Ray Tracing Technique Research Articles

Translation model for CW chord to angle Alpha derived from a Monte-Carlo simulation based on raytracing.

The Chang-Waring chord is provided by many ophthalmic instruments, but proper interpretation of this chord for use in centring refractive procedures at the cornea is not fully understood. The purpose of this study is to develop a strategy for translating the Chang-Waring chord (position of pupil centre relative to the Purkinje reflex PI) into angle Alpha using raytracing techniques. The retrospective analysis was based on a large dataset of 8959 measurements of 8959 eyes from 1 clinical centre, using the Casia2 anterior segment tomographer. An optical model based on: corneal front and back surface radius Ra and Rp, asphericities Qa and Qp, corneal thickness CCT, anterior chamber depth ACD, and pupil centre position (X-Y position: PupX and PupY), was defined for each measurement. Using raytracing rays with an incident angle IX and IY the CW chord (CWX and CWY) was calculated. Using these data, a multivariable linear model was built up in terms of a Monte-Carlo simulation for a simple translation of incident ray angle to CW chord. Raytracing allows for calculation of the CW chord CWX/CWY from biometric measures and the incident ray angle IX/IY. In our dataset mean values of CWX = 0.32±0.30 mm and CWY = -0.10±0.26 mm were derived for a mean incident ray angle (angle Alpha) of IX = -5.02±1.77° and IY = 0.01±1.47°. The raytracing results could be modelled with a linear multivariable model, and the effect sizes for the prediction model for CWX are identified as Ra, Qa, Rp, CCT, ACD, PupX, PupY, IX, and for CWY they are Ra, Rp, PupY, and IY. Today the CW chord can be directly measured with any biometer, topographer or tomographer. If biometric measures of Ra, Qa, Rp, CCT, ACD, PupX, PupY are available in addition to the CW chord components CWX and CWY, a prediction of angle Alpha is possible using a simple matrix operation.

Signatures of misalignment in x-ray cavities of cavity-based x-ray free-electron lasers

Cavity-based x-ray free-electron lasers (CBXFEL) will allow use of optical cavity feedback to support generation of fully coherent x-rays of high brilliance and stability by electrons in undulators. CBXFEL optical cavities comprise Bragg-reflecting flat crystal mirrors, which ensure x-rays circulation on a closed orbit, and x-ray refractive lenses, which stabilize the orbit and refocus the x-rays back on the electrons in the undulator. Depending on the cavity design, there are tens of degrees of freedom of the optical elements, which can never be perfectly aligned. Here, we study signatures of misalignment of the optical components and of the undulator source with the purposes of understanding the effects of misalignment on x-ray beam dynamics, understanding misalignment tolerances, and developing cavity alignment procedures. Betatron oscillations of the x-ray beam trajectory (both symmetric and asymmetric) are one of the characteristic signatures of cavity misalignment. The oscillation period is in the general case a non-integer number of round-trip passes of x-rays in the cavity. This period (unlike the amplitude and offset of the oscillations) is independent of the type of misalignment and is defined by cavity parameters. The studies are performed on an example of a four-crystal rectangular cavity using analytical and numerical wave optics as well as ray-tracing techniques. Both confocal and generic stable cavity types are studied.

Ringing the universe with cosmic emptiness: void properties through a combined analysis of stacked weak gravitational and Doppler lensing

ABSTRACT An essential aspect of cosmic voids is that these underdense regions provide complementary information about the properties of our Universe. Unlike dense regions, voids are avoided by matter and are less contaminated by baryonic processes. The first step to understanding the properties of cosmic voids is to correctly infer their mass profiles. In the literature, various techniques have been implemented. In this paper, we review them and implement a new technique that is based on Doppler lensing. We use a relativistic N-body code, Gevolution, to generate cosmological mass perturbations and implement a three-dimensional (3D) ray-tracing technique that follows the evolution of ray-bundles. We focus on the various properties of cosmic voids (e.g. void size function, 2-point correlation function, and the density profile of voids), and compare the results with their universal trends. We show that when weak lensing is combined with the Doppler lensing we obtain even tighter constraints than weak lensing alone. We also obtain better agreement between density profiles within central parts of voids inferred from lensing and density profiles inferred from halo tracers. The implication of the result relevant to the ongoing and prospective low-redshift spectroscopic surveys is briefly discussed.

UWB Indoor Radio Propagation Modelling in Presence of Human Body Shadowing Using Ray Tracing Technique

This paper presents a ray-tracing method for modelingUltra Wide Bandwidth indoor propagation channels. Avalidation of the ray tracing model with our indoor measurementis also presented. Based on the validated model, the multipathchannel parameter like the fading statistics and root mean squarerms delay spread for Ultra Wide bandwidth frequencies aresimply extracted. The proposed ray-tracing method is basedon image method. This is used to predict the propagation ofUWB electromagnetic waves. First, we have obtained that thefading statistics can be well fitted by log normal distributionin static case. Second, as in realistic environment we cannotneglect the significant impact of Human Body Shadowing andother objects in motion on indoor UWB propagation channel.Hence, our proposed model allows a simulation of propagationin a dynamic indoor environment. Results of the simulation showthat this tool gives results in agreement with those reported inthe literature. Specially, the effects of people motion on temporalchannel properties. Other features of this approach also areoutlined.

Analysis, evaluation and integration of modular natural illumination system using a rectangular Fresnel lens for high performance

Daylighting using natural illumination system (NILS) is gaining popularity due to transition to the renewable and non-conventional energy resources. In the proposed work, optomechanical design, numerical analysis, experimentation and integration of a modular Fresnel lens for NILS to effectively harness the sunlight is discussed. The modular and integrated design delivers uniform light at the receiving area of the daylight transportation system. This modular Fresnel lens is a combination of linear Fresnel lenses designed to offer a moderate concentration ratio to avoid hot spots. The distribution of solar radiation on the focal plane/entry section of the plastic optical fibre bundle (daylight transportation system) is simulated using the ray-trace technique for a lens system with a concentration ratio of 81. The irradiance distributions at the focal plane were found uniform with a radiometric and photometric transmission efficiency of 72.45% and 85.96%, respectively, for the lens element. The overall photometric transmission efficiency of the system with 10 m long plastic/acrylic optical fibre cable was found as 40.97%.

Evaluation of the smart daylighting control performance of the concentrating photovoltaic/daylighting system as the skylight in the building

Regulation of solar transmission through windows offers the potential to reduce energy consumption in buildings. Recently, the daylighting control characteristic of optical concentrators have drawn considerable research attentions owing to their variable transmittance in response to sun motion. In this research, we aim to propose and validate a novel way to smartly regulate the indoor daylighting environment while generating renewable electricity generation at the same time through the concentrating photovoltaic/Daylighting (TLWCPC-PV/D) skylight. This research particularly focuses on the evaluation of smart daylighting control (SDC) performance of it. The optical model of the TLWCPC-PV/D skylight was built with using ray-tracing simulation technique, which is also validated by experiment results. Because of the variable optical concentration process, the TLWCPC shows obvious SDC characteristic: when –32°＜θ＜32°, average daylighting efficiency is 11.15% while when −43°≤θ ≤ –32° and 32°≤θ ≤ 43°, average daylighting efficiency is 58.89%. Five cities with different latitudes are selected to perform the yearly daylighting control analysis. The comparative results indicated that orientation direction has an essential impact on SDC characteristic of the TLWCPC-PV/D skylight and the system in the North-South orientation shows excellent SDC ability i.e. it shows larger daylighting efficiency during the early morning and later afternoon periods while maintains lower daylighting efficiency during the noon period. Compared with other complex and expensive energy-saving glasses, the TLWCPC-PV/D skylight smartly adjusts the solar transmission through the optical concentration process according to sun motion and offers a new strategy of easy fabrication and multi-energy use that opens avenues for both static solar concentrator design and SDC mechanism in energy-saving buildings.

Adaptive 3D ray tracing approach for indoor radio signal prediction at 3.5 GHz

This paper explained an adaptive ray tracing technique in modelling indoor radio wave propagation. As compared with conventional ray tracing approach, the presented ray tracing approach offers an optimized method to trace the travelling radio signal by introducing flexibility and adaptive features in ray launching algorithm in modelling the radio wave for indoor scenarios. The simulation result was compared with measurements data for verification. By analyzing the results, the proposed adaptive technique showed a better improvement in simulation time, power level and coverage in modelling the radio wave propagation for indoor scenario and may benefit in the development of signal propagation simulators for future technologies.

Analytical techniques for polarimetric imaging of accretion flows in the Schwarzschild metric

Emission from an accretion disk around compact objects, such as neutron stars and black holes, is expected to be significantly polarized. The polarization can be used to put constraints on the geometrical and physical parameters of the compact sources – their radii, masses, and spins – as well as to determine the orbital parameters. The radiation escaping from the innermost parts of the disk is strongly affected by the gravitational field of the compact object and the relativistic velocities of the matter. The straightforward calculation of the observed polarization signatures involves a computationally expensive ray-tracing technique. At the same time, having fast computational routines for direct data fitting is becoming increasingly important in light of the currently observed images of the accretion flow around the supermassive black hole in M 87 by the Event Horizon Telescope and infrared polarization signatures coming from Sgr A*, as well as the upcoming X-ray polarization measurements by the Imaging X-ray Polarimetry Explorer and enhanced X-ray Timing and Polarimetry mission. In this work, we obtain an exact analytical expression for the rotation angle of the polarization plane in the Schwarzschild metric accounting for the effects of light bending and relativistic aberration. We show that the calculation of the observed flux, polarization degree, and polarization angle as a function of energy can be performed analytically with a high level of accuracy using an approximate light-bending formula, eliminating the need for the precomputed tabular models in fitting routines.

Simulation of a Low Concentrator Photovoltaic System Using COMSOL

The use of photovoltaic (PV) systems presents a great solution to high energy demand. Many factors limit the output of PV systems. One method of increasing the output of PV systems is to employ concentrators. The function of these concentrators is to increase the amount of solar radiation falling on a PV panel using optical devices. In this work, a simulation of a low concentrated photovoltaic system (LCPV) (V-trough model) will be conducted using COMSOL Multiphysics software package. The ray-tracing technique, based on the finite-element method, was used to study the performance of a V-trough without the incorporation of a tracking system. By investigating the effect of the mirrors’ inclination angles on the performance of the system, the optimum inclination angles were determined. The simulation was done for a non-tilted concentrator photovoltaic (CPV) system if placed in different geographical locations in Saudi Arabia with the inclination of the mirrors being changed every hour of the daylight. It was found that the concentration ratio of the suggested model increased for the city of Jeddah, for example, by 171% and 131% for double and partial coverage cases, respectively. In order to reduce the operation cost, the simulation was repeated with the restriction of the mirrors’ inclination to only three positions during the day. The concentration ratio decreased in this case by not more than 14%. When mirrors were fixed throughout the day, the concentration ratio dropped to about 50%. Such simulations will assist in investigating different designs of PV systems prior to their manufacturing. In addition, it could assist in determining the best geographic location for such CPV systems.

Crustal structure across the Teisseyre-Tornquist Zone offshore Poland based on a new refraction/wide-angle reflection profile and potential field modelling

This paper presents a 230-km long refraction/wide-angle reflection profile that was acquired in the southern Baltic Sea across the Teisseyre-Tornquist Zone (TTZ), the boundary between the East European Craton (EEC) and the West European Platform (WEP). This profile is nearly parallel to the western Polish coast, halfway between Poland and the Danish island of Bornholm. The data acquisition was conducted with 15 ocean bottom seismometers (OBS) and 2 land stations. We applied the trial-and-error iterative ray-tracing technique using all identified seismic phases to derive crustal models by minimizing misfit between calculated and observed P-wave travel-times for individual layers. Final velocity model was further verified by forward potential field modelling, testing various P-wave velocity (Vp) to density relationships. The Moho boundary was inferred at 33–38km depth, deepening towards the EEC, with the local ~3km rise in a 40-km-wide zone north of the Caledonian Deformation Front, corresponding to the elevated middle-crust velocities Vp > 6.5 km/s. The lower and middle crust are mostly continuous along the BalTec profile with only minor perturbations between the EEC and WEP. Nevertheless, the thickness of these crustal layers is poorly constrained by seismic data along the SW section of the profile. In contrast, the upper crust and sedimentary cover can be subdivided into three domains, corresponding, from the NE to SW, to the EEC, TTZ and WEP, respectively. The EEC is characterised by the flat top of the basement, uniformly inclined towards the SW. The TTZ shows rapid thinning of cratonic upper crust and thickening of sedimentary layer. The WEP reveals, despite limited seismic coverage, a 13-km thick sedimentary overburden. The lateral changes of seismic structure within the upper crust and sedimentary cover along the BalTec profile can be attributed to protracted phases of late Palaeozoic-Mesozoic extension punctuated by the Carboniferous and Late Cretaceous inversion phases.

Sensor-aware frontier exploration and mapping with application to thermal mapping of building interiors

The combination of simultaneous localization and mapping (SLAM) and frontier exploration enables a robot to traverse and map an unknown area autonomously. Most prior autonomous SLAM solutions utilize information only from depth sensing devices. However, in situations where the main goal is to collect data from auxiliary sensors such as thermal camera, existing approaches require two passes: one pass to create a map of the environment and another to collect the auxiliary data, which is time consuming and energy inefficient. We propose a sensor-aware frontier exploration algorithm that enables the robot to perform map construction and auxiliary data collection in one pass. Specifically, our method uses a real-time ray tracing technique to construct a map that encodes unvisited locations from the perspective of auxiliary sensors rather than depth sensors; this encourages the robot to fully explore those areas to complete the data collection task and map making in one pass. Our proposed exploration framework is deployed on a LoCoBot with the task to collect thermal images from building envelopes. We validate with experiments in both multi-room commercial buildings and cluttered residential buildings. Using a metric that evaluates the coverage of sensor data, our method significantly outperforms the baseline method with a naive SLAM algorithm.

Stochastic lattice discrete particle modeling of fracture in pervious concrete

AbstractThis article presents a stochastic modeling approach for simulating the mechanical behavior of pervious concrete, based on novel extensions of the lattice discrete particle model. Selected digital images of the internal mesostructure, obtained from physical specimens, are used to survey material features and produce statistically representative descriptions of the pore networks. A procedure for estimating the statistical features of the mesostructure is proposed, and samples of a spatially correlated random field are utilized to numerically reproduce the distribution of the large, connected pores in the material. The numerical samples are linked to the topology of the lattice network by means of two novel techniques proposed herein: (1) a random placement procedure for the poly‐sized spheres representing coarse aggregate and (2) a ray tracing technique, which is used to evaluate the effective distributions of mass, stiffness, and strength of each lattice element according to the local distribution of porosity. Numerical results demonstrate how the proposed model is capable of simulating both the large scatter in strength and the variety of failure modes that are observed when testing physical specimens of pervious concrete. The proposed procedure is generally applicable to different types of materials with varying porosity, opening up new possibilities for the simulation of porous media by means of lattice discrete particle modeling techniques.

Drag and lift coefficients of ellipsoidal particles under rarefied flow conditions.

The capability to simulate a two-way coupled interaction between a rarefied gas and an arbitrary-shaped colloidal particle is important for many practical applications, such as aerospace engineering, lung drug delivery, and semiconductor manufacturing. By means of numerical simulations based on the direct-simulation Monte Carlo (DSMC) method, we investigate the influence of the orientation of the particle and rarefaction on the drag and lift coefficients, in the case of prolate and oblate ellipsoidal particles immersed in a uniform ambient flow. This is done by modeling the solid particles using a cut-cell algorithm embedded within our DSMC solver. In this approach, the surface of the particle is described by its analytical expression and the microscopic gas-solid interactions are computed exactly using a ray-tracing technique. The measured drag and lift coefficients are used to extend the correlations, based on the sine-squared drag law, available in the continuum regime to the rarefied regime, focusing on the transitional and free-molecular regimes. The functional forms of the correlations for the ellipsoidal particles are chosen as a generalization from the spherical case. We show that the fits over the data from numerical simulations can be extended to regimes outside the simulated range of Kn. Our approach allows to achieve a higher precision when compared with existing predictive models from the literature. Finally, we underline the importance of this work in providing correlations for nonspherical particles that can be used for point-particle Euler-Lagrangian simulations to address the problem of contamination from finite-size particles in high-tech mechanical systems.

Design of an off-axis freeform diversity receiver to improve SINR performance of a multi-cell VLC system

This paper introduces a novel and promising design of a freeform diversity receiver (FDR) to reduce the inter-channel interference (ICI) of multi-cell visible light communication (VLC) system. Based on the potential of rotationally non-symmetric freeform optics, we have established the design of an off-axis VLC receiver front-end. In this study, we have performed the detailed design of the freeform surface profiles and have analysed the corresponding fabrication tolerances. Nonetheless, the communication performance of the VLC system using the proposed design has been evaluated with the help of Monte-Carlo based ray-tracing technique. Results show that the system with the proposed FDR significantly outperforms the existing state-of-the-art multi-cell VLC receivers in terms of signal-to-interference-plus-noise ratio (SINR). The spatial SINR ranges from 98 dB to 137 dB while 120.5 dB average SINR is attained over the communication floor. This compact size receiver (15.12 mm × 15.12 mm × 6.76 mm) with substantial wireless reception reliability has prospective future applications in the emerging field of visible light communication and its counterpart Li-Fi.

Towards robust constraints on axion dark matter using PSR J1745-2900

We apply novel, recently developed plasma ray-tracing techniques to model the propagation of radio photons produced by axion dark matter in neutron star magnetospheres and combine this with both archival and new data for the Galactic center magnetar PSR J1745-2900. The emission direction to the observer and the magnetic orientation are not constrained for this object leading to parametric uncertainty. Our analysis reveals that ray-tracing greatly reduces the signal sensitivity to this uncertainty, contrary to previous calculations where there was no emission at all in some directions. Based on a Goldreich-Julian (GJ) model for the magnetosphere and a Navarro-Frenk-White model for axion density in the Galactic center, we obtain the most robust limits on the axion-photon coupling, to date. These are comparable to those from the CAST solar axion experiment in the mass range $\ensuremath{\sim}4.2--60\text{ }\text{ }\ensuremath{\mu}\mathrm{eV}$. If the dark matter density is larger, as might predicted by a ``spike'' model, the limits could be much stronger. For a fixed GJ magnetosphere model, we conclude that of the two principle uncertainties considered in this work---observing angle and dark matter density---the latter is the larger of the two in our present calculations.

Numerical Study on the Influence of the Plasma Properties on the Keyhole Geometry in Laser Beam Welding

Keyhole laser welding is the benchmark for deep-penetration joining processes. It needs high incident laser beam power densities at the workpiece surface to take place. The gaseous phase plays a fundamental role to keep the deep and narrow keyhole cavity open during the process. The plasma created in this process is a mixture of ionized metal vapors and the environmental gas and it develops inside the keyhole (keyhole plasma) and above the workpiece surface (plasma plume). The presence of plasma implicates absorption, scattering, and refraction of laser beam rays. These phenomena alter the power density of the laser beam irradiating the workpiece surface and thus affect the resulting welding process. In this work, a mathematical and numerical model has been developed to calculate the keyhole shape taking into account the plasma absorption effects. The model considers the keyhole walls as the liquid-vapor interface and computes the keyhole geometry applying a local energy balance at this interface. In addition, the model takes into account the multiple reflections effects inside the cavity through an iterative ray-tracing technique, and calculates the absorption mechanism due to inverse Bremsstrahlung for each ray along its segmented path inside the keyhole. Results show the effect of plasma properties on the keyhole shape and depth.

DeepChannel: Robust Multimodal Outdoor Channel Model Prediction in LTE Networks Using Deep Learning

Accurate channel model predictions are crucial in mobile communication systems to identify the coverage area of cellular base stations. It also allows network operators to optimally choose the locations of the new sites, solve coverage gap problems and optimize the current network parameters. Current prediction models use ray tracing techniques that are too computationally expensive and depend on the 3D maps, which are costly and need to be regularly updated. This paper proposes a multi-modal channel model prediction algorithm using satellite images to extract the environmental features and other numerical features. For an accurate evaluation, experimental measurements in the 2100 <i>MHz</i> band are gathered and combined with 2D maps from two different LTE network areas with varying characteristics to practically reference our results and compare the results with the ray-tracing output. Using the well-known AlexNet architecture as a baseline for our model and introducing new numerical features, we achieve a mean absolute error (MAE) of 2.06 <i>dB</i> and 2.6 root-mean-square error (RMSE) with 4.8 <i>dB</i> enhancement compared to only using numerical features. Using transfer learning, we train the model in area one and test it in another area. We achieve 1.47 <i>dB</i> MAE and 1.99 RMSE with 77.34% reduction in the training time.

The B-Scan Image Simulation Method of a Ground-Penetrating Radar Mounted on a Drone Using a High-Frequency Technique

A B-scan image simulation method of a ground-penetrating radar mounted on a drone using a high-frequency technique is proposed. The proposed simulation method aims to predict drone mounted-GPR receiving signals in a complex three-dimensional (3D) scenario, including the reflected signal from various ground types, backscattered signals from considered underground objects, and backscattered volume clutter signals from underground random object clusters. The modeled scenario, including various 3D drone trajectories, target objects, underground random object clusters, ground types, antenna radiation patterns, and desired transmitting time-domain short pulse signals, are taken into account. A high-frequency technique consisting of the geometrical optic (GO) ray-tracing technique to find the GO ray paths, and the GO ray field approximation technique to find the electromagnetic (EM) fields of every GO ray path, are employed instead of conventional numerical methods. This is useful for EM problems with large computational domains. The efficiency in terms of computational time and computer resources is better than that of numerical techniques. Finally, the effect of drone positioning errors, ground types, underground random object clusters, and the antenna radiation patterns on A-scan and B-scan images of a drone-mounted GPR will be illustrated. It is found that the distortion of the hyperbolic signature of underground target objects in the B-scan image occurred by unwanted back-scattered signals or radar clutter from the ground surface, volume clutter from underground random object clusters, and drone positioning errors. Moreover, a high directivity antenna enhances the intensity of the hyperbolic signature. The proposed simulation method will be useful for predicting the drone mounted-GPR signals in various complex 3D scenarios, having various kinds of transmitting signals, and target object configurations and antenna types.

A general Monte Carlo method for polarized radiative transfer in multi-dimensional graded-index media

Lights propagate along space curved paths in multi-dimensional graded-index (GRIN) media, which induces a continuous change of their polarization state and makes the simulation of polarized radiative transfer more challenging. Existing methods are generally not suitable for simulating polarized radiative transfer in the media with arbitrary graded index distribution. In this paper, we present a general Monte Carlo (MC) method with the ray trajectories obtained by the Runge-Kutta ray tracing (RKRT) technique and investigate the polarized radiative transfer in multi-dimensional GRIN media with this method. The space curved trajectory of each light is discretized into a series of polylines, and the variation of polarization state along the trajectory is calculated by the transformations at each discrete point. The method is validated by the simulation of the polarized radiative transfer in a one-dimensional (1D) linear GRIN scattering medium. Furthermore, the 1D GRIN model is expanded to 2D and 3D GRIN models, and the polarized radiative transfer in both cases is investigated. Results show that, in the scattering media with multi-dimensional graded index distribution, the polarization state of lights has a notable effect on the radiative transfer, which must be taken into consideration in the fields requiring high-precision.

Channel Measurement and Ray-Tracing-Statistical Hybrid Modeling for Low-Terahertz Indoor Communications

TeraHertz (THz) communications are envisioned as a promising technology, owing to its unprecedented multi-GHz bandwidth. One fundamental challenge when moving to new spectrum is to understand the science of radio propagation and develop an accurate channel model. In this paper, a wideband channel measurement campaign between 130 GHz and 143 GHz is investigated in a typical meeting room. Directional antennas are utilized and rotated for resolving the multi-path components (MPCs) in the angular domain. With careful system calibration that eliminates system errors and antenna effects, a realistic power delay profile is developed. Furthermore, a combined MPC clustering and matching procedure with ray-tracing techniques is proposed to investigate the cluster behavior and wave propagation of THz signals. In light of the measurement results, physical parameters and insights in the THz indoor channel are comprehensively analyzed, including the line-of-sight path loss, power distributions, temporal and spatial features, and correlations among THz multi-path characteristics. Finally, a hybrid channel model that combines ray-tracing and statistical methods is developed for THz indoor communications. Numerical results demonstrate that the proposed hybrid channel model shows good agreement with the measurement and outperforms the conventional statistical and geometric-based stochastic channel model in terms of the temporal-spatial characteristics.