Ray-tracing Program Research Articles

The influence of profiled ceilings on sports hall acoustics: Ground effect predictions and scale model measurements

Over the last few years, reverberation times and sound pressure levels have been measured in many sports halls. Most of these halls, for instance those made from stony materials, perform as predicted. However, sports halls constructed with profiled perforated steel roof panels have an unexpected very low reverberation time in the 125 and 250Hz octave bands. The aim of this study was to provide an explanation for this low-frequency anomaly. A 1:20 scale model of a sports hall was constructed and placed in a small anechoic chamber. The roof could be equipped with differing ceiling types: a flat non-absorbing ceiling, a flat absorbing ceiling, two different profiled non-absorbing ceilings and a profiled absorbing ceiling. With a spark sound source and a small microphone, the impulse-response of the scale model could be registered and analysed. Moreover, a Matlab model was constructed to simulate the acoustic behaviour of the sports hall. This model included the ‘ground effect’ of the roof surface, an effect typically not included in commercial ray-tracing programs. The measurements and the simulations showed that the high sound absorption values of a perforated panel roof structure at 125 and 250Hz can be (partly) explained by its shape. The diffusing properties of the corrugated roof have an effect similar to sound absorption. Because the roof is the largest absorbing surface in a sports hall, this effect can have a significant effect on the low-frequency reverberation time.

Integration of seismic first arrival times to estimate water-air contact and initial water saturation

History matched models have helped reservoir engineers obtain a better understanding of the reservoir and optimize the future productions. Recent years, seismic data is more often to be integrated to improve the reservoir models, however, seismic data has to be inverted to seismic impedance values first.In this study, we introduce a new way to improve the initial reservoir models -integrating the seismic first arrival times to estimate the fluid contacts and initial water saturation. The key aspect of this method that distinguishes it from other methods is that seismic data is integrated directly. As a result, traditional seismic inversion step is not needed, and the data integration are through the comparison of observed first arrival times and simulated first arrival times (raytracing results).In our paper, the feasibility of using seismic first arrival times to improve initial reservoir models is discussed, and the method is verified by using sand tank experiment data. The observed seismic first arrival times were collected during the experiment, and the simulated first arrival times were calculated by seismic raytracing program. Trust region method was used to adjust water-air contact depth and initial water saturation to minimize the difference between simulated and observed data. At last, a good estimation of initial condition is achieved, and it demonstrates a potential of integrating seismic data to improve the reservoir models without an inversion step.

NCPAprop—A software package for infrasound propagation modeling

Developed by the infrasound group at the National Center of Physical Acoustics, University of Mississippi, and a few collaborators, NCPAprop is an open source software package aiming at providing a comprehensive set of tested and validated numerical models for simulating the long range propagation of infrasonic signals through the earth's atmosphere. The algorithms implemented in NCPAprop are designed for frequencies large enough that the effects of buoyancy can be neglected and small enough that propagation to ranges of hundreds to thousands of kilometers is possible without significant signal attenuation. Nominally, NCPAprop can, without modification, be used to efficiently model narrowband propagation from 0.1 to 10 Hz and broadband propagation from 0.05 Hz to 2 or 3 Hz. NCPAprop provides both geometrical acoustic and full wave models which will be presented. The geometrical acoustics part consists of 2-d and 3-d ray tracing programs as well as a non-linear ray theory model. The full wave models consist of a suite of normal mode models of increasing complexity and a Parabolic Equation (PE) model.

Ionospheric effects of magneto-acoustic-gravity waves: Dispersion relation

There is extensive evidence for ionospheric effects associated with earthquake-related atmospheric disturbances. Although the existence of earthquake precursors is controversial, one suggested method of detecting possible earthquake precursors and tsunamis is by observing possible ionospheric effects of atmospheric waves generated by such events. To study magneto-acoustic-gravity waves in the atmosphere, we have derived a general dispersion relation including the effects of the Earth's magnetic field. This dispersion relation can be used in a general atmospheric ray tracing program to calculate the propagation of magneto-acoustic-gravity waves from the ground to the ionosphere. The presence of the Earth's magnetic field in the ionosphere can radically change the dispersion properties of the wave. The general dispersion relation obtained here reduces to the known dispersion relations for magnetoacoustic waves and acoustic-gravity waves in the corresponding particular cases. The work described here is the first step in achieving a generalized ray tracing program permitting propagation studies of magneto-acoustic-gravity waves.

Theoretical simulation and analysis of large size BMP-LSC by 3D Monte Carlo ray tracing model**Project supported by the National Natural Science Foundation of China (Grant No. U1632273) and the Chinese Universities Scientific Fund (Grant No. CX3430000001).

Luminescent solar concentrators (LSC) can reduce the area of solar cells by collecting light from a large area and concentrating the captured light onto relatively small area photovoltaic (PV) cells, and thereby reducing the cost of PV electricity generation. LSCs with bottom-facing cells (BMP-LSC) can collect both direct light and indirect light, so further improving the efficiency of the PV cells. However, it is hard to analyze the effect of each parameter by experiment because there are too many parameters involved in the BMP-LSC. In this paper, all the physical processes of the light transmission and collection in the BMP-LSC were analyzed. A three-dimensional Monte Carlo ray tracing program was developed to study the transmission of photons in the LSC. A larger-size LSC was simulated, and the effects of dye concentration, the LSC thickness, the cell area, and the cell distance were systematically analyzed.

CT breast dose reduction with the use of breast positioning and organ‐based tube current modulation

This study aimed to investigate the breast dose reduction potential of a breast-positioning (BP) technique for thoracic CT examinations with organ-based tube current modulation (OTCM). This study included 13 female anthropomorphic computational phantoms (XCAT, age range: 27-65 y.o., weight range: 52-105.8kg). Each phantom was modified to simulate three breast sizes in standard supine geometry. The modeled breasts were then morphed to emulate BP that constrained the majority of the breast tissue inside the 120° anterior tube current (mA) reduction zone. The OTCM mA value was modeled using a ray-tracing program, which reduced the mA to 20% in the anterior region with a corresponding increase to the posterior region. The organ doses were estimated by a validated Monte Carlo program for a typical clinical CT system (SOMATOM Definition Flash, Siemens Healthcare). The simulated organ doses and organ doses normalized by CTDIvol were used to compare three CT protocols: attenuation-based tube current modulation (ATCM), OTCM, and OTCM with BP (OTCMBP ). On average, compared to ATCM, OTCM reduced breast dose by 19.3±4.5%, whereas OTCMBP reduced breast dose by 38.6±8.1% (an additional 23.8±9.4%). The dose saving of OTCMBP was more significant for larger breasts (on average 33, 38, and 44% reduction for 0.5, 1, and 2kg breasts, respectively). Compared to ATCM, OTCMBP also reduced thymus and heart dose by 15.1±7.4% and 15.9±6.2% respectively. In thoracic CT examinations, OTCM with a breast-positioning technique can markedly reduce unnecessary exposure to radiosensitive organs in anterior chest wall, specifically breast tissue. The breast dose reduction is more notable for women with larger breasts.

Time Series Artificial Neural Network Approach for Prediction of Optical Lens Properties

Well-designed electrostatic cylindrical lenses are commonly used to control charged particles in atomic and molecular physics instruments such as electron guns and electron microscopes. The most commonly used of these, three-element electrostatic lenses are capable of keeping magnification constant for definite image position. The correct determination of focal and aberration characteristics of these lenses is very important for experimental studies. In this study, motions of electrons in three-element electrostatic cylindrical lenses have been investigated with nonlinear autoregressive exogenous based time series artificial neural network technique. The spherical and chromatic aberrations which aect the beam are also predicted with time series artificial neural network technique. This method is a mathematical model that emulates the biological neural networks. The basic working principle of time series artificial neural network technique is training of network with the known data and then prediction of the unknown data. Simulation results from SIMION 8.1 ray-tracing program are used as training and test data set. According to the results obtained from time series artificial neural network technique technique, a considerably agreement is found between simulation and artificial neural network technique prediction results. The study shows that such an artificial neural network model which has time advantage can be applicable to various electron and ion beam apparatus.

Evaluation of loss in optical quality of multifocal intraocular lenses with glistenings

To study the impact of loss in optical quality from glistenings in diffractive multifocal intraocular lenses (IOLs) using ray tracing in a model eye. Independent research laboratory, Irvine, California, USA. Experimental study. A pseudophakic eye model was constructed in Zemax, an optical ray-tracing program, using the Arizona eye model as the basis. The Mie scattering theory was used to describe the intensity and direction of light as it scattered for a spherical particle immersed in a diffractive multifocal IOL. To evaluate the impact of glistening scatter, a more advanced eye model was constructed in Fred, a nonsequential optical ray-tracing software. An evaluation of scatter and modulation transfer function (MTF) was performed for a hydrophobic biomaterial with a refractive index of 1.54 for various sizes and densities of glistenings under mesopic conditions. As predicted by the Mie theory, the amount of scatter was a function of the change in the refractive index, size of the scatterer, and volume fraction of the scatterers. This modeling showed that an increase in density of glistenings can lead to a significant drop of MTF of the IOL. This effect was more pronounced in multifocal IOLs than in monofocal IOLs. Mathematical modeling showed that glistenings in multifocal IOLs lead to a reduction in MTF of the IOL and the pseudophakic eye. The relative loss of MTF in multifocal IOLs was more significant than in monofocal IOLs because of the nature of the design. Drs. DeHoog and Doraiswamy are consultants to Advanced Vision Science, Inc.

Design of the cold neutron triple-axis spectrometer at the China Advanced Research Reactor

The design of the first cold neutron triple-axis spectrometer at the China Advanced Research Reactor is presented. Based on the Monte Carlo simulations using neutron ray-tracing program McStas, the parameters of major neutron optics in this instrument are optimized. The neutron flux at sample position is estimated to be 5.6 ×107n/cm2/s at neutron incident energy Ei=5meV when the reactor operates normally at the designed 60MW power. The performances of several neutron supermirror polarizing devices are compared and their critical parameters are optimized for this spectrometer. The polarization analysis will be realized with a flexible switch from the unpolarized experimental mode.

Simultaneous detection of positive and negative secondary ions

A secondary ion mass spectrometer (SIMS) instrument is described that is configured with two SIMS detectors that are both low-field extraction, quadrupole-based filters. Secondary ions are generated by sputtering with a liquid-metal ion gallium source and column of the type that is common on two-beam electron microscopes. The gallium ion beam, or focused ion beam achieves sub-100 nm focus with a continuous current of up to 300 pA. Positive secondary ions are detected by one SIMS detector, and simultaneously, negative secondary ions are detected by the second SIMS detector. The SIMS detectors are independently controlled for recording mass spectra, concentration depth profiles, and secondary ion images. Examples of simultaneous positive and negative SIMS are included that demonstrate the advantage of this facility for surface analysis and depth profiling. The SIMS secondary ion collection has been modeled using the ray tracing program simion (“simion”, Scientific Instrument Services, Inc., Ringoes, NJ, 08551-1054, see http://www.simion.com) in order to understand the interaction of the secondary ions of opposite polarities in the extraction volume for the purpose of optimizing secondary ion collection.

Spectral reflectance, transmittance, and angular scattering of materials for solar concentrators

The narrow-angle spectral specular reflectance and angular scattering of conventional and novel reflective materials for solar concentrators are measured over the wavelength range 300–2500nm at incidence angles ranging from 15° to 60° using a spectroscopic goniometry system. The solar-weighted specular reflectance at near normal incidence and an acceptance half-angle of 17.5mrad is 0.941 for back-silvered glass, 0.908–0.926 for silvered polymer films, 0.895 for aluminized polyester film, 0.939–0.954 for silvered aluminum sheets, and 0.860 for aluminized aluminum sheet. The angular scattering, quantified in terms of the standard deviation of a Gaussian distribution, is found to be negligible for aluminized polyester (<0.05mrad) and back-silvered glass (<0.07mrad), and noticeable for silvered polymer films (0.27–1.12mrad) and silvered aluminum sheets (0.12–1.66mrad). In addition, the spectral transmittance of semi-transparent materials suitable for protective covers is measured, yielding solar-weighted normal transmittance values of 0.913 and 0.946 for 100μm thin films of ETFE (ethylene-tetrafluoroethylene) and FEP (fluorinated ethylene propylene), respectively. The measured optical properties are incorporated in a Monte Carlo ray-tracing program and applied to analyze the optical performance of solar concentrators.

Optical behavior of surface bubbles

The observation of diamond-like light spots produced by surface bubbles obliquely illuminated is reported. The phenomenon is discussed in terms of geometrical optics, and an explanation is provided attributing the effect to the astigmatism introduced by the deformation of the liquid surface surrounding the bubble. An essential ray tracing program is outlined and used to reconstruct the observed phenomenon numerically.

Near-infrared imaging system for nondestructive inspection of micro-crack in wafer through dicing tape.

Detection of wafer/die crack after the wafer dicing process is important for yield rate control prior to packaging. The traditional approach of microscopic examination is done after the dies are stripped from the dicing tape, and further crack propagation could result from this pick-and-place process. An on-tape crack inspection technique is proposed in this paper so that the crack from the dicing process can be clearly identified. The issues of seeing through the silicon substrate and the scattering at the dicing tape have been resolved, respectively, using a near-infrared wavelength of 1100 nm for illumination and using a feeding index matching liquid for filling the rough surface of the tape. Both the illumination and imaging optics of the inspection system have been designed and simulated with a ray-tracing program, and the prototype demonstrates the ability of seeing through the silicon substrate and dicing tape as well as detecting micro-crack down to 1.25 μm, whose resolution is sufficient for most applications of die crack inspection.

Optical performance of toric intraocular lenses in the presence of decentration.

To evaluate the optical performance of toric intraocular lenses (IOLs) after decentration and with different pupil diameters, but with the IOL astigmatic axis aligned. Optical performances of toric T5 and SN60AT spherical IOLs after decentration were tested on a theoretical pseudophakic model eye based on the Hwey-Lan Liou schematic eye using the Zemax ray-tracing program. Changes in optical performance were analyzed in model eyes with 3-mm, 4-mm, and 5-mm pupil diameters and decentered from 0.25 mm to 0.75 mm with an interval of 5° at the meridian direction from 0° to 90°. The ratio of the modulation transfer function (MTF) between a decentered and a centered IOL (MTFDecentration/MTFCentration) was calculated to analyze the decrease in optical performance. Optical performance of the toric IOL remained unchanged when IOLs were decentered in any meridian direction. The MTFs of the two IOLs decreased, whereas optical performance remained equivalent after decentration. The MTFDecentration/MTFCentration ratios of the IOLs at a decentration from 0.25 mm to 0.75 mm were comparable in the toric and SN60AT IOLs. After decentration, MTF decreased further, with the MTF of the toric IOL being slightly lower than that of the SN60AT IOL. Imaging qualities of the two IOLs decreased when the pupil diameter and the degree of decentration increased, but the decrease was similar in the toric and spherical IOLs. Toric IOLs were comparable to spherical IOLs in terms of tolerance to decentration at the correct axial position.

Aspheric subaperture stitching based on system modeling

Instead of various mathematical stitching algorithms, an aspheric subaperture stitching interferometric method relying on modern computer modeling technique is presented. Based on our previously reported non-null annular subaperture stitching interferometry (NASSI), a simultaneous reverse optimizing reconstruction (SROR) method based on system modeling is proposed for full aperture figure error reconstruction. All the subaperture measurements are simulated simultaneously with a multi-configuration model in a ray tracing program. With the multi-configuration model, full aperture figure error would be extracted in form of Zernike polynomials from subapertures wavefront data by the SROR method. This method concurrently accomplishes subaperture retrace error and misalignment correction, requiring neither complex mathematical algorithms nor subaperture overlaps. Experiment results showing the validity of SROR method are presented.

Imaging quality evaluation of aerodynamically heated faceted dome based on ray tracing

We investigated the influence exerted by the aerodynamic heating of the faceted dome on imaging quality degradation of an airborne optical system. Optical transmission through the faceted dome was simulated using the ray-tracing program based on a recursive algorithm. To validate the ray-tracing program, a ray trace through the homogeneous faceted dome was performed. The program was shown to possess great accuracy. Three kinds of imaging quality evaluation parameters were presented, wave aberration of the exit pupil, point spread function and modulation transfer function. The results show that the aerodynamic heating of the faceted dome significantly affects the airborne optical system.

Modelling high resolution Echelle spectrographs for calibrations: Hanle Echelle spectrograph, a case study

We present a modelling scheme that predicts the centroids of spectral line features for a high resolution Echelle spectrograph to a high accuracy. Towards this, a computing scheme is used, whereby any astronomical spectrograph can be modelled and controlled without recourse to a ray tracing program. The computations are based on paraxial ray trace and exact corrections added for certain surface types and Buchdahl aberration coefficients for complex modules. The resultant chain of paraxial ray traces and corrections for all relevant components is used to calculate the location of any spectral line on the detector under all normal operating conditions with a high degree of certainty. This will allow a semi-autonomous control using simple in-house, programming modules. The scheme is simple enough to be implemented even in a spreadsheet or in any scripting language. Such a model along with an optimization routine can represent the real time behaviour of the instrument. We present here a case study for Hanle Echelle Spectrograph. We show that our results match well with a popular commercial ray tracing software. The model is further optimized using Thorium Argon calibration lamp exposures taken during the preliminary alignment of the instrument. The model predictions matched the calibration frames at a level of 0.08 pixel. Monte Carlo simulations were performed to show the photon noise effect on the model predictions.

Prospective estimation of organ dose in CT under tube current modulation.

Computed tomography (CT) has been widely used worldwide as a tool for medical diagnosis and imaging. However, despite its significant clinical benefits, CT radiation dose at the population level has become a subject of public attention and concern. In this light, optimizing radiation dose has become a core responsibility for the CT community. As a fundamental step to manage and optimize dose, it may be beneficial to have accurate and prospective knowledge about the radiation dose for an individual patient. In this study, the authors developed a framework to prospectively estimate organ dose for chest and abdominopelvic CT exams under tube current modulation (TCM). The organ dose is mainly dependent on two key factors: patient anatomy and irradiation field. A prediction process was developed to accurately model both factors. To model the anatomical diversity and complexity in the patient population, the authors used a previously developed library of computational phantoms with broad distributions of sizes, ages, and genders. A selected clinical patient, represented by a computational phantom in the study, was optimally matched with another computational phantom in the library to obtain a representation of the patient's anatomy. To model the irradiation field, a previously validated Monte Carlo program was used to model CT scanner systems. The tube current profiles were modeled using a ray-tracing program as previously reported that theoretically emulated the variability of modulation profiles from major CT machine manufacturers Li et al., [Phys. Med. Biol. 59, 4525-4548 (2014)]. The prediction of organ dose was achieved using the following process: (1) CTDIvol-normalized-organ dose coefficients (horgan) for fixed tube current were first estimated as the prediction basis for the computational phantoms; (2) each computation phantom, regarded as a clinical patient, was optimally matched with one computational phantom in the library; (3) to account for the effect of the TCM scheme, a weighted organ-specific CTDIvol [denoted as CTDIvol organ,weighted] was computed for each organ based on the TCM profile and the anatomy of the "matched" phantom; (4) the organ dose was predicted by multiplying the weighted organ-specific CTDIvol with the organ dose coefficients (horgan). To quantify the prediction accuracy, each predicted organ dose was compared with the corresponding organ dose simulated from the Monte Carlo program with the TCM profile explicitly modeled. The predicted organ dose showed good agreements with the simulated organ dose across all organs and modulation profiles. The average percentage error in organ dose estimation was generally within 20% across all organs and modulation profiles, except for organs located in the pelvic and shoulder regions. For an average CTDIvol of a CT exam of 10 mGy, the average error at full modulation strength (α = 1) across all organs was 0.91 mGy for chest exams, and 0.82 mGy for abdominopelvic exams. This study developed a quantitative model to predict organ dose for clinical chest and abdominopelvic scans. Such information may aid in the design of optimized CT protocols in relation to a targeted level of image quality.

Infrasonic ray tracing applied to small-scale atmospheric structures: thermal plumes and updrafts/downdrafts.

A ray-tracing program is used to estimate the refraction of infrasound by the vertical structure of the atmosphere in thermal plumes, showing only weak effects, as well as in updrafts and downdrafts, which can act as vertical wave guides. Thermal plumes are ubiquitous features of the daytime atmospheric boundary layer. The effects of thermal plumes on lower frequency sound propagation are minor with the exception of major events, such as volcanoes, forest fires, or industrial explosions where quite strong temperature gradients are involved. On the other hand, when strong, organized vertical flows occur (e.g., in mature thunderstorms and microbursts), there are significant effects. For example, a downdraft surrounded by an updraft focuses sound as it travels upward, and defocuses sound as it travels downward. Such propagation asymmetry may help explain observations that balloonists can hear people on the ground; but conversely, people on the ground cannot hear balloonists aloft. These results are pertinent for those making surface measurements from acoustic sources aloft, as well as for measurements of surface sound sources using elevated receivers.

Highly transparent privacy filter film with image distortion.

We present a novel privacy filter film with transparent micro-cuboid arrays. The privacy filter film, which does not include any opaque materials, rarely affects the normal transparency, whereas it obscures personal information by distorting paths of oblique light rays. The effects of the cuboid size and a gap between the privacy filter and a display are analyzed using a ray-tracing program. The analysis is consistent with the experimental results carried out using the poly-dimethylsiloxane (PDMS) micro-cuboid (100 μm × 100 μm × 200 μm) arrays, which are fabricated by lithography and transfer molding.