Antiresonance Point Research Articles

Open-loop flow control design guided by the amplitude-frequency characteristics of the reduced-order model

Unsteady separated flow is a common flow condition causing many detrimental effects in aerospace and other fields. Open-loop control is a potential means to eliminate these drawbacks. At present, the unsatisfactory performance of open-loop control mainly attributes to the high-dimensional parameter optimization procedure and the lack of efficient knowledge-guided control law design methods. This paper proposes a method managing to directly obtain the anti-resonant frequency from the input and output amplitude-frequency characteristic curves of the reduced-order model of the flow-control coupled system. Simultaneously, a negative gain criterion is proposed to judge whether the target control effect can be achieved under the current parameter combination. For the control of low Reynolds number flow around a cylinder, the simulation results show that the optimal open-loop control frequency is 1.268 times the natural frequency of the flow, which is consistent with the anti-resonant frequency, and 26.8% of the lift fluctuation is suppressed. This paper also studies the influence of parameters such as flow frequency change, control start time, jet mass flow rate, and so on. Furthermore, control position is the key parameter affecting the amplitude-frequency characteristics. The anti-resonance points on the curves corresponding to different control positions can also guide the design of the optimal control frequency, and the negative gain criterion is still applicable. This method greatly reduces the time consumption in parameter optimization and improves the engineering application prospect of the open-loop control in unsteady separated flow control.

Skin effect suppression for millimeter-wave frequencies through manipulation of permeability

A new device strategy for suppressing unwanted skin effect in coplanar transmission lines at frequencies beyond 20 GHz is presented. Utilization of the anti-resonance point as a source of imaginary permeability to suppress the skin effect is proposed. This idea is backed up by Kramers-Kronig and published experiments. The principle is independent of Landau–Lifshitz-Gilbert magnetic precession damping. The present work contributes both a greater understanding of skin effect manipulation and a method for obtaining zero skin effect using known laminate materials.

Feasibility Study on the Detection of Turn-to-Turn Fault Severity in the Transformer Winding by Frequency Response Analysis and Numerical Indices

Frequency response analysis (FRA) provides valuable information on internal electrical and mechanical faults in a transformer. This information can also be used to diagnose the turn-to-turn fault (TTF) in a transformer winding. This paper concentrates on using numerical indices for the evaluation of FRA to diagnose the TTF severity of the transformer winding. This evaluation is essential for expanding the knowledge toward the interpretation of FRA results. In this paper, the FRA traces of a winding are obtained in the laboratory for a healthy and faulty transformer with various TTF severities. The test results are analyzed using the indices related to all points of FRA characteristic and the indices related to the resonance and anti-resonance points. In this analysis, the possibility of diagnosing the TTF severity is addressed. To confirm the experimental results, simulation models of different windings are implemented to repeat the evaluation. By choosing an appropriate frequency range for the evaluation, the numerical indices demonstrate a monotonic performance versus the fault severity, i.e., the TTF severity can be determined in a transformer winding by assessing the FRA results with numerical indices.

Experimental study of a two-degree-of-freedom piezoelectric cantilever with a stopper for broadband vibration energy harvesting

This paper presents a two-degree-of-freedom (2-DOF) piezoelectric energy harvesting (PEH) system with a stopper for wideband operation. The proposed system consists of a folded piezoelectric cantilever with a stopper integrated. Two cases are considered where the stopper is placed at the free end of the outer beam and inner beam, respectively. It is shown experimentally that with the proper parametric combination we can move the anti-resonance point outside the two resonant peaks and widen the frequency responses of both the peaks. Large amplitude voltage output over 11 Hz can be obtained when we focused on the dynamics of the inner beam. In addition, it is demonstrated that arranging the stopper at the free end of the inner beam yields better performance than that with the stopper placed at the outer beam. Detailed parametric studies are performed to investigate the influences of the stopper distance, amplitude of base movement, and frequency sweep directions on the voltage output. A maximum power output of 713μW is obtained.

Antiresonance in Transmission through a Heterojunction Formed by Topological Nodal‐Line Semimetals

AbstractQuantum transmission through a heterojunction formed by two types of nodal‐line semimetals is investigated. Results show that the initial energy and energy range of the quantum transmission can be modulated efficiently when the barrier region demonstrates its different energy‐band properties. Antiresonance points can also appear in the transmission function spectra. Moreover, if the barrier is parallel to the basal planes of the nodal‐line semimetals, one gap appears in the transmission function spectrum instead of the normal antiresonance point. In addition, the Klein tunneling displays new characteristics in such a heterojunction. All these results provide useful information for adjusting the transmission behaviors in the heterojunctions of nodal‐line semimetals.

Spin filtering and magnetically-controlled quantum switch in multiple triangular rings consisting of quantum dots

Electron transport characteristics through a system consisting of a series of triangular quantum dot rings are studied utilizing the non-equilibrium Green’s function. In the presence of a magnetic field, an additional anti-resonance point occurs in the conductance spectrum. As the number of triangular quantum dot rings increases, two anti-resonance points evolve into two well-defined insulating bands. The insulating band disappears as the magnetic flux takes an appropriate value, and therefore, an effective magnetically-controlled quantum switch can be achieved. If a Zeeman magnetic field is introduced, a spin-polarized window (SPW) can be formed, suggesting a physical scheme of a spin filtering. As the intradot Coulomb interactions are taken into consideration, more SPWs can be obtained. This work sheds lights onto the design of future quantum devices.

Antiresonance and its application in tri-quantum-dot systems

Antiresonance and its application in triple-quantum-dot systems are studied theoretically using nonequilibrium Green’s function method. The presence or absence of antiresonance point can be used to determine whether quantum dot impurity exists in the system. For a tri-quantum-dot ring, the conversion between 0 and 1 for the conductance can be realized by adjusting the energy levels of quantum dots, which makes the system applicable as a quantum switch. The coupling strength can be measured according to the energy level of the antiresonance point. Once the intradot Coulomb interactions are taken into account, three new Fano antiresonances emerge in the conductance spectrum. Under the action of the magnetic field, two antiresonance points disappear simultaneously. Our work sheds lights onto the design and implementation of new quantum functional devices for electronic measurements.

Antiresonance in electron transport through a four quantum dots system

A four quantum dots structure is designed. The influence of the interdot coupling strength, energy levels of quantum dots, magnetic flux and intradot Coulomb interactions on the conductance is discussed. An antiresonance point exactly emerges at the location of the energy level of side-coupled quantum dots (SCQD). The conversion between resonance band and antiresonance band can be achieved as parallel-coupled di-quantum dots with or without SCQD, which suggests a physical scheme of an effective quantum switch. The Breit–Wigner resonant and Fano antiresonant peaks may merge into one resonant band. By means of the mathematical formula, we analyze how the resonance band is formed. By varying intradot Coulomb interaction, the resonance band may evolve into a Fano antiresonance with an ultra-narrow width. This study provides theoretical basis for the design of quantum computing devices.

Anti-Resonance in a Laterally Coupled Triple-Quantum-Dot Chain

Employing the nonequilibrium Green’s function technique, electron transport characteristics through a laterally coupled triple-quantum-dot chain are investigated. The conductance versus electron energy is numerically calculated. Two anti-resonance points change into two anti-resonance bands with increasing the size of triple-quantum-dot chain. The widths of two anti-resonance bands are the same and can be regulated via adjusting the inter-dot tunneling coupling strength in the main chain or its attachment. Spin-polarized window emerges due to Zeeman splitting as an external magnetic flux is introduced. Our studies demonstrate that the system can be used as a quantum switch or an efficient spin filtering.

Fano antiresonance realized by Majorana bound states coupled to one quantum-dot system

We evaluate the quantum transport through one mesoscopic circuit with its embedded quantum dot coupled to the Majorana bound states (MBSs) at the ends of one topological-superconductor nanowire. The calculation results show that when the MBSs co-couple to the dot, antiresonance effect has an opportunity to take place, and the antiresonance point is related to the inter-MBS coupling. Moreover, once the dot-MBS coupling strengths are equal to each other, the Fano effect takes place, manifested as the Fano lineshape in the transmission-function spectrum. The results in this work can provide new information for the understanding of the MBS-contributed quantum transport through quantum-dot systems.

Novel Dynamic Model Updating Technique for Damped Mechanical System

Abstract Response surface method and Derringer’s function approach have been combined together to develop novel structural dynamic model updating technique for a damped mechanical system. Response surface models have been incorporated instead of finite element models, in order to increase computational efficiency of proposed technique. Derringer’s function approach is useful in dealing successfully with multi-objective optimization type model updating problems. Few such undamped techniques have been recently developed for undamped mechanical systems by combining the benefits of response models with Derringer’s function approach. This paper presents the theory and numerical application of a damped updating technique, which is based upon response models and Derringer’s function approach. In this technique, updating process is formulated as an optimization problem, wherein desirability functions are formulated, based on natural frequencies, modal-assurance-criterion values, resonance and anti-resonance points of frequency response functions. Desirability functions are then optimized to evaluate updated elastic parameters in stage one and updated damping constants in stage two of proposed technique. By using this technique, total absolute errors in natural frequencies, modal-assurance-criterion values, elastic parameters and frequency response functions have been reduced to 0.02%, 0.00%, 3.69% and 0.11%, respectively.

Transport through a non-Hermitian parallel double-quantum-dot structure in the presence of interdot Coulomb interaction

In this work, we investigate the effect of PT-symmetric complex potentials on the transport properties of one non-Hermitian system, which is formed by a parallel coupled double-quantum-dot geometry. It is found that the PT-symmetric complex potentials take pronounced effects to the transport properties of such a system, manifested as the occurrence of antiresonance. In the presence of the interdot Coulomb interaction, such potentials lead to the shift and increase of the antiresonance points, dependent on the Coulomb interaction strength. This study exhibits the special impact of the interplay between the interdot Coulomb interaction and PT-symmetric potentials on the quantum transport behaviors.

Quantum Switch and Efficient Spin-Filter in a System Consisting of Multiple Three-Quantum-Dot Rings**Supported by the National Natural Science Foundation of China under Grant Nos 11447132 and 11504042, the Natural Science Foundation of Heilongjiang Province under Grant No A201405, Chongqing Science and Technology Commission Project under Grant Nos cstc2014jcyjA00032 and cstc2016jcyjA1158, and the Scientific Research Project for Advanced Talents of Yangtze

Using the non-equilibrium Keldysh Green’s function technique, we investigate electron transport properties of a system consisting of multiple three-quantum-dot rings. The conductance as a function of the electron energy is numerically calculated. An antiresonance point emerges in the conductance spectra and evolves into a well-defined insulating band with the increasing number of three-quantum-dot rings. The position of the well-defined insulating band can be modulated by varying the tunneling coupling strength between adjacent three-quantum-dot rings. When an external magnetic flux is introduced, several to 100% spin-polarized windows will occur due to the Zeeman splitting. These results strongly suggest that this device may realize multiple functions including quantum switch and efficient spin filtering.

Thermoelectric effects of the single-spin state in the ferromagnetic-normal junction with artificial magnetic impurities

We theoretically analyze the thermoelectric properties of the single-spin state based on the resonant tunneling of electron in the ferromagnetic-normal junction with artificial magnetic impurities. The thermoelectric coefficients, such as electrical conductance G, thermal conductance K, thermopower S and effective figure of merit Y, have been calculated using the nonequilibrium Green function in the linear regime. It is found that the thermoelectric coefficients can achieve considerable values by adjusting key parameters of the hybrid mesoscopic structure, such as the level detuning, the interdot hopping coefficient, the external magnetic field and the angle θ. When the level detuning changes, the spectra of electrical conductance and thermal conductance exhibit the electronic Dicke-like effect in the low temperature. Two valleys of electrical conductance and thermal conductance are always located at the single-spin level of QD2 ( and ), and can achieve the antiresonant point by adjusting the interdot hopping coefficient. Thermoelectric coefficients can achieve considerable values near valleys because the Wiedemann–Franz law is strongly violated. Thermopower S and effective figure of merit Y can get larger values in the vicinity of by adjusting key parameters of the hybrid mesoscopic structure, such as the level detuning, the interdot hopping coefficient and the polarization. But the thermoelectric effect is reversed by changing the angle θ. When the angle θ increases, S and Y are suppressed in the vicinity of meanwhile, S and Y are enhanced in the vicinity of shows that an electron in the state can virtually tunnel into the spin-up (or spin-down) state of the ferromagnet. The amplitude of electron tunneling is (or ). G and K decrease (or increase) as the angle θ increases in the vicinity of (or . So theoretical fundament is provided for the design of the single spin device.

Andreev reflection in a T-shaped double quantum-dot with coupled Majorana bound states

Owing to their potential applications in topological quantum computation and because of their fundamental interest, Majorana fermions are currently attracting increasing attention. Numerous theoretical and experimental studies exactly show that the quantum dot (QD) structure is a good candidate for the detection of Majorana bound state (MBSs). QD system has many unique transport properties and interesting quantum phenomena, such as quantum interference effect, Fano effect, etc. In addition, compared with a single QD, a coupled QD structure has many adjustable parameters, and thus has more important theoretical and practical value, which provides an excellent platform to detect MBSs. In addition, QD coupled with normal metallic conductor and with superconducting electrode structure exhibits interesting transport properties. One of these properties is the so-called Andreev reflection (AR). Especially, in the subgap regime, the current almost entirely originates from the anomalous Andreev channel; such spectroscopy can thus directly probe any in-gap state. In the present paper, we consider a T-shaped double QD structure with side-coupled to MBSs and investigate the transport properties through the system by adding a normal and a superconducting lead. We calculate the AR conductance through the system in the subgap transport. Here we focus on the effects of MBSs on AR through the system. We find that the AR conductance presents a resonant peak around zero Fermi energy when only one QD (QD1) connects to metal and superconducting leads. As a consequence of quantum interference, when using another QD2 side-attached to QD1, a pair of new Fano-type resonant peaks appear and is distributed aside the zero point and the Fano antiresonant point is at the energy level of the QD2. If an MBS is introduced to couple to QD2, the AR conductance shows several new features. First, a pair of new Fano-type resonance curves appears and the original ones also persist except for the position shifting. In addition, the AR conductance value at the zero Fermi energy point is exactly equal to 1/2G0(G0=2e2/h) in the presence of QD-MBS coupling and zero inter-MBS coupling, which is not dependent on the inert-dot coupling nor the energy levels of QD nor the strength of the QD-MBS coupling. This feature is different from which the T-shaped DQD structure side-coupled to a traditional fermions, showing the robust properties of the Majorana fermions. We also show that in the Andreev reflection conductance curves appear resonance zone changes into antiresonance near zero Fermi energy by adjusting the coupling strength between the double quantum dots in the system without MBSs, while the antiresonance disappears and new resonance peaks appear if an MBS is introduced to couple to QD2. We hope that these results will be helpful for understanding the quantum interference in MBS-assisted AR and may find significant applications, especially in quantum computation.

Resonance suppression method based on digital filter for servo system

According to mechanical resonance problem in flight simulation servo system( turntable system),the principles of resonance suppression about traditional notch filter and second-order low-pass filter were analyzed. Afterwards the two-second resonance suppression digital filter was proposed. The two-second digital filter combines the characteristics of traditional notch filter and second-order low-pass filter,and it can suppress the resonance point and the anti-resonance point at the same time. Through theoretical analysis and simulation combination,the principle of the two-second digital filter restraining the resonance point and the anti-resonance point simultaneously was explained. The experiments were also conducted,in which above all filters were joined into the turntable system respectively. Experimental results show that,the proposed filter ensures high tracking precision meanwhile effectively widens the bandwidth of the servo system.

Enhancement of the thermoelectric figure of merit in DNA-like systems induced by Fano and Dicke effects.

We report a theoretical study highlighting the thermoelectric properties of biological and synthetic DNA molecules. Based on an effective tight-binding model of duplex DNA and by using the nonequilibrium Green's function technique, the thermal conductance, electrical conductance, Seebeck coefficient and thermoelectric figure of merit in the system are numerically calculated by varying the asymmetries of energies and electronic hoppings in the backbone sites to simulate the environmental complications and fluctuations. We find that due to the multiple transport paths in the DNA molecule, the Fano antiresonance occurs, and enhances the Seebeck coefficient and the figure of merit. When the energy difference is produced in every opposite backbone site, the Dicke effect appears. This effect gives rise to a semiconducting-metallic transition, and enhances the thermoelectric efficiency of the DNA molecule remarkably. Moreover, as the Fano antiresonance point is close to the Dicke resonance one, a giant enhancement in the thermoelectric figure of merit in the DNA molecule has been found. These results provide a scenario to obtain effective routes to enhance the thermoelectric efficiency in the DNA molecules, and suggest perspectives for future experiments intending to control the thermoelectric transport in DNA-like nanodevices.

Decoupling capacitors selection algorithm based on maximum anti‐resonance points and quality factor of capacitor

A decoupling capacitors (decaps) selection algorithm based on maximum anti-resonance points of the power distribution network and the quality factor (Q) of the capacitor is proposed. The experimental results show that the proposed algorithm is superior to the fast algorithm regarding the number of consuming decaps and the genetic algorithm regarding the time consumed.

Research on vibration reduction performance of dynamic vibration absorber based on damping characteristic of a new material

The absorbing effect of traditional dynamic vibration absorber (TDVA) is satisfactory only when the natural frequency is close to the excitation frequency. For this defect, a semi-active vibration absorber is designed with magnetorheological elastomer (MRE) as a stiffness element, that its stiffness can be controlled by magnetic field, to widen the frequency band of the absorber. Theory and experiments show that reducing the damp of the absorber can improve the performance of the absorber at the anti-resonance point, but it will cause the vibration of the controlled system at the new resonance point, which caused by the addition of a DVA, to be more intense. For this problem, the compatibilizer: silane coupling agent KH570, is added to the preparation of MRE to reduce material damping, at the same time, the stiffness control strategy is used to eliminate the resonance of the controlled system caused by the addition of DVA. The final experimental results show that the frequency band of vibration reduction has been broadened effectively and the vibration reduction performance has been improved considerably. Moreover, the resonance has been eliminated very well.

Optimization Design and Performance of Vibration Suppression for Delayed Dynamical Vibration Absorber with Broadband

The delayed dynamical vibration absorber is applied to suppress the vibration of the torsional vibration system. The governing equations of the two degree of freedom vibrating system consisting of crankshaft and delayed dynamical vibration absorber are obtained. The physical parameters of the dynamical vibration absorber for the passive control system are optimum designed. The frequency of anti-resonant point is located at the midpoint between two resonant points, and the optimized amplitude frequency response curve is relatively flat near the anti-resonant point. The control parameters of gain and time delay are optimum designed in the active control system. The minimum amplitude of crankshaft is selected as the optimization objective. The genetic algorithm is used to optimize these control parameters. The optimized delayed dynamical vibration absorber has achieved good performance of vibration suppression within a wide frequency band of external excitation.