Excitation Scenario Research Articles

Harvesting both wind energy and vibration energy by a zigzag structure with hybrid magnetic and piezoelectric effects

In practical environments, wind energy and vibration energy often coexist. Considering this, we introduce a new energy harvester designed to concurrently harness wind energy and vibration energy by integrating magnetic and piezoelectric effects. This harvester is composed of a zigzag structure and a bluff body. The bluff body is designed to execute galloping under incoming fluid flow and produce outputs, while the zigzag bi-stable structure can harness the energy of base excitation effectively. The introduction of magnetic interaction leads tothe softening-spring characteristic, which is verified by the nonlinear analysis. This softening-spring nonlinearity canenhance the working frequency range of the harvester. The results obtained from the numerical simulations indicate that the interaction of base excitation and wind flow can significantly improve the non-resonance region output. Corresponding validation experiments are carried out. The results are in good agreement with the numerical ones. Under stochastic excitations, the output power obtained from the hybrid scenario can reach 73.04 μW, representing a 16 % increase compared to the pure base excitation scenario.

Formation of the four terrestrial planets in the Jupiter–Saturn chaotic excitation scenario: fundamental properties and water delivery

The Jupiter–Saturn chaotic excitation (JSCE) scenario proposes that the protoplanetary disk was dynamically excited and depleted beyond ∼1–1.5 au in a few Myr, offering a new and plausible explanation for several observed properties of the inner solar system. Here, we expanded our previous work by conducting a comprehensive analysis of 37 optimal terrestrial planet systems obtained in the context of the JSCE scenario. Each optimal system harbored exactly four terrestrial planets analogs to Mercury, Venus, Earth, and Mars. We further investigated water delivery, feeding zones, and accretion history for the planet analogs, which allowed us to better constrain the water distribution in the disk. The main findings of this work are as follows: 1) the formation of four terrestrial planets with orbits and masses similar to those observed in our solar system in most of our sample, as evidenced by the dynamically colder and hotter orbits of Venus–Earth and Mercury–Mars analogs, and the high success rates of similar mutual orbital separations (∼40–85%) and mass ratios of the planets (∼70–90%) among the 37 systems; and 2) water was delivered to all terrestrial planets during their formation through the accretion of water-bearing disk objects from beyond ∼1–1.5 au. The achievement of Earth’s estimated bulk water content required the disk to contain sufficient water mass distributed within those objects initially. This requirement implies that Mercury, Venus, and Mars acquired water similar to the amount on Earth during their formation. Several of our planet analogs also matched additional constraints, such as the timing of Moon formation by a giant impact, Earth’s late accretion mass and composition, and Mars’s formation timescale.

Reinforcement learning optimisation for graded metamaterial design using a physical-based constraint on the state representation and action space

The energy harvesting capability of a graded metamaterial is maximised via reinforcement learning (RL) under realistic excitations at the microscale. The metamaterial consists of a waveguide with a set of beam-like resonators of variable length, with piezoelectric patches, attached to it. The piezo-mechanical system is modelled through equivalent lumped parameters determined via a general impedance analysis. Realistic conditions are mimicked by considering either magnetic loading or random excitations, the latter scenario requiring the enhancement of the harvesting capability for a class of forcing terms with similar but different frequency content. The RL-based optimisation is empowered by using the physical understanding of wave propagation in a such local resonance system to constrain the state representation and the action space. The procedure outcomes are compared against grading rules optimised through genetic algorithms. While genetic algorithms are more effective in the deterministic setting featuring the application of magnetic loading, the proposed RL-based proves superior in the inherently stochastic setting of the random excitation scenario.

Molecular Properties of 3d and 4f Coordination Compounds Deciphered by Raman Optical Activity Spectroscopy.

Molecular properties of coordination compounds can be efficiently studied by vibrational spectroscopy. The scope of Raman spectroscopy has been greatly enhanced by the introduction of Raman optical activity (ROA) sensitive to chirality. The present review describes some of its recent applications to study the coordination compounds. 3d and 4f metal complexes often absorb the excitation light, or exhibit luminescence. Therefore, effects caused in ROA spectra by electronic circular dichroism (ECD) and circularly polarized luminescence (CPL) must be taken into consideration.In 3d metal complexes ECD and circularly-polarized Raman scattering compete with the resonance ROA (RROA) signal. Pure RROA spectrum can thus be obtained by subtracting the so-called ECD-Raman component. CPL is frequently encountered in 4f systems. While it can mask the ROA spectra, it is useful to study molecular structure. These electronic effects can be reduced by using near-infrared excitation although vibrational ROA signal is much weaker compared to the usual green laser excitation scenario. The ROA methodology is thus complex, but capable of providing unique information about the molecules of interests and their interaction with light.

Passive acoustic mapping with absolute time-of-flight information and delay-multiply-sum beamforming.

Passive acoustic mapping (PAM) is showing increasing application potential in monitoring ultrasound therapy by spatially resolving cavitation activity. PAM with the relative time-of-flight information leads to poor axial resolution when implemented with ultrasound diagnostic transducers. Through utilizing the absolute time-of-flight information preserved by the transmit-receive synchronization and applying the common delay-sum (DS) beamforming algorithm, PAM axial resolution can be greatly improved in the short-pulse excitation scenario, as with active ultrasound imaging. However, PAM with the absolute time-of-flight information (referred as AtPAM) suffers from low imaging resolution and weak interference suppression when the DS algorithm is applied. This study aims to propose an enhanced AtPAM algorithm based on delay-multiply-sum (DMS) beamforming, to address the shortcomings of the DS-based AtPAM algorithm. In DMS beamforming, the element signals delayed by the absolute time delays are first processed with a signed square-root operation and then multiplied in pairs and finally summed, the resulting beamformed output is further band-pass filtered. The performances of DS- and DMS-based AtPAMs are compared by experiments, in which an ultrasound diagnostic transducer (a linear array) is employed to passively sense the wire signals generated by an unfocused ultrasound transducer and the cavitation signals generated by a focused therapeutic ultrasound transducer in a flow phantom. The AtPAM image quality is assessed by main-lobe width (MLW), intensity valley value (IVV), area of pixels (AOP), signal-to-interference ratio (SIR), and signal-to-noise ratio (SNR). The single-wire experimental results show that compared to the DS algorithm, the DMS algorithm leads to an enhanced AtPAM image with a decreased transverse MLW of 0.15mm and an improved SIR and SNR of 31.50 and 18.77dB. For the four-wire images, the transverse (axial) IVV is decreased by 18.37dB (13.11dB) and the SIR (the SNR) is increased by 26.13dB (18.47dB) when using the DMS algorithm. The cavitation activity is better highlighted by DMS-based AtPAM, which decreases the AOP by 0.81 mm2 (-10-dB level) and 4.43 mm2 (-20-dB level) and increases the SIR and SNR by 20.14 and 10.48dB respectively. The pixel distributions of AtPAM images of both wires and cavitation activity also indicate a better suppression of the DMS algorithm in sidelobe and noise. The experimental results illustrate that the DMS algorithm can improve the image quality of AtPAM compared to the DS algorithm. DMS-based AtPAM is beneficial for detecting cavitation activity during short-pulse ultrasound exposure with high resolution, and further for monitoring short-pulse ultrasound therapy.

A data-driven physics-informed stochastic framework for hurricane-induced risk estimation of transmission tower-line systems under a changing climate

Hurricanes are one of the most devastating natural hazards which result in significant damage to civil infrastructure. The transmission tower-line system is specifically highly vulnerable to hurricane effects. Recent studies have indicated that the collapse of the transmission tower-line system during hurricane events is mainly due to the joint occurrence of wind and rain. Therefore, it is important to assess the failure probabilities of these structures under wind and rain-induced loads. With climate change, those probabilities are expected to significantly change where the brunt of the damage and economic losses would be disproportionately borne by coastal communities. This study proposes a hybrid risk-responsive, data-driven and physics-informed framework which evaluates the hurricane-induced damage to transmission lines in vulnerable regions and communities under several climate scenarios. The framework is founded upon an advanced physics informed hurricane simulation model followed by a Gaussian kernel density technique to efficiently estimate the intensity measures and quantify the associated uncertainties accurately. The generated hazard intensities are coupled with fragility surfaces expressed in terms of wind speed and rain intensity. Then, the failure probabilities are obtained for the transmission tower-line system under the joint excitation and future climate scenario. The framework is applied to several coastal cities along the US east coast. It is shown that, due to the involved system nonlinearity, the obtained failure probabilities change drastically with the future climate scenario. In addition, rainfall-induced loads which significantly impact the failure probabilities of the transmission tower-line systems are not only function of the selected sites, but also depend on the considered limit state and climate scenario. Therefore, their consideration is important for the structural design and estimation of the system performance.

Demonstration of dipole-induced transparency using mirrored split-ring resonator metasurface for microwave applications

In this paper, the Dipole-Induced Transparency (DIT) in the microwave frequency regime is proposed and verified using experimental and simulation studies. A single-layer mirrored Split-Ring Resonator (SRR) array configured in the H⊥ excitation scenario is used to create an out-of-phase oscillating electric dipole moment for a normal incident plane wave. The destructive interference between these out-of-phase oscillating electric dipole moments nullifies far-field scattering resulting in the emergence of the transparency window. We used the multipole scattering theory to validate the results computationally. The coupling effects are studied numerically, and the emergence of the transparency window is studied experimentally using transmission measurements inside an anechoic chamber using a vector network analyzer.

LFT-Based Identification of Lateral Vehicle Dynamics

This paper presents a novel estimation and identification approach for lateral vehicle dynamics. The algorithm leverages on a Linear Fraction Transform (LFT) reformulation of vehicle and tyre models, allowing for a simple and computationally efficient inclusion of complex and nonlinear dynamic models, like, for example, two-wheels, four-wheels or single-track as vehicle model, and Pacejka, brush or Fiala as tyre model. As a result, this technique can be easily adopted in the development of an online identification system, able to run on a standard embedded device, implementing a flexible identification procedure that can handle different driving conditions, up to the limits of handling, different vehicle modelling approaches, and different input measurements. Experimental results demonstrate the effectiveness of the proposal, either in a persistent excitation and in a non-persistent excitation scenario.

Investigating the performance of tri-stable magneto-piezoelastic absorber in simultaneous energy harvesting and vibration isolation

Tri-stable magneto-piezoelastic oscillators exhibit superior performance in terms of broadband resonance frequency and lower excitation threshold, compared to linear and bi-stable systems. Furthermore, inclusion of magnets renders them applicable, tunable, and simple designs. However, the potential of this oscillators for the purpose of simultaneous vibration suppression and energy harvesting has not been investigated. This study aims to investigate simultaneous energy harvesting and vibration isolation through a tri-stable magneto-piezoelastic absorber (TMPA). The absorber comprises a bimorph cantilever beam carrying a magnetic tip mass and two external magnets. The interplay between magnets generates a nonlinear restoring force in the TMPA structure. This absorber is attached to a host vibrating beam, which is under a transient or periodic forcing, in order to reduce its vibrations and harvest electrical energy. The nonlinear magneto-electromechanical equations governing the coupled system are obtained by employing the Hamilton's principle, Euler-Bernoulli beam theory, and a recently proposed magnetic force relationship. First, the mechanisms of tri-stability formation are investigated via bifurcation diagrams. Next the potency of the TMPA in the transient excitation scenario is examined. Furthermore, the performance of the TMPA in the presence of the periodic excitation with different forcing levels is investigated. Specifically, frequency and time domain analyses are carried out to characterize the response of the system and efficiency of the absorber when TMPA performs periodic in-well, aperiodic inter-well and periodic inter-well oscillations. In addition, to provide a better insight regarding the TMPA performance, the kinetic energies, harvested power, and dissipated power for the region of strongly modulated response are also studied. Moreover, the efficacy of the TMPA in periodic snap-through oscillations is examined by the means of the harmonic balance method in conjunction with pseudo-arclength continuation scheme. Finally, the results disclosed that the proposed tri-stable absorber outperforms a linear absorber in vibration annihilation and energy harvesting.

Role of dynamic water rivulets in the excitation of rain–wind-induced cable vibration: A critical review

It has been more than 30 years since Hikami Y and Shiraishi N (1988) Rain–wind-induced vibrations of cable-stayed bridges. Journal of Wind Engineering and Industrial Aerodynamics 29: 409–418 first reported the rain–wind-induced vibration (RWIV) of stay cables in the construction stage of Meikonishi Bridge, Japan. After that, considerable research efforts have been devoted to understanding the RWIV of stay cables, and the role of the upper rivulet has been gradually realized and studied. This study presents a selective review on recent progress of RWIV and its controversial excitation mechanism. The available knowledge and up-to-date understanding of this complex fluid-structure interaction are presented in some detail. The formation, dynamics of water rivulet, and its role in affecting the near-wall boundary layer properties and in the excitation scenario of RWIV are of particular interest in this study. Finally, some limitations of previous studies are concluded, with some perspective suggestions for further study of excitation mechanism of RWIV.

Subcritical Andronov-Hopf scenario for systems with a line of equilibria.

Using numerical simulation methods and analytical approaches, we demonstrate hard self-oscillation excitation in systems with infinitely many equilibrium points forming a line of equilibria in the phase space. The studied bifurcation phenomena are equivalent to the excitation scenario via the subcritical Andronov-Hopf bifurcation observed in classical self-oscillators with isolated equilibrium points. The hysteresis and bistability accompanying the discussed processes are shown and explained. The research is carried out on an example of a nonlinear memristor-based self-oscillator model. First, a simpler model including Chua's memristor with a piecewise-smooth characteristic is explored. Then, the memristor characteristic is changed to a function being smooth everywhere. Finally, the action of the memristor forgetting effect is taken into consideration.

Optimal excitation mechanism for combustion enhancement of supersonic shear layers with pulsed jets

Supersonic shear layers (convection Mach number = 0.6) with flow direction excitation are studied by a canonical Large Eddy Simulation (LES) method with quasi-laminar turbulent reaction model. By modulating velocity of central jet through ideal square wave under four excitation periods (τ = 20, 40, 60, and 80 μs), the present study aims to explore the optimal excitation mechanism for combustion enhancement. As the excitation period increases, combustion efficiency tends to increase and then decrease. The maximum combustion efficiency is achieved at τ=40μs, which is nearly four times that in the no excitation scenario. The analysis of mixing characteristics of the nonreacting cases reveals that mixing enhancement mainly explains combustion gain of different excitation modes. From the limiting formation of vortex, the size of the vortex core has fully developed to reach axial contact at τ=40μs. Any further increase in excitation intervals implies a larger vortex spacing, which leads to poor fluid mixing while lower excitation case forms continuous small vortices with less mixing region. The comparison of the circulation decomposition of the main vortex and trailing wakes indicates the pinch-off characteristic of the limiting formation of vortical structure. On the basis of these results, an optimal forcing criterion is proposed according to the limiting vortex formation with dimensionless excitation time scale τ∗≈1.64. This study provides a novel perspective for the optimal combustion enhancement of supersonic shear layers from the aspect of vorticity dynamics.

Electro-thermal excitation of parametric resonances in double-clamped micro beams

We report on a simple yet efficient approach allowing direct electrothermal excitation of parametric resonance (PR) in double-clamped flexible nano- and microscale beams. The application of a time-harmonic voltage between the beam's ends leads to the electric current and Joule's heating of the entire beam, which induces a time-periodic axial stress and results in excitation of the structure lateral vibrations through the PR mechanism. The proposed approach has an advantage, simplifying fabrication and integration and reducing the influence of residual stress, and thermal mismatch, unlike conventional piezoelectric, photothermal, or electrostatic actuation approaches, which require additional piezoelectric layers, light sources, or electrodes in the proximity of a vibrating beam. Single crystal silicon, nominally 500 μm long, 30 μm wide, and 5 μm thick beams were fabricated by deep reactive ion etching and operated at a pressure of ≈1.9 mTorr. The experimental results, consistent with the reduced order and numerical model predictions, demonstrate the feasibility of the suggested excitation scenario, which could be implemented in resonant sensors, timing devices, signal processing, and micro and nanomechanical logical elements.

Influence of internal electrical losses on optimization of electromagnetic energy harvesting

A lot of effort has been made to optimize linear electromagnetic energy harvesters under harmonic or random excitation, connected to simple or more complicated electrical extraction circuits. Nevertheless, the internal electrical losses of electromagnetic coils are often neglected in these optimization analyses. To this end, the present paper investigates systematically and for the first time the influence of internal impedance of coils on energy harvesting performance under various types of ambient excitation sources, which are, respectively, external force acting directly on the seismic mass, base displacement-induced motion and disturbance generated by base acceleration. Our analysis highlights that under sinusoidal excitation, the resonant load outperforms its non-resonant counterpart in terms of energy harvesting performance when the internal resistance is very small, while its increase deteriorates significantly the broadband harvesting capability of resonant circuits. When subjected to random vibration, the resonant load presents no advantage compared to the latter one. The optimum design of non-resonant circuit is then carried out in each excitation scenario leading to well-known criteria and expanding to cases where no optimal conditions were defined or obtained. It is also reported that the neglect of internal losses underestimates the maximum available power.

Numerical investigation of transient response of a coupled two-degrees-of-freedom symmetric airfoil before flutter

In this study, the numerical investigation of free dynamic response of a rigid, symmetric airfoil having two coupled degrees of freedom is performed. The airfoil is excited using two different mechanisms. Firstly, a mechanical excitation scenario is simulated using initial conditions for both the degrees of freedom. Dynamic airfoil response in terms of amplitudes of oscillation is recorded under no flow as well as uniform upstream flow conditions. In the second scenario, an upstream flow perturbation is introduced in the form of a gust superimposed on the otherwise uniform in-flow. Transient energy amplification behavior of the airfoil under both scenarios is monitored. The findings are presented in terms of dimensionless aerodynamic coefficients, oscillations amplitudes, and total energy of the airfoil. Detailed comparisons of the experimental data and results obtained using analytical models are developed and discussed using a very simple simulation methodology.

A RECONFIGURABLE BROADBAND DUAL-MODE DUAL-POLARIZED ANTENNA FOR SECTORIAL/OMNIDIRECTIONAL MOBILE BASE STATIONS

© 2018, Electromagnetics Academy. All rights reserved. This paper proposes a new design of reconfigurable three-sector dual-mode dual-polarized antenna for use primarily in mobile communication base stations. The design offers the flexibility to be used as a sectorial (directive) or omnidirectional base station antenna whenever required. The two different radiating modes (omnidirectional and sectorial) depend only on the excitation scenario. The proposed antenna has the advantages of offering broadband, stable radiation pattern and high polarization purity within the desired frequency band, and a simple feeding structure with a very compact size (less than 800 cm3) and low profile. The achieved fractional bandwidth is 55.3% (1.7 - 3GHz). A prototype antenna was constructed and tested with the two modes of operation. Results demonstrate the principle of the design and show how the design may be packaged in a compact size to offer excellent omnidirectional or sectorial performance which makes this new design an ideal candidate for reconfigurable dual-mode mobile base stations.

Selective detection of intermolecular response in benzonitrile through double-pulse excitation in optical Kerr effect spectroscopy

We report on the decomposition of the molecular contribution to the optically heterodyne-detected optical Kerr effect (OHD-OKE) in benzonitrile C6H5CN in the process of double-pulse laser excitation. The pump pulses with linear orthogonal polarizations, controllable intensities and timing enable us to manipulate the amplitudes of various molecular responses due to the fact that the OHD-OKE signal is formed by the superposition of independent third-order responses associated with each pump pulse. We apply this technique to detect the intermolecular response selectively by using an excitation scenario with suppression of orientational and intramolecular responses. A detailed comparative analysis of third-order optical responses indicates strongly that the double-pulse excitation of the OHD-OKE is the useful spectroscopic technique to obtain precise information on the intermolecular spectrum in liquids.

A Metamaterial Backed Dipole Antenna for High Gain Directional Communications

The enhanced radiation performance of a dipole antenna backed by the split ring resonator-continuous wire pair array working in the H┴ excitation scenario is presented in this paper. The H┴ excitation scenario of the metamaterial is used to get zero reflection phase resulting in enhanced gain performance. The two layer meta-structure along with the dipole is fabricated on a low cost substrate of dielectric constant 4.4 and height 1mm. The reflection properties of the metamaterial structure and its effect on the radiation performance of the dipole antenna are presented in this paper.

Biosensing with Asymmetric High Refractive Index Contrast Gratings

We propose a novel label-free optical biosensor configuration based on a spectral refractive index sensing method by utilizing asymmetric high index contrast dielectric gratings. The characterization and performance evaluation of the designed biosensor are carried out by using 2D and 3D finite-difference time-domain methods. The designed sensor is illuminated in-plane with transverse-electric polarized light wave. The salient properties of the device are compactness, having a simple measurement technique, easy excitation scenario, operating label-free, and possessing high sensitivity value reaching up to a level of 450 nm/RIU. The proposed sensor configuration may bring new impetus to the field of alternative biochemical sensing approaches.

Nonresonant double-pulse selective spectroscopy of interaction-induced response in liquids through an optically-heterodyne-detected optical-Kerr-effect

We propose and analyze theoretically the implementation of two pump pulses with orthogonal linear polarization for the separate measurement of an interaction induced response in liquids through the optically-heterodyne-detected optical-Kerr-effect. The key parameters controlling the specificity of the double-pulse excitation scenarios are the pulse duration, the delay between pulses and the relation between the pump pulses amplitudes. We use acetonitrile as an example to model the fifth-order optical response and consider some principles of the scenarios construction. We show that it is possible to adjust the excitation scenario in such a way that the intramolecular and orientational responses are removed from the detected signal. The theoretical analysis reveals that the double-pulse excitation technique can be useful for the selective spectroscopy of the interaction induced responses of the molecules in liquid.