Resonant Velocity Research Articles

Sc and Er Co-Doped AlN Surface Acoustic Wave Devices

Co-doping AlN film with various elements of rare earth or transition metals has been considered as a good method to significantly improve its piezoelectric responses of surface acoustic wave (SAW) devices. In this paper, we investigated the influences of different Er/Sc atomic percentage ratio on the piezoelectric and acoustic wave properties of the Er and Sc co-doped AlN films prepared by RF magnetron sputtering. Results show that c/a-axis ratio of the AlN films decreases after doped with Sc, whereas those of the AlN films co-doped with Er and Sc increase as the Er/Sc ratio increases. The reasons can be explained from the competitions of Sc and Er elements for occupying the Al atoms sites, and the larger ion radius of the Er compared that of Sc, which causes significant increase of c/a. Resonant frequency and Rayleigh wave velocity of the SAW resonators fabricated using these co-doped AlN films decrease as the Er/Sc ratio increases. Electromechanical coupling coefficient (k2 eff ) of the SAW devices increases after the AlN film is single doped with either Sc or Er element, but decreases after co-doping with both Er and Sc.

Direct observation of mass-dependent collisionless energy transfer via Landau and transit-time damping

The energy transfer from wave to particle occurs in collisionless plasma through the interaction between particle and wave, associated with the deformation of ion velocity space from Maxwell-Boltzmann distribution. Here we show the direct observation of mass-dependent collisionless energy transfer via Landau and transit-time damping in a laboratory plasma. The Landau and transit-time damping are confirmed by the bipolar velocity-space signature of the ion velocity distribution function, measured by fast charge exchange spectroscopy with a time resolution less than ion-ion collision time. The excellent agreement between the resonant phase velocity evaluated from the bipolar velocity-space signature and the wave’s phase velocity, estimated from the frequency of the magnetohydrodynamics oscillation measured with the plasma displacement is clear evidence for the Landau damping. The energy transfer from solitary wave to fully ionized carbon impurity ions is larger than that of bulk ions 2-3 times due to heavier mass.

Amplitude-Modulation Vibro-Acoustic Technique for Damage Evaluation

This study proposes an amplitude-modulation vibro-acoustic (AMVA) technique to track the evolution of thermal damage in pristine graphene mortar. In the proposed amplitude-modulation technique, the pump wave is amplitude-modulated using three different methods: (1) the pure amplitude-modulated (PAM) method, (2) the suppressive amplitude-modulated (SAM) method and (3) the transmitted amplitude-modulated (TAM) method. The nonlinear parameters , and corresponding to the PAM, SAM and TAM methods, respectively, are theoretically established and experimentally demonstrated that the nonlinear parameters associated with the material nonlinearity, and they can be used to quantitatively characterize different damage stages of thermal damage. Meanwhile, the resonant frequency (RF) and ultrasonic pulse velocity (UPV) tests are conducted. The linear measurements, dynamic elastic modulus obtained from RF test and ultrasonic pulse velocity collected by UPV test, are used to compare with the nonlinear parameters. The results show that the proposed AMVA technique is more sensitive and feasible to serve as the tool for thermal damage detection in cement-based material compared with the conventional RF and UPV techniques.

Nonlinear Signatures of VLF‐Triggered Emissions: A Simulation Study

AbstractWe conduct a particle‐in‐cell simulation reproducing triggering process of whistler‐mode rising‐tone emissions by injecting a wave with a fixed frequency at the equator. Rising‐tone elements with multiple subpackets with monotonically increasing frequencies are generated from the triggering wave. Generation regions of the subpackets move upstream or downstream depending on the group velocities and resonance velocities for different frequencies. Because of the motion of a source region to the upstream, a long rising‐tone subpacket is generated self‐sustainingly through formation of an electron hole in velocity phase space stretched over the generation region. The long rising‐tone subpacket is modulated with increasing magnitude, splitting into smaller subpackets through propagation. The amplitude modulations in the subpacket arise from two different processes; resonant trapping oscillation of electrons at the equatorial region and enhancement of amplitude variations through propagation in the downstream.

Modeling the Dynamics of a Gyroscopic Rigid Rotor with Linear and Nonlinear Damping and Nonlinear Stiffness of the Elastic Support

This study analytically and numerically modeled the dynamics of a gyroscopic rigid rotor with linear and nonlinear cubic damping and nonlinear cubic stiffness of an elastic support. It has been shown that (i) joint linear and nonlinear cubic damping significantly suppresses the vibration amplitude (including the maximum) in the resonant velocity region and beyond it, and (ii) joint linear and nonlinear cubic damping more effectively affects the boundaries of the bistability region by its narrowing than linear damping. A methodology is proposed for determining and identifying the coefficients of nonlinear stiffness, linear damping, and nonlinear cubic damping of the support material, where jump-like effects are eliminated. Damping also affects the stability of motion; if linear damping shifts the left boundary of the instability region towards large amplitudes and speeds of rotation of the shaft, then nonlinear cubic damping can completely eliminate it. The varying amplitude (VAM) method is used to determine the nature of the system response, supplemented with the concept of “slow” time, which allows us to investigate and analyze the effect of nonlinear cubic damping and nonlinear rigidity of cubic order on the frequency response at a nonstationary resonant transition.

Evaluation of ultrasonic parameters as a non-invasive, rapid and in-field indicator of water stress in Citrus plants

Non-Contact Resonant Ultrasound Spectroscopy (NC-RUS) has emerged as a powerful tool to determine plant water status in a non-destructive, non-invasive and rapid way. In this study, ultrasonic parameters directly obtained from experimental measurements in the field using NC-RUS - such as resonant frequency (fres), velocity (v) and Q-factor - were evaluated as potential water stress indicators in Citrus plants. The experiments were carried out in two-year-old mandarin trees (Citrus clementina Hort. ex Tan. ‘Clemenules’) grown in pots in an open greenhouse where two different groups of plants were tested: a Control group (full irrigation) and a Drought Stress group (DS) whose irrigation was withdrawn during 7 days, followed by a 16 days recovery period. Soil water content, leaf water potential (Ψleaf) and the considered ultrasonic parameters were measured in the same leaves. fres detected changes between control and DS at day 7 without irrigation. Conversely, v showed differences after day 3, which were statistically significant at day 7, enabling discrimination between C and DS groups. Hence, Q-factor was the ultrasonic parameter that showed statistically significant differences between C and DS groups at days 3 and 7. Consequently, Signal Intensity in Q during the drought treatment showed a similar evolution to Ψleaf, although with slightly lower performance. However, Q-factor sensitivity excels Ψleaf at each day studied. Finally, a linear correlation (R2=0.57) between Ψleaf and Q-factor of all experimental data measured in DS group plants along the drought treatment was found. In conclusion, the ultrasonic parameters obtained using NC-RUS and in particular the Q-factor, demonstrated to be potential new water stress indicators in Citrus trees, with the novelty of being non-destructive, non-invasive and rapid. Future work should explore its suitability for its use in irrigation scheduling for Citrus trees.

Electron Heat Flux Instabilities in the Inner Heliosphere: Radial Distribution and Implication on the Evolution of the Electron Velocity Distribution Function

Abstract This Letter investigates the electron heat flux instability using the radial models of the magnetic field and plasma parameters in the inner heliosphere. Our results show that both the electron acoustic wave and the oblique whistler wave are unstable in the regime with large relative drift speed (ΔV e ) between electron beam and core populations. Landau-resonant interactions of electron acoustic waves increase the electron parallel temperature that would lead to suppressing the electron acoustic instability and amplifying the growth of oblique whistler waves. Therefore, we propose that the electron heat flux can effectively drive oblique whistler waves in an anisotropic electron velocity distribution function. This study also finds that lower-hybrid waves and oblique Alfvén waves can be triggered in the solar atmosphere, and that the former instability is much stronger than the latter. Moreover, we clarify that the excitation of lower-hybrid waves mainly results from the transit-time interaction of beaming electrons with resonant velocities v ∥ ∼ ω/k ∥, where ω and k ∥ are the wave frequency and parallel wavenumber, respectively. In addition, this study shows that the instability of quasi-parallel whistler waves can dominate the regime with medium ΔV e at the heliocentric distance nearly larger than 10 times of the solar radius.

Reimagining full wave rf quasilinear theory in a tokamak

The velocity dependent resonant interaction of particles with applied radiofrequency (rf) waves during heating and current drive in the presence of pitch angle scattering collisions gives rise to narrow collisional velocity space boundary layers that dramatically enhance the role of collisions as recently shown by Catto (J. Plasma Phys., vol. 86, 2020, 815860302). The behaviour is a generalization of the narrow collisional boundary layer that forms during Landau damping as found by Johnston (Phys. Fluids, vol. 14, 1971, pp. 2719–2726) and Auerbach (Phys. Fluids, vol. 20, 1977, pp. 1836–1844). For a wave of parallel wave number ${k_{||}}$ interacting with weakly collisional plasma species of collision frequency $\nu$ and thermal speed ${v_{\textrm{th}}}$ , the effective collision frequency becomes of order $\nu {({k_{||}}{v_{th}}/\nu )^{2/3}} \gg \nu $ . The narrow boundary layers that arise because of the diffusive nature of the collisions allow a physically meaningful wave–particle interaction time to be defined that is the inverse of this effective collision frequency. The collisionality implied by the narrow boundary layer results in changes in the standard quasilinear treatment of applied rf fields in tokamaks while remaining consistent with causality. These changes occur because successive poloidal interactions with the rf are correlated in tokamak geometry and because the resonant velocity space dependent interactions are controlled by the spatial and temporal behaviour of the perturbed full wave fields rather than just the spatially local Landau and Doppler shifted cyclotron wave–particle resonance condition associated with unperturbed motion of the particles. The correlation of successive poloidal circuits of the tokamak leads to the appearance in the quasilinear operator of transit averaged resonance conditions localized in velocity space boundary layers that maintain negative definite entropy production.

Aero-acoustic response of flat plates at sub-sonic flow

Natural aero-acoustic resonance of single and double flat plates was experimentally investigated. Ten single plates of six different chord-to-thickness ratios were tested for flow around single plate, and four different gap-to-thickness ratios were tested for flow around two plates in tandem. For the case of single plates, a tool for the prediction of resonant flow velocities was established using reduced velocity. For tandem plates, the acoustic response was characterized by the presence of double resonance response that is the excitation of first acoustic mode in two different ranges of flow velocities. Reduced velocity range of low-frequency resonance fits to the range of Mode1 in single plates, this is because both resonances are natural. For high-velocity resonance, a common range could hardly be identified although the increase of gap distance showed an increase in the onset reduced velocity at resonance. It is hypothesized that the first resonance of the double response is caused by normal shedding of vortices in the gap between the plates, whereas the latter resonance is due to vortices caused by the interaction of shear layers with the downstream plate. This mechanism is different than that present in case of tandem cylinders due to the difference in separation points. It was also shown that the downstream plate can serve as a duct modification that leads to the excitation of new acoustic modes that were not excited in the case of single plates.

Controlling self-excited vibration of a nonlinear beam by nonlinear resonant velocity feedback with time-delay

In this paper, the efficacy of velocity feedback based nonlinear resonant controller is proposed to control the free and forced self-excited vibration of a nonlinear beam. The velocity signal obtained from the sensor is fed through a second-order filter and the nonlinear function of the derivative of the filter variable is used to obtain the control force. The resulting control system being a band-pass one, is believed to be superior to other resonant control schemes like Positive Position Feedback (PPF) control and Acceleration Feedback Control (AFC). To the best of the authors’ knowledge, it is the first attempt to explore the efficacy of resonant nonlinear velocity feedback controller for mitigating self-excited vibration. Analytical results are obtained using multiple time-scale method, are validated with the data obtained from direct numerical simulation carried out in Matlab Simulink model. Analytical results of the uncontrolled system show the periodic, quasi-periodic as well as chaotic behavior. It is observed that the proposed controller can reduce the amplitude of vibration by a significant level near primary resonance. Moreover, the Hopf bifurcations are eliminated by the control action. It is also observed that the proposed controller can reduce the amplitude of the chaotic oscillation significantly. The effect of the actuation delay in the feedback loop is also explored. It is observed that the effect of time delay is detrimental to system performance.

Autogenous healing performance of internal curing agent-based self-healing cementitious composite

In this study, a series of cementitious composite with internal curing agent incorporating ranging from 0% to 30% were prepared to evaluate their autogenous healing performance. The Clinoptilolite Zeolite was utilized as an internal curing compound to replace parts of sand for storing the water inside the cement matrix. The mechanical properties were examined via compressive and splitting tensile tests. To quantify the self-healing behavior of this cementitious composites, the samples were pre-damaged using splitting tensile method and placed in the wet/dry cycle for several days. Two non-destructive testing methods, including resonant frequency and ultrasonic pulse velocity tests, were employed to assess the healing efficiency. The results revealed that the incorporation of zeolite could enhance the compressive strength and the self-healing performance of the proposed cementitious composites. However, if the replacement percentage of zeolite was higher than 15%, the healing efficiency decreased due to the “blocking effect”, which was further investigated by the water absorption test and thermogravimetric analysis (TGA).

Rotobreather in a carbon nanotube bundle

Carbon nanotube (CNT) bundles exhibit unusual mechanical properties, but nonlinear dynamics and possible energy localization in such systems have not yet been analyzed. The dynamics of a rotobreather in the form of a CNT rotating around its axis and placed in an array of similar CNTs is analyzed using a molecular dynamics model with a reduced number of degrees of freedom. The height of the Peierls–Nabarro potential associated with the discreteness of CNTs is estimated. It is found that if a CNT is given rotational kinetic energy not sufficient to overcome the Peierls–Nabarro potential, it does not rotate. Several resonant angular velocities are identified at which the rotating CNT loses its kinetic energy relatively quickly and eventually stops rotating. CNT with a sufficiently large, non-resonant angular velocity emits the rotational energy very slowly.

Raman velocity filter as a tool for collinear laser spectroscopy

The velocity distribution of a hot ionic beam can be filtered with a narrow stimulated Raman process to prepare a colder subensemble, as substantiated in this theoretical analysis. Using two counter-propagating, far-detuned lasers, we can define a $\pi$-pulse for the resonant velocity to transfer atoms within the linewidth of the Raman resonance between the ground-states of a $\Lambda$-system. Spontaneous emission from the two single-photon resonances, as well as the ground-state decoherence induced by laser noise, diminishes the efficiency of the filter. From a comprehensive master equation, we obtain conditions for the optimal frequency pair of the lasers and evaluate the filter performance numerically, as well as analytically. If we apply this analysis to current $^{40}$Ca$^+$ ion experiments, we obtain a sensitivity for measuring high ion acceleration voltages on the ppm level or below.

Specifications of Resonant Acoustic Rotating Waves in Circular and Annular Domains

Circular and annular domains of hydroacoustic vibration are very common in modern technology due to their simplicity. On the other hand it turns out that such a shape possesses remarkable vibration properties. It is determined that there are two classes of resonant rotating waves, predominantly tangential and predominantly radial, in terms of prevalence of tangential or radial components of the vectors of vibrational velocities and displacements. The complete map of resonant angular velocities shows that all predominantly tangential angular velocities for all values of ring thickness are assembled into the self-isolating unique single low-frequency branch, whereas predominantly radial ones fill the entire high-frequency region very densely.

Moving Load Spectrum for Analyzing the Extreme Response of Bridge Free Vibration

In order to more effectively establish the relationship between moving load speed and the extreme response of bridge free vibration, a novel analysis method is presented based on the moving load spectrum, which is deduced from Fourier transform in this paper. By analyzing the moving load spectrum in detail, the moving load velocities which lead to the extreme responses of bridge free vibration under single moving constant force or harmonic force are obtained, and the corresponding formula for calculating the moving load velocity which leads to the maximum response of bridge free vibration is put forward. Finally, the moving load spectrum for analyzing the extreme response of bridge free vibration is validated by a large number of calculations in the time domain in this paper. The results show that the moving velocities corresponding to the extreme points in the moving load spectrum are consistent with the velocities corresponding to the extreme points of the bridge vibration response obtained in the time domain, and the forced and free vibration displacement responses of bridge are not the largest when the single moving constant force or harmonic force passes through the bridge at the resonant velocity compared to other speeds.

Magnetic Field Tunable Ferromagnetic Shape Memory Alloy-Based Piezo-Resonator

In this letter, we have performed a comprehensive analysis of the influence of the magnetic field on BAW resonator consisting of a highly magnetostrictive layer and AlN thin film. The fundamental resonant frequency of the fabricated BAW resonator is about ~4.22 GHz. In the presence of a magnetic field, we studied the effect on the resonator parameters such as resonant frequency, acoustic velocity, and coupling coefficient. For the magnetic field of strength 1200 Oe, the resonant frequency significantly shifts by ~360 MHz. Resonant frequency increases and electromechanical coupling coefficient ( $\text{k}_{t}$ ) decreases with the increase in the DC magnetic field. The maximum acoustic velocity of ~7350 m/sec was observed at the magnetic field of 1500 Oe when applied parallel to the surface. Agilent Advanced Design Software (ADS) was used to extract the equivalent Modified Butterworth-Van Dyke circuit parameters (R m , C m , and L m ) of the resonator. Further, in the presence of the magnetic field, we obtained the variation in values of R m , C m , and L m of the resonator structure. Such tunable resonators can be useful and vital in dealing with varying frequency bands for sustainable growth in wireless communication and magnetic field sensor applications.

Boosting the dark matter signal with Coulomb resonances

We show that the presence of nearby Coulombic resonances at finite energy could lead to the enhancement of the dark matter annihilation cross section at specific non-zero velocities correlated with the mass splitting between the dark matter pair and that of the resonance. If one of these resonant velocities approximately matches the velocity of dark matter in our local neighbourhood, we would see this enhancement in existing indirect-detection measurements, such as the measurements of the continuum photon spectrum made by HESS and Fermi-LAT. We explore this effect in the context of pure Higgsino and Wino dark matter with a variable splitting between charged and neutral components, controlled by the Wilson coefficient of a higher-dimension operator. For electroweak WIMPs a relevant and appreciable enhancement from Coulomb resonances requires tuning the charged-neutral splitting to be of order the Coulomb binding energies. This leads to strong exclusions of Higgsino dark matter with charged-neutral splittings in the narrow ranges (2, 2.5) and (8.5, 10.5) MeV. In contrast, by decreasing the charged-neutral splitting for the thermal Wino, we can move the Yukawa resonance away from the thermal relic mass, decreasing the indirect-detection signal to a level that is compatible with HESS measurements in the window (25, 35) MeV.

Collisionless energy transfer in kinetic turbulence: field–particle correlations in Fourier space

Turbulence is commonly observed in nearly collisionless heliospheric plasmas, including the solar wind and corona and the Earth’s magnetosphere. Understanding the collisionless mechanisms responsible for the energy transfer from the turbulent fluctuations to the particles is a frontier in kinetic turbulence research. Collisionless energy transfer from the turbulence to the particles can take place reversibly, resulting in non-thermal energy in the particle velocity distribution functions (VDFs) before eventual collisional thermalization is realized. Exploiting the information contained in the fluctuations in the VDFs is valuable. Here we apply a recently developed method based on VDFs, the field–particle correlation technique, to a $\unicode[STIX]{x1D6FD}=1$ , solar-wind-like, low-frequency Alfvénic turbulence simulation with well-resolved phase space to identify the field–particle energy transfer in velocity space. The field–particle correlations reveal that the energy transfer, mediated by the parallel electric field, results in significant structuring of the VDF in the direction parallel to the magnetic field. Fourier modes representing the length scales between the ion and electron gyroradii show that energy transfer is resonant in nature, localized in velocity space to the Landau resonances for each Fourier mode. The energy transfer closely follows the Landau resonant velocities with varying perpendicular wavenumber $k_{\bot }$ and plasma $\unicode[STIX]{x1D6FD}$ . This resonant signature, consistent with Landau damping, is observed in all diagnosed Fourier modes that cover the dissipation range of the simulation.

The Effects of Thermal Electrons on Whistler Mode Waves Excited by Anisotropic Hot Electrons: Linear Theory and 2‐D PIC Simulations

AbstractThe wave normal angle of excited whistler waves was previously considered to be controlled by the parallel plasma beta (β∥h) of anisotropic hot electrons, while the effects of thermal electrons were usually neglected. By combining both the linear theoretical and 2‐D particle‐in‐cell (PIC) simulation models, we have investigated the effects of thermal electrons on the whistler anisotropy instability. In the high‐beta (β∥h ≥ 0.025) regime, the wave normal angle of the dominant whistler mode with the largest growth rate is always 0°, which is not affected by thermal electrons, while, its wave frequency and linear growth rate decrease with the density and temperature of thermal electrons. These results are also confirmed by PIC simulations. In the low‐beta (β∥h ≤ 0.025) regime, with the increase of the density and temperature of thermal electrons, the wave normal angle of the dominant whistler mode turns to zero from a large value. This change could be due to the stronger damping caused by thermal electrons for oblique whistler mode, since oblique wave usually has a smaller cyclotron resonant velocity than parallel wave. PIC simulations also show a consistent result, but reproduce a broad magnetic spectrum, even in the case including sufficient thermal electrons. Furthermore, thermal electrons with large parallel velocities are resonantly accelerated in the perpendicular direction, while parts of hot electrons are trapped and accelerated in the parallel direction. Our study suggests that the wave normal angle of whistler mode in the Earth's magnetosphere could be determined by both anisotropic and thermal electrons.

Stability analysis of secondary modes, driven by the phase space island

We present a new theoretical approach, based on the Hamiltonian formalism, to investigate the stability of islands in phase space, generated by trapping of energetic particles (EPs) in plasma waves in a tokamak. This approach is relevant to MHD modes driven by EPs (EP-MHD) such as toroidal Alfvén eigenmodes (TAEs), EP-driven geodesic acoustic modes (EGAMs) or fishbones. A generic problem of a single isolated EP-MHD mode is equivalent to and hence can be replaced by a 2D Hamiltonian dynamics in the vicinity of the phase space island. The conventional Langmuir wave/bump-on-tail problem is then used as a representative reduced model to describe the dynamics of the initial EP-MHD.Solving the Fokker–Planck equation in the presence of pitch angle scattering, velocity space diffusion and drag and retaining plasma drifts in a model, we find a ‘perturbed’ equilibrium, associated with these phase space islands. Its stability is then explored by addressing the Vlasov/Fokker–Planck–Poisson system. The Lagrangian of this system provides the dispersion relation of the secondary modes and allows an estimate of the mode onset. The secondary instabilities have been confirmed to be possible but under certain conditions on the primary island width and in a certain range of mode numbers. The threshold island width, below which the mode stability is reached, is calculated. The secondary mode growth rate is found to be maximum when the associated resonant velocity approaches the boundary of the primary island. This, in turn, leads to a conclusion that the onset of the secondary mode can be prevented provided the primary wave number is the lowest available.