Excitation Of Waves Research Articles

Normal form for bifurcations of ion acoustic traveling waves in positive-negative ion species plasmas

The normal form for saddle-node and transcritical bifurcation of nonlinear ion-acoustic waves is derived in complex negative-positive plasmas. The physical parameters of four different kinds of multi-ion plasmas which mainly comprise of positive ions (i.e. Xe+ and Ar+) with a minority constituent of negative ions (i.e. and F −), inspired from the experimental studies, are examined on the types of bifurcations and nonlinear wave profiles. We find that such multi-ion plasmas admit transcritical bifurcation preceding the onset of saddle-node bifurcation. The fractional concentration of negative ions controls the dynamics of ion acoustic traveling waves and causes the appearance of solitary structures and supernonlinear periodic waves. When two nonlinear waves disappear via a saddle-node bifurcation on increasing the negative ion concentration, a nonlinear periodic wave is formed. Further, we reveal critical values of ion density marking the transition between nonlinear modes. Such critical points that can be detected analytically give rise to the propagation of new solitary structures. The results obtained here not only limited to laboratory plasmas, but can also be applied to explain wave excitations in space plasma environments.

Energy-Trapping Characteristics of Lateral Field Excited GdCOB Crystal Bulk Acoustic Wave Devices Based on Stepped Electrodes.

In this work, high-frequency forced vibrations of lateral field excitation (LFE) devices with stepped electrodes based on monoclinic crystals GdCOB are modeled, and the influence laws of the device parameters (the step number, size, and thickness of the stepped electrodes) on the energy-trapping effects of the device are revealed. The results show that the step number has a significant effect on the energy-trapping effect of the device: with the increase in the step number, the stronger energy-trapping effect of the device can be obtained; with the increase in the thickness difference of two layers of electrodes, the energy-trapping effect of the device becomes stronger; with the increase in the difference of the electrode radius, the energy-trapping effect of the device is enhanced gradually. The results of this work can provide an important theoretical basis for the design of stepped-electrode LFE resonators and sensors with high-quality factors based on monoclinic crystals.

Mistuning identification and model updating of a blisk with piezoelectric excitation components

Integrally bladed disks (blisks) are extensively used in military and commercial aircraft engines. There are inevitable deviations between blades called mistuning, leading to the vibration localization of blisks, which potentially results in high cycle fatigue (HCF). Furthermore, the dynamic performance is sensitive to mistuning patterns. Hence, to predict the vibration response of mistuned blisks accurately, the mistuning pattern needs to be identified experimentally and verified under traveling wave excitation (TWE). Piezoelectric TWE is a promising testing technique for blisk dynamics in a non-rotating state, offering advantages such as high excitation force, wide bandwidth, and a simple setup. However, piezoelectric materials are generally arranged on blades forming an electromechanically coupled structure, which challenges the existing mistuning identification methods. In this paper, an integral mistuning identification and model updating method with traveling wave excitation verification is developed. The detuning strategy is used to split natural frequencies of blades, whereupon the response is measured blade by blade. Measured response functions of isolated blades can be retrieved by data reconstruction. Then, the mistuning patterns of elastic modulus and damping ratio are identified by Kirchhoff-plate theory and half-power bandwidth method, respectively. Experimental studies are carried out to validate the method. A dummy blisk with piezoelectric patches is designed and the dynamic properties are calculated. Blade-by-blade measurement and TWE test are conducted. Results show that natural frequencies of the updated model are in excellent agreement with the measured ones. Under TWE, the deviations of natural frequencies for all blades are less than 0.25%. The response deviation of the updated model is decreased by 89.4% on average compared with the original model and the average response deviation of the updated model is 7.4%.

Development of dual-main excitation mechanism modes electromagnet EMAT for testing ferromagnetic materials

ABSTRACT In the ultrasonic testing of the mechanical properties of ferromagnetic materials, the main excitation mechanism modes of ultrasonic waves are Lorentz force mechanism ultrasonic and magnetostriction mechanism ultrasonic. Lorentz force mechanism ultrasonic mainly detects the conductive characteristics of materials, while magnetostriction mechanism ultrasonic mainly detects the hysteresis characteristics of materials. However, conventional electromagnetic acoustic transducers (EMATs) cannot simultaneously characterise these two characteristics of ferromagnetic materials. In this study, we conclude from the finite element simulation that a quantitative lift-off distance (i.e. the distance between EMAT and the specimen) can change the main mechanism mode of the excited ultrasonic wave. Based on this conclusion, an electromagnet electromagnetic acoustic transducer with dual main excitation modes (DM-E-EMAT) is designed, which can realise the dual mode switching of the main Lorentz force mechanism and main magnetostriction mechanism by adding or removing hollow square gasket. The ultrasonic testing of ferromagnetic materials based on the two main mechanisms of DM-E-EMAT can simultaneously characterise the conductivity and magnetostriction properties of ferromagnetic materials, which enables the characterisations of two types of characteristic parameters with one transducer, improves the efficiency of electromagnetic ultrasonic non-destructive testing of the mechanical properties and reduces the detection errors of ferromagnetic material.

Spatial asymmetry of optically excited spin waves in anisotropic ferromagnetic film

We analytically discuss and micromagnetically prove the ways to tune the spatial asymmetry of the initial phase, amplitude, and wavevectors of magnetostatic waves driven by ultrafast laser excitation. We consider the optical pulse to heat a thin ferromagnetic metallic film and abruptly decrease the saturation magnetization and the parameter of uniaxial anisotropy. The two corresponding terms of laser-induced torque have different azimuthal symmetries, with the 4-fold symmetry of the demagnetization-related term, and the isotropic distribution of the anisotropy-related term. As a result, the initial phase and amplitude of excited magnetostatic waves have a non-trivial azimuthal distribution tunable with the angle between the external magnetic field and anisotropy axis, and the laser spot diameter. Moreover, the variation of these parameters tunes the distribution of wavevectors, resulting in additional asymmetry between the spectral components of the waves propagating in different directions.

A Control Framework for Ocean Wave Energy Conversion Systems: The Potential of Moments

The control of wave energy converters (WECs) to maximize power capture is a challenging problem. In particular, the nature of the wave excitation, which is in general panchromatic (or multi-sinusoidal), presents a reciprocating energy source that needs to be rectified through some means. In addition, the development of suitable control-oriented models is also challenging, requiring correct representation of system hydrodynamics and power take-off (PTO) components, while also lending themselves to control synthesis and real-time computational performance, along with a challenging optimal control problem. This article presents a moment-based mathematical framework for the formulation and solution of WEC control. It shows that moments are ideally suited to WEC control in terms of their ability to accurately characterize the nature of the wave excitation force (and the consequent evolutions in the system variables) while also gracefully including hydrodynamic and PTO nonlinearities as well as a natural extension to WEC arrays. Model reduction, to mold the system model into a control-friendly form, is also a feature of this framework. Expected final online publication date for the Annual Review of Control, Robotics, and Autonomous Systems, Volume 7 is May 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

From Bloch surface waves to cavity-mode resonances reaching an ultrahigh sensitivity and a figure of merit

We report on a new sensing concept based on resonances supported by a one-dimensional photonic crystal (1DPhC) microcavity resonator in the Kretschmann configuration. For a 1DPhC comprising six bilayers of TiO2/SiO2 with a termination layer of TiO2 employed to form a microcavity, we show that when the angle of incidence is changed, the Bloch surface waves (BSWs) can be transformed into cavity-mode resonances exhibiting an ultrahigh sensitivity and a figure of merit. Using wavelength interrogation, we demonstrate that Bloch surface TE wave excitation shows up as a sharp dip in the reflectance spectrum with a sensitivity and a figure of merit (FOM) of 70 nm per refractive index unit (RIU) and 19.5 RIU−1, respectively. When the angle of incidence decreases, cavity-mode resonances for both TE and TM waves are resolved for RI in a range of 1.0001–1.0005. The sensitivity and FOM can reach 52,300 nm/RIU and 402,300 RIU−1 for the TE wave, and 14,000 nm/RIU and 2154 RIU−1 for the TM wave, respectively. In addition, resonances are confirmed experimentally for a humid air with a sensitivity of 0.073 nm per percent of the relative humidity (%RH) for BSW resonance and is enhanced to 1.367 nm/%RH for the TM cavity-mode resonance. This research, to the best of the authors’ knowledge, is the first demonstration of a new BSW-like response that can be utilized in a simple sensing of a wide range of gaseous analytes.

Trapped re-entry challenges the binary view on cardiac arrhythmias

Abstract Background There is currently a binary view on cardiac arrhythmias: (1) arrhythmias are present and thereby affect the atria or ventricles as a whole, or (2) they are not present and therefore the heart is in sinus rhythm. However, complex fractionated atrial electrograms (CFAEs) under sinus rhythm (SR) are observed in patients with atrial fibrillation (AF), raising the question whether both cardiac states (arrhythmia and SR) could coexist. Although CFAEs in AF patients have been associated with functional and structural heterogeneities (e.g. dense fibrotic regions), the underlying mechanisms of fractionation under SR remain incompletely understood. Purpose To test the hypothesis that an arrhythmia can exist locally with the majority of cardiac tissue in sinus rhythm, made possible through dense local fibrotic regions forming a small electrically isolated re-entrant circuit that can "trap" excitation waves, which can only be "released" under dynamic tissue changes at an isthmus connected to the bulk of the tissue. Methods By harnessing the unique possibilities of light-gated depolarizing ion channels (CatCh) to precisely control in vitro cardiac excitability in time and space, complemented with advanced computational modelling of whole human atria, we explored the geometry of such an electrically isolated circuit and assessed its clinical relevance. Results Optical mapping studies, in monolayers of CatCh-activated neonatal rat atrial cardiomyocytes (n=8), revealed that re-entry can be established and trapped by creating an electrically isolated pathway with a bulk-connecting isthmus causing source-sink mismatch. A tachyarrhythmia was shown to exist locally with SR prevailing in the bulk of the monolayer. Next, conditions were found under which re-entry could escape this pathway, thereby converting a local dormant arrhythmic source into an active driver with global impact. Escape could be established by overcoming the source-sink mismatch through widening of the isthmus or a reduction of the gap junctional coupling. In a digital twin of the human atria, it was revealed that the conditions for "trapped re-entry" and its release can be realized as well. Unipolar pseudo-electrograms derived from these complementary computational 3D studies showed CFAEs at the site of "trapped re-entry" in coexistence with normal electrograms of SR in the bulk of the atria. Upon release of the re-entry, acute arrhythmia onset occurred, affecting the complete atria as evidenced by wave front and electrogram visualization. Conclusion Through the concept of "trapped re-entry", we not only present a new mechanism of acute manifestation of focal tachyarrhythmias, but also provide novel insight into the origin of fractionated electrograms. This insight may provide new rationales for treatment of cardiac arrhythmias, especially for ablation by site-directed targeting.Trapped re-entry in vitro and in silico

Intense Energetic Electron Precipitation Caused by the Self‐Limiting of Space Radiation

AbstractUnderstanding intense electron precipitation is crucial for characterizing radiation belt loss and assessing related impacts on the atmosphere. We investigate the evolution of electron flux during an ensemble of 70 geomagnetic storms, focusing on equatorial and low‐Earth orbit observations of trapped and precipitating ∼30–100 keV energy electrons. We reveal that the most intense electron precipitation is associated with equatorial flux capping through self‐limiting processes, for example, as described theoretically by Kennel and Petschek (1966, https://doi.org/10.1029/jz071i001p00001). Our results indicate that the most intense electron precipitation is caused by electron injections associated with self‐limiting processes. Dawn side injections are observed to have fluxes that exceed the Kennel‐Petschek limit, consistent with the excitation of strong chorus waves and resulting in intense precipitation and return of the trapped flux to the Kennel‐Petschek limit. Our results clearly demonstrate the important role of self‐limiting processes in affecting the dynamics of newly injected electrons and driving intense electron precipitation.

Modeling of autowave processes in active media with inhomogeneous properties

This paper shows the results of computer modeling of the processes of excitation and propagation of autowaves in distributed active media with inhomogeneous properties. The study of autowaves by the cellular automata method is based on the Wiener–Rosenbluth model, according to which each element of the active environment can be in one of three states: rest, excitation and refractoriness. The software module "AutoWaveModel" has been developed in C++ using the Qt library and OpenGL technology for modeling dynamic processes of excitation of spiral waves and pacemakers. The heterogeneity of the properties of the active environment in the model under consideration is set, in particular, by introducing into the field (volume) of modeling a certain number of inactive elements distributed according to a random law. It is established that the decay of autowaves occurs when about 30-60% of inactive elements are introduced from their total number in the model, moreover, the wave propagation process becomes more stable with an increase in the decay coefficient of the activator of all elements. As one of the factors creating heterogeneity of the active distributed environment, the change in the decay coefficient of the activator in its volume is also considered. In this case, each cell of the model is assigned a random value of the specified coefficient, lying in a given interval from the minimum to the maximum value. With a significant difference in the values of the activator decay coefficient in near areas of the active environment and a sufficiently high excitation threshold, the wave front is curved due to its acceleration or deceleration. In this case, the destruction of the wave is also observed, which is unable to overcome the area with a reduced decay coefficient of the activator.

High efficiency and wideband wave energy capture of a bistable wave energy converter with a displacement amplifier

Ocean wave energy is a kind of renewable energy with huge reserves, which can play an important role in the future construction of smart oceans. The low capture efficiency and narrow bandwidth of traditional wave energy capture devices seriously restrict the large-scale application of wave energy. To address these issues, a rack-pinion-lever-spring (RPLS) adaptive bistable Power Take-Off (PTO) mechanism with a time-varying potential barrier is proposed and applied to a point absorber wave energy converter (WEC). In the proposed nonlinear PTO system, a rack-pinion-lever (RPL) mechanism, as a displacement amplifier, has an effect on enhancing the poor amplitude sensitivity issue of the negative stiffness mechanism. Based on linear wave theory, a special nonlinear one-and-half-degree of freedom dynamic model is developed to describe the adaptive bistable wave energy converter (AB WEC). In comparison with the traditional bistable WEC (TB WEC) and equivalent linear WEC, the numerical results show that the AB WEC can greatly enhance the capture efficiency of lower frequency energy, especially at small wave excitations. The energy capture efficiency of the AB WEC is close to that of the TB WEC even at large wave amplitudes and is higher than that of the equivalent linear WEC. Finally, the wave energy capture characteristics of the three kinds of systems are studied based on the wave distribution diagram of a certain sea area in the South China Sea. The results show that the AB WEC has a large wave height adaptability in the low frequency region. The AB PTO mechanism with a displacement amplifier proposed in this paper can provide a technical reserve for the highly efficient and wide bandwidth capture of low frequency ocean wave energy.

Seismic vulnerability analysis on an extra-large highway-railway dual-used arch bridge

The seismic vulnerability analysis is of great important for the design, operation and maintain. The selected extra-large highway and railway dual-used arch bridge contains high geometric nonlinearity and is one of the transportation junctions. Therefore, it is necessary to conduct seismic response analysis. The research results can provide reference for the seismic design and seismic response analysis of target bridge and similar typed bridges. Thus, it has high theoretical value for the design and promotion of similar bridges. This paper starts with a theoretical analysis, using the finite element software LS-DYNA to build a dynamic calculation model of the real bridge and carry out modal and time response analyses. The strength, vulnerable components and stability of the bridge under three-way seismic action at for different earthquake excitation waves (Wenchuan earthquake, Chichi earthquake, Kobe earthquake and El-Centro earthquake) are investigated. Through analysis and comparison of numerical calculations, the seismic performance of the target bridge was comprehensively evaluated.

Anisotropic honeycomb stack metamaterials of graphene for ultrawideband terahertz absorption

Abstract Graphene aerogels have implied great potential for electromagnetic wave absorption. However, the investigation of their design for broadband absorption in the terahertz (THz) range remains insufficient. Here, we propose an anisotropic honeycomb stack metamaterial (AHSM) based on graphene to achieve ultrawideband THz absorption. The absorption mechanism is elucidated using the effective medium method, offering deeper physics insights. At low THz frequencies, the impedance matching from the air to the AHSM can be improved by reducing the chemical potential of graphene for high absorption. There is a suppression of absorption at the intermediate frequencies due to constructive interference, which can be avoided by shortening the sizes of honeycomb edges. With the aim to elevate absorption at high frequencies, one can increase the stack layer number to enhance multiple reflections and destructive interference within the metastructure. Based on the above principles, we design an AHSM that achieves a broadband absorbance of over 90 % from 1 THz to 10 THz. This absorption can tolerate a wide range of incident angles for both TE and TM wave excitations. Our research will provide a theoretical guide to future experimental exploration of graphene aerogels for THz metamaterial absorber applications.

Study of Electron Impact Excitation of Na-like Kr Ion for Impurity Seeding Experiment in Large Helical Device

In this work, a krypton gas impurity seeding experiment was conducted in a Large Helical Device. Emission lines from the Na-like Kr ion in the extreme ultraviolet wavelength region, such as 22.00 nm, 17.89 nm, 16.51 nm, 15.99 nm, and 14.08 nm, respective to 2p63p(2P1/2o)−2p63s(2S1/2), 2p63p(2P3/2o)−2p63s(2S1/2), 2p63d(2D3/2)−2p63p(2P3/2o), 2p63d(2D5/2)−2p63p(2P3/2o), and 2p63d(2D3/2)−2p63p(2P1/2o) transitions, are observed. In order to generate a theoretical synthetic spectrum, an extensive calculation concerning the excitation of the Kr25+ ion through electron impact was performed for the development of a suitable plasma model. For this, the relativistic multiconfiguration Dirac–Hartree–Fock method was employed along with its extension to the relativistic configuration interaction method to compute the relativistic bound-state wave functions and excitation energies of the fine structure levels using the General Relativistic Atomic Structure Package-2018. In addition, another set of calculations was carried out utilizing the relativistic many-body perturbation theory and relativistic configuration interaction methods integrated within the Flexible Atomic Code. To investigate the reliability of our findings, the results of excitation energies, transition probabilities, and weighted oscillator strengths of different dipole-allowed transitions obtained from these different methods are presented and compared with the available data. Further, the detailed electron impact excitation cross-sections and their respective rate coefficients are obtained for various fine structure resolved transitions using the fully relativistic distorted wave method. Rate coefficients, calculated using the Flexible Atomic Code for population and de-population kinetic processes, are integrated into the collisional-radiative plasma model to generate a theoretical spectrum. Further, the emission lines observed from the Kr25+ ion in the impurity seeding experiment were compared with the present plasma model spectrum, demonstrating a noteworthy overall agreement between the measurement and the theoretical synthetic spectrum.

Beat wave excitation of electron plasma wave by cross-focused q-Gaussian laser beams in thermal quantum plasmas

Beat wave excitation of electron plasma wave by cross-focused q-Gaussian laser beams in thermal quantum plasmas

A view on wave excitation by W dust influx in tokamak SOL

The contamination by W impurity originating from dust released from Plasma Facing Components (PFCs) is a crucial issue of ITER and future reactors, expected to be fitted with an all-W first wall. In all existing experiments, information on dust pollution is obtained from post-mortem analysis and the data provided are accumulated over many discharges, and generally no shot-by-shot analysis is available. Real-time detection of W dust ‘footprints’ in the form of electrostatic waves can be useful to monitor edge T e and n e pedestal evolution in high performance tokamaks.

Pore Pressure Diffusion Waves Transmission in Oil Reservoir

Recent studies on seismic wave excitation have revealed that mesoscopic wave-induced fluid flow (WIFF) is a process that attenuates the compressional (P) waves in reservoir rocks at seismic frequency bands. Fluid flow and Biot's slow diffusion (pressure) waves are produced when the P-waves create fluid-pressure gradients at mesoscopic-scale heterogeneities. Pore pressure continuity can be sustained by converting seismic energy into diffusion waves that diffuse away from the interfaces or boundaries. Biot’s diffusion waves fail to comply with a square-law approach because of their slow propagation velocity and higher attenuation. It is currently uncertain how to characterize reservoir fluids in mature oil reservoirs during seismic wave-based enhanced oil recovery (EOR). A simplified 1D two-layer reservoir model was investigated in this study. The findings demonstrate that diffusion wave propagation in oil reservoirs is frequency-dependent and affected by rock permeability and fluid viscosity. At a formation layer interface, it was discovered that diffusion waves obeyed the accumulation-depletion relationship rather than the reflection-refraction approach. Therefore, pore pressure diffusion waves can characterize reservoir fluid during seismic EOR and monitor the CO2 front in depleted reservoirs during storage for CCUS projects. It can also detect shale gas transport in low permeability layers and identify the propagation of fractures during gas/oil recovery.

Universal Dynamics of Rogue Waves in a Quenched Spinor Bose Condensate.

Isolated many-body systems far from equilibrium may exhibit scaling dynamics with universal exponents indicating the proximity of the time evolution to a nonthermal fixed point. We find universal dynamics connected with the occurrence of extreme wave excitations in the mutually coupled magnetic components of a spinor gas which propagate in an effectively random potential. The frequency of these rogue waves is affected by the time-varying spatial correlation length of the potential, giving rise to an additional exponent δ_{c}≃1/3 for temporal scaling, which is different from the exponent β_{V}≃1/4 characterizing the scaling of the correlation length ℓ_{V}∼t^{β_{V}} in time. As a result of the caustics, i.e., focusing events, real-time instanton defects appear in the Larmor phase of the spin-1 system as vortices in space and time. The temporal correlations governing the instanton occurrence frequency scale as t^{δ_{I}}. This suggests that the universality class of a nonthermal fixed point could be characterized by different, mutually related exponents defining the evolution in time and space, respectively. Our results have a strong relevance for understanding pattern coarsening from first principles and potential implications for dynamics ranging from the early Universe to geophysical dynamics and microphysics.

Вторичный магнитоупругий резонанс в структуре: тонкая магнитная пленка – толстая упругая подложка

The task about excitation of connected magnetic and elastic vibrations in flat-parallel structure consisted of normal magnetized thin magnetic film applied on thick nonmagnetic substrate is considered. As a result of estimated task solution the amplitude-frequency characteristics of magnetic and elastic vibrations are found. It is shown that in conditions when the ferromagnetic resonance frequency is higher then own elastic vibration of the structure on the amplitude-frequency characteristics of magnetic vibrations applied the equidistance net of elastic resonances of structure. For the interpretation of observed resonance net it is proposed the model of phase synchronization between initial excitation and elastic wave which experience two passages along the thickness of structure. It is shown that the frequency of maximum elastic vibrations rounding exceeds frequency of maximum magnetization characteristic. The existence of own rounding elastic vibrations characteristic is named the second elastic system resonance. It is investigated the dependence of maximum second resonance characteristic from value of magnetoelastic interaction constant. It is shown that by increasing of this constant the frequency distance between both characteristic maxima increases. As a hypothesis of this increasing it is proposed the analogy with splitting of amplitude-frequency characteristic of system consisted of two connected resonators. It is investigated the amplitude-frequency characteristics magnetic and elastic vibrations in wide frequency region. On the equidistance elastic resonances net amplitude-frequency characteristic it is found the narrow equidistance disposed resonance depressions which are correspond to decreasing of amplitude more then two orders of value. It is shown that the frequency interval between neighbouring depressions is back proportional to distance between point of elastic vibrations registration and surface of substrate opposite to magnetic film. For the interpretation of depressions formation it is proposed the model which takes into account the phase opposition in registration point between wave which goes out of the excitation point and wave which is reflected from the opposite end of structure. Briefly noted some physical analogies of investigated phenomena.

Secondary Excitation of Spin Waves: How Electromagnetic Crosstalk Impacts Magnonic Devices

Secondary Excitation of Spin Waves: How Electromagnetic Crosstalk Impacts Magnonic Devices