supermodel of resonance absorption, SRA) in the structure, respectively, when the electric field of the electromagnetic wave is incident perpendicular to the opening. The strong frequency selectivity at 0.836 THz with a Q-factor of 167.20 and 0.996 THz with a Q-factor of 166.00 is due to the common effect of the FRA and SRA. Then, the effect of polarized electromagnetic wave modes (TE and TM modes) at different angles of incidence (θ) and the size of the open rings on the device performance is analyzed. We find that for the TM mode, the absorption of the resonance peak changes only slightly at θ = 0–80°, which explains this phenomenon. The frequency shift of the absorption peaks caused by the size change of the open rings is described reasonably by an equivalent RLC resonant circuit. Next, by adjusting two-dimensional materials and photosensitive semiconductor materials embedded in the unit structure, the designed metasurface absorber has excellent tunable modulation. The absorption modulation depth (MD) reaches ≈100% using the conductivity of photosensitive semiconductor silicon (σSI-ps), indicating excellent control of the absorption spectrum. Our results can greatly promote the absorption of terahertz waves, absorption spectrum tunability, and frequency selectivity of devices, which are useful in the applications such as resonators, bio-detection, beam-controlled antennas, hyperspectral thermal imaging systems, and sensors.

Bluntness and incidence effects in hypersonic flows with large separated regions

This paper describes a numerical investigation on the effects of small to large bluntness as well as the angle of incidence on the leading-edge separation in a laminar hypersonic flow. The results show that both bluntness and incidence strongly influence separation characteristics. A combined bluntness and incidence parameter is proposed and applied to plateau pressures in the separated region and is shown to demarcate effects of small and large bluntness at different angles of incidence. The investigation also showed profound changes in the internal structure of the separation bubble with changes in incidence and bluntness. The significance of the relationship between the two shear stress minima and the separation length is highlighted.

Electromagnetic wave focusing with 2-D gridded parabolic reflector made of parallel circular PEC wires at oblique incidence

We consider the two-dimensional (2-D) scattering of the TE- and TM-polarized plane electromagnetic waves from a discrete grid-like parabolic reflector consisting of parallel circular perfectly electrically conducting (PEC) wires at oblique incidence. Our analysis is performed in the exact formulation, fully taking into account the wave interactions between the wires. We use the method of separation of variables in the local cylindrical coordinate systems in combination with Graf’s addition formulas for cylindrical functions. The near field in the vicinity of the reflector is calculated at different angles of incidence. The dependences of the maximum field amplitude in the focal area and the position of this maximum on the angle of incidence are plotted. The far field scattered patterns, total scattering cross-sections and backward scattering cross-sections are calculated and discussed.

Angular absorptance and thermal degradation analysis of TiB2/Ti(B,N)/SiON/SiO2 multilayer solar absorber coating

AbstractMultilayer solar selective absorber coatings have been developed in the last few decades. The thermal stability in terms of microstructure gives an insightful understanding of the optical properties of such coatings. In this context, we extensively utilized transmission electron microscopy (TEM) analysis to establish the thermal stability of TiB2/Ti(B,N)/SiON/SiO2 coating, under thermal cycling/continuous heating to 500°C in vacuum for 250 h. In particular, this work reports the variation in the solar absorptance of TiB2/Ti(B,N)/SiON/SiO2 coating with different angles of incidence of the solar radiation. Extensive analysis using the TEM technique reveals the presence of oxide interlayers that act as diffusion barrier layers to enhance the thermal stability of the coating. Computational simulation using SCOUT software validates the measured reflectance spectrum of the developed multilayer coating. The minor changes in absorptance and emissivity after heat treatment in vacuum at 500°C, together with high solar absorptance over a broad angular variation, establish the potential application of TiB2/Ti(B,N)/SiON/SiO2 as a selective coating in concentrated solar power systems.

Light absorption enhancement in thin film GaAs solar cells using dielectric nanoparticles

Cost-effective and lightweight solar cells are currently demanded in strategic fields such as space applications or integrated-wearable devices. A reduction of the active layer thickness, producing thin-film devices, has been a traditional solution to accomplish both requirements. However, this solution also reduces the efficiency of the device. For this reason, alternative strategies are being proposed. In this work, light trapping effects of an array of semiconductor nanoparticles located on the top surface of a thin-film GaAs solar cell are investigated to improve the optical absorption and current density in active layer, under the standard AM-1.5 solar spectrum. The numerical results are compared with other previous proposals such as an aluminum nanoparticle array, as well as conventional solar cells with and without a standard anti-reflective coating (ARC). The inclusion of semiconductor nanoparticles (NPs) shows an improved response of the solar cells at different angles of incidence in comparison to solar cell with an ARC. Furthermore, the efficiency increases a 10% respect to the aluminum nanoparticles (NPs) architecture, and a 21% and a 30% respect to solar cells with and without ARC, respectively.

TMM-Fast, a transfer matrix computation package for multilayer thin-film optimization: tutorial.

Achieving the desired optical response from a multilayer thin-film structure over a broad range of wavelengths and angles of incidence can be challenging. An advanced thin-film structure can consist of multiple materials with different thicknesses and numerous layers. Design and optimization of complex thin-film structures with multiple variables is a computationally heavy problem that is still under active research. To enable fast and easy experimentation with new optimization techniques, we propose the Python package Transfer Matrix Method - Fast (TMM-Fast), which enables parallelized computation of reflection and transmission of light at different angles of incidence and wavelengths through the multilayer thin film. By decreasing computational time, generating datasets for machine learning becomes feasible, and evolutionary optimization can be used effectively. Additionally, the subpackage TMM-Torch allows us to directly compute analytical gradients for local optimization by using PyTorch Autograd functionality. Finally, an OpenAI Gym environment is presented, which allows the user to train new reinforcement learning agents on the problem of finding multilayer thin-film configurations.

Rotational freedom thin‐film solar cell using a reconfigurable nano‐antenna with 4‐Dimethyl‐Amino‐N‐methyl‐4‐Stilbazolium Tosylate

In this paper, we proposed a new method to realize the rotational freedom of thin-film solar cells. In this method, an array of reconfigurable nano-patches fed by a plasmonic waveguide is integrated inside the solar cell to receive and trap light in the active layer. The reconfigurable nano-antenna is designed to achieve beam steering by bias voltage in the direction of sunlight during the day using 4-Dimethyl-Amino-N-methyl-4-Stilbazolium Tosylate as an active electro-optic material integrated into the plasmonic waveguide. The proposed solar cell is investigated using the finite-difference frequency-domain method and the drift-diffusion equations of COMSOL Multiphysics software at different wavelengths of light and a wide range of angles of incidence for transverse magnetic (TM) and transverse electric (TE) polarizations. The numerical results show increase in the absorption in large wavelengths of sunlight for the thin-film solar cell with nano-antenna, resulting in a short circuit current enhancement of 1.48 and 1.45 for TE and TM polarisations, respectively. Also, another advantage of the proposed reconfigurable structure is maintaining the performance in different angles of incidence, which may open up a new opportunity in solar energy harvesting.

Direction of arrival estimation in time modulated linear arrays using matrix pencil method with single snapshot and optimized time steps

The direction of arrival estimation by the time modulated linear array with a proposed novel approach has been analyzed and proven. By merging Matrix Pencil method with time modulated linear array, a great advantage has been obtained by the virtue of using a single snapshot. A new formulation is developed by the authors which combines the Time Modulation and Matrix Pencil methods. The time steps were optimized using differential evolution algorithm for the estimation of the angle of incidence. The effects of the noise level, the number of signal sources, the number of antenna elements and different angles of incidence were examined with the simulations and comparisons were presented. Compared to traditional methods, the simulation results show that the proposed novel approach maintains significant advantages from the viewpoint of estimation accuracy, especially for scenarios with single snapshot number and low SNR.

A method for the experimental characterisation of novel drag-reducing materials for very low Earth orbits using the Satellite for Orbital Aerodynamics Research (SOAR) mission

The Satellite for Orbital Aerodynamics Research (SOAR) is a 3U CubeSat mission that aims to investigate the gas–surface interactions (GSIs) of different materials in the very low Earth orbit environment (VLEO), i.e. below 450 km. Improving the understanding of these interactions is critical for the development of satellites that can operate sustainably at these lower orbital altitudes, with particular application to future Earth observation and communications missions. SOAR has been designed to perform the characterisation of the aerodynamic coefficients of four different materials at different angles of incidence with respect to the flow and at different altitudes in the VLEO altitude range. Two conventional and erosion-resistant materials (borosilicate glass and sputter-coated gold) have first been selected to support the validation of the ground-based Rarefied Orbital Aerodynamics Research (ROAR) facility. Two further, novel materials have been selected for their potential to reduce the drag experienced in orbit whilst also remaining resistant to the detrimental effects of atomic oxygen erosion in VLEO. In this paper, the uncertainty associated with the experimental method for determining the aerodynamic coefficients of satellite with different configurations of the test materials from on-orbit data is estimated for different assumed gas–surface interaction properties. The presented results indicate that for reducing surface accommodation coefficients the experimental uncertainty on the drag coefficient determination generally increases, a result of increased aerodynamic attitude perturbations. This effect is also exacerbated by the high atmospheric density at low orbital altitude (i.e. 200 km), resulting in high experimental uncertainty. Co-rotated steerable fin configurations are shown to provide generally lower experimental uncertainty than counter-rotated configurations, with the lowest uncertainties expected in the mid-VLEO altitudes (sim300 km). For drag coefficient experiments, configurations with two fins oriented at 90^{circ } were found to allow the best differentiation between surfaces with different GSI performance. In comparison, the determination of the lift coefficient is found to be improve as the altitude is reduced from 400 to 200 km. These experiments were also found to show the best expected performance in determining the GSI properties of different materials. SOAR was deployed into an orbit of 421 km times 415 km with 51.6^{circ } inclination on 14 June 2021. This orbit will naturally decay allowing access to different altitudes over the lifetime of the mission. The results presented in this paper will be used to plan the experimental schedule for this mission and to maximise the scientific output.

Adaptive design of dual excitation ultra‐low wavenumber Raman spectroscopy system

AbstractUltra‐low wavenumber or ultra‐low frequency (ULF) Raman spectroscopy using holographic optics is an emerging technique to obtain spectral signatures of chemicals in low energy corresponding to their phases, crystallinity, isomerism, and environmental conditions such as temperature. Commercial turn‐key systems employ mechanical turrets and other such optomechanical moving elements to accommodate multiple laser excitations, which are incident normally on the sample, and the Raman signal is collected in a 180° backscattering configuration. Here, we have developed a system consisting of two single‐longitudinal mode (SLM) lasers and a single‐stage spectrometer. Selected notch filters were based on the volume holographic grating technology providing output beam at a certain angle, which facilitates the possibility of different angles of incidence of the excitation laser on the sample. This adaptive ULF Raman system, therefore, is not only able to acquire high‐quality low‐wavenumber spectral fingerprints of various chemicals but can also be easily reconfigured for differential spectral studies.

Angular dependence of coaxial and quasi-coaxial monitoring systems for process radiation analysis in laser materials processing

Process monitoring is becoming increasingly important in laser-based manufacturing and is of particular importance in the field of additive manufacturing [e.g. Laser Powder Bed Fusion (LPBF)]. Process monitoring enables a reduction of production costs and a lower time-to-market. Furthermore, the data can be used to create a digital twin of the workpiece. There are already many established processing head-integrated monitoring systems for such applications as the multispectral analysis of process radiation. However, the monitoring of complex signals in systems with F-Theta scanner lenses is very challenging and requires specially adapted optics or measuring sensors.In this paper a potential arrangement for spectroscopy-based process monitoring in pre-objective scanning is presented. The process radiation was monitored using a coaxial and a quasi-coaxial observation system. The measurements were carried out on both a solid and a powder coated sample of 2.4668 (Inconel 718) to show the potential use of these systems in laser-based additive manufacturing. In order to obtain comprehensive data about the process signal, the process zone was analyzed at different angles of incidence (AOI) of the laser using a high-speed camera (HSI) and a spectrometer. The connection between the HSI and the spectral measurements is discussed. The ionization of the material and the formation of a plasma was observed and found to lose intensity as the angle of incidence increases. A model of the system that demonstrates the intensity of the emitted radiation of the plasma was created. It enables the measured values to be corrected. The corrected measurement data can be used to detect impurities or a non-ideal energy input across the entire processing field, which is a move towards robust process monitoring.

Dispersion of organic exciton polaritons—a novel undergraduate experiment

We report on an innovative and simple way to perform an experiment which utilizes the properties of a quantized electromagnetic field coupled to Frenkel excitons in organic materials, forming exciton–polaritons (EP). We present an optical setup, which allowed to perform precise measurements of transmission of organic optical cavities at different angles of incidence and to study the dispersion relation of EP. We provided the full theoretical background of EP and demonstrated that the experimental results are in good agreement with theoretical predictions. Furthermore, we extracted the strong coupling strength and the excitonic–photonic weights of organic cavity samples.