Resonance Frequency Region Research Articles

Electromagnetically induced grating via amplitude and phase modulations in a three-level V-type atomic medium

Abstract A probe laser beam can be completely absorbed in an atomic resonance frequency region, however, if a coupling laser beam is further applied to the atom, the atomic medium can exhibit electromagnetically induced transparency (EIT), i.e, the probe beam can be completely transmitted through the atomic medium. Thus, if the coupling beam is a standing wave field with nodes and antinodes, it will cause in space a periodic modulation of the transmitted spectrum of the probe field. This means that the probe field propagates through the atomic medium just as it passes through a diffraction grating which is called electromagnetically induced grating (EIG). Based on amplitude or phase modulation of transmission function, the absorption grating or the phase grating can be formed, respectively. In this work, based on controllable absorption and dispersion properties of a three-level V-type atomic system, we study the control of the absorption grating and the phase grating with respect to the intensity and the frequency of the laser fields. The absorption diffraction pattern at the two-photon resonance is obtained, while the phase diffraction pattern appears when there is a frequency shift of either the coupling frequency or the probe frequency compared to the corresponding atomic resonance frequency. By adjusting the coupling or/and probe laser frequency, the absorption grating can be converted into the phase grating and the high-order diffraction efficiency can also be improved.

Aluminum panel vibration reduction using single lead zirconate titanate and resonant circuit

This study aimed to reduce the vibration of an aluminum plate using a single lead zirconate titanate (PZT) electrical circuit. First, the natural frequencies and modes of the aluminum plate were analyzed using an analytical method to determine the dynamic characteristics of the plate. The frequency domain was used to derive the vibration characteristics of the acoustically excited aluminum plate. It was noted that the resonance region where the vibration of the panel increased rapidly was at 390 Hz, which was then set as the reduction target. Thereafter, the vibration reduction performances of the circuit that connects only the resistance element to the PZT panel and the resonant circuit that uses an inductor were compared. Through actual acoustic excitation, the vibration reduction of the aluminum panel using the PZT panel based on resistance and resonance circuits was validated. The results demonstrated that the vibration in the resonant frequency region of 384 Hz was reduced by 20% through the implementation of a resonant circuit, comprising an inductor and a resistor, added to a single PZT, whose weight was 0.08% of the weight of the aluminum panel. Therefore, this study confirmed that the vibration of aluminum plates can be effectively reduced using a low-weight PZT patch.

Piezoelectric-triboelectric energy harvester with elastic double-side stoppers

An impact-based piezoelectric and triboelectric energy harvester with elastic double-side stoppers for wideband operation and efficient energy capture is proposed. The coupled nonlinear governing equations of the energy harvesting system are derived based on Hertz's contact model. The dynamic behavior of the energy harvester is enriched from linear to nonlinear regime by introducing stoppers to broaden the energy harvesting frequency range. The dynamic mechanism and energy harvesting performance of the harvester are explored through frequency sweeps, which identify comprehensive dynamic states and evaluate the energy harvesting performance. The time history diagram, phase diagram, Poincaré mapping and bifurcation diagram are used to discuss the single-period, double-period, multi-period and chaotic period vibrations of the energy harvester. Detailed parametric studies investigate the effects of the initial gap, mass ratio, stopper stiffness and excitation amplitude on the voltage and power output. Four models with different stoppers are compared to identify the best energy harvesting performance. Results show that compared with the cantilever without stopper, the proposed model with elastic double-side stoppers significantly broadens the resonance frequency region by 172.5 %, and increases the output cumulative voltage by 0.89 V. A maximum voltage of 1.2 V with a 0.6-V-bandwidth of 6.9 Hz is achieved when the energy harvester is actuated at 0.8 g acceleration. The RMS voltage of triboelectric nanogenerator is highest at 25 Hz, reaching 1.99 V, and the peak-to-peak output voltage reaches 15.59 V.

Extracting Pole Characteristics of Complex Radar Targets for the Aircraft in Resonance Region Using RMSPSO_ARMA

The extraction algorithm of target characteristics resonance set at the high-frequency band plays a significant role in defense applications like early warning. The paper proposes a new method to extract the characteristic resonance set of radar targets in the resonance frequency region using an autoregressive moving average model optimized by root mean square propagation particle swarm optimization. Considering that the total scattering response in the resonant region consists of early-time and late-time responses, the autoregressive moving average model approximate the total scattering responses to avoid errors caused by intercepting the late-time response. Further, the paper investigated the impact of the swarm optimization algorithm on the accuracy of moving average model parameters when obtaining the resonance set at different target aspects. The extracted characteristic resonance results within a range of azimuth directions through an aircraft target paradigm indicate that the new method is more convenient and precise than the matrix beam prediction method.

Torsional vibration suppression for a high-damped rotor using dynamic vibration absorber based on weighted dual estimation of equivalent linearization techniques

In the rotating systems, the torsional vibration of damped rotors usually appears and induces the imbalance of systems. The dynamic vibration absorber (DVA) is used for reducing the torsional vibration of damped rotors. Recent researches have shown that traditional methods are suitable for reducing the torsional vibration of weak damped rotors. However, the traditional methods will cause significant errors for high-damped rotors. Therefore, a novel method is proposed to suppress the torsional vibration of high-damped rotors using a dynamic vibration absorber based on Weighted Dual Estimation (WDE) of equivalent linearization techniques. The high-damped rotor is replaced approximately by an equivalent undamped rotor based on the WDE of equivalent linearization techniques. Two closed-form expressions for a suitable system of springs and viscous dampers of the optimal DVA are determined to suppress the torsional vibration of high-damped rotors. The numerical analysis results show that the torsional vibration of the high-damped rotor has surprisingly reduced at the resonant frequency region by using the optimal DVA. The proposed expressions for a suitable system of springs and viscous dampers of the optimal DVA are reliable for suppressing the torsional vibration of a highly damped rotor.

Nonlinear response of magnetization obeying inertial dynamics to superimposed dc and ac fields and dynamic magnetic hysteresis

The nonlinear ac stationary responses of magnetization and the dynamic magnetic hysteresis of ferromagnetic particles with uniaxial anisotropy acted on by both external dc and ac magnetic fields are evaluated by employing the inertial Landau–Lifshitz–Gilbert equation. Analytical expressions are obtained for the components of the second- and third-order nonlinear susceptibility tensors using the perturbation method. The dynamic nonlinear susceptibility strongly depends on the dc field strength. The effect of inertia on the area and slope of the dynamic magnetic hysteresis loop is demonstrated. In addition to nutation resonance, the main nonlinear effects previously observed in the ferromagnetic resonance region (frequency doubling and appearance of weak subharmonic resonance peaks) are predicted in the nutation resonance frequency region.

Rice husk silica blended fillers for engine mount application

The functional properties of engine mounts largely depend on the rubber compound formulation. This study proposes the use of rice husk–derived silica (RHS) blended with carbon black (N772) as an effective and environmentally friendly substitute for fillers used in rubber engine mounts (REMs). CV-60 natural rubber was filled with the blended fillers at various ratios, and their compatibility for use as rubber engine mounts (REMs) was assessed. Grey Relational Analysis was utilised to determine the optimal blend loading levels for use in rubber engine mounts, resulting in 40 phr of N772 and 20 phr of RHS cured at 130 °C and 2.5 MPa for 20 min. The developed REMs and conventional REMs had low vibration data variation during the performance assessment. Their resonance transmissibility was 5.03 and 3.74, corresponding to natural frequencies of 24.27 Hz and 26.94 Hz, respectively. The RHS/N772 REMs had excellent damping characteristics and lower transmissibility in the isolation zone of the vibration isolation curve, which is outside of the resonant frequency region. The efficiency curves showed that the blended fillers are a better and more effective material for REMs at all frequencies, balancing static deflection and vibration isolation.

Colossal Kerr nonlinearity without absorption in a five-level atomic medium

In this work, we present an analytical method to achieve giant Kerr nonlinearity without absorption in a five-level atomic medium. By using iterative perturbation technique on density matrix equations, we have derived the analytical expressions of nonlinear susceptibility and Kerr nonlinear coefficient in the presence of spontaneously generated coherence (SGC) and relative phase between applied laser fields. It shows that, this five-level atomic medium exhibits multiple electromagnetically induced transparency (EIT) at three different frequencies, at the same time, the Kerr nonlinear coefficient is enhanced around three transparent spectral regions; in each such EIT region appears a pair of positive–negative peaks of Kerr nonlinear coefficient. In particular, these nonlinear peaks are moved to the center of the EIT windows via SGC. This means that the Kerr nonlinear coefficient is enhanced with completely suppressed absorption at different transparency frequencies. Furthermore, the magnitude and the sign of the Kerr nonlinear coefficient are easily controlled according to the SGC strength, the coupling laser intensity, and the relative phase between applied laser fields. Such a giant nonlinear medium can be useful for photonic devices working in the resonant frequency region without absorption. As a typical application, this giant Kerr nonlinear material has been applied to an interferometer for the formation of optical bistability, and showed the appearance of OB at the resonant frequency with significantly reduced threshold intensity and OB width.

Effect of electric impedance on the electromechanical characteristics of tunable spherical piezoelectric transducer

Spherical piezoelectric transducers are a critical component of ultrasonic vibration systems with significant applications in various practical scenarios such as underwater acoustic detection and structural health monitoring. The existing spherical piezoelectric transducers have fixed electromechanical characteristics that limit their applications in scenarios with multi-frequency or frequency variation requirements. It would therefore be intriguing, from the viewpoints of both science and technology, to break through this limit by introducing external electric load impedance. Here we propose a tunable spherical piezoelectric transducer (TSPT) capable of adjusting the electromechanical characteristics by changing the resistance, inductance, and capacitance applied to the passive piezoceramic shell. The theoretical and numerical results show that when the resistance is exerted on the inner and outer piezoceramic shells, the resonance is accompanied by large variations at low values of resistance, while it becomes almost constant at high values of resistance. When the inductance is exerted on the outer piezoceramic shell, the resonance frequency obtained by the finite element method can be changed from 72730 Hz to 42928 Hz by adjusting the inductance, indicating that the TSPT can realize a rich and selective resonance frequency region. The resonance/antiresonance frequency decreases while the effective electromechanical coupling coefficient increases, when the capacitance applied on the inner and outer piezoceramic shells increases. The experiments are conducted to verify the effectiveness of the proposed TSPT, which is in agreement with the simulated results and theoretical predictions. Our methodology will offer possibilities to extend the working frequency range of the existing piezoelectric spherical transducer for underwater acoustic detection, hydrophones, and the spherical smart aggregate for civil structural health monitoring.

Active damping of LCL-Filtered Grid-Connected inverter based on parallel feedforward compensation strategy

Resonance related to the LCL-filter grid-connected inverter (GCI) is one of the most challenging issues in power electronics. Active damping is a widely used methodology to damp the resonance problem due to its effective control structure. In capacitor current feedback active damping methodologies, a compensator is primarily required in the feedback loop where the damping efficiency depends on the imitated features of the compensator. Such capacitor current feedback damping techniques encounter restrictions in their layout at the critical resonance frequency and may need extra amendment in the delay to assure stability. This paper proposes a different design method called parallel feedforward compensation method, which designs an almost strictly real positive plant and achieved damping with enhanced stability features. In the proposed alternative, a first-order high pass filter is used as a compensator across the LCL filter plant and filter capacitor current feedback loop. The resultant output of this augmented plant is then transmitted back at the reference point of a GCI system to attenuate the undesirable resonance peak. The key benefits of the proposed method are efficient damping without any limitation of critical resonance frequency region, better control characteristics, improved damping area, and better robustness under variations in filter parameters. The simulation and experimental outcomes based on transient response and steady-state analysis are demonstrated to validate the efficacy of the suggested method.

A quasi-3D layer-wise finite element model for vibroacoustic analysis of finite sandwich plates with frequency-dependent viscoelastic core

This article presents a quasi-3D layer-wise finite element approach to investigate the vibroacoustic characteristics of finite constrained layer damping (CLD) plates with a viscoelastic material (VEM) core. The frequency-dependent properties of the VEM core are integrated into the kinematic governing equation. The sound transmission loss (STL) behavior under oblique plane sound wave excitation is studied in narrow frequency bands, thus the variation caused by resonance modes can be captured clearly. Results show that the STL values of the two CLD plates configurations are significantly increased in resonance frequency regions. The symmetric configuration is found to have better sound insulation performance.

Fluid resonance in the narrow gap for a box close to a bottom-mounted wall with permeable bed

The behavior of fluid resonance in a narrow gap formed between a ship and a wharf on a permeable bed is investigated by using a two-dimensional viscous numerical model based on OpenFOAM package. The influence of the permeable bed is significant in the region of low-frequency and resonant frequency ranges, where the decreased free surface amplitude in the narrow gap can be observed, especially for large box draft and large porosity. The increased effect of permeable bed can be generated by large bed thickness and small bed width. With the increase of incident wave amplitude, the influence of permeable bed gives rise to weak. All of these phenomena can be explained by the variation of the fluid entering the seepage surface, where the large vertical velocity and more fluid volume entering the permeable bed can be computed for the cases of larger permeable bed effect. Finally, the variation tendency of wave forces on the box and the wall is consistent with that of wave amplitude in the narrow gap.

Effect of Control–Structure Interaction Using Torsional Servomotor for Active Tuned Mass Damper Control System

The control–structure interaction (CSI) affects the performance and robustness of protective structures in active control system, and it is important to consider the CSI effect to achieve high performance in structural vibration control. In this paper, the electro-mechanical model of the torsional servomotor is derived by establishing dynamic voltage equilibrium equation. Three different active control models (non-CSI, reduced-order CSI, and higher-order CSI model) which considering different accuracy requirements of the electro-mechanical relationship are established to investigate the influence of the CSI on active tuned mass damper (ATMD) control system. The frequency- and time-domain responses of a three-story steel frame structure during different excitations are investigated, and as a comparison, the responses of the uncontrolled and tuned mass damper (TMD) control system are also studied. It can be concluded that the control performance of the active control system is reduced due to the CSI effect, especially at resonance frequency region of the structure (around 2.7 Hz, 8.2 Hz, and 13.2 Hz). The input voltage, velocity of the top floor, velocity of active mass, and higher-order of control forces have an important influence on the servomotor output control force. Furthermore, it can be found that, to achieve the same control effect, the required control voltage has been significantly increased due to the CSI effect.

Handheld laser scanning microscope catheter for real-time and in vivo confocal microscopy using a high definition high frame rate Lissajous MEMS mirror.

A handheld confocal microscope using a rapid MEMS scanning mirror facilitates real-time optical biopsy for simple cancer diagnosis. Here we report a handheld confocal microscope catheter using high definition and high frame rate (HDHF) Lissajous scanning MEMS mirror. The broad resonant frequency region of the fast axis on the MEMS mirror with a low Q-factor facilitates the flexible selection of scanning frequencies. HDHF Lissajous scanning was achieved by selecting the scanning frequencies with high greatest common divisor (GCD) and high total lobe number. The MEMS mirror was fully packaged into a handheld configuration, which was coupled to a home-built confocal imaging system. The confocal microscope catheter allows fluorescence imaging of in vivo and ex vivo mouse tissues with 30 Hz frame rate and 95.4% fill factor at 256 × 256 pixels image, where the lateral resolution is 4.35 μm and the field-of-view (FOV) is 330 μm × 330 μm. This compact confocal microscope can provide diverse handheld microscopic applications for real-time, on-demand, and in vivo optical biopsy.

Vortex beam manipulation through a tunable plasma-ferrite metamaterial

This paper is devoted to the study of vortex beam transmission from an adjustable magnetized plasma-ferrite structure with negative refraction index. We use the angular spectral expansion technique together with the 4times 4 matrix method to find out the transmitted intensity and phase profiles of incoming Laguerre-Gaussian beam. Based on numerical analysis we demonstrate that high transparency and large amount of Faraday rotation in the proximity of resonance frequency region, reverse rotation of spiral wave front, and side-band modes generation during propagation are the remarkable features of our proposed structure. These controllable properties of plasma-ferrite metamaterials via external static magnetic field and other structure parameters provide novel facilities for manipulating intensity and phase profiles of vortex radiation in transmission through the material. It is expected that the results of this work will be beneficial to develop active magneto-optical devices, orbital angular momentum based applications, and wavefront engineering.

Damped (linear) response theory within the resolution-of-identity coupled cluster singles and approximate doubles (RI-CC2) method.

An implementation of a complex solver for the solution of the linear equations required to compute the complex response functions of damped response theory is presented for the resolution-of-identity (RI) coupled cluster singles and approximate doubles (CC2) method. The implementation uses a partitioned formulation that avoids the storage of double excitation amplitudes to make it applicable to large molecules. The solver is the keystone element for the development of the damped coupled cluster response formalism for linear and nonlinear effects in resonant frequency regions at the RI-CC2 level of theory. Illustrative results are reported for the one-photon absorption cross section of C60, the electronic circular dichroism of n-helicenes (n = 5, 6, 7), and the C6 dispersion coefficients of a set of selected organic molecules and fullerenes.

Transformer Secondary Voltage Based Resonant Frequency Tracking for LLC Converter

Unregulated LLC resonant converters operating at resonant frequency have been adopted in numerous applications due to its high efficiency characteristic. However, in practice, resonant frequency operation cannot always be guaranteed due to the tolerances and variations of circuit parameters. Therefore, in this brief, a simple resonant frequency tracking method based on the transformer secondary voltage is proposed. When LLC converter operating in the below resonant frequency region, the ratio of the average transformer secondary voltage and output voltage is less than unity, while the ratio is unity at resonant frequency. By adopting this characteristic, the resonant frequency tracking is achieved by comparing the calculated voltage ratio and unity, then the switching frequency is adjusted to track the resonant frequency. To reduce the sampling circuit complexity, the rectified transformer secondary voltage is sensed, and the voltage ratio becomes 0.5 at resonant frequency. The effectiveness of the proposed resonant frequency tracking method has been experimentally validated under different scenarios.

Analytical study of resonance regions for second kind commensurate fractional systems

<p style='text-indent:20px;'>The aim of this paper is to determine analytically the resonance limits for second kind commensurate fractional systems in terms of the pseudo damping factor <inline-formula><tex-math id="M1">\begin{document}$ \xi $\end{document}</tex-math></inline-formula> and the commensurate order <inline-formula><tex-math id="M2">\begin{document}$ v $\end{document}</tex-math></inline-formula> and in addition specify the different resonance regions. In the literature, these limits and regions have never been discussed mathematically, they are determined numerically. Second kind commensurate fractional systems are resonant if the equation : <inline-formula><tex-math id="M3">\begin{document}$ \Omega^{3v}+3\xi cos(v \pi/2)\Omega^{2v}+(2\xi^{2}+cos(v\pi))\Omega{^v}+\xi cos(v\pi/2) = 0 $\end{document}</tex-math></inline-formula>, obtained by setting the first derivative of the amplitude-frequency response equal to zero, has at last one strictly positive root. As in the conventional case, resonance limits correspond to zero discriminant of the last equation. This discriminant is a cubic equation in <inline-formula><tex-math id="M4">\begin{document}$ \xi{^2} $\end{document}</tex-math></inline-formula> whose coefficients change depending on <inline-formula><tex-math id="M5">\begin{document}$ v $\end{document}</tex-math></inline-formula>. To resolve this equation, the tangent trigonometric solving method is used and the relationship between <inline-formula><tex-math id="M6">\begin{document}$ \xi $\end{document}</tex-math></inline-formula> and <inline-formula><tex-math id="M7">\begin{document}$ v $\end{document}</tex-math></inline-formula> is established, which represents the resonance limits expression. To search resonance regions, a mathematical study is conducted on the first equation to find the positive roots number for each (<inline-formula><tex-math id="M8">\begin{document}$ v $\end{document}</tex-math></inline-formula>, <inline-formula><tex-math id="M9">\begin{document}$ \xi $\end{document}</tex-math></inline-formula>) combination. Compared to works already achieved, a new region appeared in the region of single resonant frequency with an anti-resonant one. The results are tested through numerical examples and applied to a fractional filter.

Analysis of Forced Longitudinal Vibrations of Columns Taking into Account Internal Resistance in Resonance Zones

In analytical form, formulas are obtained for the amplitude of forced harmonic longitudinal vibrations of reinforced concrete and fiber-reinforced concrete columns with fixed edges. In order to verify the proposed approach, columns were simulated in the ANSYS program and calculated by the finite element method. Analysis of the calculations shows that a significant raise in the amplitude of the forced vibrations is observed only in the region of the first resonant frequency. It has been established that the value of the maximum amplitude of the vibrations of the fiber reinforced concrete column is 16% less than that for a reinforced concrete column.

Multibody Interactions of Floating Bodies with Time-Domain Predictions

The applications of the three-dimensional transient panel code ITU-WAVE based on potential theory is further extended to take into account the multibody interactions in an array system using linear and square arrays. The transient wave-body interactions of first-order radiation and diffraction hydrodynamic parameters are solved as the impulsive velocity potential to predict Impulse Response Functions (IRFs) for each mode of motion. It is shown that hydrodynamic interactions are stronger when the bodies in an array system are close proximity and these hydrodynamic interactions are reduced considerably and shifted to larger times when the separation distances are increased. The numerical predictions of radiation (added-mass and damping coefficients) and exciting (diffraction and Froude-Krylov) forces are presented on each floating bodies in an array system and on single structure considering array as single floating body. Furthermore, the numerical experiment shows the hydrodynamic interactions are more pronounced in the resonant frequency region which are of important for fluid forces over bodies, responses and designs of multibody floating systems. The present numerical results of ITU-WAVE are validated against analytical, other numerical and experimental results for single body, linear arrays (two, five and nine floating bodies) and square arrays of four truncated vertical cylinders.