Ray Tracing Technique Research Articles

A Hybrid Model for Analysis of Laser Beam Distortions Using Monte Carlo and Shack–Hartmann Techniques: Numerical Study and Experimental Results

The hybrid model for analyzing distortions of a laser beam passed through a moderately scattering medium with the number of scattering events up to 10 is developed and investigated. The model implemented the Monte Carlo technique to simulate the beam propagation through a scattering layer, a ray-tracing technique to propagate the scattered beam to the measurements plane, and the Shack–Hartmann technique to calculate the scattered laser beam distortions. The results obtained from the developed model were confirmed during the laboratory experiment. Both the numerical model and laboratory experiment showed that with an increase of the concentration value of scattering particles in the range from 105 to 106 mm−3, the amplitude of distortions of laser beam propagated through the layer of the scattering medium increases exponentially.

Deflection angle analysis under the influence of non-plasma medium and plasma medium for regular black hole with cosmic string

By applying the Keeton and Petters technique, we find the deflection angle as a series expansion with a specific factor of mass. We investigate the shadow structure of a regular black hole with cosmic string with a non-magnetized, pressure-free plasma around it. In order to separate the Hamilton equation and locate the photon areas, certain plasma distributions are taken into consideration. Moreover, by utilizing a new ray-tracing technique, we analyze the photon’s path around a regular black hole with cosmic string in the presence of plasma whose density depends on the radius coordinate. We also analyze the plasma effects on the shadow of black hole. We obtain an analytical formula that describes the boundary curve of the shadow for such a black hole in an expanding universe for an observer at any finite location outside the horizon. In the presence and absence of plasma, we detect deviations that are further investigated by analyzing the geometry of shadow angle at a particular value of plasma frequency.

Bifocal Dual Reflectarray with Curved Main Surface

This paper presents a novel approach to synthesizing curved reflectarrays using Geometrical Optics (GO). It introduces the concepts of virtual normal and path length shift, which enable a vector-based formulation of the problem that can be solved using ray tracing techniques. The formulation is applied for the design of two different versions of a Dual Bifocal Reflectarray with a parabolic main surface and a flat subreflectarray. The first version aims to enhance the performance of the multibeam antenna by providing a focal ring located at the feed cluster plane. The second version focuses on improving the scanning characteristics of the antenna in the horizontal plane by incorporating two foci. The synthesis procedure yields samples of the path length shift or its derivatives. To reconstruct the phase distribution, an interpolation scheme is employed and described in this paper. Numerical results are presented for both the focal-ring and two-foci configurations, demonstrating the feasibility of this solution for multibeam or scanning satellite antennas operating in the Ka.

Bending the light: Next generation anamorphic sculptures

This paper presents a new method for generating artworks that extends the classical anamorphic archetype to use freeform reflective and refractive media and 3D surfaces instead of images. The methodology uses a mix of raytracing and surface deformation techniques to determine the proper deformation the object should undergo to be corrected by the optical tool once viewed by the observer in a specific location. Our approach also includes an optimization process that modifies the point of view and the location of the target image to avoid unwanted optical effects or occlusions. We successfully tested our technique on several practical examples and employed it to produce actual artworks.

Radiative view factor correlations in particulate media from ray tracing simulations and data-driven modeling

Thermal radiation has been extensively modeled in static particulate media with effective radiative properties or with statistical ray tracing techniques. However, these techniques are not directly compatible to evaluate radiative fluxes on discrete particles, which is more suitable for particle flow systems. This study focuses on such a discrete approach to compute radiative fluxes by developing view factors correlations for particle-particle and particle-wall. Training data is generated from physics-based Monte Carlo ray tracing simulations on a monodisperse, packed bed with solid volume fractions ranging from 0.016 to 0.45. This data was used to develop reduced-order correlations to determine particle-particle and particle-wall radiative view factors as a function of particle-particle and particle-wall separation distance, viewing angle, and the number of shading particles. Uniquely, we determine best-fit functions that are physically interpretable to account for shading effects by particles. A sigmoid function with a non-linear dependence on viewing angle governs the extent of shading by an intermediate particle. A correction factor with the particle-wall normal separation distance as the feature variable is introduced to account for shading effects between a particle and a planar wall surface. View factor correlations result in reliable and reasonably accurate predictions. For a solid volume fraction of 0.45, the root mean squared errors of particle-particle and particle-wall view factors are 2.7e-4 and 0.021 with corresponding training data in the ranges of 0–0.08 and 0–0.5 respectively. To scale these correlations for large number of particles, restricting shading detection up to 5 nearest neighbors is demonstrated to be an effective strategy to balance prediction accuracy with computational efficiency. With thousands of particles, the computational cost of proposed view factor correlations with thresholding of 5 shading particles is about 100 times faster than serial Monte Carlo ray tracing simulations for a solid volume fraction of 0.45.

Analytical Modeling of Electromagnetic Scattering and HRRP Characteristics from the 3D Sea Surface with a Plunging Breaker

Electromagnetic (EM) scattering of sea surface may exhibit sea-spikespikes when there exist breaking waves. As sea-spikes are usually mistaken for targets, the investigation of EM scattering characteristics and high-range resolution profiles (HRRPs) of three-dimensional (3D) sea surfaces with a plunging breaker is meaningful for target detection and recognition. To describe the basic features of a plunging breaker, this paper developed a feasible and wind-related plunging breaker model. Here, profiles of a plunging breaker in its life cycle are modeled according to the wind speed and time factor, and the small-scale roughness is considered. Then, the sea surface and plunging breaker are combined to obtain the composite model. Additionally, a hybrid algorithm based on the Capillary Wave Modification Facet Scattering Model (CWMFSM) and ray tracing technique is developed to calculate the EM scattering of 3D sea surface with a plunging breaker. Simulation results show that the sea-spike phenomenon is more likely to occur for the upwind and large incident angles. The amplitude of the backscattering electric field from the plunging breaker is much stronger than that of the sea surface. Furthermore, the HRRPs of 3D sea surface with a plunging breaker and target are computed. Sharp peaks from the plunging breaker that exhibit obvious target-like features are observed.

Characteristics of Boomerang Whistler‐Mode Waves Emitted From the DSX Spacecraft

AbstractThe Air Force Research Laboratory's Demonstration and Science Experiments (DSX) spacecraft carried a high‐voltage very low frequency transmitter and a sensitive broadband receiver to medium Earth orbit in 2019. During many pulsed transmission experiments, DSX detected apparent “boomerang” echoes when its emitted waves refracted in the magnetosphere and returned to the spacecraft. We simulated a series of these detected pulses using cold plasma ray tracing to characterize their likely wavelengths, indices of refraction, and initial wave normal angles. The waves were shown to remain relatively local to DSX, to be lightly damped, and to have a wide variety of wavelengths and indices of refraction, but they were all emitted with very oblique wave normal angles tightly clustered about half a degree from the Gendrin angle, which theoretical antenna models predict is preferentially excited. Our results are remarkably consistent with this prediction but are statistically biased closer to the resonance cone, possibly because of limitations in the ray tracing technique. The result is robust to perturbations of the simulation and confirms a very narrow beam of oblique radiation quite unlike the behavior of a dipole in vacuo.

Hybrid thermal and optical modeling of a solar air heater with a non-flat plate absorber

In this study, we developed a model based on a SAH. We can enhance air turbulence by creating a non-flat plate on a SAH absorber using a ratio of (e/H = 6), thereby increasing the solar collector’s convective heat transfer coefficient, Nusselt number, and thermal performance. A validation experiment was conducted to determine the accuracy of the developed model. Ray tracing and FEM simulation techniques were used to analyze the optical and thermal properties of the system simultaneously. Various operational and structural conditions were applied to analyze the system’s thermal performance under inhomogeneous heat flux on the absorber’s surface. The data demonstrate that non-flat plate surfaces contribute to wall-induced turbulence, which affects air temperatures. Outcomes demonstrate that mass flow rate excessively affects thermal efficiency, useful energy, and outlet temperatures. Thus, when the inlet air flow rate increases from 0.02 to 0.06 kg/s, the average hot air temperature at the SAC outlet during the daytime reduces from 55.6 to 47.82 °C, applicable heat energy increase from 646.5 to 970 W, and the average thermal efficiency increased from 28.8 to 54.7 %. Instantaneous non-flat absorber plates increased average thermal efficiency and heat transfer coefficient (h) to 9.10 and 27.24 % compared with flat plate absorbers (e/H = 1) at the same mass flow rate (0.05 kg/s). The highest Nusselt number increase observed during the day is 141.5% for non-flat plate compared to flat plates.

Exploring departures from Schwarzschild black hole in f(R) gravity

Different astrophysical methods can be combined to detect possible deviations from General Relativity. In this work, we consider a class of f(R) gravity models selected by the existence of Noether symmetries. In this framework, it is possible to determine a set of static and spherically symmetric black hole solutions, encompassing small departures from the Schwarzschild geometry. In particular, when gravity is the only dominating interaction, we exploit the ray-tracing technique to reconstruct the image of a black hole, the epicyclic frequencies, and the black hole shadow profile. Moreover, when matter dynamics is also affected by an electromagnetic radiation force, we take into account the general relativistic Poynting–Robertson effect. In light of the obtained results, the proposed strategy results to be robust and efficient: on the one hand, it allows to investigate gravity from strong to weak field regimes; on the other hand, it is capable of detecting small departures from General Relativity, depending on the current observational sensitivity.

Channel Modeling for UAV-to-Ground Communications With Posture Variation and Fuselage Scattering Effect

Unmanned aerial vehicle (UAV)-to-ground (U2G) channel models play a pivotal role in reliable communications between UAV and ground terminal. This paper proposes a three-dimensional (3D) non-stationary hybrid model including large-scale and small-scale fading for U2G multiple-input-multiple-output (MIMO) channels. Distinctive channel characteristics under U2G scenarios, i.e., 3D trajectory and posture of UAV, fuselage scattering effect (FSE), and posture variation fading (PVF) are incorporated into the proposed model. The channel parameters, i.e., path loss (PL), shadow fading (SF), path delay, and path angle, are generated incorporating machine learning (ML) and ray tracing (RT) techniques to capture the structure-related characteristics. In order to guarantee the physical continuity of channel parameters such as Doppler phase and path power, the time evolution methods of inter- and intra- stationary intervals are proposed. Key statistical properties, including temporal auto-correction function (ACF), power delay profile (PDP), level crossing rate (LCR), average fading duration (AFD), and stationary interval (SI), are analyzed with the impact of the change of fuselage and posture variation. It is demonstrated that both posture variation and fuselage scattering have crucial effects on channel characteristics. The validity and practicability of the proposed model are verified by comparing the simulation results with the measured ones.

Robust Outdoor Positioning Via Ray Tracing

Positioning problem can be solved with several approaches in 5G. This paper introduces RT (Ray Tracing) technique for small-cell Outdoor positioning and tracking for systems with distributed architecture with multipath processing gain. Proposed approach exploits high-resolution angular spectrum estimation and known radio propagation environment. It solves positioning problem robustly even in NLOS cases via CoMP (Cooperative Multi Point) reception and joint processing at cloud CPU. The aim of this paper is to disclose proposed algorithm for NR and compare it to GNSS measurements.

Supervised Learning Technique for First Order Multipaths Identification of V2V Scenario

In geometrical localization techniques, the propagated signal’s first-order multipath (FOMP) characteristics are used to calculate the location based on geometrical relationships. Utilizing the characteristics of higher order multipath (HOMP) results in a significant localization error. Therefore, distinguishing between FOMPs and HOMPs is an important task. The previous works used traditional methods based on a deterministic threshold to accomplish this task. Unfortunately, these methods are complicated and insufficiently accurate. This paper proposes an efficient method based on supervised learning to distinguish more accurately between the propagated FOMP and HOMP of millimeter-Wave Vehicle-to-Vehicle communication in an urban scenario. Ray tracing technique based on Shoot and Bounce Ray (SBR) is used to generate the dataset’s features including received power, propagation time, the azimuth angle of arrival (AAOA), and elevation angle of arrival (EAOA). A statistical analysis based on the probability distribution function (PDF) is presented first to study the selected features’ impact on the classification process. Then, six supervised classifiers, namely Decision Tree, Naive Bayes, Support Vector Machine, K-Nearest Neighbors, Random Forest, and artificial neural network, are trained and tested, and their performance is compared in terms of HOMP misclassification. The effect of the considered features on the classifiers’ performance is further investigated. Our results showed that all the proposed classifiers provided an acceptable classification performance. The proposed ANN showed the best performance, whereas the NB was the worst. In fact, the HOMP misclassification error varied between 2.3% and 16.7%. The EAOA exhibited the most significant influence on classification performance, while the AAOA was the least.

Coupling radiative, conductive and convective heat-transfers in a single Monte Carlo algorithm: A general theoretical framework for linear situations.

It was recently shown that radiation, conduction and convection can be combined within a single Monte Carlo algorithm and that such an algorithm immediately benefits from state-of-the-art computer-graphics advances when dealing with complex geometries. The theoretical foundations that make this coupling possible are fully exposed for the first time, supporting the intuitive pictures of continuous thermal paths that run through the different physics at work. First, the theoretical frameworks of propagators and Green's functions are used to demonstrate that a coupled model involving different physical phenomena can be probabilized. Second, they are extended and made operational using the Feynman-Kac theory and stochastic processes. Finally, the theoretical framework is supported by a new proposal for an approximation of coupled Brownian trajectories compatible with the algorithmic design required by ray-tracing acceleration techniques in highly refined geometry.

Shadows of black holes with dark matter halo

We investigate the shadow of an exact black hole solution of Einstein's equations recently proposed by Cardoso et al., to describe a supermassive black hole immersed in a dark matter halo. We analyze and discuss the light rings and the gravitational lensing of this spacetime comparing them with an isolated Schwarzschild black hole. Using backward ray-tracing techniques, we study the shadows cast by such black hole when illuminated by a celestial sphere that emits radiation isotropically. We find that when the dark matter distribution concentrates near the event horizon of the black hole, multiple light rings emerge. In this high compactness regime, the shadows and gravitational lensing are significantly different from the Schwarzschild one. We also use the M87* and SgrA* shadow data, obtained by the Event Horizon Telescope collaboration, to constrain the parameters of the dark matter halo.

Stylized versus voxel phantoms: quantification of internal organ chord length distances

Dosimetric calculations, whether for radiation protection or nuclear medicine applications, are greatly influenced by the use of computational models of humans, called anthropomorphic phantoms. As anatomical models of phantoms have evolved and expanded, thus has the need for quantifying differences among each of these representations that yield variations in organ dose coefficients, whether from external radiation sources or internal emitters. This work represents an extension of previous efforts to quantify the differences in organ positioning within the body between a stylized and voxel phantom series. Where prior work focused on the organ depth distribution vis-à-vis the surface of the phantom models, the work described here quantifies the intra-organ and inter-organ distributions through calculation of the mean chord lengths. The revised Oak Ridge National Laboratory stylized phantom series and the University of Florida/National Cancer Institute voxel phantom series including a newborn, 1-, 5-, 10- and 15 year old, and adult phantoms were compared. Organ distances in the stylized phantoms were computed using a ray-tracing technique available through Monte Carlo radiation transport simulations in MCNP6. Organ distances in the voxel phantom were found using phantom matrix manipulation. Quantification of differences in organ chord lengths between the phantom series displayed that the organs of the stylized phantom series are typically situated farther away from one another than within the voxel phantom series. The impact of this work was to characterize the intra-organ and inter-organ distributions to explain the variations in updated internal dose coefficient quantities (i.e. specific absorbed fractions) while providing relevant data defining the spatial and volumetric organ distributions in the phantoms for use in subsequent internal dosimetric computations, with prospective relevance to patient-specific individualized dosimetry, as well as informing machine learning definition of organs using these reference models.

Assessment of sound propagation for the urban air mobility

The noise generated by vertical takeoff and landing vehicles (VTOL) operating in urban environnement is a determinant factor for the community acceptance. The ray-tracing method used for predicting road and raylway noise in urban areas can also be applied to the Urban Air Mobility context. In densely populated urban area, the multipath of sound wave occurs due to numerous reflections on the buildings walls. Such a configuration generates both constructive and destructive interferences, given rise to a complex shape of the spectra, that can be difficult to explain. To assess ray codes dedicated to road noise for this kind of configurations, simple test cases such as a corner and a canyon based on image sources are proposed. The prediction is performed in octave bands in the frequency range 63 Hz to 8000 Hz, including acoustical source at high altitudes to account for the VTOL flight. A good agreement is found between the reference solution derived from the image-source and the ray tracing technique. In particular close to the corner a significant increase of about 9 dB can be found. When both the source and the microphone are in the canyon, an inscrease up to 14dB can be found.

Observational predictions of LQG motivated polymerized black holes and constraints from Sgr A* and M87*

Loop quantum gravity inspired partial polymer quantization in four-dimensional spacetime leads to a globally regular black hole with a single horizon. The polymerized black hole metric is characterized by the minimum length parameter k, and mimics the Schwarzschild black hole in the weak-field limit. We present an analytic and numerical investigation of the strong gravitational lensing and shadow morphology to determine the observational impacts of quantum effects. Interestingly, the light deflection angle, the angular separation between the outermost relativistic image, and magnification are significantly larger than those for the Schwarzschild black hole. Using the ray-tracing technique, we simulate the black hole shadows under three distinct optically thin accretion models: static spherical accretion, radially infalling spherical accretion, and the thin accretion disk model. Polymerized black holes' shadow morphology strongly depends on k. We derive constraints on k from the M87* and Sgr A* black hole shadow observations from the Event Horizon Telescope.

Channel Characterization and Ray-Tracing Assisted Stochastic Modeling for Urban Vehicle-to-Infrastructure Terahertz Communications

To support intelligent vehicular services, vehicular ad-hoc networks (VANET) require high-speed communications from vehicles to infrastructure (V2I). To meet such demands, the Terahertz (THz) band, with abundant spectrum resources, is envisioned as a promising solution. However, a premise problem is channel modeling for THz V2I communications. In this paper, ray-tracing (RT) techniques are utilized to analyze the V2I channel in an urban scenario at 300 GHz. Channel statistics, including path loss, shadow fading, etc, are thoroughly characterized. The parameters of multi-path components (MPCs) and similarity of MPCs existing on identical streets are analyzed and modeled. Furthermore, the birth and death processes of MPCs are carefully characterized and modeled. A new criterion, namely, the virtual transmitter position scheme, is proposed to determine the birth and death of MPCs and the evolution of MPCs during their lifetime. Based on this, a ray-tracing assisted stochastic channel model (RTA-SCM), is proposed, which combines the RT technique and stochastic processes. The effectiveness and accuracy of RTA-SCM are validated by comparing it against RT data and geometry-based stochastic models. The proposed model can be utilized in time-varying THz V2I communications.

Early detection and assessment of invisible cracks in compressed oral solid dosage forms

In the pharmaceutical manufacturing industry, real-time in situ quality monitoring for detecting defects at an early stage is a desirable ability, especially in high-rate production, to minimize downstream quality-related issues, financial losses, and timeline risks. In this study, we focus on the early detection of crack formation in compressed oral solid dosage (OSD) forms at its onset before complete delamination and/or capping in downstream processing. The detection of internal tablet cracks related to local micro-stress/strain states, internal granularity (texture), and micro-structure failures is rather unlikely by traditional testing methods, such as the USP reference standards for friability, fracturing, or hardness testing. In addition, these tests do not permit the objective and quantitative evaluation of the influence of formulation and process parameters, which are critical for the development of high-quality drug products manufactured at high rates on a large scale. Internal cracks (potentially resulting in ‘capping’ and/or ‘lamination’) under high-strain compaction of highly visco-elastic powder materials are a common failure mode. In the current study, two approaches are introduced and utilized for non-destructively detecting and evaluating hidden cracks in pharmaceutical compacts based on (i) varying axial load–displacement measurements and (ii) ultrasonic reflection ray tracing. The reflection ray tracing technique is a non-destructive, inexpensive, rapid, and material-sparing approach, which makes it advantageous for real-time quality monitoring and defect characterization applications. The varying axial load–displacement technique is more suitable for analytical studies, especially in the design and development phases of compressed OSD products. In this study, as a model application, utilizing these two approaches, it is demonstrated how internal and external cracks can be detected, localized, characterized, and analyzed as a function of disintegrant ratio and main compression force. Various uses of these two techniques in practice, such as in Continuous Manufacturing (CM) and Real-Time Release Testing (RTRT), are also discussed.

Thin accretion disc luminosity and its image around rotating black holes in perfect fluid dark matter

ABSTRACTMotivated by the fact that the universe is dominated by dark matter and dark energy, we consider rotating black holes surrounded by perfect fluid dark matter and study the accretion process in thin disc around such black holes. Here, we are interested in how the presence of dark matter affects the properties of the electromagnetic radiation emitted from a thin accretion disc. For this purpose, we use the Novikov–Thorne model and obtain the electromagnetic spectrum of an accretion disc around a rotating black hole in perfect fluid dark matter and compare with the general relativistic case. The results indicate that for small values of dark matter parameter we considered here, the size of the innermost stable circular orbits would decrease and thus the electromagnetic spectrum of the accretion disc increases. Therefore, discs in the presence of perfect fluid dark matter are hotter and more luminous than in general relativity. Finally, we construct thin accretion disc images around these black holes using the numerical ray-tracing technique. We show that the inclination angle has a remarkable effect on the images, whereas the effect of dark matter parameter is small.