Asymmetric Potential Well Research Articles

Dynamic characteristics and energy performance of a magnetically induced multi-array piezoelectric energy harvester with asymmetric potential wells

Dynamic characteristics and energy performance of a magnetically induced multi-array piezoelectric energy harvester with asymmetric potential wells

The dynamical evolution of exciton-polaritons in asymmetric ring-step potential well

The exciton-polariton, a quasi-particle formed by the coupling of excitons and photons, exhibits a semi-light-semi-matter nature, inheriting the advantages of both constituents and capable of achieving Bose-Einstein condensation at room temperature. This paper investigates the evolution of superposition states of semiconductor microcavity exciton-polariton Bose–Einstein condensate (BEC) within a ring-shaped structure. By employing theoretical modeling, the time-dependent dynamics of the superposition states of exciton-polaritons bound within a unique asymmetric ring-step potential well structure are analyzed, focusing on halide perovskite semiconductor materials. The study reveals correlations between the potential well structure of this step-like configuration and the transition of exciton-polariton BEC superposition states, shedding light on the evolution paths of BEC systems under specific structural influences and the fluctuation patterns of excitonic fields. These findings hold relevance for experimental manipulations of exciton-polariton superposition states within microcavities. This research demonstrates that ring-step potential well structures influence the excitation and evolution of exciton-polariton BEC superposition states, leading to transitions towards higher or lower order states. This transition is reflected macroscopically in alterations in the number and spatial distribution of interference petals in the superposition states. We consider initial states with orbital angular momentum quantum number l = 2, 3, 4, respectively. By exploiting the different structural relationships of ring-step potential wells, we achieve controlled evolutions of macroscopic occupation states, with interference petal numbers ranging from 4 to 6, 4–8, 6–8, 6–10, 8–10, 8–12, and 6–4.

Quantifying trapping stability of optical tweezers with an external flow

Optical tweezers (OTs) can immobilize and manipulate objects with sizes that span between nano- and micro-meter scales. The manipulating ability of OTs is traditionally characterized by stability factor (S), which can only indicate an empirical “hit-or-miss” process. Additionally, the current quantitative models for trapping stability rarely consider the influence of external flow. In this paper, a comprehensive analysis to quantify the optical trapping stability in a perturbed asymmetric potential well is presented from the perspective of statistics, especially for weak trapping scenarios. Our analytical formulation takes experimentally measurable parameters including particle size, optical power, and spot width as inputs and precisely outputs a statistically relevant mean trapping time. Importantly, this formulation takes into account general and realistic cases including fluidic flow velocity and other perturbations. To verify the model, a back-focal-plane-interferometer-monitored trapping experiment in a flow is set up and the statistical characteristics of trapping time demonstrate good agreement with theoretical predictions. In total, the model quantitatively reveals the effects of external disturbance on trapping time, which will find applications where optical trapping stability is challenged by external perturbations in weak trapping conditions.

Fourier transform microwave spectroscopy of the 13C- and 18O-substituted tropolone. Proton tunneling effect for the isotopic species with the asymmetric potential wells.

Fourier-transform microwave spectroscopy has been applied for the 13C/18O-substituted tropolone to observe tunneling-rotation transitions as well as pure rotational transitions. The tunneling-rotation transitions were observed between the 13C-4 and -6 forms as well as between 13C-3 and -7, between 13C-1 and -2, and between 18O-8 and -9 (we denote these tunneling pairs as 13C-46, etc., below) although they have an asymmetric tunneling potential due to the difference in the zero point energy (ZPE). From the observed tunneling splittings ΔEij (0.9800-1.6824 cm-1), the differences in ZPE Δij for the 13C-46, -37, -12, and 18O-89 species are derived to be -0.1104, 0.5652, -1.3682, and 1.3897 cm-1 to agree well with the DFT calculation. The state mixing ratio of the tunneling states decreases drastically from (44%:56%) to (8.7%:91.3%) for 13C-46 and 18O-89 with an increase in the asymmetry Δij of the tunneling potential function. The observed tunneling-rotation interaction constants Fij decrease from 16.001 to 9.224 cm-1 as the differences in ZPE Δij increase, while the diagonal tunneling-rotation interaction constants Fu increase from 1.767 to 13.70 cm-1, explained well by the mixing ratio of the tunneling states.

Effects of vacancies on quantum transport of zigzag graphene nanoribbons

Using the Green’s function method, we investigate the effect of vacancies on conductance and local density of states (LDOS) in zigzag graphene nanoribbons within a symmetric and asymmetric potential wells. The results differ from ideal ribbons in that there are no conductance plateaus and a decline in conductance for varied N (number of atoms in the unit cell) and M (number of unit cells) values following vacancy incorporation. LDOS and conductance in symmetrical and asymmetrical circumstances are examined alongside vacancies and accordingly, they are affecting the respective edge states.

A Hybrid Tri-Stable Piezoelectric Energy Harvester with Asymmetric Potential Wells for Rotational Motion Energy Harvesting Enhancement

This paper proposes an asymmetric hybrid tri-stable piezoelectric energy harvester for rotational motion (RHTPEH). The device features an asymmetric tri-stable piezoelectric cantilever beam positioned at the edge of a rotating disk. This beam is uniquely configured with an asymmetric arrangement of magnets. Additionally, an elastic amplifier composed of a vertical and a rotating spring connects the beam’s fixed end and the disk. This setup enhances both the rotational amplitude and vertical displacement of the beam during motion. A comprehensive dynamical model of the RHTPEH was developed using Lagrange’s equations. This model facilitated an in-depth analysis of the system’s behavior under various conditions, focusing on the influence of key parameters such as the asymmetry in the potential well, the stiffness ratio of the amplifier springs, the radius of the disk, and the disk’s rotational speed on the nonlinear dynamic response of the system. The results show that the asymmetric hybrid tri-stable piezoelectric energy harvester makes it easier to harvest the vibration energy in rotational motion and has excellent power output performance compared with the symmetric tri-stable piezoelectric energy harvester. The output power magnitude of the system at higher rotational speeds increases as the radius of rotation expands, but when the rotational speed is low, the steady-state output power magnitude of the system is not sensitive to changes in the radius of rotation. Theoretical analysis and numerical simulations validate the effectiveness of the proposed asymmetric RHTPEH for energy harvesting in low-frequency rotating environments.

Stochastic resonance impact signal detection method based on a novel single potential well model

Our research introduces a novel stochastic resonance (SR) model featuring a single potential well and develops a dedicated detection system designed to address the challenging problem of detecting impact signals within a highly noisy background. We begin by examining the limitations of conventional metrics, such as the cross-correlation coefficient and kurtosis index, in identifying nonperiodic impact signals, and subsequently introduce an improved metric. By harnessing parameter-adjusted SR, this innovative potential well model and metric is integrated to formulate an adaptive detection method for nonperiodic impact signals. This method automatically adjusts system parameters in response to the input signal. Subsequently, numerical simulations of the system is conducted so as to perform a comparative analysis with experimental results obtained from both asymmetric single potential well and periodic potential systems. Our findings conclusively demonstrate the enhanced effectiveness of our proposed method in detecting impact signals within a high-noise environment. Furthermore, the method provides more accurate estimates of both the intensity and precise location of the input impact signal from the output results.

Bi-stable electromagnetic generator with asymmetrical potential wells for low frequency vibration energy harvesting

Efficient energy harvesting from low and broadband frequency has always been a challenging problem. This paper proposes a solution in the form of an electromagnetic bi-stable vibration energy harvester (BVEH) with asymmetric potential barriers, in which the vibrator is attracted to the top magnet and repelled from the bottom magnet. By combining a magnetic spring and a mechanical spring, the BVEH achieves bi-stability with asymmetric potential barriers, enabling large amplitude vibration as the vibrator travels between the two potential wells. The traditional magnetic force model is modified to establish an electromechanical coupling model that accurately predicts the output of the BVEH. Numerical simulation results solved by the Runge-Kutta method show good agreement with experimental results. In addition, a prototype is fabricated and the system parameters are adjusted to achieve high-energy oscillation at the lowest frequency of 4 Hz. Under a sinusoidal excitation with an amplitude of 4 mm, the BVEH's bandwidth is expanded to 6 Hz, and the maximum power can reach 72.76 mW. Finally, the feasibility of the BVEH is demonstrated by powering different electrical appliances. The study provides a new technical approach for energy harvesting under low and broadband frequency vibration excitation.

Bifurcations and nonlinear dynamics of asymmetric tri-stable piezoelectric vibration energy harvesters

Tri-stable piezoelectric vibration energy harvester (TPVEH) with asymmetric potential wells has lower potential difference and more unstable potential wells than the symmetric counterpart, which may benefit to improve the energy harvesting performance. Although some progress has been made, there is still few research on the asymmetric TPVEH compared to the symmetric counterparts. The bifurcation mechanism of equilibrium solutions, the transition mechanism of multi-stability state and the nonlinear dynamics of the asymmetric TPVEH are different from those of the symmetric one, and have not been well explored at present. This work presents an asymmetric TPVEH which is composed of a piezoelectric linear oscillator (PLO) and a magnet–mass–spring oscillator (MMSO) to theoretically and experimentally investigate the bifurcations, the transition mechanism and the nonlinear dynamics. A general nonlinear dynamic model of the asymmetric TPVEH is derived and its equilibrium solutions are calculated to reveal the bifurcation and transition mechanism. The steady-state response solutions and their stability analysis are successively deduced to theoretically investigate the nonlinear dynamics and the enhancing mechanism of energy harvesting. Experiments are consequently performed to validate the theoretical results. The results show that the MMSO can not only change the distribution position of the stable and unstable equilibrium points, but also change the potential barriers height by adjusting the horizontal interval in real-time. In addition, suitable spring stiffness of the MMSO benefits to enhance the dynamic response outputs and frequency bandwidth. Compared to the symmetric TPVEH, the asymmetric TPVEH can access the interwell oscillations more easily and generate larger response outputs over a wide frequency range under lower excitation level. For the suitable spring stiffness of 1000 N/m, the maximum voltage, power obtained by experiments and the acceleration threshold for snap-through of the asymmetric TPVEH are 7 V, 4.8 × 10−5 W and 8 m/s2, respectively, which are far better than the symmetric TPVEH, whose corresponding values are 3 V, 0.8 × 10−5 W and 18 m/s2, respectively.

Dynamics of Bose-Einstein condensation in an asymmetric double-well potential

Josephson effect of Bose-Einstein condensate in double-well potential is an obvious manifestation of macroscopic quantum coherence. Most of researches focus on the symmetric double-well potential. In this work, we investigate the dynamic of Bose-Einstein condensates in an asymmetric double-well potential by using two-mode theory and computer simulation. In the absence of the interaction between atoms, the dynamic equation of condensate can be solved analytically. The amplitude as a function of energy difference of two wells is obtained. We can find that the change of energy difference will lead to the different dynamic behaviors of condensate. If the energy difference is relatively large, the condensate will primarily occupy the well that is occupied more than the other well at the beginning time. It is interesting that such a trap phenomenon is not dependent on the position of the high energy potential well nor the position of low energy potential well. If the energy difference becomes small, the tunneling and oscillation of condensate will be enhanced. When the interaction between atoms is present, our numerical calculations show that as the nonlinear interaction increases, the dynamic behavior of condensate exhibits different characteristics, such as trapping in a well, enhancing the tunneling and oscillation between two wells, and enhancing the trapping in a well at large nonlinear interaction, which is similar to the dynamic change caused by the energy difference in the case of ideal condensate. That is to say, on the one hand, the nonlinear interaction can lead to the trap of condensate as well as the dynamic trap to happen in symmetric double-well potential. On the other hand, the nonlinearity can promote the tunneling of condensate, counteracting the effect of the asymmetry of potential. And, this counteracting effect is related to the difference in energy between asymmetric potential wells. To understand the underlying mechanism, the full dynamic behavior of two-mode model is illustrated and the dynamic transition can be seen clearly. Combining the results obtained with and without interaction, regarding nonlinear interaction as effective potential provides a clear way to explain dynamic transition of condensate in an asymmetric double-well potential. In addition, we also perform the numerical simulations of the Gross-Pitaevskii equation, and the results are consistent with the conclusions obtained by using the two-mode theory.

Energy Harvesting Using a Nonlinear Resonator with Asymmetric Potential Wells

This paper presents the results of numerical simulations of a nonlinear bistable system for harvesting energy from ambient vibrating mechanical sources. Detailed model tests were carried out on an inertial energy harvesting system consisting of a piezoelectric beam with additional springs attached. The mathematical model was derived using the bond graph approach. Depending on the spring selection, the shape of the bistable potential wells was modified including the removal of wells’ degeneration. Consequently, the broken mirror symmetry between the potential wells led to additional solutions with corresponding voltage responses. The probability of occurrence for different high voltage/large orbit solutions with changes in potential symmetry was investigated. In particular, the periodicity of different solutions with respect to the harmonic excitation period were studied and compared in terms of the voltage output. The results showed that a large orbit period-6 subharmonic solution could be stabilized while some higher subharmonic solutions disappeared with the increasing asymmetry of potential wells. Changes in frequency ranges were also observed for chaotic solutions.

Subharmonic responses of a nonlinear energy harvester with an asymmetric double well potential

A nonlinear energy harvester with asymmetric potential wells is studied numerically. An energy transducing piezoelectric patch is attached to the cantilever elastic beam to harvest kinetic energy of the moving frame. To obtain an asymmetric effect in the double well potential induced by permanent magnets, an elastic ferromagnetic beam resonator misaligned with respect to the magnets' distribution axis of symmetry was used. The system response under the frequency-swept excitation reporting bifurcations to subharmonic and chaotic solutions was analysed. The sensitivity of the system solutions to the parameters responsible for potential asymmetry and electro-mechanical coupling was also investigated.

Modeling and performance evaluation of a bi-stable electromagnetic energy harvester with tri-magnet levitation structure

A novel tri-magnet levitation bi-stable electromagnetic energy harvester (BEEH) is proposed in this work. The bi-stable nonlinear mechanism is realized by using the single-sided bipolarity of the ring magnet. To balance the asymmetric bi-stable potential wells caused by the self-weight of the levitating magnet, how the potential energy varies when the size of the top magnet changes is investigated. The results show that enhancing the attraction of the top magnet can balance the self-weight of the levitating magnet. Furthermore, for the structure with determined magnet dimensions, the spacing and depth of the two potential wells can be adjusted by changing the spacing of the two ring magnets. In experiments, the output performance of the device with different ring magnet spacing is investigated to confirm that this device has a tunable operating bandwidth and that a wider bandwidth requires the partial sacrifice of output power. The results show that the present device exhibits a frequency bandwidth of 6.25–9.5 Hz and generates a peak power of 6.02 mW under 9.5 Hz and 0.5 g, implying the estimated normalized power density of about 891W/(m3g2). A performance comparison between the proposed BEEH and other multi-stable magnetic levitating harvesters proves that the former is more suitable for microdevices.

Bistable programmable origami based soft electricity generator with inter-well modulation

Kresling origami features an axial compression and torsion coupled motion mechanism. The nonlinear stiffness is generated by this unique deformation mode, allowing Kresling origami to be employed in wave propagation control, mechanical storage devices, digital computing, and soft robotics. In this paper, a soft bistable electricity generator is developed based on Kresling origami. This soft electricity generator is capable of initiating inter-well motion for broadband energy harvesting at low frequency and low amplitude excitation based on delicately designed structural parameters, programmable bistable energy landscape and soft origami structure fabrication. Two asymmetric potential energy wells are obtained through combining the elastic potential energy of the origami structure with the gravitational potential energy of top mass. The prototype of the bistable Kresling origami structure is fabricated by a two-step mold procedure and the theoretical model is verified through quasi-static and dynamic experiments. The number of the stable states is tunable and the energy curve is programmable by varying the top mass, initial height hs and initial torsional angle. The nonlinear bistable origami has complex dynamic phenomena such as intra-well motion, inter-well motion and chaotic motion. Compared with intra-well motion, the harvested power of inter-well motion is increased by 18.5 times. The origami structure can be excited to the inter-well orbit under low intensity excitation of 0.19 m/s2 and low frequency of 2.5 Hz. An origami-based shoe pad is fabricated by integrating the origami generator into the shoe pad to not only harvest the energy but also measure the gait and motion information from the human motions. The proposed soft electricity generator of bistable programmable origami provides a competitive solution for broadband energy harvesting under low excitation acceleration and low frequency environment, i.e., human motion and bridge vibration, showing the great potential as power supply for wearable devices and bridge monitoring devices.

Electromagnetic field effect on weak-coupling piezoelectric polaron in an asymmetrical Gaussian confinement potential quantum well

The properties of an electron weakly coupled to piezo-acoustic phonon in asymmetrical Gaussian confinement potential quantum well (AGCPQW) subject to external electric field (EF) and magnetic field (MF) has been investigated using the Lee-Low-Pines unitary transformation and linear combination operation methods. We have obtained the ground state energy (GSE) and the ground state binding energy (GSBE) of piezoelectric polaron. The effects of the EF, the MF, the range of the asymmetrical Gaussian confinement potential (RAGCP), Debye cut-off wavenumber (DCOW) and the electron–phonon coupling strength on the GSE and the GSBE are also analyzed. It is found that the GSE is an increasing function of the EF and the cyclotron frequency (CF), whereas it is a decreasing one of the RAGCP, the DCOW and electron–phonon coupling strength. The GSBE is an increasing function of the DCOW and the electron–phonon coupling strength. It is also an aggrandizing function with decreasing of the RAGCP, whereas it is a decayed one of the EF and CF. It is shown that the EF, the RAGCP, the MF, the DCOW and electron–phonon coupling strength are important factors that have great influence on the properties of the piezoelectric polaron in AGCPQW.

Certain Aspects of Quantum Transport in Zigzag Graphene Nanoribbons

We have investigated the Fano factor and shot noise theoretically in the confined region of the potential well of zigzag graphene nanoribbon (ZGNR). We have found that the Fano factor is approximately 1, corresponding to the minimum conductivity (σ) for both symmetrical and asymmetrical potential wells. The conductivity plot with respect to Fermi energy appears as symmetrical plateaus on both sides of zero Fermi energy. Moreover, a peak observed at zero Fermi energy in the local density of states (LDOS) confirms the edge states in the system. The transmission properties of ZGNR in the confined region of the potential well are examined using the standard tight-binding Green’s function approach. The perfect transmission observed in the confined region of the potential well shows that pnp type transistors can be made with ZGNR. We have discussed the Fano factor, shot noise, conductivity, and nanohub results in the continuation of previous results. Our results show that the presence of van-Hove singularities in the density of states (DOS) matters in the presence of edge states. The existence of these edge states is sensitive to the number of atoms considered and the nature of the potential wells. We have compared our numerical results with the results obtained from the nanohub software (CNTbands) of Purdue University.

Dynamic Characteristics and Experimental Research of Linear-Arch Bi-Stable Piezoelectric Energy Harvester

Collecting vibration energy in the environment is expected to solve the problem of the self-power supply of wireless monitoring nodes in underground coal mines. By introducing nonlinear factors, a linear-arch bi-stable piezoelectric energy harvester (LBPEH) is designed. In order to reveal the influence of system parameters on the dynamic characteristics of LBPEH, the magnetic force model is established by the magnetizing current method, and the restoring force model is acquired through experimental measurement. The electromechanical coupling dynamics model of the system is established based on the Lagrange equation and Kirchhoff’s law. The influence of excitation amplitude and excitation frequency on the dynamic characteristics of the piezoelectric energy harvester is simulated and analyzed. Moreover, experiments are designed to verify the results of the simulation. The results reveal that the restoring force of the linear-arch beam is nonlinear, and the LBPEH constructed by the linear-arch beam has an asymmetric potential well. Changing the excitation frequency or excitation amplitude can make the system in the well chaotic and achieve a large periodic motion state. With the increase of excitation amplitude, it is beneficial for the system to realize large periodic motion. The research provides theoretical guidance for the design of piezoelectric energy harvesters for different excitation conditions.

Asymmetrical semi-exponential potential effect of exciton in strong-coupling alkali halide quantum well

Within the framework of the method of Lee-Low-Pines unitary transformations and variations, strong-coupling exciton-longitudinal-optical (LO) phonon interaction in asymmetric semi-exponential potential quantum wells was investigated. It is shown that the self-trapping energy, effective potential and vibration frequency of the exciton, depends significantly on the parameters of the confined potential, electron-hole distance and electron-hole mass.

The effect of parabolic potential on ground state energy and vibration frequency of magnetopolaron in asymmetric Gaussian potential quantum wells

Anisotropy parabolic potential (APP) effects on ground state (GS) energy [Formula: see text] and the vibration frequency (VF) [Formula: see text] of weak-coupled magnetopolaron (MP) in asymmetric Gaussian quantum wells (AGQWs) were investigated using the linear combination operator and unitary transformation method. The obtained results showed that [Formula: see text] and [Formula: see text] were increased by increasing the barrier height [Formula: see text] of AGQWs as well as transverse and longitudinal confined strengths [Formula: see text] and [Formula: see text] of APP and decreased with increase in the asymmetric Gaussian confinement potential (AGCP) range [Formula: see text] and transverse and longitudinal effective confined lengths [Formula: see text] and [Formula: see text] of APP. Thus, the GS energy and VF of MP could be changed by adjusting the confinement parameters of the APP and AGCP. The study of quantum wells’ semiconductor materials has broad potential applications in semiconductor lasers, optoelectronic devices and quantum information.

A Peridynamic Model for the Dynamics of Defects with Asymmetric Potential Wells

A Peridynamic Model for the Dynamics of Defects with Asymmetric Potential Wells