Wave Form Research Articles

Study of Acoustic Emission from the Gate of Gallium Nitride High Electron Mobility Transistors

Nitrides are the leading semiconductor material used for the fabrication of high electron mobility transistors (HEMTs). They exhibit piezoelectric properties, which, coupled with their high mechanical stiffness, expand their versatile applications into the fabrication of piezoelectric devices. Today, due to advances in device technology that result in a reduction in the size of individual transistor elements and due to increased structural complexity (e.g., multi-gate transistors), the integration of piezoelectric materials into HEMTs leads to an interesting occurrence, namely acoustic emission from the transistor gate due to piezoelectric effects. This could affect the device’s performance, reliability, and durability. However, this phenomenon has not yet been comprehensively described. This paper aims to examine this overlooked aspect of AlGaN/GaN HEMT operation, that is, the acoustic emission from the gate region of the device induced by piezoelectric effects. For this purpose, dedicated test structures were designed, consisting of two narrow 1.7 μm-wide metallization strips placed at distances ranging from 5 μm to 200 μm fabricated in AlGaN/GaN heterostructures to simulate and examine the gate behavior of the HEMT transistor. For comparison, the test device structures were also fabricated on sapphire, which is not a piezoelectric material. Measurements of acoustic and electrical interactions in the microwave range were carried out using the “on wafer” method with Picoprobe’s signal–ground–signal (SGS)-type microwave probes. The dependence of reflectance |S11| and transmittance |S21| vs. frequency was investigated, and the coupling capacitance was determined. An equivalent circuit model of the test structure was developed, and finite element method simulation was performed to study the distribution of the acoustic wave in the nitride layers and substrate for different frequencies using Comsol Multiphysics software. At frequencies up to 2–3 GHz, the formation of volume waves and a surface wave, capable of propagating over long distances (in the order of tens of micrometers) was observed. At higher frequencies, the resulting distribution of displacements as a result of numerous reflections and interferences was more complicated. However, there was always the possibility of a surface wave occurrence, even at large distances from the excitation source. At small gate distances, electrical interactions dominate. Above 100 µm, electrical interactions are comparable to acoustic ones. With further increases in distance, weakly attenuated surface waves will dominate.

A comparative study on waveform prediction between SPH and S-ALE methods in impact welding

To explore the optimal method for simulating impact welding, we compared detailedly the smoothed particle hydrodynamics (SPH) and structured arbitrary Lagrangian-Eulerian (S-ALE) methods in predicting bonding interface. Based on the experimental results of Cu-Q235 steel atmospheric explosive welding, an in-depth analysis was presented. The results show that the SPH and S-ALE methods converged at element sizes of 2.5 and 2 μm, respectively. When the element size was further reduced to 0.5 % of the wavelength, the errors of both methods were less than 5 %. Benefiting from the gradient mesh, the efficiency of the S-ALE method was 2–4 times that of the SPH method at the same element size. With the addition of the gas medium, the S-ALE method derived the formation mechanism of the gap gas shockwave and indicated that the pressure distribution is not uniform. Furthermore, the local high pressure of the gas shockwave prevents the vortex closure during the wave formation, generating the pore. The calculated pressure and velocity of the wavefront were 20 MPa and 3500 m s−1, respectively. In conclusion, the SPH is suitable for fast previewing waveform interfaces, while the S-ALE method has the advantage of capturing fine waveform structures under various environmental conditions.

A new version of trial equation method for a complex nonlinear system arising in optical fibers

In this study, the dissipation problem of nonlinear pulse in mono mode optical fibers which is governed by the Fokas system (FS) is considered. The solutions of this system have an important role in comprehending the different wave structures in physical settings. Therefore, a new version of the trial equation method (NVTEM) is employed to present the new exact wave solutions of the FS. The advantage of the NVTEM is to use different root possibilities of a polynomial which shape the solutions of the related model. Primarily this system is converted to a nonlinear ordinary differential equation (NODE) via the traveling wave transform to apply the proposed method. Various exact wave solutions to the FS are obtained such as rational function, exponential function, hyperbolic function, and Jacobi elliptic function solutions. Thus, we have revealed solutions featly which are unlike the wave solutions previously found by other analytical methods. The present results depict the formation and development of such waves and their interactions. The exhibition of the solutions is given by 3D plots together with the corresponding 2D plots. The outcomes have shown that the proposed technique is abundant in achieving different wave solutions of many nonlinear differential equations in the field of optics.

Ion kinetic effects on the formation of intense laser-driven shock waves

The ion kinetic effect on the formation of intense laser-driven collisional shock waves is investigated via hybrid fluid-particle-in-cell simulations. It is found that the ion heat flux dominates the shock formation, which is considerably larger than the electron heat flux in the shock region. The rise of the temperature due to the laser energy deposition drives a heatwave into the overdense plasma, creating an electron–ion energy exchange zone between the critical surface and heat wave front. The heated ions, which are generated at the electron–ion energy exchange zone via the friction force, are found to travel to the high-density region and cause a tail distribution gain. Despite the small quantity, the heated tail ions contribute most of the ion heat flux during the shock formation. Additionally, as the electron heat flux decreases, the population of the heated tail ions is reduced, leading to a fall in the ion heat flux. This results in the delay or even suppression of the shock formation, because the ions are in a non-equilibrium state in the vicinity of the shock region, the ratio of the downstream ion temperature to the upstream ion temperature tends to a modestly decrease in comparison to the theory. The study provides a clear picture of the formation process of laser-driven shock waves.

The Kirkwood–Bethe hypothesis for bubble dynamics, cavitation, and underwater explosions

Pressure-driven bubble dynamics is a major topic of current research in fluid dynamics, driven by innovative medical therapies, sonochemistry, material treatments, and geophysical exploration. First proposed in 1942, the Kirkwood–Bethe hypothesis provides a simple means to close the equations that govern pressure-driven bubble dynamics as well as the resulting flow field and acoustic emissions in spherical symmetry. The models derived from the Kirkwood–Bethe hypothesis can be solved using standard numerical integration methods at a fraction of the computational cost required for fully resolved simulations. Here, the theoretical foundation of the Kirkwood–Bethe hypothesis and contemporary models derived from it are gathered and reviewed, as well as generalized to account for spherically symmetric, cylindrically symmetric, and planar one-dimensional domains. In addition, the underpinning assumptions are clarified and new results that scrutinize the predictive capabilities of the Kirkwood–Bethe hypothesis with respect to the complex acoustic impedance experienced by curved acoustic waves and the formation of shock waves are presented. Although the Kirkwood–Bethe hypothesis is built upon simplifying assumptions and lacks some basic acoustic properties, models derived from it are able to provide accurate predictions under the specific conditions associated with pressure-driven bubble dynamics, cavitation, and underwater explosions.

Numerical simulation of the air-water interface effects of an airboat

This paper describes the Air-Water Interface (AWI) occurrence effects of the airboat at various speed, draught, and trim angle. This evaluates the dynamics of AWI with focus on the mechanisms involved in air displacement, the formation of air cushion, boundary layer turbulence, surface tension and wave generation. The analysis involves the change in speed, draught, and trim (0, 1, 1.5 and 2 degrees). The speed of 1.01 and 3.35m/s for displacement and planning regions of the airboat operation were examined. At the AWI, the thin layer of water molecules is affected by the airboat movement at the said trim, it is observed that the layer at the boundary will experience turbulence due to passing air over the layer and the interaction between the air and water at the interface causes mixing and creates waves or ripples at that trim. The wave generated at various trim angles will also create unique wave even at the same speed and draught with a change in trim. The difference in wave formation is seen not to be the same with the change in trim and these changes are observed at the bow and the aft of the vessel. This is also connected to the volume displacement of the boat, the resistance of the vessels, the angle of trim of the airboat and the hull form of the boat. This shows that displacement, resistance, angle of trim and hull form of the boat play critical and crucial roles in wave formation especially for the airboat.

Waves of Precision: A Practical Guide for Reviewing New Tools to Evaluate Mechanical In-Exsufflation Efficacy in Neuromuscular Disorders.

Mechanical insufflation-exsufflation (MI-E) is essential for secretion clearance, especially in neuromuscular disorders. For the best outcomes, initiation of MI-E should be started at the correct time with regular evaluation to the response to treatment. Typically, cough peak flow has been used to evaluate cough effectiveness with and without MI-E. This review highlights the limitations of this and discussed other tools to evaluate MI-E efficacy in this rapidly developing field. Such tools include the interpretation of parameters (like pressure, flow and volumes) that derive from the MI-E device and external methods to evaluate upper airway closure. In this review we pinpoint the differences between different devices in the market and discuss new tools to better titrate MI-E and detect pathological responses of the upper airway. We discuss the importance of point of care ultrasound (POCUS), transnasal fiberoptic laryngoscopy and wave form analysis in this setting. To improve clinical practice newer generation MI-E devices should allow real-time evaluation of waveforms and standardize some of the derived parameters.

Photons in Physics with real Magnetic Charges and the Falsity Existing Notion of Expansion Universe (How Physicists; "Yawn" Real Magnetic Charges, Curved Space and Sentenced the Universe to Expansion)

The experiments of F. Ehrenhaft as well as the experimental and theoretical studies of the author showed that it is magnetic charges are the direct sources of the magnetic field. Eddy currents of magnetic charges (rotating magnetic dipoles g- - g+) which actually exist in atoms and substance, are untwisted by electric current in conductors, are direct sources of the well-known vortex magnetic field rotH. Together with electric charges, magnetic charges make up the shells of atoms, which are actually electromagnetic, not electronic. It is the electromagnetic shells of atoms that are the sources of the vortex electromagnetic (gravitational) field, which is described by the vortex vector rot[E – H]. The vector character of GF is in many respects similar to the vortex magnetic field, which has been known for hundreds of years, but no one has come up with the version of spatial magnetic waves. Therefore, the notion of gravitational waves, according to the author, is another fake, inspired by crooked physics, in which there is absolutely no representation of the real physics of the gravitational field. The introduction of real magnetic charges into the basic physical representations, as well as the discovery by the author of the World Physical Triad, made it possible to clarify the essence of spinor fields which are flows of elementary particles of the world Energo-medium, which are formed by spinor (charged) particles. In addition, the article proves that the concept of the expansion of the Universe was the result of E. Hubble's erroneous (extremely superficial) perception, back in 1929, of the manifestation of the cosmological redshift of the photon frequency, which he interpreted as a Doppler shift in the frequency of the so-called light waves. The inclusion of real magnetic charges in the physical representations showed that the frequency processes in photons are determined exclusively by the intra-photon physics embedded in into at the moment of formation and cannot be the result of any spatial wave formations in the environment, i.e. the shifts of photonic frequency ∆ω have nothing to do with the Doppler effect and depend only on changes in the translational velocity of their source. In other words, the redshift of the photon frequency under the conditions of the translational motion of their sources is exactly the same, both in the case of the source moving to the observer, and in the case of its movement at the same speed away from the observer. As for the violet shift of the photon frequency, this is an unambiguous sign of the rotational dynamics of photon source, and in the case of combined motion of source (translational and rotational), the mechanism of photon frequency pulsations is possible.

Experimental study on the physical mechanism of pulse noise in the tail of a recoilless gun

During the firing process of a recoilless gun, there is a high-intensity pulse noise phenomenon in its rear breech area. In order to obtain the physical mechanism of the pulse noise formation, this article designed experiments and used high-speed cameras and overpressure sensors to discover a “three peaks” phenomenon in the pulse noise at the shooter’s position. Using resistance strain sensors, the changes of strain with time in the chamber and nozzle expansion section of the recoilless gun during the firing process were recorded. By comparing the micro-strain data and overpressure data, the shock waves at the shooter’s position can be categorized into two types: internal shock waves and external shock waves. Internally, the opening of the blocking sheet initiates the formation of the initial shock wave, followed by the formation of a second pressure wave within the combustion chamber. The peak-to-peak interval between these two shock waves is nearly fixed, and the ratio of the dual peaks increases with the distance of the measurement position. The third shock wave forms externally to the nozzle, induced by the explosion of unburned propellant. As the weapon’s distance from the ground increases, the peak values of the overpressure data decrease, and the waveform of this explosion-induced shock wave transitions from a single-peak phenomenon to a double-peak phenomenon. This study can provide a reference for the study of the potential risk of injury to operators using single soldier recoilless guns and similar weapons.

The propagation behavior of reaction wave for Ni/Al clad particle composites under shock loading.

Prior studies indicate that the reaction wave can propagate from the impact surface, but the possibility and the influencing factors of the reaction wave formation are still unclear. This work investigates the propagation behavior of the shock-induced reaction wave for Ni/Al clad particle composites with varying stoichiometry (from 0.5 to 0.75 of the Ni mole fraction) through molecular dynamics simulations. It is found that the solid-state reaction processes with or without wave propagation strongly depend on the conjunction of stoichiometry and shock intensity. Within the cases of wave propagation, the calculated propagation velocity (in the range of 135-170m/s) increases linearly or exponentially with the Ni mole fraction. Furthermore, the thermodynamic criteria for the reaction wave formation, including Al melting at the collision surface and higher temperature gradient, are established by analysis of the shock-induced high-entropy layer. In addition, microstructural characterization reveals the intrinsic mechanisms of the propagation of the reaction wave and the formation of additional reaction wave, namely, the dissolution of Ni into Al and the coalescence of reaction zones. Apart from the propagation behavior, the initial stoichiometry influences the crystallization-dissolution of B2-NiAl during reaction processes, notably through an exponential growth relationship between maximum crystallinity and the Ni mole fraction. These findings may provide a physical basis for improving traditional reaction rate models to break through phenomenological understanding.

Numerical study on the damage of liquid-filled containers subjected to shaped charge jet impact

In the studies of the vulnerability of armored vehicles, the impact of high-velocity penetrators on liquid-filled container components is one of the critical concerns. The purpose of this study is to investigate the structural damage of the liquid-filled container subjected to shaped charge jet impact utilizing the Structural Arbitrary Lagrangian–Eulerian method in ANSYS/LS-DYNA. The numerical model is validated against available experimental data. The validation effort of the numerical model showed very good agreements with experiments in terms of radial shock wave and radial crater formation as a function of time. Using the validated model, the liquid pressure, the energy transfer as well as the influence of overmatch on the impact process were analyzed. The results indicate that the structural damage modes of containers under shaped charge jet impact include perforation and wall deformation. Perforation results from the penetration of the jet tip and tail, while wall deformation is caused by the high-velocity impact of the flowing liquid. In cases where the overmatch (OM) is equal to 1, the contribution of the tip to front and back wall perforation increment primarily depends on the impact velocity. In cases with OM less than 1, the “filtering effect” of the Rolled Homogeneous Armor (RHA) armor plate leads to the loss of the tail's contribution to front wall perforation.

A new car following model based on weighted average velocity field

In real traffic, the motion status of forward moving vehicles play an important role in influencing the following vehicle’s motion behaviour. Nowadays, autonomous and electric vehicles have been incorporated with car-following mode when the control process is more complicated and more meaningful. As a result, researchers are studying car-following control strategies for vehicles to attain stability in traffic. Based on this, we propose a new car following model considering weighted average velocity field to describe the average effect of multi-vehicle interaction on the whole road. The weighted average velocity field can be regarded as the weighted average of velocities of finite number of vehicles preceding the objective vehicle with more weightage to more preceding vehicle. The stability condition is derived through stability analysis. Subsequently, the modified Korteweg–de Vries (mKdV) equation is formulated to unveil traffic congestion in the form of the kink-antikink density wave. Theoretical findings indicate that the weighted average velocity field yields larger stability regions compared to the average velocity field. Numerical simulations were conducted, and the results obtained demonstrate that the weighted average effect of multi-vehicle interactions play a crucial role in suppressing traffic jams faster than a simple average.

Low-order modelling of three-dimensional surface waves in liquid film flow on a rotating disk

Using low-dimensional numerical simulations, we investigate the characteristics of complex and three-dimensional surface waves in a liquid film flowing over a rotating disk, focusing on large flow rates from a nozzle. Existing integral boundary layer (IBL) models, which are based on spatially averaged variables along the direction normal to the disk surface, have primarily focused on the formation of axisymmetric waves under relatively small flow rates. In this study, an extended IBL model that accounts for both laminar and turbulent regimes is developed by considering the non-uniformity of the local flow rate in the spreading film flow and incorporating closure models dependent on the local Reynolds number. Our numerical results successfully capture the generation of concentric waves by an impinging circular liquid jet and their transition into three-dimensional solitary waves. These findings are in good agreement with visualization images and time-series data of free-surface fluctuations from a displacement sensor. The backscattering of small-scale three-dimensional turbulence into large-scale horizontal turbulence inside the film plays a critical role in determining the transition of wave modes and the nonlinear dynamics of the waves in the turbulent regime. Furthermore, the behaviour of three-dimensional waves in the downstream region, including frequent wave coalescence in the transition region and the breakup of small-scale solitons, is distinct from that of gravity-driven falling film flows. The amplitude of the three-dimensional waves is inversely related to the generalized Reynolds number defined for rotating films.

Spinal Cord Stimulation Waveforms for the Treatment of Chronic Pain.

Since the advent of spinal cord stimulation (SCS), advances in technology have allowed for improvement and treatment of various conditions, especially chronic pain. Additionally, as the system has developed, the ability to provide different stimulation waveforms for patients to treat different conditions has improved. The purpose and objective of the paper is to discuss basics of waveforms and present the most up-to-date literature and research studies on the different types of waveforms that currently exist. During our literature search, we came across over sixty articles that discuss the various waveforms we intend to evaluate. There are several publications on several waveforms used in clinical practice, but to our knowledge, this is the only educational document teaching on waveforms which provides essential knowledge. There is a gap of knowledge related to understanding wave forms and how they work.

Generation and Propagation of Flexoelectricity-Induced Solitons in Nematic Liquid Crystals.

Solitons in nematic liquid crystals facilitate the rapid transport and sensing in microfluidic systems. Little is known about the elementary conditions needed to create solitons in nematic materials. In this study, we apply a combination of theory, computational simulations, and experiments to examine the formation and propagation of solitary waves, or "solitons", in nematic liquid crystals under the influence of an alternating current (AC) electric field. We find that these solitary waves exhibit "butterfly"-like or "bullet"-like structures that travel in the direction perpendicular to the applied electric field. Such structures propagate over long distances without losing their initial shape. The theoretical framework adopted here helps identify several key factors leading to the formation of solitons in the absence of electrostatic interactions. These factors include surface irregularities, flexoelectric polarization, unequal elastic constants, and negative anisotropic dielectric permittivity. The results of simulations are shown to be in good agreement with our own experimental observations, serving to establish the validity of the theoretical concepts and ideas advanced in this work.

Microscopic state of BHs and an exact one body method for binary dynamics in general relativity

In gravitational collapses, the horizon and singularity’s realisation in the finite future of the proper time used co-moving observer happens in the future of infinitely far away future of the normal time used outside probe. To the latter the horizon and singularity defined in the singularity theorem are physical realities only in the sense of uncertainty principle and ensemble interpretation. We provide two exact time dependent solution families to the Einstein equation and show that they form a pair of complementary description for the microscopic state of black holes by showing that the Bekenstein–Hawking entropy formula follows properly from their canonical wave function’s degeneracy. We also develop an eXact One Body method for general relativity two-body dynamics whose conservative part calls no post newtonian approximation as input and applies to the full three stages of black hole binary merger events. By this method, we analytically calculate the gravitational wave forms following from such merger processes. In the case black holes carry exact and apriori horizon and singularity our wave forms agree with those following from conventional effective one body method but exhibit more consistent late time behaviour. In the case black holes carry only asymptotic horizon and extended inner structure thus experiencing banana shape deformation as the merger occurs, our wave forms exhibit all features especially the late time quasi-normal mode type oscillation seen in real observations.

Numerical Analysis of the Discrete MRLW Equation for a Nonlinear System Using the Cubic B-Spline Collocation Method

By employing the cubic B-spline functions, a collocation approach was devised in this study to address the Modified Regularized Long Wave (MRLW) equation. Then, we derived the corresponding nonlinear system and easily solved it using Newton’s iterative approach. It was established that the cubic B-spline collocation technique exhibits unconditional stability. The dynamics of solitary waves, including their pairwise and triadic interactions, were meticulously investigated utilizing the proposed numerical method. Additionally, the transformation of the Maxwellian initial condition into solitary wave formations is presented. To validate the current work, three distinct scenarios were compared against the analytical solution and outcomes from alternative methods under both L2- and L∞-error norms. Primarily, the key strength of the suggested scheme lies in its capacity to yield enhanced numerical resolutions when employed to solve the MRLW equation, and these conservation laws show that the solitary waves have time and space translational symmetry in the propagation process. Finally, this paper concludes with a summary of our findings.

Abundant dynamical solitary waves solutions of M -fractional Oskolkov model

This work uses a truncated M-fractional derivative variant of the Oskolkov model to investigate the dynamic behavior of solitary wavefronts. The methods used in this framework produce a variety of solitary waveforms, such as bright and dark solitons. A suitable choice of the free parameters is used to investigate the geometrical structures for the wave solutions, which are further characterized by stable bright periodic and soliton waves. The coefficient of the highest-order derivative and the effects of fractionality are shown in the figures. Moreover, the graphics are arranged to highlight the characteristics of novel soliton wave propagation. The findings of this research demonstrate that the fractional Oskolkov model may accommodate fundamental and higher-order soliton behaviors, each of which has unique characteristics. The fractional form of the several dynamical solitary waves seen in the study represents their practical ramifications. These waves can be seen as transmission waves via a Kelvin-Voigt fluid.

Visualization of Deformation and Stress Waves in Wooden Solid and Glued Elements of Building Structures.

The basis of the research hypothesis is the assumption that in wooden structures, deformations and stresses propagate in waves. The numerical experiment demonstrated a correct qualitative visual picture of the wave propagation of deformations, with wave manifestations and characteristic effects on the surface of the sample, at axial and corner points. Visually, the numerical model showed Rayleigh waves on the surface layer of the sample, depending on the ratio of the external geometric dimensions of the sample model, with pronounced wave interference on the outer shell. The visual manifestation of deformation on the outer sides (faces) and the reflection of deformation waves from the outer boundaries of the elastic medium of the sample in the form of Rayleigh waves confirm the correctness of the general hypothesis and the implemented model. Visualization of the process of emergence, propagation and attenuation of deformation waves on the surface of the sample shows that in the quantitative description of the deformation gradient, areas dangerous for the material can be identified.

A multidimensional examination of phase separation in single-component fluids

A thermodynamic instability in a homogeneous fluid can lead to spontaneous formation of distinct domains within the fluid. This process involves not only the spatial redistribution of fluid density but also transient exchanges of pressure, temperature, and energy. However, classical theoretical frameworks, such as the Ginzburg–Landau and Cahn–Hilliard models, lack incorporation of these essential thermodynamic aspects. To investigate the dynamics of multiple physical fields during phase separation, we numerically solve a two-dimensional van der Waals fluid model. Thermodynamic consistency is demonstrated by verifying the coexistence curve. While the equilibrium pressure remains similar across the unstable region of the isotherm, we demonstrate that the energy in the system depends on the initial density. Although the majority of energy is stored as heat at typical values of the heat capacity, high-density domains contain less specific energy compared to their low-density counterparts due to interparticle attraction. Consequently, the transition of low-density domains into high-density through the process of coalescence releases excess energy, which redistributes in the form of longitudinal waves and heat. We also highlight the role of parameters, such as heat capacity and thermal conductivity, in less intuitive phenomena, including elevated temperature fluctuations and memory preservation.