Incident Rays Research Articles

IoT Enabled Low Cost Distributed Angle Measurement Fault Detection System for LFR Plants

The advances in renewable solar energy generation have led to the development of Linear Fresnel Reflector (LFR) technology, in which solar energy is focused by means of a set of longitudinal mirrors onto a tubular receiver. The efficiency in the energy generation process is mainly given by the relation between the angle of incidence of incoming sunlight rays and the fixed location of the elevated tubular receiver. In order to maximize efficiency, the tilt angles for each one of the longitudinal mirrors should vary as a function of solar position tracking. The angular variation process is generally based on the use of encoders implementing a closed-loop feedback system to provide information to the controller in relation with actual mirror angular position. An alternative that has recently emerged is the use of inclinometers in order to obtain angular information, providing a cost-effective solution in order to employ angular information for mirror position control. In this work, a low cost monitoring system for LFR plants is presented, based on the use of a distributed configuration to obtain information related to mirror inclination angles. The proposed system is based on the use of accelerometers coupled to low cost wireless transceivers, enabling distributed real time data collection. The system allows fault or damage detection at all monitored mirror sections, avoiding long periods of efficiency loss of the LFR plant. The configuration and location of the wireless sensor nodes has been analyzed by means of deterministic 3D Ray Launching channel modeling, in order to optimize coverage/capacity relations within the scenario under test. The proposed system has been implemented enabling remote LFR facility monitoring by means of cloud-based infrastructure. In addition, the system is highly scalable, allowing the inclusion of other interesting applications such as intruder detection for security.

Effect of the cold Nazca Slab on the depth of the 660 km discontinuity in South America

The Nazca plate subducting beneath South America makes the 660 km discontinuity deeper and the mantle transition zone (MTZ) thicker under the continent. MTZ variations are often associated with mantle temperature and, therefore, can help confirm the slab position at greater depths. Recent P- and S-wave tomography results show the Nazca plate, near 20° S, being held below the MTZ for longitudes between 70° W and 55° W. We used 63,809 P-wave receiver functions from 1216 stations (using the LQT components of the incident ray system) to image the MTZ in South America. The receiver functions were corrected for move-out, stacked in cells of 3° x 3° degrees every 1° x 1°. We obtained 54,389 RF traces imaging the 410 km and the 660 km discontinuities. The discontinuity times were corrected using the SL2013 global tomography model to obtain depths. A thickened MTZ follows the trend of the Nazca plate beneath the sub-Andes. To the north of 18oS the thickened MTZ is only about 250 km wide; to the south, the thickened zone reaches up to a 1100 km width. This observation clearly indicates that the Nazca slab flattens close to the 660 km discontinuity lowering the mantle temperature and thickening the MTZ. The 660 km discontinuity is more affected than the 410 km, which is consistent with the Nazca slab being held just below the MTZ and not inside the MTZ in most of the region.

Uniform-over-size approximation of the internal fields for scatterers with low refractive-index contrast

We improved the Wentzel-Kramers-Brillouin (WKB) approximation for calculating the electric field inside a scatterer. The new method, named WKBr, additionally takes into account refraction (rotation) of the incident rays at the particle-medium interface. For large particles the WKBr is equivalent to the geometric optics in the limit of relative refractive index m approaching 1. Thus, the resulting accuracy is determined by (m − 1) uniformly for all particle sizes, in contrast to the original WKB, which accuracy deteriorates with increasing size. We extensively studied several versions WKBr for the case of a homogeneous sphere. These versions additionally account for Fresnel transmission and wavefront focusing for rays entering the scatterer, combination of intersecting rays, and the vanishing of the electric field in the shadow region. While keeping the same order of errors with varying (m − 1), they significantly reduce the errors for moderate values of m (from 1.1 to 1.3). Further, we tested the WKB and WKBr as an initial guess in the iterative solution of the linear system in the framework of the discrete dipole approximation (DDA). It allowed us to accelerate the DDA solution without compromising the final accuracy. The acceleration becomes more pronounced with increasing size, while the WKBr becomes clearly superior to the WKB. Moreover, the new initialization of the iterative solver extends the practical applicability of the DDA to size parameter equal to 250, 160, and 140 for m = 1.1, 1.2, and 1.3, respectively. They could not be reached previously due to the stagnation of the iterative solution. We expect similar DDA acceleration for particles of other shapes. One can easily test it for the case of the WKB, since it is already implemented in the open-source ADDA code.

Transient Response of Ventilated Room Enclosure Subjected to Solar Radiation Load

The effect of incident solar radiation ray’s penetration through glassed windows of duct - ventilated room enclosure air is investigated assuming constant solar intensity. The room is supplied with cold dry air through rectangular duct and the air is distributed through two grid ceiling fans located at the duct exit. The effect of fixed solar intensity penetration with variable fans rotational speed at specified time intervals is investigated upon the room temperature distribution and is simulated using the ANSYS CFX package. The results showed the variation in room temperature distribution at a specified time period (1, 2, 3 minutes) with increased fan speed becomes more efficient, also the transient room temperature distribution response to the solar radiation is significantly present in the simulation noticing fans effect on accelerating heat transfer rate through the domain.

Compact periscope-type objective based on wedge-shaped prisms with free-form surfaces

Peculiarities of the optical layout configuration of a periscope-type objective based on wedge-shaped prisms with free-form surfaces are considered. Guidelines on the correction of aberrations of the initial optical system and control of ray incidence angles on the prism surfaces in the areas where ray reflection and refraction zones overlap are formulated. The effectiveness of these guidelines is demonstrated by calculation of a compact periscope-type objective operating in a spectral interval spanning visible and near-infrared ranges. Elements of the optical layout of the objective are fabricated using advanced commercially available types of plastic.

Generalization of ray tracing in symmetric gradient-index media by Fermat's ray invariants.

Ray tracing in gradient-index (GRIN) media has been traditionally performed either by using the analytical or numerical solutions to the Eikonal equation or by creating a layered medium where Snell's law is calculated in each layer. In this paper, an exact general method to perform ray tracing in GRIN media is presented based on the invariants of the system as stated by Fermat's principle when the media presents symmetries. Its advantage, compared with other methods reported in the literature, relies on its easy implementation. Besides the GRIN distribution and the initial conditions of the incident ray, once the invariants of the system are stated the resulting math is simple to solve and interpret. To benchmark the algorithm, ray tracing in typical cases of GRIN media is calculated, finding minimal discrepancies between the analytical solutions and our simulations. The used media are axial refractive index and parabolic index fiber and lenses with spherical gradient-index symmetry, such as: Luneburg's, Gutman's, generalized Maxwell's Fish-eye, Eaton's, and concentrator lenses. Our method can be further applied to distributions with symmetries associated with other common curvilinear orthogonal coordinate systems, in particular to those associated to the separability of the Helmholtz equation that would allow us to investigate wave optics in these GRIN media with the associated geometries.

Development of low-cost reflective plate thermal energy absorber systems for application in South Africa

An innovative solar heat collector system was developed from low-cost materials by applying innovative design technology and using adaptive technologies. The system design entails placing long black polymer pipes connected in series circulation, mounted and positioned in grooves of inverted box rib galvanised steel plating. The grooves reflect and focus the incident rays on the centre piping, concentrating incident sun rays on the black piping and increasing the absorption of thermal energy in the piping filled with circulating water. The circulation of the water is facilitated by a direct-current solar-driven pump powered by a small photovoltaic panel. The thermal energy as collected is stored in a standard household geyser tank. A 3 × 4 m heat absorber of this type collects approximately 10 kWh of energy per day. The estimated cost of the system, considering the capital outlay over an expected ten-year life cycle for the product was estimated at R0.25 per kWh. This pricing competes extremely favourably with the general cost of grid electricity in South Africa for medium-sized households, which is of the order of R2 per kWh up to 1000 kWh per month, including taxes. With an estimated electricity cost escalation of above 5% every year, the ten-year saving for a household using this prototype can be approximately R200 000. The technology and designs developed through the study can create many new business opportunities in South Africa in both urban and rural environments, through manufacturing, installing, repairing, and maintaining the systems.

Intensifying Solar Interfacial Heat Accumulation for Clean Water Generation Excluding Heavy Metal Ions and Oil Emulsions

Solar‐driven interfacial steam generation has emerged as an innovative technique for seawater desalination due to its high photothermal conversion efficiency and potential industrial applications. Herein, a superior interfacial heat accumulation structure composed of semiconductive in situ polymerization (polypyrrole) of nickel foam (IPNF) is reported. The IPNF photothermal layer is assembled with superhydrophilic polyurethane substrate for synchronous water transport and excellent thermal insulation. The 2D ultrablack mesh induces multiple incident rays within the diffused polymerized surface, which allows omnidirectional solar absorption (88.5 %) and intensifying heat localization (49.5 °C @ 1 sun). The state‐of‐the‐art evaporation performances reveal that the integrated IPNF solar evaporator exhibits an excellent evaporation rate (1.74 kg m−2 h−1) and solar‐to‐vapor conversion efficiency (90% excluding heat losses) under 1 kW m−2 solar intensity. Besides this, the long‐term evaporation experiments show negligible discrepancy under seawater conditions (13.27 kg m−2/8 h under 1 kW m−2) and engrain its functioning potential for multimedia and salt rejection (3.2 g × NaCl/240 min). More importantly, herein, insights into different water states in the polymeric network systems during solar‐driven evaporation are provided. This work shows a significant potential to generate freshwater excluding heavy metals and other oil emulsions for industrial applications.

Sound Propagation with Undulating Bottom in Shallow Water

An undulating bottom in shallow water has a significant effect on sound propagation. An acoustic propagation experiment was carried out in the East China Sea in 2020. Measurements along two separate propagation tracks with flat and undulating bottoms were obtained. Abnormal transmission losses (TLs) were observed along the track with the undulating bottom. By using the parabolic equation model RAM and ray theory, these abnormal TLs and the distribution of the sound field energy were analyzed. Numerical simulations indicate that under the shallow water condition with a negative thermocline and for a high frequency (1000 Hz), the incidence and reflection angles of sound rays on the sea bottom are changed due to the undulating sea bottom. The larger the inclination angle of the undulating bottom, the greater the grazing angle changes. These angles changes lead to different sound propagation paths for the undulating bottom and the flat bottom, resulting in the difference of TLs at a certain distance and depth. The undulating bottom will cause energy convergence in the mixed layer when the source and receiver locate above the thermocline.

Coherent Raman scattering imaging with a near-infrared achromatic metalens.

Miniature handheld imaging devices and endoscopes based on coherent Raman scattering are promising for label-free in vivo optical diagnosis. Toward the development of these small-scale systems, a challenge arises from the design and fabrication of achromatic and high-end miniature optical components for both pump and Stokes laser wavelengths. Here, we report a metasurface converting a low-cost plano–convex lens into a water-immersion, nearly diffraction-limited and achromatic lens. The metasurface comprising amorphous silicon nanopillars is designed in a way that all incident rays arrive at the focus with the same phase and group delay, leading to corrections of monochromatic and chromatic aberrations of the refractive lens, respectively. Compared to the case without the metasurface, the hybrid metasurface-refractive lens has higher Strehl ratios than the plano–convex lens and a tighter depth of focus. The hybrid metasurface-refractive lens is utilized in spectroscopic stimulated Raman scattering and coherent anti-Stokes Raman scattering imaging for the differentiation of two different polymer microbeads. Subsequently, the hybrid metalens is harnessed for volumetric coherent Raman scattering imaging of bead and tissue samples. Finally, we discuss possible approaches to integrate such hybrid metalens in a miniature scanning system for label-free coherent Raman scattering endoscopes.

IMPROVING 3D SURFACE MEASUREMENT OF MECHANICAL DETAILS BY STRUCTURED LIGHT USING HIGH DYNAMIC RANGE

The measurement methods using structured light have the advantage of being fast, accurate, and noncontact with the surface of the object. However, these methods have reached its limitation when measuring mechanical details with high surface gloss, due to the unpredictable reflection of incident rays after reaching to object’s surface that, consequently, leads to the simultaneous appearance of several regions with different brightness. To address this problem, we proposed a method of synthesizing extended dynamic range images based on changing the exposure time of the camera and adjusting the illumination of the projector light source so that 3D point coordinates in both bright and dark areas could be obtained through the process. The dual-camera structured light experimental model and the lightcrafter 4500 projector are synchronized through the trigger, using the gray code in combination with the line-shift projection pattern. Experimental results show that the proposed method can precisely reconstruct the 3D surface of mechanical details, while providing higher performance than the state-of-the-art methods.

Teaching and Learning Crystal structures through Virtual Reality based systems

Teaching and learning through Virtual Reality(VR) is an emerging technology in the last few years. In this article, the development and use of a VR based teaching–learning system for crystal structures are discussed. The VR system is designed as a lab environment where a user can do experiments related to crystal structures. The VR system is designed in Unity,11https://www.unity.com/. and Oculus Rift S22https://www.oculus.com/rift-s/. is used as a VR headset. Currently, the system consists of three phases; in the first phase user can visualize the crystal lattice structures, wherein the second one a user can visualize the light interaction with the crystal lattice structure using a virtual torch ray. The third phase is the X-ray Diffraction (XRD) experiment. In this phase, users can perform the XRD experiment in the lab environment by taking a random crystal from a crystal dispenser machine and placing it in the X-ray machine which identifies the chosen crystalline material and analyses the unit cell. The incident ray colour changes when there is a peak found in the crystal for a better understanding of the user. There is also an interactive display where users can increase/decrease the angles of the radiation and also lock and unlock the experiment to view the diffraction plot for the crystal structure. In many cases, it was found that XRD and the crystal structure is available in the course syllabus but there are no experiments to enhance their learning. Therefore an experiment with 39 participants was performed where the maximum participants are new to crystallography. The study was conducted in two phases; in the first phase, participants are asked to watch video tutorials of the topic followed by questionnaires; in the second phase participants are asked to do the VR based experiment and followed by questionnaires related to overall study and experiment. From the analysis of the study we found that everyone found VR based teaching methods are better than traditional book/video studies. Study results give an average score of 56.74% in comparison to VR based learning approach with an average score of 93.81%. Participants who took part in the experiment found the experience interactive and motivating and found it helpful to learn elusive concepts, which can be learned when simulated. For example, one participant wrote: “The VR experience was surreal and was easy to control. Lucid user experience. Got a view of XRD like never seen before”.

Computational Performance of GTD-RT Applied for Evaluation of Electromagnetic Scattering on Rough Surfaces

In this paper, a new robust computational method that applies the geometrical theory of diffraction (GTD) in conjunction with the ray tracing (RT) technique is developed to evaluate the electromagnetic scattering pattern due to a plane wave represented as beam of parallel rays incident on a rough surface of quite arbitrary statistical parameters. The development of the proposed technique is explained in detail taking into consideration the generation of the geometrical model of the rough surface. The Fresnel reflection model is applied under the assumption of arbitrary electrical and optical properties of the rough surface material. Also the polarization of the plane wave primarily incident on the rough surface is taken into consideration. The algorithm developed in the present work accounts for multiple bounces of an incident ray and, hence, it can be considered arbitrary higher-order GTD-RT technique. The accuracy of the obtained results is verified through the comparison with the experimental measurements of the scattering pattern of a light beam incident on rough sheets with specific statistical properties. The numerical results of the present work are concerned with investigating the dependence of the scattering pattern on the surface roughness, refractive index, angle of incidence, and the resolution of the geometric model of the rough surface. Also, it is shown that, for limited resolution of the rough surface model, the accuracy of the calculated scattered field depends on the angle of incidence of the primary beam and the surface roughness.

Investigation of Best Practices in Volumetric Reconstruction for Plenoptic PIV

This paper investigates the effect of smoothing operation in 3D reconstruction using a plenoptic camera. A plenoptic camera - also known as light field camera - features a commercial off the shelf camera with added microlens array (MLA) behind the imaging lens, directly in front of the sensor. The main lens focuses the light to the MLA plane, where each microlens then re-directs the light to small regions of pixels behind, each pixel corresponding to different angle of incident (T. Fahringer (2015)) (Adelson and Wang (1992)). Thus, MLA encodes angular information of incident light rays into the recorded image that assist to acquire 4D information (u,v,s,t) of light-field including both position and angular information of light rays captured by the camera (Ng et al. (2005)) (Adelson and Wang (1992)).

Real-time pre-rectification of aberrations for 3D light-field display based on a constructed virtual lens and ray path tracing

Aberrations caused by optical lens refraction in a light-field display (LFD) are minimized based on real-time pre-rectification. A virtual optical lens with the high precision surface is developed the constructive solid geometry under minimum primitives to rectify the sampling rays, and the virtual lens exhibits the same response to different incident ray wavelengths as the real lens in the LFD optical domain. In addition, assembly misalignment is taken into consideration during the partitioning of the elemental image array so that all the elemental images and the covering lenses can be precisely aligned. After rectifying the sampling rays with the constructed virtual lens, the rays are launched in parallel in the GPU, and path tracing is conducted to shade the element image array. The proposed approach ensures the consistency of the integral photography and LFD processes, which minimize the distortion and increasing the depth of field for three-dimensional (3D) images. Experimental results verify the feasibility of our proposed method. The structural similarity index is improved by 0.1, and 3D images at different depths are correctly expressed. Only three primitives are introduced to the system as a whole, meaning that the extra computation has little impact on the rendering efficiency. Consequently, the real-time generation of 3D light-field images is possible.

A new range‐only measurement‐based glass line feature extraction method

This letter addresses a new range-only measurement-based glass line feature extraction method, which allows a low-cost light detection and ranging (LiDAR) sensor to detect glass-like objects without intensity and multi-echo data. The principle that the emitted LiDAR ray incidence angle with respect to a glass surface is close to 0° is concerned. The geometric relationship between the sensor and glass objects is also considered for successful glass feature extraction. The extracted features are accumulated and reformulated for the generation of glass line features using the RANdom SAmple Consensus algorithm (RANSAC). Two experiments with different robot paths were conducted in a glass environment. The results showed that the proposed method accurately represented glass objects without any false-positive glass feature.

Performance evaluation of a beta-spectrometer comprising a plastic scintillator and multi-wire chamber using a coincidence method

This paper describes an experimental setup developed to measure the beta-ray energy spectrum as well as a Geant4 simulation study conducted to characterize the properties of a beta-spectrometer. The beta-spectrometer comprises a multi-wire chamber to generate signals to indicate the incidence of beta rays and a plastic scintillation detector to measure its energy. The coincidence method of the detector signals was used to remove high gamma-ray interference. To evaluate the performance of the developed spectrometer, the energy spectra were measured with the radionuclide sources (137Cs and 207Bi) emitting internal conversion electrons and gamma rays. The gamma-ray interference removal rate of the spectrometer using the coincidence method was 99.12 ± 0.09%. To reconstruct the beta spectrum from the measured spectrum, Monte Carlo simulations using the Geant4 toolkit were performed to calculate the coefficient related to the effect of gamma rays. The obtained spectrum confirmed that the energy resolution and intrinsic internal conversion peak detection efficiency of the beta-spectrometer were 10.2% at 1 MeV and 91.6%, respectively.

Large-depth-of-field imaging system using a square aperture overlapped micro-lens array

The application of a light-field camera based on an overlapped square aperture micro-lens array (MLA) is reported. The location and direction of the incident light rays are recorded and reconstructed with a large depth of field by this imaging system. The optimized square MLA for light-field imaging, which increases the fill factor and utilization efficiency of the image sensor, is proposed. The array is fabricated by ultra-precision machining and micro-injection molding, which is economical and ensures that the array remains in high accuracy and consistency. Finally, a light-field imaging system is built with lens groups, an MLA, and an adjustable square stop. A comparative study of the field in-depth and super-resolution image is conducted. The experimental results show that the system significantly increases the range of the depth of the field. The reconstructed image is also enhanced with higher resolution and clarity.

Performance analysis of a passive tubular skylight using rectilinear parabolic-profile integrated with plane reflectors and wedge prism

A tubular skylight (TS) is an effective system for transporting natural sunlight into the building interiors. However, the passive nature of the system may not account for the changing orientation of the sun and the conventional daylight collector designs like transparent dome are less effective under low altitude sun. This paper focuses on the performance evaluation of specifically designed TS having rectilinear parabolic-profile reflectors integrated with plane surface reflectors and wedge-shaped prism for daylight collection. The designed configuration redirects the low altitude incident rays efficiently into a vertical mirror light pipe having a rectangular cross-section and aims at giving desired levels of lighting throughout the sunny day. Numerical analysis of the same was carried out for various sky conditions. Experimental results for the proposed TS design show improved lighting levels during the low-altitude sun and reduced but consistent lighting during the mid-day. Average illuminance of ~ 400 lx was observed on the floor of the experiment room for the most part of the day. Along with capturing beam sunlight a significant amount of diffuse daylight capturing ability under clear sky conditions is observed using the proposed TS. The average illuminance value obtained on the work plane during winter solstice through the most optimized configured TS was more than twice the lighting value achieved by a conventional daylight-collecting transparent dome and almost twice the lighting value achieved by a TS with a prismatic dome collector. Under overcast sky conditions, the performance of the proposed configuration of TS is at par.

Multi-scale dynamics simulations of molecular polaritons: The effect of multiple cavity modes on polariton relaxation.

Coupling molecules to the confined light modes of an optical cavity is showing great promise for manipulating chemical reactions. However, to fully exploit this principle and use cavities as a new tool for controlling chemistry, a complete understanding of the effects of strong light-matter coupling on molecular dynamics and reactivity is required. While quantum chemistry can provide atomistic insight into the reactivity of uncoupled molecules, the possibilities to also explore strongly coupled systems are still rather limited due to the challenges associated with an accurate description of the cavity in such calculations. Despite recent progress in introducing strong coupling effects into quantum chemistry calculations, applications are mostly restricted to single or simplified molecules in ideal lossless cavities that support a single light mode only. However, even if commonly used planar mirror micro-cavities are characterized by a fundamental mode with a frequency determined by the distance between the mirrors, the cavity energy also depends on the wave vector of the incident light rays. To account for this dependency, called cavity dispersion, in atomistic simulations of molecules in optical cavities, we have extended our multi-scale molecular dynamics model for strongly coupled molecular ensembles to include multiple confined light modes. To validate the new model, we have performed simulations of up to 512 Rhodamine molecules in red-detuned Fabry-Pérot cavities. The results of our simulations suggest that after resonant excitation into the upper polariton at a fixed wave vector, or incidence angle, the coupled cavity-molecule system rapidly decays into dark states that lack dispersion. Slower relaxation from the dark state manifold into both the upper and lower bright polaritons causes observable photo-luminescence from the molecule-cavity system along the two polariton dispersion branches that ultimately evolves toward the bottom of the lower polariton branch, in line with experimental observations. We anticipate that the more realistic cavity description in our approach will help to better understand and predict how cavities can modify molecular properties.