Critical Angle Of Incidence Research Articles

Air-Coupled Ultrasound Sealing Integrity Inspection Using Leaky Lamb Waves in a Simplified Model of a Lithium-Ion Pouch Battery: Feasibility Study.

Inspecting the sealing integrity of lead tabs is an important means of ensuring the reliability and safety of pouch-type lithium-ion (Li-ion) batteries with a thin multi-layered aluminum (Al) laminated film. This paper presents a new air-coupled ultrasonic non-destructive testing (NDT) inspection method based on leaky Lamb wave transmission; and reception for evaluating the sealing integrity between the lead tab and the Al pouch film. The proposed method uses the critical incidence angle between the air and the layer with the fastest Lamb wave velocity to maximize the signal-to-noise ratio in the through-transmission mode. To determine the critical incidence angle, phantom experiments with two test pieces (i.e., an Al tab and an Al tab sealed with an Al pouch film) are conducted. In addition, 2D scans are performed at various incidence angles for an inhouse pouch-type Li-ion battery with a 1-mm-wide foreign material inserted as a defect. At the critical incidence angle (i.e., 22°), the proposed air-coupled ultrasonic NDT method in through-transmission mode successfully identifies the shape and location of the defect through c-scan image reconstruction. These preliminary results indicate that the proposed air-coupled ultrasonic NDT method with leaky Lamb waves can be used to inspect the sealing integrity of Li-ion pouch batteries in dry test conditions.

Transmission spectra of the ultrarelativistic quasielectrons in the single barrier structures based on the gapped graphene

Contact structures composed of three regions of graphene are considered, the middle of which is the potential barrier for the quasielectrons. Within the framework of the continuum model, based on the Dirac-type equation, the transmission coefficient T of quasielectrons is calculated and analyzed: In one of them the barrier region (which is believed to be of a rectangular shape) is represented by the gapped graphene and out-of-barrier regions—by the gapless one (structure “b”), in another structure on the contrary, the barrier region is a massless graphene, out-ofbarrier regions—massive graphene (structure “a”). It is believed that there is an electrostatic barrier, as well as the Fermi velocity barrier due to the fact that this quantity may acquire different values in the barrier and out-of-barrier regions (υF2 and υF1, respectively) of the considered structure. The presence of an energy gap can lead to significant reduction of T. This fact can be used in the development of transistor-type devices based on graphene. The transmission coefficient T is very sensitive to the parameter ɛ = υF2/υF1. The resonances of the Fabry-Perot type as well as the presence of a critical angle of incidence of quasielectrons on the barrier play an important role in the formation of the transmission spectra. The analysis of the coefficient T dependence on the quasielectron energy and other (except for ɛ) problem parameters, such as the energy gap, the barrier width, is also provided.

Incident-angle dependence of deformation characteristics of aluminum surface under low-energy xenon-ion impact

Ion thruster is a revolution technology with potential applications in space mission but the thruster’s operation lifetime is limited by the sputtering from thruster components. In this work, molecular dynamic simulations are performed to explore the dependence of deformation characteristics of an aluminum surface on incident angle and kinetic energy under low-energy xenon-ion impact. The fraction of non-12-coordinated atoms is used to quantitatively characterize the microstructural evolution and defect density levels. It is found that defect density level has a linear relation with incident energy, and there exists a critical incident angle around 20°, at which the aluminum surface has the maximum defect density level. In addition, a collision model is developed to theoretically reveal the physical mechanisms behind the dependence. Our findings may helpful in developing long endurance electric propulsion devices for practical applications.

Energy reflection and transmission characteristics of acoustic waves in a functionally graded piezoelectric plate immersed into non-viscous fluid

In this work, the reflection and transmission coefficients characteristics of plane waves in a functionally graded (FG) piezoelectric plate immersed in non-viscous liquid (water) are investigated using the stiffness matrix method (SMM). The general solutions of the displacement and the stress are expressed in terms of the eigenvalues and eigenvectors. These are derived from a system of first-order ordinary differential equations with variable coefficients of eight ranks. The SMM is employed to find the relation between the displacements and the tractions on the upper and lower interfaces of the multilayer. Subsequently, the reflection and transmission coefficients of a plane acoustic wave propagating in the FG piezoelectric plates are derived by computing the Poynting vector of each partial wave. The convergence of the SMM is studied through several numerical examples. The effects of the wave incident angle and the gradient coefficients of FG plate on the reflection/transmission characteristics and critical angle are discussed. It is found that the critical angle of incidence is strongly affected by the variation of the linear and the exponential gradient coefficient as well, the resonance frequency shifts to the lower frequency range with the increase of the gradient coefficient.

A study of confinement induced surface structure of P3HT and P3HT/PCBM blend using grazing incidence diffraction

Thin films of P3HT and its blend with PCBM were investigated for vertical segregation of the crystalline structure using grazing incidence diffraction. The films were cast from a solution (P3HT/PCBM) on silicon substrates using the spin-coating technique, and their thickness (170–580 Å) were determined using x-ray reflectivity. In the grazing incidence diffraction technique, the scattered intensity is measured below and above the critical angle of incidence to distinguish the surface structure from the structure of the film underneath. We obtained a diffraction peak due to the lamellar alignment of P3HT perpendicular to the substrate. For thick films of pristine P3HT, the surface was more crystalline as compared to that of the entire film. In the blend films, the surface was found to be amorphous with crystalline structure underneath. The substrate interaction strongly influenced the crystal formation upon annealing at 110 °C as the structure of thicker films (∼600 Å) was strongly modified, whereas that of thinner films (170–290 Å) was negligibly affected.

Pressure and force measurement-based investigations on aerodynamic characteristics of a trapezoidal section

Trapezoidal cross-section with overhangs/lateral cantilevers are being increasingly adopted for medium span cable stayed bridges. Wind tunnel investigations have been carried out to study the aerodynamic characteristics of a trapezoidal section using pressure and force measurement. Simultaneous measurement of fluctuating pressures and overall forces have been carried out under uniform, smooth inflow low for various angles of wind incidence, in the range of −15° and 15° at a wind speed of 12.6 m/s. The variation of mean and fluctuating components of aerodynamic coefficients, viz, drag, lift and torsional moment coefficients with angle of wind incidence have been presented. It has been observed that the mean aerodynamic coefficients evaluated using pressure measurement and force measurement are comparable. From the slope reversal of mean lift coefficient and occurrence of maximum value of mean lift coefficient, the critical angle of wind incidence has been identified as + 6°. Further, it has been observed that the trapezoidal section is stable against transverse galloping and torsional galloping on the basis of quasi-steady assumption.

The interaction between atomic-scale pores and particles

Using first-principles calculations for angstrom-sized pores (3–10 Å), we investigate pore-particle interaction. The translocation energy barrier (TEB) plays important role for the angstrom-scale pores created in 2D-materials such as graphene which is calculated for the translocation of rare gases (He, Ne, Ar, Xe), diatomic molecules (H2 and N2), CO2, and CH4. The critical incident angle (the premeance beyond that is zero) was found to be 40°, which is different from classical model’s prediction of 19–37°. The calculated TEB (Δ) and the surface diffusion energy barrier (Δ′) for the particles with small kinetic diameter (He, Ne and H2), show that the direct flow is the dominant permeation mechanism (Δ ≈ 0 and Δ′ > 30 meV). For the other particles with larger kinetic diameters (Ar, Kr, N2, CH4 and CO2), we found that both surface diffusion and direct flow mechanisms are possible, i.e. Δ and Δ′ ≠ 0. This work provides important insights into the gas permeation theory and into the design and development of gas separation and filtration devices.

Sound reflection of acoustic porous metasurfaces under uniform mean flow

Acoustic metasurfaces are artificial 2D structures with a sub-wavelength thickness that can realize some exotic properties such as non-trivial refraction, broadband and low frequency absorption. However, most relevant studies are still in a static medium, hindering their realistic applications in aviation, where background flow exists. To address it, the effects of mean flow on the acoustic performance of metasurfaces, which is designed based on the generalized Snell's law (GSL) to achieve anomalous reflections, are systemically studied. Firstly, an analytical model of GSL taking the effect of background uniform mean flow into account is built, in which the wavenumbers of both incident and reflected waves are corrected. Then, taking an acoustic porous metasurface for instance, the effectiveness of the derived model is validated by numerical simulations. Results reveal that the reflected waves are deflected in the presence of background flow. The critical incident angle, at which the incident sound wave is converted to surface wave, decreases with the increasing flow velocity. Since the converted surface wave can only propagate along the metasurface, there is little sound energy radiated into far field, which is benefit for the noise attenuation in the presence of flow.

Impact of Nonlocality on Group Delay and Reflective Behavior Near Surface Plasmon Resonances in Otto Structure.

In this work, we study the effects of nonlocality on the optical response near surface plasmon resonance of the Otto structure, and such nonlocality is considered in the hydrodynamic model. Through analyzing the dispersion relations and optical response predicted by the Drude’s and hydrodynamic model in the system, we find that the nonlocal effect is sensitive to the large propagation wavevector, and there exists a critical incident angle and thickness. The critical point moves to the smaller value when the nonlocal effect is taken into account. Before this point, the absorption of the reflected light pulse enhances; however, the situation reverses after this point. In the region between the two different critical points in the frequency scan calculated from local and nonlocal theories, the group delay of the reflected light pulse shows opposite behaviors. These results are explained in terms of the pole and zero phenomenological model in complex frequency plane. Our work may contribute to the fundamental understanding of light–matter interactions at the nanoscale and in the design of optical devices.

Power loss due to soiling on photovoltaic module with and without anti-soiling coating at different angle of incidence

ABSTRACT This paper evaluates the electrical performance of photovoltaic (PV) modules with and without anti-soiling coating at different incidence angles and layers of soiling. Two test coupons were evaluated, one of which was uncoated and the other was coated with an anti-soiling coating. Preliminary examinations for the presence of inherent defects were carried out using Ultraviolet Fluorescence and Electroluminescence imaging techniques. The coupons were then exposed to different layers of soil, accumulated naturally, using an outdoor soiling setup. The short-circuit current (ISC) was measured at different angle of incidence (AOI) before and after the deposition of soil. The maximum drop in the ISC was recorded to be 8.79% and 5.47% at 60° AOI for clean uncoated and coated coupons respectively. The ISC of soiled modules also depicted a similar downward trend in the ISC. Further, it was found under soiled conditions, the critical AOI for the coated coupon was found to be enhanced by 5–15 degrees in comparison to the uncoated one. Henceforth, the significant reduction in soiling loss would ultimately result in the improved efficiency of the module.

Seismic reflectivity and transmissivity parametrization with the effect of normal in situ stress

SUMMARY In situ stress has a significant effect on the properties of underground formations, including seismic wave velocity, porosity and permeability, and further affects seismic reflectivity and transmissivity. Research works on the effect of in situ stress are helpful to construct more precise seismic reflection and transmission coefficient equations. However, previous studies on seismic reflectivity equations did not take the effect of normal in situ stress into consideration. The mechanism of stress on seismic reflectivity and transmissivity is still ambiguous. In this study, we propose new explicit equations to help analyse the changes of seismic reflectivity and transmissivity under the effect of normal in situ stress. First, we deduce the Christoffel equation on the basis of solid acoustoelastic theory. Then, we utilize appropriate boundary conditions to formulate analytical equations of the reflectivity at the interface between two stressed formations, which can provide some new insights into the role of in situ stress. The shear wave birefringence will vanish because we assume that the wave propagates in the X–Z plane. Different rock models with different lithology and saturation are used to analyse the variation of seismic reflectivity and transmissivity with normal stress and incident angle at the interface. The main effect of normal stress on reflection and transmission coefficients is to change amplitude and critical incident angle. When the upper and lower layers are sandstones, the critical incident angle decreases with the increase of normal in situ stress, which is consistent with previous studies. In addition, the reflectivity equation can be degenerated to the Zoeppritz equation when the normal in situ stress vanishes, which further validates that the equation proposed is correct. Seismic reflectivity equations that couple the effect of stress can lay a foundation for direct prediction of in situ stress.

Maximum mean square response and critical orientation under bi-directional seismic excitation

Power Spectrum Analysis (PSA) consists one of the seismic analysis methods proposed by modern code provisions. In the context of PSA, the computation of seismic behavior is achieved by a stochastic analysis that yields mean square values. A method that can be used for the determination of maximum or mean square response is the response history analysis. In the present study, analytical formulas are developed for the determination of the maximum mean square value and the corresponding critical incident angle of any scalar response quantity under two horizontal seismic components for any time interval of ground motion within the context of linear response history analysis. An R/C building is analyzed in order to demonstrate the variation of the maximum mean square response with the incident angle. The maximum mean square response values over all incident angles are calculated using the developed formulas. The results show that the application of the earthquake components along the structural axes can underestimate the mean square response.

Optical properties of molybdenum disulfide based photonic crystal

In this paper, the transmission properties of a one-dimensional photonic crystal containing molybdenum disulfide ( $$MoS_2$$ ) monolayers are studied theoretically using the transfer matrix method. The considered photonic crystal structure contains $$MoS_2$$ monolayers, which are embedded between dielectric layers. It is found that the presence of $$MoS_2$$ causes to creation of a new photonic band gap which is almost omnidirectional and also polarization insensitive. Besides, the spatial distribution of the tangential component of the electric field for a TE-polarized plane wave has been shown for some wavelengths. It is found that the behaviour of the waves from the $$MoS_2$$ induced band gap is different from that of Bragg gaps. Finally, the Gaussian beam propagation inside and outside of the photonic crystal have been simulated using the finite element method for critical wavelengths and different incident angles which verify the behavior of field profiles.

Study of three types of wave leading edge on the performance of industrial turbine blade cascade

PurposeThe blade profile and its geometrical features play an important role in the separation of the boundary layer on the blade. Modifying the blade geometry, which might lead to the delay or elimination of the flow separation, can be considered as a passive flow control methodology. This study aims to find a novel and inexpensive way to reduce loss with appropriate modifications on the leading edge of the turbine blade.Design/methodology/approachThree types of wave leading edges were designed with different wavelengths and amplitudes. The selected numbers for the wave characteristics were based on the best results of previous studies. Models with appropriate and independent meshing have been simulated and studied by a commercial software. The distribution of the loss at different planes and mid-plane velocity vectors were shown. The mass flow average of loss at different incidence angles was calculated for the reference blade and modified ones for the sake of comparison.FindingsThe results show that in all three types of modified blades compared to the reference blade, the elimination of flow separation is observed and therefore the reduction of loss at the critical incidence angle of I = –15°. As the amplitude of the wave increased, the amount of loss growing up, while the increase in wavelength caused the loss to decrease.Originality/valueThe results of the present numerical analysis were validated by the laboratory results of the reference blade. The experimental study of modified blades can be used to quantify numerical solutions.

Wind loading of a finite prism: aspect ratio, incidence and boundary layer thickness effects

A systematic set of low-speed wind tunnel experiments was performed at Re = 6.5x104 and 1.1x105 to study the mean wind loading experienced by surface-mounted finite-height square prisms for different aspect ratios, incidence angles, and boundary layer thicknesses. The aspect ratio of the prism was varied from AR = 1 to 11 in small increments and the incidence angle was changed from α = 0° to 45° in increments of 1°. Two different boundary layer thicknesses were used: a thin boundary layer with δ/D = 0.8 and a thick boundary layer with δ/D = 2.0–2.2. The mean drag and lift coefficients were strong functions of AR, α, and δ/D, while the Strouhal number was mostly influenced by α. The critical incidence angle, at which the prism experiences minimum drag, maximum lift, and highest vortex shedding frequency, increased with AR, converged to a value of αc = 18° ± 2° once AR was sufficiently high, and was relatively insensitive to changes in δ/D. A local maximum value of mean drag coefficient was identified for higher-AR prisms at low α. The overall behaviour of the force coefficients and Strouhal number with AR suggests the possibility of three flow regimes.

Intuitive Model of Surface Modification Induced by Cluster Ion Beams.

Topography development is one of the main factors limiting the quality of depth profiles during depth profiling experiments. One possible source of topography development is the formation of self-organized patterns due to cluster ion beam irradiation. In this work, we propose a simple model that can intuitively explain this phenomenon in terms of impact-induced mass transfer. By coupling our model with molecular dynamics simulations, we can predict the critical incidence angle, which separates the smoothening and roughening regimes. The results are in quantitative agreement with experiments. It is observed that the problems arising from topography development during depth profiling with cluster projectiles can be mitigated by reducing the beam incidence angle with respect to the surface normal or increasing its kinetic energy.

Peak seismic response of a symmetric base-isolated steel building: near vs. far fault excitations and varying incident angle

Since the peak seismic response of a base-isolated building strongly depends on the characteristics of the imposed seismic ground motion, the behavior of a base-isolated building under different seismic ground motions is studied, in order to better assess their effects on its peak seismic response. Specifically, the behavior of a typical steel building is examined as base-isolated with elastomeric bearings, while the effect of near-fault ground motions is studied by imposing 7 pairs of near- and 7 pairs of far-fault seismic records, from the same 7 earthquake events, to the building, under 3 different loading combinations, through three-dimensional (3D) nonlinear dynamic analyses, conducted with SAP2000. The results indicate that near-fault seismic components are more likely to increase the building\'s peak seismic response than the corresponding far-fault components. Furthermore, the direction of the imposed earthquake excitations is also varied by rotating the imposed pairs of seismic records from 0° to 360°,with respect to the major construction axes. It is observed that the peak seismic responses along the critical incident angles, which in general differ from the major horizontal construction axes of the building, are significantly higher. Moreover, the influence of 5% and 10% accidental mass eccentricities is also studied, revealing that when considering accidental mass eccentricities the peak relative displacements of the base isolated building at the isolation level are substantially increased, while the peak floor accelerations and interstory drifts of its superstructure are only slightly affected.

Critical seismic incidence angle of transmission tower based on shaking table tests

Transmission tower-line systems have come to represent one of the most important infrastructures in today's society. Recent strong earthquakes revealed that transmission tower-line systems are vulnerable to earthquake excitations, and that ground motions may arrive at such structures from any direction during an earthquake event. Considering these premises, this paper presents experimental and numerical studies on the dynamic responses of a 1000 kV ultrahigh-voltage (UHV) transmission tower-line system under different seismic incidence angles. Specifically, a 1:25 reduced-scale experimental prototype model is designed and manufactured, and a series of shaking table tests are carried out. The influence of the seismic incidence angle on the dynamic structural response is discussed based on the experimental data. Additionally, the incidence angles corresponding to the maximum peak displacement of the top of the tower relative to the ground (referred to herein as the critical seismic incidence angles) are summarized. The experimental results demonstrate that seismic incidence angle has a significant influence on the dynamic responses of transmission tower-line systems. Subsequently, an approximation method is employed to orient the critical seismic incidence angle, and a corresponding finite element (FE) analysis is carried out. The angles obtained from the approximation method are compared with those acquired from the numerical simulation and shaking table tests, and good agreement is observed. The results demonstrate that the approximation method can properly predict the critical seismic incidence angles of transmission tower-line systems. This research enriches the available experimental data and provides a simple and convenient method to assess the seismic performance of UHV transmission systems.

Development of acoustic and diffuse mismatch models for predicting the Kapitza resistance

This paper is devoted to the acoustic mismatch model and diffusion mismatch model of Kapitza thermal resistance. We consider that diffusion in the transition layer can be represented by variable composition and finite thickness instead of previous assumptions of a “black box” approximation. The effect of heat flow on the interface is reviewed in the acoustic mismatch model where energy is transferred between two different materials and the critical incident angles are taken into account. Finally we provide calculations of the Kapitza resistance for several interfaces (Metal-Sapphire and Metal-Silicon).

Acoustic properties of overheated liquid with gas nuclei during temperature increasing

The characteristics of the reflection and refraction of harmonic waves at its oblique incidence on an interface between a “pure” liquid and liquid with bubbles filled with a vapor–gas mixture have been studied. For the considered problem, we have obtained the dispersion equation and carried out a numerical analysis of the effect of the perturbation frequencies in the range 102–106 s–1 on the dependence of the angle of refraction on that of incidence for three equilibrium temperatures T0. The dependence of the critical angle of incidence on the parameters of a two-phase system and the perturbation frequencies has been studied for the same reflection.