Excitation Of Different Modes Research Articles

A multi-directional and multi-modal galloping piezoelectric energy harvester with tri-section beam

A traditional wind energy harvester based on galloping can only harvest wind energy from one specific direction, which fails to work efficiently in a natural erratic environment. In this study, we propose a galloping-based piezoelectric energy harvester that can collect energy from wind flow in a wide range of incident directions with multiple vibrational modes being excited. The proposed harvester is composed of a tri-section beam with bonded piezoelectric transducers and a square bluff body with splitters. Finite element analysis of the tri-section beam structure is first performed and confirms the clustered natural frequencies that ease the excitation of different modes. Then, the aerodynamic characteristics of various bluff bodies is conducted through computational fluid dynamics to compare the capability of galloping. Finally, the wind tunnel experiment is carried out to test the wind energy harvesting performance by utilizing the harvester’s multi-modal characteristics. The results of this study demonstrate that the proposed harvester can harvest wind energy in multiple directions with the capability of galloping in multiple vibrational modes, and superior performance is achieved when the second bending mode is triggered. The novel design of the harvester from this work provides a viable solution for harvesting wind energy in a natural environment with varying wind conditions.

Tunable dielectric resonator antenna with circular polarization and wide bandwidth for terahertz applications

In this paper, a tunable wideband circularly polarization (CP) dielectric resonator antenna (DRA) is designed and simulated. The antenna is fed by slot coupling and circular polarization is achieved by the design of the slot configuration and by the excitation of different modes. The tunable response is provided by coating graphene on the top of the radiating dielectric resonator. The proposed antenna provides a wide 10 dB impedance bandwidth of 49% (2.7–4.46 THz) and an overlapped axial ratio bandwidth of 17.34% (2.87–3.43 THz).

Five-minute oscillations of photospheric and chromospheric swirls

Context. Swirls are ubiquitous in the solar atmosphere. They are thought to be related to the excitation of different modes of magnetohydrodynamic waves and pulses, as well as spicules. However, statistical studies of their collective behaviour are rare. Aims. We aim to study the collective as well as the individual behaviour of photospheric and chromospheric swirls detected by the automated swirl detection algorithm (ASDA) from observations obtained by the Swedish 1-m Solar Telescope and the Hinode satellite. Methods. We performed a detailed analysis of six different parameters of photospheric and chromospheric swirls with the wavelet analysis. Two clusters with periods with significant wavelet power, one from 3 − 8 min and the other from 10 − 14 min, were found. The former coincides with the dominant period of the global p-mode spectrum. The wavelet and fast Fourier transform analysis of example swirls also revealed similar periods. Results. These results suggest that global p-modes might be important in triggering photospheric and thus chromospheric swirls. A novel scenario of global p-modes providing energy and mass fluxes to the upper solar atmosphere via generating swirls, Alfvén pulses, and spicules is then proposed.

Hybrid simulations of sub-cyclotron compressional and global Alfvén eigenmode stability in spherical tokamaks

A comprehensive numerical study has been conducted in order to investigate the stability of beam-driven, sub-cyclotron-frequency compressional Alfvén eigenmodes (CAEs) and global Alfvén eigenmodes (GAEs) in low-aspect-ratio plasmas for a wide range of beam parameters. The presence of CAEs and GAEs has previously been linked to anomalous electron temperature profile flattening at high beam powers in NSTX experiments, prompting a further examination of the conditions necessary for their excitation. Linear simulations have been performed with the hybrid MHD–kinetic initial value code HYM in order to capture the general Doppler-shifted cyclotron resonance that drives the modes. Three distinct types of modes were found in the simulations—co-CAEs, cntr-GAEs, and co-GAEs—with differing spectral and stability properties. The simulations revealed that unstable GAEs are more ubiquitous than unstable CAEs, which is consistent with experimental observations, as they are excited at lower beam energies and generally have larger growth rates. Local analytic theory is used to explain key features of the simulation results, including the preferential excitation of different modes based on beam injection geometry and the growth rate dependence on the beam injection velocity, critical velocity, and degree of velocity space anisotropy. The background damping rate is inferred from the simulations and analytically estimated for relevant sources absent from the simulation model, indicating that co-CAEs are closer to marginal stability than modes driven by the cyclotron resonances.

Otto–Kretschmann Hybrid Configuration for Excitation of Different Modes of Surface Plasmon–Polaritons

Results of simulation, synthesis, and investigation of a double-resonance plasmon structure for excitation of different modes of surface plasmon–polaritons are presented. It is shown that a combination of the Kretschmann and Otto configurations on a single asymmetric multilayer structure can be used for excitation of the plasmon–polariton resonances. Parameters of such a structure are optimized for the maximum excitation efficiency of the surface plasmon–polaritons. Possible applications of the proposed double-resonance plasmonic structure in an autonomous plasmon–polariton sensor and a sensor element of a plasmonic biosensor are considered.

Tracking the effect of chlorine as a substituent on vibrational coupling and energy transfer

The selective excitation of different modes and the detection of the effect of substituents on coupling and energy transfer via CARS spectroscopy were carried out using benzene derivatives.

Experimental Study of Multi-Mode Dynamics of THz-Band Pulsed Magnetic Field Gyrotron

The multi-mode dynamics of pulsed magnetic field gyrotron due to excitation of different modes at the fronts of high voltage pulse was investigated. Detailed and accurate measurements of start-up scenario and excitation of the operating and spurious modes in the 0.5 THz pulsed magnetic field gyrotron were made for the first time. The performed numerical simulations of multi-mode dynamics of the gyrotron showed a good qualitative agreement with the experimental results. The presented information looks useful for future development of high frequency pulsed gyrotrons.

Cooperation and competition of viscoelastic fluids and elastomeric microtubes subject to pulsatile forcing

The cooperation and competition of viscoelastic fluids, subject to pulsatile forcing, with the elastomeric microtubes that confine them is explored. Tuning of system parameters allows for the excitation of different modes, and resonances can be achieved by driving the fluid with the appropriate pulsatile pressure drop. The results are relevant at microscales and potentially useful for tailoring composite microfluidic devices, where one can induce an increase or decrease of the amplitude of the longitudinally averaged flow, relative to the one of tubes made of a single material.

Giant nonlinear magneto-optical response of magnetoplasmonic crystals

Magnetoplasmonics provides unique possibilities for magnetic field control over light flow. A special interest in this field is attracted to magnetoplasmonic crystals (MPCs) that are nanostructured metal-dielectric materials with rich resonant spectra that can be tuned by a magnetic field. We show that MPC demonstrates enhanced nonlinear-optical effects such as optical second harmonic generation (SHG) and a giant nonlinear magneto-optical effect. Contrary to the linear-optical case, the main mechanism underlying the observed effects is the resonant enhancement of the local field achieved both for the surface-plasmon-polariton modes at metal/dielectric interfaces and for the waveguide modes in a dielectric slab, which provides an up to 25% magnetic field controlled SHG intensity variation. These effects are treated as an interplay of excitation of different modes that leads to Fano-type resonances in the nonlinear-optical response.

Two-frequency excitation of single-mode Faraday waves

AbstractThe purpose of this work is to investigate, for the first time, excitation of Faraday waves in small containers using two commensurate frequencies. This spatial restriction, which is encountered at low frequencies, leads to a wave composed primarily of one spatial eigenmode of the container. When two frequencies are used, the mode resonates primarily with one frequency, while the role of the second is to alter the instability threshold and the resulting nonlinear dynamics. As the parameter space expands greatly as a result of the introduction of three new degrees of freedom, viz. the frequency, amplitude and phase of the new component, the linear theory is first used as a guide to highlight basic two-frequency phenomena. These predictions and nonlinear phenomena are then studied experimentally with the system of Batson, Zoueshtiagh & Narayanan (J. Fluid Mech., vol. 729, 2013, pp. 496–523), who studied single-frequency excitation of different modes in a cylindrical cell. The two-frequency experiments of this work focus on excitation of the fundamental axisymmetric mode, and are quantitatively compared to the model via a posteriori Fourier decomposition of the parametric input. In doing so, experimental dependence of the instability on the new degrees of freedom is demonstrated, in accordance with the model predictions. This is done for a variety of frequency ratios, and overall agreement between the observed and predicted onset conditions is identical to that already reported for the single-frequency experiment. For each frequency ratio, the nonlinear behaviour is experimentally characterized by bifurcation and time series data, which is shown to differ significantly from comparable single-frequency excitations. Finally, we present and discuss a wave in which both temporal frequencies are used to simultaneously excite different spatial modes.

Cantilevered single walled boron nitride nanotube based nanomechanical resonators of zigzag and armchair forms

In this paper, the dynamic response analysis of single walled boron nitride nanotubes (SWBNNTs) has been done using a finite element method (FEM). To this end, different types of zigzag and armchair layups of SWBNNTs are considered with cantilever configuration to analyze the mass detection application, as a SWBNNT based nanomechanical resonator. Using three dimensional elastic beams and point masses, single walled boron nitride nanotubes are approximated as atomistic finite element models. Implementing the finite element simulation approach, the resonant frequency of cantilevered nanotubes obtained and observed the shifts in it mainly due to an additional nanoscale mass to the nanotube tip. The effect on resonant frequency shift due to dimensional variation in terms of length as well as diameter is explored by considering different aspect ratios of nanotubes. The effect of intermediate landing positions of added mass on resonant frequency shift is also analyzed by considering excitations of different modes of vibration. Also, the effect of chiralities compared for resonant frequency variations to check the effect on sensitivity due to different forms of SWBNNTs. The present approach is found to be effectual in terms of dealing different chiralities, boundary conditions and consideration of added mass to analyze the dynamic behavior of cantilevered SWBNNT based nanomechanical resonators. The simulation results are compared with the analytical results based on continuum mechanics and found in good agreement as one of the toolkits for systematic analysis approach for novel design of SWBNNT based nanomechanical resonators for wide range of applications.

Selective modal excitation in coupled piezoelectric microcantilevers

We study in detail the first vibration modes of a piezoelectric resonator based on two coupled micro-cantilevers, also known as tuning-forks. A multiple electrode geometry lying on a layer of piezoelectric AlN allows the selective excitation of different modes, including in-plane modes. A complete optical characterization of the devices in the z- and also the x-direction has been performed employing a Doppler vibrometer. The measurements confirm the excitation and inhibition of different modes depending on the actuation signals distribution on the electrodes. The influence of the dimensions of the resonator on the coupling between the microcantilevers has also been studied. Quality factors above 4,300 have been measured for the first anti-phase in-plane mode.

Characteristics of acoustic emissions during nucleation of superheated droplets

Superheated droplet nucleation and subsequent bubble oscillation produces an acoustic pressure pulse that contains valuable information about the nucleation process. Spectral analysis of the pressure pulse indicates excitation of different modes of bubble oscillations in the nucleation process. In the present study it is observed that gamma induced droplet nucleation excites higher modal oscillations and also emits higher intensity acoustic emission compared to that of spontaneous nucleations.

Excitation and imaging of resonant optical modes of Au triangular nanoantennas using cathodoluminescence spectroscopy

Cathodoluminescence (CL) imaging spectroscopy is an important technique to understand the resonant behavior of optical nanoantennas. The authors report high-resolution CL spectroscopy of triangular gold nanoantennas designed with near-vacuum effective index and very small metal-substrate interface. This design helped in addressing issues related to background luminescence and shifting of dipole modes beyond visible spectrum. Spatial and spectral investigations of various plasmonic modes are reported. Out-of-plane dipole modes excited with a vertically illuminated electron beam showed high-contrast tip illumination in panchromatic imaging. By tilting the nanostructures during fabrication, in-plane dipole modes of antennas were excited. Finite-difference time-domain simulations for electron and optical excitations of different modes showed excellent agreement with experimental results. Their approach of efficiently exciting antenna modes by using low index substrates is confirmed both with experiments and numerical simulations. This should provide further insights into a better understanding of optical antennas for various applications.

Chirp effects on impulsive vibrational spectroscopy: a multimode perspective

The well-documented propensity of negatively-chirped pulses to enhance resonant impulsive Raman scattering has been rationalized in terms of a one pulse pump-dump sequence which "follows" the evolution of the excited molecules and dumps them back at highly displaced configurations. The aim of this study was to extend the understanding of this effect to molecules with many displaced vibrational modes in the presence of condensed surroundings. In particular, to define an optimally chirped pulse, to investigate what exactly it "follows" and to discover how this depends on the molecule under study. To this end, linear chirp effects on vibrational coherences in poly-atomics are investigated experimentally and theoretically. Chirped pump-impulsive probe experiments are reported for Sulforhodamine-B ("Kiton Red"), Betaine-30 and Oxazine-1 in ethanol solutions with <10 fs resolution. Numerical simulations, including numerous displaced modes and electronic dephasing, are conducted to reproduce experimental results. Through semi-quantitative reproduction of experimental results in all three systems we show that the effect of group velocity dispersion (GVD) on the buildup of ground state wave-packets depends on the pulse spectrum, on the displacements of vibrational modes upon excitation, on the detuning of the excitation pulses from resonance, and on electronic dephasing rates. Akin to scenarios described for frequency-domain resonance Raman, within the small-displacement regime each mode responds to excitation chirp independently and the optimal GVD is mode-specific. Highly-displaced modes entangle the dynamics of excitation in different modes, requiring a multi-dimensional description of the response. Rapid photochemistry and ultrafast electronic dephasing narrow the window of opportunity for coherent manipulations, leading to a reduced and similar optimal chirp for different modes. Finally, non-intuitive coherent aspects of chirp "following" are predicted in the small-displacement and slow-dephasing regime, which remain to be observed in experiment.

Whistler wave radiation from a loop antenna located in a cylindrical density depletion

Electromagnetic radiation from sources in a magnetoplasma containing a radially nonuniform cylindrical density depletion is considered. Using a rigorous solution for the total field comprising both the discrete and continuous parts of the spatial spectrum of excited waves, the radiation resistance of a loop antenna and the efficiency of excitation of different modes by such a source are determined in the whistler range. Based on the numerical results, conditions are revealed under which the power radiated from a loop antenna located in a density depletion is dominated by the contribution of either discrete- or continuous-spectrum modes. It is found that the radiation resistance of the loop antenna in a weakly nonuniform density depletion can be notably greater than that in a homogeneous magnetoplasma whose parameters coincide with those near the depletion axis. The results are relevant to the basic properties of whistler wave excitation in the presence of field-aligned plasma density irregularities and can be useful for wave diagnostics in laboratory and space plasmas.

On the surface plasmon polariton wave at the planar interface of a metal and a chiral sculptured thin film

The solution of a dispersion equation indicates the theoretical existence of multiple modes of surface plasmon polariton wave propagation at the planar interface of a metal and a chiral sculptured thin film (STF). One mode appears to occur over a wide range of the structural period of the chiral STF, while all other modes exist only above some minimum value of the structural period, the minimum value being different for each mode. In order to excite the different modes, the interface can be incorporated in the commonplace Kretschmann configuration, for which our calculations show that the efficient excitation of different modes would require different numbers of structural periods of the chiral STF.

Do Vibrational Excitations of CHD 3 Preferentially Promote Reactivity Toward the Chlorine Atom?

The influence of vibrational excitation on chemical reaction dynamics is well understood in triatomic reactions, but the multiple modes in larger systems complicate efforts toward the validation of a predictive framework. Although recent experiments support selective vibrational enhancements of reactivities, such studies generally do not properly account for the differing amounts of total energy deposited by the excitation of different modes. By precise tuning of translational energies, we measured the relative efficiencies of vibration and translation in promoting the gas-phase reaction of CHD3 with the Cl atom to form HCl and CD3. Unexpectedly, we observed that C-H stretch excitation is no more effective than an equivalent amount of translational energy in raising the overall reaction efficiency; CD3 bend excitation is only slightly more effective. However, vibrational excitation does have a strong impact on product state and angular distributions, with C-H stretch-excited reactants leading to predominantly forward-scattered, vibrationally excited HCl.

Polariton bandstructure of disordered metallic photonic crystal slabs

AbstractWe analyze the influence of disorder on the polaritonic bandstructure of metallic photonic crystal slabs. Different disorder types with varying next‐neighbor correlations and disorder amounts are implemented. Angle‐resolved transmission measurements allow to determine the relation of bandstructure and disorder. We found that uncorrelated disorder retains the bandstructure and only reduces the splitting between the gaps. Correlated disorder, however, leads to the complete destruction of the bandstructure for moderate disorder amounts due to the excitation of different modes. We present a model that shows a good agreement with the measurements. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Characteristics of a microstrip‐excited high‐permittivity rectangular dielectric resonator antenna

AbstractThe radiation characteristics of a microstrip‐line‐excited rectangular dielectric resonator antenna (DRA) are studied experimentally. The radiation characteristics and excitation of different modes are highly influenced by the orientation of the DR, feed line parameters, and finite size of the ground plane. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 40: 316–318, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11366