Wave Modes Research Articles

Anisotropy of acoustic properties in thin-sheet rolled low-carbon manganese steel

Thin-sheet rolled low-carbon manganese steel 09G2S with a thickness of 0,8 mm which has strong property anisotropy due to texture and residual stresses, was experimentally studied using SH-wave with horizontal polarization and zero-order symmetric Lamb wave mode. The velocities of elastic wave propagation along the sheet were analyzed as their direction and polarization varied relative to the rolling direction in the range of angles from 0 to 180 degrees. The excitation and reception of normal waves in the sheet were carried out by piezoelectric transducers with dry point contact, providing tangential force application. The results of the research on the anisotropy of acoustic properties, X-ray structural analysis of residual stresses and inverse pole figures, and metallographic studies were obtained.

Superconductivity and strain-enhanced phase stability of Janus tungsten chalcogenide hydride monolayers

Janus transition metal-dichalcogenide materials have attracted a great deal of attention due to their remarkable physical properties arising from the two-dimensional geometry and the breakdown of the out-of-plane symmetry. Using first-principles density functional theory, we investigated the phase stability, strain-enhanced phase stability, and superconductivity of Janus WSeH and WSH. In addition, we investigated the contribution of the phonon linewidths from the phonon energy spectrum responsible for the superconductivity and the electron-phonon coupling as a function of phonon wave vectors and modes. Previous work has examined hexagonal 2H and tetragonal 1T structures, but we found that neither is a ground-state structure. The metastable 2H phase of WSeH is dynamically stable with Tc≈11.60K, similar to WSH. Compressive biaxial strain—the two-dimensional equivalent of pressure—can stabilize the 1T structures of WSeH and WSH with Tc≈9.23K and 10.52 K, respectively. Published by the American Physical Society 2024

Influence of species kinetics on discharge characteristics in oxygen helicon plasma

Abstract Oxygen (O2) helicon plasmas in multiple wave modes were excited by a right-helical antenna with an upper metal endplate at low pressure. Mode transitions were observed at increasing input power or magnetic field, characterized by obvious jumps of plasma parameters. Blue Core appears at high magnetic fields (~700 G) and input powers (~1700 W), with a large radial gradient of plasma density, ion line intensity, and electron temperature. Emission spectra demonstrate that the blue lights originate from O II lines. We found that the intensity ratio of O II to O I of Blue Core in O2 is lower by one order than that in N2 or Ar despite their similar ionization rates and plasma densities in Blue Core area. A high-temperature B-dot probe together with a waveform fitting procedure was used to present the measured oscillating waveforms of m =+1 helicon waves, showing distinct wave structures of different eigenmodes. Cavity mode resonance is suggested to be responsible for the formation of standing waves of discrete eigenmodes. A pressure balance model was developed to estimate the species densities around the central area in different modes, showing massive dissociation of O2 molecules and high density of O atoms locally, so that O2 helicon plasma behaves a species feature of monatomic gas discharge. The obviously low intensity of O II lines compared to O I lines of Blue Core in O2 is related to the quite high excitation threshold of O+ ions (~30 eV) although electron density and temperature are relatively high. The combined effects of dispersed reaction energy distribution, massive molecule dissociation and negative ion creation are considered to be the main causes for requirement of much higher RF power and magnetic field for Blue Core formation in O2 helicon plasma than that in Ar. The calculated radial profile of power deposition and the captured plasma morphology confirm that the dominant central electron heating is the essential reason for the large radial gradients of plasma density and electron temperature which contributes to the serious neutral depletion and Blue Core formation.

Localized topological states beyond Fano resonances via counter-propagating wave mode conversion in piezoelectric microelectromechanical devices

A variety of scientific fields like proteomics and spintronics have created a new demand for on-chip devices capable of sensing parameters localized within a few tens of micrometers. Nano and microelectromechanical systems (NEMS/MEMS) are extensively employed for monitoring parameters that exert uniform forces over hundreds of micrometers or more, such as acceleration, pressure, and magnetic fields. However, they can show significantly degraded sensing performance when targeting more localized parameters, like the mass of a single cell. To address this challenge, we present a MEMS device that leverages the destructive interference of two topological radiofrequency (RF) counter-propagating wave modes along a piezoelectric Aluminum Scandium Nitride (AlScN) Su-Schrieffer-Heeger (SSH) interface. The reported MEMS device opens up opportunities for further purposes, including achieving more stable frequency sources for communication and timing applications.

The power of 810 nm near-infrared photobiomodulation therapy for human asthenozoospermia

Sperm motility is a crucial factor in male fertility. Photobiomodulation (PBM) has been reported to increase sperm motility, but a consistent approach suitable for identifying standardizable protocols is lacking. We collected asthenozoospermic (n = 70) and normozoospermic (n = 20) semen. The asthenozoospermic samples were irradiated with an 810 nm diode laser, in continuous wave mode, at 0.25 W, 0.5 W, 1 W and 2 W for 60 s on a circular area of 1 cm2 through a novel handpiece with an innovative flat-top profile. Sperm motility was assessed immediately, after 30 and 60 min. A sample size calculator, unpaired t-test and one-way ANOVA with post-hoc Tukey HSD tests were used for statistics. One and 2 W were the most effective outputs in increasing progressive motility compared to control (p < 0.001). The maximum effect was immediately after 1 W-PBM (p < 0.001) and decreased after 60 min (p < 0.001). Time physiologically decreased vitality (p < 0.001), but less in the 1 W-PBM samples (p < 0.05). 1 W-PBM did not affect chromatin condensation. Asthenozoospermic samples displayed an impairment of 80% in oxygen consumption and ATP production and a slight inefficiency of oxidative phosphorylation compared to normozoospermic samples (p < 0.001). 1 W-PBM partially restored the functionality of aerobic metabolism (p < 0.001) by recovery of oxidative phosphorylation efficiency. PBM did not affect lactate dehydrogenase (glycolysis pathway). No irradiated samples increased accumulated malondialdehyde, a marker of lipidic peroxidation. In conclusion, PBM improves progressive motility in asthenozoospermia through increased mitochondrial energetic metabolism without harmful oxidative stress.

Comparison and parametric study of characteristics of eleven types of anisotropic woods based on the behaviour of Lamb wave propagation

AbstractKnowledge in advance of the nine orthotropic independent elastic constants (Cij) of the wood medium is essential for evaluating its mechanical properties. The most prominent technique to retrieve Cij is the ultrasonic testing technique. This technique uses guided waves that can propagate through the material under test. Accordingly, it is worth noting that the numerical modelling of the phase and group velocities of guided waves is an unavoidable preliminary step before experimentally producing guided wave modes. Therefore, the main goal of the present work is to numerically calculate the phase velocity, group velocity and the relevant optimal incidence angles of Lamb waves in anisotropic wood that can be used as a numerical parametric study for any future experimental setup. Here, Lamb dispersion curves are calculated for eleven types of woods, where the Legendre polynomial method is employed to solve the wave equations. Moreover, the optimal incidence angle for each Lamb mode is calculated according to the Snell–Descartes law. By calculating out the three parameters of phase velocity, group velocity and optimal incidence angle of Lamb modes in eleven types of anisotropic woods, we hope to fast-track the researchers in considering the present work to facilitate their experimental measurements.

Buoyancy Modes in a Low Entropy Bubble

AbstractIn the nightside region of Earth's magnetosphere, braking oscillations or buoyancy modes have been associated with the occurrence of low entropy bubbles. These bubbles form in the plasma sheet, particularly during geomagnetically disturbed times, and because of interchange, move rapidly earthward and may eventually come to rest in the inner plasma sheet or inner magnetosphere. Upon arrival, they often exhibit damped oscillations with periods of a few minutes and are associated with Pi2 pulsations. Previously we used the thin filament approximation to compare the frequencies and modes of buoyancy waves using magnetohydrodynamic (MHD) ballooning and classic interchange theory. Interchange oscillations differ from the more general MHD oscillations by assuming constant pressure along a magnetic field line. It was determined that MHD ballooning and interchange modes are similar for plasma sheet field lines but differ for field lines that map to the inner magnetosphere. This suggested that the classic interchange formulation was only valid in the plasma sheet. This paper tests the hypothesis that the agreement between MHD ballooning and classic interchange could be restored inside a bubble. We create a small region of entropy depletion in the magnetotail and compare the buoyancy mode properties. At some locations inside the bubble, the MHD ballooning buoyancy modes resemble interchange modes but with lower frequencies than those of the unperturbed background. Unstable modes are found on the earthward edge of the bubble, while at the tailward edge, MHD ballooning predicts a slow mode wave solution not seen in the pure interchange solution.

Measurements of microwave transmission mode in HL-3 tokamak relevant ECH corrugated waveguides transmission line

The transmission modes of high-power millimeter wave in corrugated waveguides transmission line (TL) are crucial, especially for the long-pulse operation for long-distance TL. The microwave transmission mode in the TL on HL-3 tokamak relevant the electron cyclotron heating system are studied for the purpose according to the phase retrieval method based on intensity distribution measured by an infrared camera at several different locations away from the outlet of TL. A specific high power test platform with about 40-meter TL is established and the mode contents in the middle and the end of the TL are analyzed. In the middle of the TL, the proportion of main transmission mode LP01 mode is about 97% and other high-order modes contents are less than 3%. In the end of the TL, the main mode purity is about 94%, and the high-order mode, LP11 even mode is excited about 4.6%. These mode analysis results indicate that the high-power and long-pulse millimeter wave corrugated waveguides TL are designed and machined well, and the alignment method for long distance transmission line installation is highly useful for high-purity wave mode transmission.

Improving ambient noise crosscorrelations using a polarization-based azimuth filter

Seismic interferometry is widely used to image and monitor earth structures at different scales by extracting an empirical Green’s function (EGF) from the crosscorrelation of ambient noise under the assumption of diffuse wavefields or energy equipartitioning. However, EGFs may be incorrectly estimated and lead to a misunderstanding of subsurface structures because the distribution of ambient noise sources is neither isotropic nor stationary. To extract reliable EGFs from the nonideal ambient noise data, we develop a polarization-based azimuth filter (PAF) to attenuate the ambient noise energy of nonstationary sources to improve the quality of crosscorrelation functions. The PAF is a time-frequency domain azimuth filter for 3C seismic data, which uses time-frequency polarization analysis to measure the azimuths of ambient noise signals and then filters the 3C data to obtain the signals from desired directions. Based on the stationary-phase theory, we use the PAF to extract the ambient noise signals from stationary-phase zones, which improves the quality of the crosscorrelation function and eliminates the requirement for long observations. A synthetic test and two short-time engineering examples demonstrate that uneven source distributions might cause serious spurious signals in EGFs, and we demonstrate the improvement in EGFs using our method. In addition, the PAF may allow for the complete separation of the fundamental and higher modes of Rayleigh waves, which uncovers more information implicit in the ambient noise data.

Wave mode observation of hydrogen/oxygen driven rotating detonations in the hollow and annular rotating detonation rocket engine

The rotating detonation rocket engine (RDRE) fueled by hydrogen/oxygen propellant represents a promising propulsion technology due to its high thermodynamic efficiency and propellant superior specific impulse. The rotating detonation wave (RDW) must propagate in a specific propagation mode while maintaining the self-sustaining state to ensure stable operation. An experimental system of hydrogen/oxygen fueled RDRE was developed in the present study. The operation of RDRE and propagation mode of RDW were investigated under atmospheric pressure conditions, and both hollow and annular combustors were tested. The high-frequency pressure fluctuations in the RDRE were measured by the dynamic pressure transducer, while a high-speed camera was used to capture images of flame luminescence at the rear end of the RDRE. The experimental results showed that the RDW could be initiated and reached a self-sustaining propagation state with hydrogen/oxygen propellant in the hollow and annular RDRE. A single-wave mode, a two-wave co-rotating mode, and a three-wave co-rotating mode were visualized under different conditions. With the increase in the equivalence ratio, the number of rotating detonation fronts decreased, and the variations in the RDW propagation modes were consistent in the hollow and annular RDRE. However, when the equivalence ratio exceeds 1.2, the propagation velocity decreases sharply in the annular combustor, while in the hollow combustor the RDW propagates stably, revealing a higher upper limit for the equivalence ratio. Also, the dominant frequency distribution was more concentrated in the hollow combustor. The findings provide valuable insight into the variations in detonation modes related to the equivalence ratio and combustor configuration.

Traveling wave mode analysis of a coherence collapse regime semiconductor laser with optical feedback

A highly developed traveling wave model for a semiconductor laser system supports sophisticated mode analysis of the coherence collapse regime in semiconductor lasers with delayed optical feedback. The concept of instantaneous optical modes is used. Time-frequency representations of chaotic trajectories are constructed and interpreted. This involves synthesizing the calculated optical modes with their corresponding steady states, analysis of the mode driving and coupling sources, and field expansion into modal components. The results support detailed physical interpretation of the optical and radiofrequency spectra throughout the coherence collapse regime. This includes simulation results for the transition out of coherence collapse at high optical feedback. Also key frequencies observed in the radiofrequency spectrum of the chaotic output are linked to the modes that mix to generate them.

Electrodynamic analysis of a sinusoidal antenna for small wave sizes

Background. The work is aimed at developing and researching rigorous methods for calculating thin-wire structures with a complex generatrix shape, having small wave sizes, as well as studying the physical processes occurring in them. A special case of such structures is a sinusoidal antenna operating in a standing current wave mode. Aim. In progress the solution of internal and external problems of electrodynamics is carried out for a sinusoidal antenna of small wave sizes located above an infinitely extended ideal reflector. The currents on the elements of the structure are calculated, its input resistance and radiation characteristics are determined. Methods. The research is based on a strict electrodynamic approach, within the framework of which, for the specified structure in the thin-wire approximation, an integral representation of the electromagnetic field is formed, which, when considered on the surface of conductors together with boundary conditions, is reduced to a system of Fredholm integral equations of the second kind, written relative to unknown current distributions on conductors (internal task). Results. A mathematical model of the radiating structure is proposed, determined: the input resistance of the structure and the basic characteristics of its radiation. It is shown that the operating range of a sinusoidal antenna in the standing wave mode is determined by the quality factor of the input impedance resonances; An increase in the width of the sinusoidal conductor leads to a decrease in the resonant frequencies of the input resistance with a simultaneous increase in the quality factor of the resonances. Conclusion. From a practical point of view, the use of the considered structure allows significantly reduce the dimensions in comparison with a thin electric vibrator, however in this case, the operating range will be correspondingly narrowed, which is determined, due to the weak dependence of the radiation characteristics on frequency, by the quality factor of the resonances. The current distribution on the generatrix of the structure can be considered as a «projection» standing surface wave localized in the plane of a sinusoidal conductor, and resulting from the superposition of forward and backward surface (slow) waves propagating at a speed significantly lower than the speed of light. To further clarify the physics of the processes occurring in the structure, one should use spectral analysis of current functions and study the distributions of the electromagnetic field in the near zone of the structure.

ULTRASONIC INTERROGATION TECHNIQUE FOR DETECTING HATCH ANGLE VARIATIONS IN ADDITIVE MANUFACTURING BY PHONONIC LATTICE STRUCTURES

Abstract Additive Manufacturing/3D Printing (AM/3DP) has revolutionized part production by enabling the creation of intricate internal structures and complex geometries from diverse materials directly from digital design files. Among powder-based metal AM/3DP methods, Selective Laser Melting (SLM) is widely used in advanced applications such as biomedical devices and aerospace parts. Despite considerable progress in AM/3DP and SLM, at present, challenges in print quality persist, and vast resources for post-production quality assessment are allocated. The quality of SLM prints is influenced by various process and design parameters, such as the accuracy of hatch angle deposition, laser intensity/power, scanning speed of the laser beam, print line spacing, layer depth, printing chamber conditions, and the material's physical and chemical properties. Direct ultrasonic Non-Destructive Evaluation (NDE) offers comprehensive internal inspection and real-time data acquisition ability; however, in AM/3DP it faces severe limitations due to a build's intricate internal and external geometric features. In the current study, we present a Phononic Crystal Artifact (PCA)-based real-time ultrasonic NDE quality monitoring framework and show offline its utility in detecting and evaluating hatch angle variations, a critical process parameter. A PCA is substantially simpler and smaller than the actual build but represents its critical geometric and structural intricacies and mechanical properties. The current offline study demonstrates that hatch angle variations can be monitored from ultrasonic responses' spectral modal frequency peaks and wave dispersion relations.

Multi-bolt looseness monitoring using guided waves: a cross-correlation approach of the wavelet energy envelope

Abstract This paper proposes a novel approach for monitoring multi-bolt looseness using guided waves and the cross-correlation of the wavelet energy envelope. By assessing variations in the wave packet, the looseness in multi-bolt assemblies can be estimated. First, the dispersion effects of Lamb waves were theoretically analyzed using the Rayleigh-Lamb equation. Next, the wavelet energy was derived through wavelet transform, and the Lamb wave envelope was obtained as a criterion for accurately separating the wave packet. Cross-correlation analysis was employed to quantitatively evaluate the dispersion of wave packets for varying levels of bolt looseness. A looseness index, termed the normalized decorrelation coefficient of wavelet energy (NDCWE), was defined. Then, validation experiments were conducted using a joint with five M8 bolts, each tightened to a standard torque of 42 N·m. Two piezoelectric transducers were attached to the periphery of the bolt group. Three preload conditions were tested for each bolt: fully tightened, 80% of the standard torque, and 10% of the standard torque, corresponding to no looseness (NL), minor looseness (ML), and significant looseness (SL), respectively. Results showed that when significant looseness occurs, the NDCWE value exceeds 0.4, confirming the effectiveness of NDCWE in detecting substantial reductions in bolt preload. Experiments assessing the effect of temperature revealed that temperature has a negligible effect on the waveforms of the S0 and A0 mode waves. Finally, to quantitatively evaluate the efficiency of the ultrasonic transducers, the bolt-to-sensor ratio (BSR) was introduced. In this study, the BSR reached 2.5, indicating that a single piezoelectric transducer can monitor the preload of 2.5 bolts. The proposed approach shows great potential for multi-bolt looseness monitoring.

Micromagnetic study of the dynamics of toron chains

This work analyzes the nucleation and stabilization of torons in cylindrical nanopillars with bulk DMI and easy-plane anisotropy. A micromagnetic study reveals the dependence of toron chains on the nanopillar length and the different behaviors when nucleating an even or odd number of torons in a magnetic nanopillar. Spin wave resonant modes in these systems are explored, evidencing differences according to the number of torons. The interplay between torons, chiral bobbers, and their associated spin wave modes is analyzed, which is relevant for applications demanding dynamical modes in the range of gigahertz.

Double-slot micro-ring resonators with trapezoidal subwavelength grating as ultra-sensitive biochemical sensors

Silicon-based refractive index sensors are of significance in the detection of gases, biological substances and chemical compounds. Among these, optical microcavities can confine the optical field to the micrometre-scale region, and possess the advantages of high Q factor, small size and easy integration. In this paper, a trapezoidal subwavelength grating (SWG) is introduced into a slot micro-ring resonator, and the mode splitting is employed to enrich the supported standing wave modes and optimize the spatial profiles of the resonant modes. The modes’ Q factor is improved and the high sensitivity and low detection limit is achieved. The optimal trapezoidal subwavelength grating double slot micro-ring resonator (T-SWGDSMRR) structure is obtained by designing the structural parameters and analyzing their effects on the sensing performance parameters and spectral characteristics. The T-SWGDSMRR, designed for detecting the glucose solution, demonstrated a low detection limit of 3.3×10−5 RIU and an ultra-high Q factor of up to 100825, accompanied by a refractive index sensitivity of 424 nm/RIU. Finally, a cascaded double micro-ring sensor is proposed using the vernier effect, through cascading the T-SWGDSMRR with a referential ring, the sensitivity is enhanced to 12828 nm/RIU, and the limit of detection is 3.12×10−6 RIU.

Boundary Layers of Circumplanetary Disks around Spinning Planets. II. Global Modes with Azimuthal Magnetic Fields

The accretion of material from disks onto weakly magnetized objects invariably involves its traversal through a material surface, known as the boundary layer (BL). Our prior studies have revealed two distinct global wave modes for circumplanetary disks with BLs exhibiting opposite behaviors in spin modulation. We perform a detailed analysis of the effects of magnetic fields on these global modes, highlighting how magnetic resonances and turning points could complicate the wave dynamics. The angular momentum flux becomes positive near the BL with increasing magnetic field strength. We also examine the perturbation profile to demonstrate the amplification of magnetic fields within the BL. The dependence of growth rates on the magnetic field strength and the spin rate are systematically investigated. We find that stronger magnetic fields tend to result in lower terminal spin rates. We stress the potential possibility of the formation of angular momentum belts and pressure bumps. The implications for the spin evolution and quasiperiodic oscillations observed in compact objects are also briefly discussed. Our calculations advance the understanding of magnetohydrodynamical accretion processes and lay a foundation for observational studies and numerical simulations.

Evolution of linear internal waves over large bottom topography in three-layer stratified fluids

Evolutions of internal waves of different modes, particularly mode 1 and mode 2, passing over variable bathymetry are investigated based on a new numerical scheme. The problem is idealized as interfacial waves propagating on two interfaces of a three-layer density stratified fluid system with large-amplitude bottom topography. The Dirichlet-to-Neumann operators are introduced to reduce the spatial dimension by one and to adapt the three-layer system and significant topographic effects. However, for simplicity, nonlinear interactions between interfaces are neglected. Numerical techniques such as the Galerkin approximation, proven effective in previous works, are applied to save computational costs. Shoaling of linear waves on an uneven bottom is first studied to validate the proposed formulation and the corresponding numerical scheme. Then, for two-dimensional numerical experiments, mode transition phenomena excited by locally confined bottom obstacles and quickly varying topographies, including the Bragg resonance, mode-2 excitation, wave homogenization, etc., are investigated. In three-dimensional simulations, internal wave refraction by a Luneberg lens is considered, and good agreement is found in comparison with the ray theory. Finally, in the limiting case, when the top layer can be negligible (for example, a gas layer of extremely small density), the problem is reduced to a two-and-a-half-layer fluid system, where an interface and a surface are unknown free boundaries. In this situation, the surface signature of an internal wave is simulated and verified by introducing the realistic bathymetry of the Strait of Gibraltar and qualitatively compared with the satellite image.

High-Efficiency Microwave Wireless Power Transmission via Reflective Phase Gradient Metasurfaces and Surface Wave Aggregation.

Microwave Wireless Power Transfer (MWPT) technology is crucial for emergency power supply during natural disasters and powering off-grid equipment. Traditional antenna arrays, however, suffer from low energy capture efficiency, difficult impedance matching, complex synthetic networks, and intricate manufacturing processes. This paper introduces a microwave energy receiver design utilizing Reflective Phase Gradient Metasurfaces (R-PGMs) and surface wave energy convergence technology. The design leverages the effective plane wave-to-surface wave conversion capability of R-PGMs to transform incident microwave energy into a surface wave mode, which is then efficiently harvested using a circular energy convergence array before being output to a coupling port. By optimizing R-PGM parameters, an ideal 60° phase gradient distribution is achieved, facilitating the focus of surface wave energy via dispersion characteristics. These components are integrated into a hybrid antenna array, complemented by a matched energy output port structure. Numerical simulations show that this array can efficiently convert microwave energy from plane waves to surface waves, achieving a conversion efficiency of 85.32% and a collection efficiency of 68.26%. Experimental results corroborate these findings, with peak energy collection efficiency reaching 64.68% at 5.8 GHz and an RF-DC conversion efficiency of 42%, confirming the design's efficacy. Compared to conventional methods, this design simplifies the system by avoiding complex combining networks and significantly enhances the efficiency of microwave MWPT.

Modulation instability of whistler wave with electron loss cone distribution in magnetized plasma

Abstract The modulation instability of whistler mode waves caused by thermal electron anisotropy is studied. Based on MHD equations, the nonlinear schrödinger equation (NLSE) that describes the nonlinear modulation of whistler waves is derived by Using the Krylov-Bogoliubov-Mitropolsky (KBM) method. The condition for wave modulation instability is obtained from the loss cone distribution function of thermal electron anisotropy, revealing that the nonlinear growth of the waves tends towards electron perpendicular temperature anisotropy. By setting up continuous background waves and introducing small ion low frequency perturbations, we find that the change in the amplitude of the modulated wave is related with wave number. This finding has been validated through simulations that align with our analytical results. Additionally, we also calculate the maximum amplitude of the wave with loss cone angle and times, which revealed that the electron vertical temperature anisotropy will lead to the modulation instability of the whistler wave. This further confirms the occurrence of the modulation instability of the whistler wave in laboratory plasmas and strengthens their credibility.&amp;#xD;