Ray-tracing Simulation Results Research Articles

Simulation of light propagation in medium with an ultrasonically induced refractive index gradient

Modulation of the refractive index in a medium by external stimuli enables fast and reversible control of light propagation. This technology for controlling light has led to new discoveries in a wide range of research fields from physics to life sciences and has played a major role in the development of photonics devices. In this article, we focus on ultrasound as an external stimulus and have devised a method to control the refractive index of a medium using ultrasound. Our research group has previously discovered that a giant refractive-index gradient (Δn on the order of 10−2) was induced when water was irradiated with high-frequency (100 MHz range), high-intensity (on the order of MPa) ultrasound. Here, we report ray-tracing simulations in a medium with a refractive-index gradient induced by ultrasonic radiation. A numerical model of the refractive-index gradient was developed based on the experimental data, and ray-tracing simulations were performed using the Euler–Lagrange equation. The ray-tracing simulation results were close numerically to the profiles of the laser beam observed in the experiment when the laser beam was incident on the refractive-index-gradient medium.

Efficiency and resolution characterisation of a high-resolution bent crystal X-ray spectrometer using ray-tracing simulations

We report the characterisation of the efficiency and resolution of a high-resolution bent crystal spectrometer under Johannson geometry, using ray-tracing simulations. The spectral resolution is measured experimentally from electron-beam and fast ion-beam interactions with thin solid foils. The X-rays emitted by target atoms as well as projectile ions are studied. The results of the ray-tracing simulations are in very good agreement with the beam-foil spectroscopy experiments. The geometrical factors affecting the resolution are also discussed in detail. We also characterise the detection efficiency of the spectrometer by simultaneous measurements of X-rays using a semiconductor detector, i.e. Si(Li) detector, with known detection efficiency. These results are also compared with the ray-tracing simulation results.

Fully implantable and battery-free wireless optoelectronic system for modulable cancer therapy and real-time monitoring

Photodynamic therapy (PDT) is attracting attention as a next-generation cancer treatment that can selectively destroy malignant tissues, exhibit fewer side effects, and lack pain during treatments. Implantable PDT systems have recently been developed to resolve the issues of bulky and expensive conventional PDT systems and to implement continuous and repetitive treatment. Existing implantable PDT systems, however, are not able to perform multiple functions simultaneously, such as modulating light intensity, measuring, and transmitting tumor-related data, resulting in the complexity of cancer treatment. Here, we introduce a flexible and fully implantable wireless optoelectronic system capable of continuous and effective cancer treatment by fusing PDT and hyperthermia and enabling tumor size monitoring in real-time. This system exploits micro inorganic light-emitting diodes (μ-LED) that emit light with a wavelength of 624 nm, designed not to affect surrounding normal tissues by utilizing a fully programmable light intensity of μ-LED and precisely monitoring the tumor size by Si phototransistor during a long-term implantation (2–3 weeks). The superiority of simultaneous cancer treatment and tumor size monitoring capabilities of our system operated by wireless power and data transmissions with a cell phone was confirmed through in vitro experiments, ray-tracing simulation results, and a tumor xenograft mouse model in vivo. This all-in-one single system for cancer treatment offers opportunities to not only enable effective treatment of tumors located deep in the tissue but also enable precise and continuous monitoring of tumor size in real-time.

Evaluation of DNA lesions and radicals generated by a 233nm far-UVC LED in superficial ex vivo skin wounds.

The application of a far-ultraviolet C (UVC) light emitting diode (LED) of 233nm showed significant bactericidal efficacy at an applied dose between 20 and 80mJcm-2 as reported recently. In addition, only minor epidermal DNA lesions were observed in ex vivo human skin and in vitro epidermal models <10% of the minimal erythema dose of UVB radiation. To broaden the potential range of applications of such systems, e.g. to include postoperative application on wounds for the purpose of decontamination, we assessed how a disruption of normal anatomic skin structure and function influences the skin damage induced by light from 233nm far-UVC LEDs. Thus, we induced superficial skin wounds by mechanical detachment of the stratum corneum in ex vivo human skin. Barrier-disruption of the skin could be successfully determined by measuring an increase in the transepidermal water loss (TEWL) and the stratum corneum loss could be determined morphologically by 2-photon microscopy (2-PM). After far-UVC irradiation of the skin, we screened the tissue for the development of cyclobutane pyrimidine dimers (CPDs) and 6-4 photoproducts (6-4PPs). The abundance of DNA lesions was elevated in wound skin in comparison to intact skin after irradiation with far-UVC. However, no increase in DNA lesions was detected when artificial wound exudate consisting of cell culture medium and serum was applied to the disrupted skin surface prior to irradiation. This effect agrees with the results of ray tracing simulations of the absorption of far-UVC light incident on a superficial skin wound. Interestingly, no significant deviations in radical formation between intact skin and superficially wounded skin were detected after far-UVC irradiation as analyzed by electron paramagnetic resonance (EPR) spectroscopy. In conclusion, 233nm LED light at a dose of 60mJ/cm2 could be applied safely on superficial wounds for the purpose of skin antisepsis as long as the wounds are covered with wound fluid.

Diamond-optic enhanced photon collection efficiency for sensing with nitrogen-vacancy centers.

We present a design to increase the amount of collected fluorescence emitted by nitrogen-vacancy color centers in diamond used for quantum-sensing. An improvement was measured in collected fluorescence when comparing oppositely faced emitting surfaces by a factor of 3.8(1). This matches ray-tracing simulation results. This design therefore improves on the shot noise limited sensitivity in optical readout-based measurements of, for instance, magnetic and electric fields, pressure, temperature, and rotations.

Study on Source Region and Generation Mechanism of Oblique Whistler‐Mode Waves in the Earth's Magnetosphere

AbstractOblique whistler‐mode waves are as important as quasi‐parallel waves in regulating electron dynamics in radiation belts. However, their generation mechanism and corresponding source region are still under debate. By analyzing nearly 7‐year Van Allen Probe‐A data, we have thoroughly investigated lower‐band (&lt;0.5) and upper‐band (&gt;0.5) oblique whistler‐mode waves in the Earth's inner magnetosphere. We found the majority of poleward propagating oblique waves preferentially occur at relatively larger magnetic latitudes (MLATs), and their favored MLATs are strongly dependent on magnetic local time. Combined with ray tracing simulation results, it is proposed that parallel waves generated at the equator propagate toward poles and turn oblique to the ambient magnetic field, leading to oblique waves detected at large |MLAT|. This propagation effect is the main cause of oblique whistler‐mode waves in the Earth's magnetosphere. There also exist some equatorward propagating oblique waves, which are mainly confined within around midnight and considered to be locally excited. Our study provides a comprehensive understanding of the generation and distribution of oblique whistler‐mode waves in the Earth's magnetosphere.

Operational status of the X-ray powder diffraction beamline at the SESAME synchrotron.

The Materials Science (MS) beamline at SESAME (Synchrotron-light for Experimental Science and Applications in the Middle East), dedicated to the X-ray powder diffraction technique, started its operational phase in December 2020 by hosting its first users. The MS endstation comprises a two-circle diffractometer coupled with a PILATUS 300K area detector, with which direct beam images are collected and compared with the initial ray-tracing simulation results. We present a detailed description of the beamline components and the experimental characterization of the main instrumental parameters relying on the instrumental profile and the angular resolution. A representative example for microstructure investigations of a nanocrystalline material is demonstrated.

Simulations of radio-wave anisotropic scattering to interpret type III radio burst data from Solar Orbiter, Parker Solar Probe, STEREO, and Wind

Aims. We use multi-spacecraft observations of individual type III radio bursts to calculate the directivity of the radio emission. We compare these data to the results of ray-tracing simulations of the radio-wave propagation and probe the plasma properties of the inner heliosphere. Methods. We used ray-tracing simulations of radio-wave propagation with anisotropic scattering on density inhomogeneities to study the directivity of radio emissions. Simultaneous observations of type III radio bursts by four widely separated spacecraft were used to calculate the directivity and position of the radio sources. The shape of the directivity pattern deduced for individual events is compared to the directivity pattern resulting from the ray-tracing simulations. Results. We show that simultaneous observations of type radio III bursts by four different probes provide an opportunity to estimate the radio source positions and the directivity of the radio emission. The shape of the directivity varies from one event to another and it is consistent with anisotropic scattering of the radio waves.

Elevation-angle based two-ray path loss model for Air-to-Ground wireless channels

Air-to-Ground (A2G) communication is considered as a significant enabler technology in next-generation networks. To make this a reality, a comprehensive understanding of the A2G channels is vital. This paper presents an Elevation Angle (EA) based two-ray mean path loss model for the A2G channels. In particular, we present closed-form expressions for the path loss with respect to the elevation angle and compare the results with ray-tracing simulation results. Our results show that mean path loss for the A2G channels can be accurately characterized by the proposed EA based two-ray model. Our study investigates different altitudes of the aerial terminal, different types of terrains, and two polarizations, wherein the proposed EA-based two-ray model matches well with the ray-tracing simulation results. Furthermore, a comparison of the proposed model with the other known path loss models in the literature is conducted. Finally, this work reveals an interesting relationship between the elevation angle and the signal down-fades, that these signal down-fades appear at approximately the same elevation angles regardless of the platform altitude.

Vehicle-to-Vehicle Channel Characterization Based on Ray-Tracing for Urban Road Scenarios

In this paper, the vehicle-to-vehicle (V2V) channel characteristics in peak hours at the 5.9 GHz band in two typical urban road scenarios, the urban straight road and the intersection, are investigated. The channel characteristics, such as path loss, root mean square (RMS) delay spread, and angular spread, are derived from the ray-tracing (RT) simulations. Due to the low height of antennas at both the transmitter (Tx) and the receiver (Rx), the line of sight (LOS) between the Tx and the Rx will often be obstructed by other vehicles. Based on the RT simulation results, the shadowing loss is modelled by the multimodal Gaussian distribution, and path loss models in both LOS and non-LOS (NLOS) conditions are obtained. And the RMS delay spread in two scenarios can be modelled by the Weibull distribution. In addition, the deployment of an antenna array is discussed based on the statistics distribution of the angular spread.

Synchrotron X-ray Topography Characterization of Commercial GaN Substrates for Power Electronic Applications

Commercial GaN substrates from different vendors were characterized by synchrotron X-ray topography (XRT) as well as high resolution X-ray diffraction (HRXRD) to evaluate their defect and strain distributions. Synchrotron monochromatic beam X-ray topographs reveal the various dislocation types and their distribution in the GaN materials grown by different methods. By correlating the dislocation contrast with ray-tracing simulation results, the Burgers vectors of dislocations were successfully determined. The ammonothermal-grown GaN material using native seed show the highest quality with low dislocation densities. Patterned HVPE GaN wafers have heterogeneous distribution of dislocations with large areas of low threading dislocation densities. Regular HVPE GaN substrate and ammonothermal GaN grown on an HVPE GaN seed show a very high level of strain, and the dislocation densities are much higher than ammonothermal and patterned HVPE samples.

Homogeneous Flux Distribution in High-Flux Solar Furnaces

Comparisons between experimental data and ray-tracing simulation results are presented for the high-flux SF60 solar furnace available at the Plataforma Solar de Almeria, Spain, which has an estimated thermal power of 60 kW. Since an important issue in many applications of solar concentrated radiation is to obtain a radiation distribution that is as homogeneous as possible over the central working area, so-called radiation homogenisers were also used but the degree of success achieved is just satisfactory, as the results show. Finally, further modelling studies using ray-tracing simulations aiming to attain a homogenous distribution of flux by means of double reflexion using two paraboloid surfaces are presented.

Vehicular Channel in Urban Environments at 23 GHz for Flexible Access Common Spectrum Application

With the development of the vehicular network, new radio technologies have been in the spotlight for maximizing the utilization of the limited radio spectrum resource while accommodating the increasing amount of services and applications in the wireless mobile networks. New spectrum policies based on dynamic spectrum access technology such as flexible access common spectrum (FACS) have been adopted by the Korea Communications Commission (KCC). 23 GHz bands have been allocated to FACS bands by the KCC, which is expected extensively for vehicular communications. The comprehensive knowledge on the radio channel is essential to effectively support the design, simulation, and development of such radio technologies. In this paper, the characteristics of 23 GHz vehicle-to-infrastructure (V2I) channels are simulated and extracted for the urban environment in Seoul. The path loss, shadow factor, Ricean K-factor, root-mean-square (RMS) delay spread, and angular spreads are characterized from the calibrated ray-tracing simulation results, and it can help researchers have a better understanding of the propagation channel for designing vehicular radio technologies and a communication system in a similar environment.

Omnidirectional Light Capture by Solar Cells Mimicking the Structures of the Epidermal cells of Leaves

It is important to develop solar cells that can capture and utilize omnidirectional light in urban environments, where photovoltaic (PV) devices are installed in fixed directions. We report a new design for such light capture, which mimics the structure of a leaf epidermis. First, we analyzed the epidermal structures of different plant species in detail so that we could copy them and fabricate light-trapping layers with different shapes: as lens arrays, pillars, and lens arrays with rough surfaces. Then we analyzed the results of two-dimensional ray-tracing simulations of perfectly aligned and Gaussian-scattered incident light in terms of light-trapping capabilities. Based on these results, we prepared high-performance dye-sensitized solar cells with light-trapping layers that exhibited omnidirectional light capturing functionality. Our layers enhanced the efficiency of obliquely incident light capture by 70%. Therefore, we expect that new possibilities for next-generation PVs, extending beyond the current rigid concepts, will arise upon the application of these results and from findings that build on these results.

Overall detail comparison for a building integrated concentrating photovoltaic/daylighting system

This paper aims to validate an efficient way to use the low-concentration ratio concentrator for the building integrated concentrating photovoltaic/daylighting system, which is able to collect maximum solar energy for the renewable electricity generation and provide the function of daylighting. A 2-D static concentrator has been designed by leaving the lower portion of the outer parabolas near the base area uncoated to form the “daylighting window”, which is named as CPVD (indicating that the concentrator is for the concentrating photovoltaic/daylighting system), while the concentrator with the same structure but can only achieve the onefold function of the electricity generation is named as CPV. In order to address the interaction effects between the concentrating PV performance and daylighting performance, the overall detail comparison is made for the CPVD module and CPV module through the ray-tracing simulation and experimental characterization. It's found that CPVD and CPV have similar optical performance (indicated by concentrating PV performance, optical efficiency, opto-electric gain and flux distribution on the receiver etc.) at various incidence angles, which validates that setting the “daylighting window” have no native effects on the optical performance of the concentrator. At last, in order to quantify the beneficial harvest for the daylighting, the conducive lighting transmittance through the “daylighting window” under two different sky conditions: clear and overcast sky conditions are investigated through the outdoor experiments. The outdoor concentrating photovoltaic/daylighting experiment test rig is built and the transmittance of the CPVD is measured under two different sky conditions. Under the clear sky condition, the daily average transmittance of the CPVD is measured to be 8.73% which is pretty much consistent with the ray-tracing simulation results. Under the overcast sky condition, the transmittance value is lower, the daily average value of which is 7.11%.

Channel Characterization for Intra-Wagon Communication at 60 and 300 GHz Bands

In this paper, the intra-wagon channels at 60 and 300 GHz bands are characterized through measurement-validated ray-tracing (RT) simulations. To begin with, an in-house-developed three-dimensional RT simulator is calibrated and validated by a series of millimeter-wave and Terahertz channel measurements inside a high-speed train wagon. Then, the validated RT simulator is used to conduct extensive simulations with different transmitter (Tx) and receiver deployments. At low frequencies, the channel is strongly influenced by the line of sight (LOS), and therefore, is usually classified into LOS and non-LOS (NLOS) regions. However, the simulation results at 60 and 300 GHz bands show that the first-order reflection also imposes a significant impact on the channel characteristics. This motivates us to further classify the NLOS region into light-NLOS (L-NLOS) and deep-NLOS (D-NLOS) according to the existence of the first-order reflection. Through analyzing the area ratios of LOS, L-NLOS, and D-NLOS regions, we evaluate the Tx deployment strategies and suggest the optimum one. Based on RT simulation results, totally 12 cases (three propagation regions with two Tx deployments at two frequencies) are characterized in terms of path loss, shadow fading, root-mean-square delay spread, Rician $K$ -factor, azimuth/elevation angular spread of arrival/departure, cross-polarization ratio, and their cross correlations. All these parameters are fed into the 3GPP-like quasi-deterministic radio channel generator (QuaDRiGa). The good agreement between QuaDRiGa and RT proves that the 13 tables provided in this paper effectively parameterize the intra-wagon scenario for the standard channel model family. These results provide valuable insights into the system design and evaluation for intra-wagon communications.

Spatial Correlation and Diversity of Low-Latitude Multipath Multimode HF Skywave Radio Channels

To support the reliability and coverage of long-range skywave HF radio communication systems, it is necessary to consider technologies that involve multiple links, such as site diversity, network relay, or cooperative communication. This paper reports a study on the spatial correlation of signals between two HF skywave links with a common end and the benefit of site diversity systems using such links. For this study, two links in a low-latitude region are considered, each with a groundrange of 3044 km and 1895 km, both having a common transmitter and different receivers separated 1900 km apart. The correlation is evaluated from the results of ray-tracing simulations, verified with measurements and simulations for different dates. This study confirms that the correlation between two HF links is low, which can be explained as being the result of sum of multiple paths with random, uncorrelated phase-shifts. The study also proves that site diversity using two convergent links with selective combining can provide diversity gain and reduce the probability of outage significantly. To enhance the benefit of site diversity, a joint space-frequency diversity involving two different frequencies with opposite diurnal characteristics on the primary and alternative link is recommendable.

Simulating the optical alignment of the multiconjugate adaptive optics module for the extremely large telescope

Adaptive optics (AO) instruments for the future extremely large telescopes (ELTs) are characterized by advanced optical systems with diffraction-limited optical quality. Low geometric distortion is also crucial for high accuracy astrometric applications. Optical alignment of such systems is a crucial step of the instrument integration. Due to relative inaccessibility of these giant instruments, automatic alignment methods are also favored to improve the instrument availability after major events, such as extraordinary maintenance. The proposed alignment concept for these systems is described: the notable example which is analyzed here is the case of the multiconjugate AO relay for the future ELT. The results of ray-tracing simulations carried out to validate the method are discussed in detail, covering the error sources, which could degrade the alignment performance.

Modelling and experimental analysis of low concentrating solar panels for use in building integrated and applied photovoltaic (BIPV/BAPV) systems

Geometrically equivalent V-trough and compound parabolic concentrators (CPC) were simulated to characterise the variation in optical efficiency using ray tracing modelling with COMSOL Multiphysics. The effect of CPC truncation and V-trough side wall angles were studied. The truncated CPC demonstrated much improved light acceptance outside the designed angle of acceptance when compared to the original CPC design and V-trough-like characteristics past the original design acceptance angles, consequently reducing material consumption for the manufacture of truncated CPC and therefore reduction in the cost of the system. Truncated CPCs showed optical efficiency equal to their full height counterparts, but a lower concentration ratio (4 at full, 3.6 at half and 2.7 at 50 mm height) due to an equivalent reduction of the inlet aperture size. The V-trough had a higher optical concentration ratio over 15–30° angle of incidents (AoI), with the CPC taking over from 30° AoI upwards. Experiments were performed on a 50 mm truncated CPC and a 22° Trough Wall Angle (TWA) V-trough collector under outdoor conditions. Experimentally measured data showed good correlation with ray tracing simulation results. Both experimental and the ray tracing analyses showed the CPC concentrator achieving a 2.4% higher power output compared to the V-trough design.

Improving the Accuracy of Millimeter-Wave Ray-Tracing Simulations by Modeling Roadside Trees

In recent years, ray-tracing simulation is widely adopted to model outdoor radio propagation. However, existing studies have not focused on the blockage effect of roadside trees. In this study, we model roadside trees using a variety of techniques to analyze their effect on the accuracy of channel modeling using ray-tracing simulation. The roadside trees were modeled as objects transmitting, reflecting, and diffracting electromagnetic waves. We noted that the results of ray-tracing simulations that included roadside trees were more accurate than simulations without tree effects, based on the deviations from the experimentally measured results.