Reflection Phenomena Research Articles

Effect of Variations in Diameter of Extended Inlet on Transmission Loss of Single Expansion Chamber Reactive Muffler with Extended Inlet

Objectives: Muffler with extended inlet has an additional dimension of variable compared to normal mufflers, that is the diameter. Understanding the effect of change in this diameter value affects Transmission Loss. Muffler used for experimentation is a reactive muffler, which cancels the noise waves using reflection phenomenon. Comparison of Computer Aided Engineering (CAE) in experiments to signify the technology advancement. Methods: MATLAB program is created for running the data and analytical solution. Finite element analysis with COMSOL Multiphysics using 3D model of muffler and computer aided engineering is done considering boundary conditions. The real experiment is carried out to evaluate confidence in simulated results where two load method is applied. Findings: Experimental setup results are showing results close to Numerical analysis. Analysis of the study suggest increase in diameter leads to rise in transmission loss. The experimental results of selected dimensions setup also prove same. Various geometric variation in muffler have effect of 10 to 30% on TL, while changing diameter from 10 to 20 mm of extended inlet raise the peak of TL to almost double and increase the average TL by 28%. Novelty: A diameter variation in extended inlet is an empty space in literature till now. This research combines analytical and experimental setups and comparison of results leads to a strong conclusion toward better muffler design. Keywords: Transmission Loss (TL); Single Expansion Chamber reactive muffler; Numerical analysis; Twoload method; Acoustics

Inverse design of broadband acoustic metasurfaces for reflective wavefront modulation through the topology optimization method

The design of broadband acoustic metasurfaces is an important research challenge. Topology optimization with a genetic algorithm (TOGA) is used in this paper to design a set of reflection acoustic metasurfaces with discrete phase shift characteristics. This method allows the design of selective single-frequency and broadband metasurfaces. First, nine metasurface units are designed with a total phase gradient of 2π at 3500 Hz. Simulations and experiments verify the anomalous reflection phenomenon of the metasurface in the reflected sound field and achieve wave focusing and self-bending functions by adjusting the position distribution of the units. Compared with single-frequency optimization studies, broadband acoustic metasurface units are designed with a linear phase dispersion in the range of 2000–5000 Hz, which achieves anomalous reflection with the same reflection angle and acoustic focusing phenomenon under broadband incident sound conditions. The ability of the algorithm to modulate the acoustic phase dispersion and the potential mechanism of generating different phase differences are further investigated. This method provides more accurate phase controllability for broadband acoustic metasurface optimization design and provides some ideas for the design of broadband structures in related fields.

Design of optical elements for an extended light source

Using the previously developed optimization method for an extended light source [Byzov EV, Kravchenko SV, Moiseev MA, Bezus EA, Doskolovich LL. Optimization method for designing double-surface refractive optical elements for an extended light source. Opt Express 2020; 28(17): 24431-24443. DOI: 10.1364/OE.400609], we designed a compact refractive optical element (the ratio of the element height to the light source size being 1.55) providing a uniform illuminance distribution in a shifted rectangular region. An application of the optimization method for calculating the so-called TIR-elements, exploiting the phenomenon of the total internal reflection of rays, is considered. For an extended light source, compact TIR-elements with freeform exit surfaces that generate uniform illuminance distributions in a rectangular region are designed. The results of the work show promise for a wide class of problems of designing compact optical elements for light-emitting diodes.

Experiment on gas flow field of large-caliber hypersonic balance gun in half-space

As one of the main methods to study the characteristics of an object, experiment is the main way to verify the correctness and reliability of numerical results. The hypersonic projectile near the ground launch involves many complex physical phenomena, so the ground surface has an important impact on the flight stability of the projectile and the structural characteristics of the gas flow field. In this paper, we carried out a whole process experiment of a hypersonic projectile from the bottom of the tube to the muzzle based on the 300 mm balance gun. The muzzle pressure and the initial velocity of the muzzle were monitored by the data acquisition system. We obtained the influence of the ground on the gas flow field of the hypersonic projectile through the overpressure data on the ground near the muzzle. Meanwhile, the dynamic characteristics of the launch process are recorded by high-speed photography. The experimental results show that the muzzle shock wave meets the ground, and the reflection phenomenon occurs, forming a wavefront with opposite directions of propagation. It makes the pressure in the lower half of the domain significantly higher than that in the upper half. By analyzing the experimental phenomena and experimental data, this paper shows the development characteristics of the projectile’s flow field, as well as the influence of the ground on the flow field and the motion stability of the projectile.

Research on ultrasonic phased array detection algorithm for TA15/Ti2AlNb multi-layer gradient material structure

Conventional ultrasonic detection methods can detect a TA15/Ti2AlNb gradient material multi-layer structure with many layers; the reflection and refraction phenomena of ultrasonic waves at the partition interface result in considerable attenuation of ultrasonic energy. It is difficult to achieve accurate focusing control of multi-array element synthetic beams, and internal defects cannot be detected. We explored the ‘ultrasonic velocity scale coefficient K’ algorithm to determine the ultrasonic beam propagation refraction path of a multi-layer gradient material structure. The algorithm makes full use of the refraction characteristics of ultrasonic waves on each material layer interface, establishes the acoustic ray-tracing model, analyzes the acoustic ray-tracing propagation path of each array element, and quickly obtains the focusing law. A TA15/Ti2AlNb gradient material specimen was prepared using laser melting deposition (LMD) technology, and a multi-layer structure model was established based on the finite difference time domain (FDTD) method to verify the focusing law. The experimental results of the ultrasonic phased array showed that the proposed algorithm effectively improved the defect detection signal-to-noise ratio (SNR) and imaging quality of the TA15/Ti2AlNb gradient material.

Spin Hall Effect of Nonlinear Photons

AbstractPhotonic spin Hall effect (SHE) refers to the transverse separation of spin photons in refraction and reflection phenomena. The photonic SHE has been investigated in various optical systems including air–glass interfaces, interfaces containing 2D materials, random media, etc. Here, the spin–orbit coupling (SOC) in nonlinear uniaxial crystals is investigated, and the SHE of second‐harmonic photons is demonstrated theoretically and experimentally. The generation and evolution processes of nonlinear spin photons within the crystal are visualized by the derived four wave coupling equations and wavevector‐varying Berry phases. For a focused fundamental beam, two cascaded SOCs occurring in the fundamental and second‐harmonic fields are connected by the nonlinear wave mixing near the focal position. Thus the SHE of nonlinear photons depends on the focal position, different strongly from linear photons whose SHE is independent of the focal position. Similar to the focal‐position‐dependent SHE, the focal‐position‐dependent optical vortex generations are also demonstrated for the nonlinear fields. Finally, a high‐speed modulation scheme for the SHE is proposed based on an electro‐optical polarization controller, which routes nonlinear spin photons into different destinations. These findings deepen the understanding of spin–orbit coupling in nonlinear systems and facilitate the development of spin multiplexed electrooptic devices.

Reflection of plane waves in a rotating nonlocal fiber-reinforced transversely isotropic thermoelastic medium

The present investigation is concerned with the reflection of plane waves from the free surface of a rotating nonlocal, fiber-reinforced, transversely isotropic thermoelastic medium in the context of Lord-Shulman theory. It has been observed that three coupled plane waves travel in the medium with distinct speeds. Using appropriate boundary conditions, the amplitude ratios for the reflected waves are derived and the numerical computations have been carried out using MATLAB software. The modulus of amplitude ratios is presented graphically to exhibit the effects due to presence of fiber-reinforcement, nonlocal and rotation parameters. The expressions of energy ratios have also been derived in explicit form and are portrayed graphically as functions of angle of incidence. The phase velocities of plane waves in transversely isotropic medium are found to depend upon the incident angle, whereas these attain constant values in isotropic medium. The energy conservation law is also justified during the reflection phenomena.

Research on the detection of silica/phenolic composite surface cracks using instantaneous high-power xenon lamp-induced chirp-pulsed radar thermography

In this present study, the high-power instantaneous xenon lamp-induced chirp-pulsed radar thermography was introduced to detect the surface crack of the silicon/phenolic composite which was widely used in the engine nozzle insulation sleeve. Two crack defect specimens were artificially made and detected by chirp-pulsed radar thermography to verify the detection ability of this approach. The cracks of two specimens were made by the diamond scribing process and laser ablation respectively. The differences between them were analyzed by the crack defect detection experiment. The crack defect made by the diamond scratching method is more consistent with the real situation according to the experimental results. The chirp-pulsed radar signal was extracted by the time/frequency signal extraction algorithms [cross-correlation (CC) and dual-orthogonal demodulation algorithms (DOD)]. The influence of parameters such as the power of xenon lamps, excitation frequency, reference pulse width or pulse time, and reference signal delay time on the detection results is mainly investigated by quantitative detection experiments. The results demonstrated that the CC peak and DOD amplitude are more sensitive than the phase when detected the surface crack of silica/phenolic composites. Meanwhile, the reflective phenomenon of the specimen’s surface has a great impact on the detection results. The larger the excitation parameters (such as the excitation frequency and the signal pulse width), the larger the contrast of the crack defect and the smaller the signal-to-noise ratio (SNR). The delay time of the reference signal has a small impact on the SNR and contrast of crack detection. In summary, instantaneous high-power xenon lamp-induced chirp-pulsed radar thermography can realize the reliable quantitative detection of surface cracks of silicon/phenolic composite.

Nd3+-Ion-Sensitized PZT:Er3+/Yb3+ Gradient Luminescent Layers Using Pulsed Laser Deposition as Alternative to Microlens Array Arrangement for Improving Efficiency of Si Solar Photovoltaic

Using the pulsed laser deposition (PLD) technique via Nd:YAG laser ablation, a transparent luminescent phosphor thin film of homogeneous thickness was created that could effectively absorb both near-infrared (NIR) and ultraviolet (UV) light while simultaneously upconverting and downconverting it to visible light. In single-junction microcrystalline silicon solar photovoltaics (SPV), the use of the gradient luminous phosphor Nd3+-sensitized Er3+/Yb3+ codoped zirconate titanate (PZT) layer was examined. The addition of an Nd3+/Er3+/Yb3+ doped PZT luminescent layer to the back of the solar cell could dramatically extend the lifetime of the device when compared to that of a reference Si solar cell. The proposed model’s light motion was also examined using a theoretical simulation (COMSOL). An attempt was made to find an alternative to existing luminescent solar cell concentrators, i.e., microlens array (MLA) configuration, that functions as spatial light modulators in solar cells in this work. The reported gradient phosphor three-layer design is unique and works as an efficient light-trapping design following the phenomena of total internal reflection in multimode optical fibers. The proposed solar photovoltaics was also created with a nanomirror configuration employing semiconductor nanoparticles for effective light absorption in the back reflector layer. When compared to Si-SPV without the luminescent layer, the frequency upconverted visible emissions can be reabsorbed by the SPV and boost the photocurrent, which increases the overall fill factor from 5.30 to 5.99%. The current methodology offers a simple approach for a high-performance luminescent SPV design.

DEČJE MISKONCEPCIJE O SVETLOSNIM FENOMENIMA

In the context of the subjects World around us and Nature and Soci- ety, numerous complex and abstract natural phenomena are studied, which students often misinterpret. The first step in these teaching situations is gaining a deeper insight into the meaning and sources of such naive beliefs. The aim of this research was to investigate misconceptions of students from the first to the fourth grade of elementary school about light phenomena such as sources and propagation of light, nature of sight, transparency of materials, reflection and refraction of light, and shadows, through interviews. Conversa- tions with 24 students, six from each grade, from three elementary schools in Sombor and the surrounding area, were recorded and transcribed. Students’ responses were classified based on similarities and categorized as spontaneous, mixed, “I don’t knowˮ, and scientific. The results indicate the presence of a large number of diverse misconceptions about the examined concepts regardless of the students’ age. Specifically, students often define light based on visible effects it creates (glowing, sparkling, shining) as opposed to darkness (il- luminating darkness, which is not dark), by listing examples of light sources (fire, the Sun, light bulbs, car headlights), and through incomplete descriptions of its nature (source of energy, heat, or life). Widespread misconceptions were also confirmed, such as the Moon being a source of light, light “existingˮ only in sources and on illuminated surfaces (light cannot pass through the air because..., it cannot pass through water because...), and some objects (white paper, fluorescent vest) being visible without light. Unlike the concept of material transparency, which is clear to most students, understanding the formation and characteristics of shadows (shape, position, size, and number) as well as the phenomena of reflection and refraction of light is much more challenging. It can be concluded that within the context of predominantly traditionally designed teaching practices, concept of light represents a significant challenge for younger students. To introduce these and similar concepts correctly into students’ system of concept, adequate and effective teaching ap- proaches are necessary, taking into account children’s misconceptions, the detection of which is also facilitated by this research.

RGB-LED-PHOTOMETER AND THE DIGITAL IMAGE-BASED METHOD USING A SMARTPHONE FOR CHEMISTRY AND PHYSICS TEACHING

This work describes the analysis of molecular spectroscopy in the UV/Vis region, as well as the study of transmittance, absorption, and reflectance phenomena in an undergraduate class using an LED (light emitting diodes)-photometer and digital image-based (DIB) method using a smartphone to compare with a benchtop spectrophotometer and literature data employing paired T-test for 95% confidence. The novelties of this work are focused on the use of simple, low-cost, and portable analytical instrumentation, based on an RGB-LED photometer and DIB using a smartphone, for teaching Chemistry to undergraduate classes. Moreover, discussions were held on concepts related to the Beer-Lambert law, spectroscopy, pH, equilibrium shift, and calculation for determining the equilibrium constant and pKa of bromothymol blue, which was used as proof of concept. The advantages are the use of low-cost instrumentation for teaching Chemistry, students’ access to concepts, such as radiation source, photodetector, transmittance calculation from analog data, regulation of the power of the light emitted by the LED, and details to understand the interaction between matter and light were described by undergraduate students in Physics and Chemistry throughout the course of Experiments in Thermodynamic and Chemical Equilibrium. The better understanding of theoretical concepts and the possibility of taking the RGB-LED-photometer and DIB instrumentation to schools, exhibitions, science fairs, and Chemistry teaching meetings were pointed out by students as the main advantages of the instrumentation and methods described.

Modeling the Geometry of an Underwater Channel for Acoustic Communication

The achievement of efficient data transmissions via underwater acoustic channels, while dealing with large data packets and real-time data fed by underwater sensors, requires a~high data rate. However, diffraction, refraction, and reflection phenomena, as well as phase and amplitude variations, are common problems experienced in underwater acoustic (UWA) channels. These factors make it difficult to achieve high-speed and long-range underwater acoustic communications. Due to multipath interference caused by surface and ocean floor reflections, the process of modeling acoustic channels under the water's surface is of key importance. This work proposes a~simple geometry-based channel model for underwater communication. The impact that varying numbers of reflections, low water depth values, and distances between the transmitter and the receiver exert on channel impulse response and transmission loss is examined. The high degree of similarity between numerical simulations and actual results demonstrates that the proposed model is suitable for describing shallow underwater acoustic communication environments.

Probability increase of target recognition by unmanned complex artificial intelligence.

The thermal imager, which helps operator to orient on area, detect and recognize target in the night conditions, is included as rule in structure of battle modules of unmanned complexes. Partially these tasks are placing on electronics at implementation of artificial intelligence into unmanned complex. But classical thermal imager optical system forms on digital photodetector the two-dimensional image of surrounding space. It hinders the target recognition by battle unmanned complex artificial intelligence at night conditions. It is well known from fundamental theory of phenomena of light reflection and refraction on border “medium-air”, which is described by Fresnel’s low for metals and dielectrics, the polarization rate of thermal objects depends on position of normal of object elementary small surface relatively to direction of its observation (relatively to optical axis of observation device). At the same time, polarization rate of surface own irradiation is increasing at rise of angle between irradiation direction and normal to irradiation surface. And that angle is changing within wide diapason, for example, during exploration from unmanned complex board. On that base there is possibility to determine the third coordinate of target elementary small surface and to image a 3D target on thermal imager display screen or to recognize a target by unmanned complex artificial intelligence. Authors show, including of infrared polarizer, rotating around the thermal imager optical system axis on fixed angles, into thermal imager structure permits to determine the third target coordinate and to increase a probability for its recognition by unmanned complex artificial intelligence in that case.

Investigating wave transmission and reflection phenomena in pantographic lattices using a second-gradient continuum model

In this study, linear plane wave propagation in pantographic lattices is investigated using a two-dimensional (2D) second-gradient continuum model. Primarily, we aim to investigate wave transmission and reflection phenomena occurring when a pantographic lattice is attached to a material modeled by classical first-gradient theory. From a practical point of view, this would be a possible application for pantographic lattices due to their promising mechanical behavior. From a theoretical point of view, this investigation let us to elucidate wave propagation between second- and first-gradient continua. The adapted second-gradient model is first linearized, and the dispersion relations are obtained. Boundary and jump conditions at the discontinuity surface are identified accordingly. It is shown how elastic constants may affect the wave propagation between the two continua and can be tuned to control such wave propagation phenomena.

Dark-Channel Enhanced-Compensation Net: An end-to-end inner-reflection compensation method for immersive projection system.

Immersive projection display system is widely adopted in virtual reality and various exhibition halls. How to maintain high display quality in an immersive projection environment with uneven illumination and the color deviation caused by the inter-reflection of light is still a challenging task. In this paper, we innovatively propose a deep learning-based radiation compensation for an L-shaped projector-camera system. This method employs complex reflection phenomena to simulate the light transport processing in an L-shaped environment, we also designed a Dark-Channel Enhanced-Compensation Net (DECNet) which composed of a convolutional neural network called Compensation Net, a DarkChannelNet and another subnet (such as sensing network) aiming at achieving high-quality reproduction of projected display images. The final output of DECNet is the compensation image to be projected. It is always a critical problem to establish appropriate evaluation and analysis indexes throughout the research of light pollution compensation algorithms. In this paper, PSNR, SSIM, and RMSE are proposed to quantitatively analyze the image quality. The experimental results show that this method has certain advantages in reducing the inter-reflection of the projection plane. And our method could also well replace the traditional process using the backlight transmission matrix. It can be concluded to a certain that this method can be extended to other more complex projection environments with strong scalability and inclusiveness.

Comprehensive study of singular points in a PT-symmetric Thue-Morse multilayer

Parity-time symmetric optical systems have a non-Hermitian Hamiltonian with a purely real spectrum. These systems have been extensively explored owing to their ability to generate exotic photon transport phenomena. In this work, we report the spectral singularity of the one-dimensional aperiodic odd-generation Thue-Morse photonic lattice with parity time symmetry. We showed that this multilayer in addition to obvious unidirectional and bidirectional transparencies, displays interesting and singular properties including absorption, lasing and coherent perfect absorption-lasing singularities. Based on the transfer matrix and scattering matrix (S matrix) methods, the behavior of these singular points and reflectionless and invisibility properties of the structure is analyzed with respect to the thickness of the passive film sandwiched between active layers due to phase shift changes, frequency and incident angle of light. The available values of the structural parameters are investigated to obtain extraordinary transmission and reflection phenomena. These optical systems may possess the potential in the design of novel lasing and coherent perfect absorption optical devices with adjustable applications.

Plane wave propagation in a fiber-reinforced thermoelastic rotating medium with variable thermal conductivity under modified Green–Lindsay model

The present investigation is concerned with the reflection of thermoelastic plane waves in an anisotropic, rotating, fiber-reinforced medium having variable thermal conductivity. Modified Green–Lindsay theory (MGL) is used to formulate the problem. It is shown that there exist three kinds of coupled quasi-waves, namely, (quasi longitudinal displacement), (quasi thermal) and (quasi transverse displacement). Using appropriate boundary conditions, the reflection coefficients, phase velocities and energy ratios of these reflected waves have been calculated numerically and shown graphically to exhibit the effects of rotational and fiber-reinforcement parameters. The characteristics of MGL model are discussed by comparing the numerical results procured for the present model with those procured in the case of Green–Lindsay (GL) model. It has been shown that during reflection phenomenon, the sum of energy ratios is equal to unity at each angle of the incident.

Simulation of thermoelastic wave propagation in 3-D multilayered half-space media

SUMMARY Thermal phenomena are common in both the generation and propagation of seismic waves. To investigate the propagation characteristics of thermoelastic waves generated by point sources in a 3-D multilayered half-space, herein, we develop a method that can solve problems involving coupled mechanical and thermal motions. The method first transforms the governing equations into two sets of first-order ordinary differential equations with a unified form in the frequency–wavenumber domain and then solves them by a generalized reflection and transmission coefficient method. To verify the correctness of our method and the corresponding computer program, we compare our solutions with analytical solutions. We further apply the method to different multilayered models, and the numerical results clearly demonstrate the reflection and transmission phenomena of thermoelastic waves within the interlayer. Furthermore, the generated thermal and seismic signals are synchronous, and the two P waves predicted by generalized thermoelastic theory can be converted into each other. The records on the ground show that thermal motions influence our observation of direct waves, especially in the presence of high thermal conductivity subsurface media, it can significantly impact the propagation of both body and surface waves, making surface seismic observations more complex than those predicted by elastic theory.

A Numerical Study of Wave Propagation and Cracking Processes in Rock-Like Material under Seismic Loading Based on the Bonded-Particle Model Approach

An earthquake is usually followed by a considerable number of aftershocks that play a significant role in earthquake-induced landslides. During the aftershock, the cracking process in rocks becomes more complex because of the formation of faults. In order to investigate the effects of seismic loading on the cracking processes in a specimen containing a single flaw, a numerical approach based on the bonded-particle model (BPM) was adopted to study the seismic loading applied in two orthogonal directions. The results reveal that no transmission and reflection phenomena were observable in the small specimens (76 mm × 152 mm) because they were considerably smaller than the wavelength of the P-wave. Furthermore, under seismic loading, the induced crack was solely tensile in nature. Repeated axial seismic loading did not induce crack propagation after the first axial seismic loading. Cracks began to propagate only when the seismic loading direction was changed from axial to lateral, and then back to axial, ultimately resulting in the failure of the specimen.

Site-Specific Radio Propagation Model for Macrocell Coverage at Sub-6 GHz Frequencies

This article presents a radio propagation model for macrocell coverage predictions in built-up areas for sub-6-GHz frequency band. The proposed two-ray model is a combination of various individual propagation models available in the literature, namely the discrete mixed Fourier transform split-step parabolic-equation (DMFT-SSPE) to characterize reflection and diffraction phenomena due to the presence of buildings and terrain irregularities, the building-transmission model (BTM) to account for the signal attenuation through the nearby buildings and the International Telecommunication Union of Radio-communications (ITU-R) model for attenuation in vegetation to weight the excess attenuation caused by the surrounding vegetation. The performance of the proposed modeling approach was assessed against measurement results obtained from an extensive measurement campaign conducted in Rio de Janeiro, Brazil. The receiver (RX) antenna was assembled on an automotive van, and it was made to travel around the city recording the received signal level. Several drive tests were conducted, including different transmitter (TX) locations and scenarios, and at various frequencies foreseen for 5G systems, namely 750 MHz, 2.5 GHz, and 3.5 GHz.