Bistable Characteristics Research Articles

Piezomagnetoelastic energy harvesting from bridge vibrations using bi-stable characteristics

Harvesting energy from bridge vibration is a promising solution to self-powering the wireless sensors that are distributed in the bridge for safety monitoring. In this study, a novel harvester is proposed to scavenge bridge vibration energy caused by travelling vehicles. The harvester employs bi-stable characteristics to enhance the harvesting efficiency, which is realized by magnetic interaction between the tip and fixed magnets. The influences of distance between the magnets on the potential energy and restoring force are studied. The results show that an appropriate distance can give a desired bi-stable potential energy function. The experiment study is carried out. The results prove that the proposed bi-stable harvester could produce a large-amplitude vibration and achieve a significant improvement in vibration energy harvesting. It can keep large electric output for a wide range of vehicle speed. In addition, the bi-stability characteristics from magnetic attraction can protect the harvester from damage while the excitation is excessively large. This study may provide a practical method for efficiently harvesting energy from bridge vibration.

Stability of thermally bistable states and their switching in superconducting weak link

Superconducting weak link (WL), acting as a Josephson junction (JJ), is one of the widely used elements in superconductor science and quantum circuits. A hysteretic JJ with robust switching between its superconducting and resistive state is an excellent candidate for single-photon detection. However, the ubiquitous fluctuations in the junction strongly influence the stability of the states and, thus, the transition from one to the other. Here, we present an experimental study of switching statistics of critical and retrapping currents of a JJ based on niobium WL in its hysteretic regime. The mean lifetimes of the two metastable states, namely, the zero-voltage superconducting state and finite-voltage resistive state, are estimated from the distributions. Further, close to the hysteresis crossover temperature, observed telegraphic noise in the time domain due to random switching between the states provides their lifetimes directly. We present a thermal model introducing a double-well (bistable) feature with an intriguing quantity with respect to the devices’ temperature states. The effects of temperature fluctuations on the stability of the states are shown. We discuss our results toward further improvement of the efficiency of superconducting WL or nanowire single-photon detectors.

Colored Correlated Noises Induced Regime Shifts in a Time-delayed Lake Eutrophication Ecosystem

The catastrophic regime shifts in the lake eutrophication ecosystems may be usually caused by environmental perturbations, and the lake dynamics exhibit bistability characteristics with oligotrophic and eutrophic states. This paper is devoted to investigate the time delay effect in a time-delayed lake eutrophication ecosystem (TD-LEE), where the dynamics ecosystem is deemed to be disturbed by both multiplicative and additive noises. On the basis of small delay approximation, we derive the expression of the generalized effective potential function in the TD-LEE and discuss the impact of stochastic delay on the regime shifts between oligotrophic and eutrophic states. In the view of dynamical behaviors on the TD-LEE model, we also revealed that the combination with time delay and colored correlated noises can expedite the regime shift from the eutrophication to oligotrophication, thereby inhibiting the development of lake eutrophication and protecting the stability of lake ecosystem.

Hamiltonian dynamics and targeted energy transfer of a grounded bistable nonlinear energy sink

A two-degree-of-freedom nonlinear mechanical system describing a damped linear oscillator weakly coupled to a lightweight grounded bistable nonlinear energy sink is proposed to investigate the targeted energy transfer (TET) under asymmetric local nonlinear potentials. The bifurcations of equilibria are discussed to reflect the bistable and asymmetric characteristics of the system. Through projections of isoenergetic manifolds, the topological features of the Hamiltonian dynamics under 1:1 internal resonance have been investigated, which induces conditions for energy localization and exchange. In the general case, the topological features of the Hamiltonian dynamics related to the nonlinear normal modes (NNMs) are classified by the Poincaré map, the relations between the NNMs and the Hamiltonian dynamics have been interpreted through the frequency energy plots. The results show that introducing the asymmetric characteristics may enhance the TET and realize the complete TET.

Soybean-inspired nanomaterial-based broadband piezoelectric energy harvester with local bistability

Bistable nonlinear energy harvesters are effective structures for scavenging broadband energy from frequency-varying vibration sources. The bistable characteristic of such structures is typically induced by introducing magnetic fields, prestress, and nonuniform geometries or fixtures. However, the complicated structures or single deformation modes of these structures limit their practical application. Inspired by the structure of soybean pods, a bionic metallic nanomaterial-based bistable piezoelectric energy harvester is developed in this study. The nanoplate substrate with a local bistable region mimics the configuration of a soybean pod. To the best of the authors’ knowledge, the local bistable configuration represents a novel energy harvesting strategy. The local bistable nanoplate is fabricated using a mature surface mechanical attrition treatment technique that generates a gradient nanostructure to enhance the mechanical properties of the bistable structure. The energy harvesting performance and nonlinear dynamic characteristics of the energy harvester are evaluated through frequency-sweep and fixed-frequency vibration tests and numerical simulations with a new two-step finite element (FE) model. The harvester characteristics in three vibration modes (single-well vibration (SV), intermittent cross-well vibration (ICV), and continuous cross-well vibration (CCV)) are discussed. The experimental and numerical results demonstrate that the voltage output and working bandwidth of the proposed harvester increase by five times in the ICV and CCV modes when the excitation acceleration increases from 0.5 g to 3.0 g. The bionic nanomaterial-based bistable piezoelectric energy harvester can be potentially used in various applications such as vehicle suspension systems, tires, and vehicle-bridge systems.

Fabrication and experimental characterisation of a bistable tensegrity-like unit for lattice metamaterials

The peculiar nonlinear mechanical behaviour of tensegrity structures and their engineering applications have attracted considerable interest in the last two decades. However, the difficulties in their traditional fabrication and assembling methods represent current limitations to their widespread use. This paper presents a novel design and fabrication procedure for bistable tensegrity-like units. Starting from the classical triangular tensegrity prism and using stereolithography technology, a double tensegrity-like unit was designed and realised monolithically as a compliant mechanism. High repeatability of compression tests confirmed the activation of the designed bistable twisting mechanism in large displacements, proving that the bistability of a tensegrity-like unit with null selfstress and no cables can dependably be achieved. Numerical simulations showed that a reduced-order stick-and-spring model is able to provide predictions on the nonlinear mechanical behaviour of the unit in close agreement with experimental results. Low relative density and bistable characteristics make this type of tensegrity-like unit suitable to manufacture highly-customisable multistable metamaterials. The proposed procedure could be applied to transform and additively manufacture other types of tensegrity structures with different nonlinear responses into corresponding tensegrity-like versions. • Stereolithography fabrication of tensegrity-like units without pin-joints or cables. • Experimental investigation on the compressive behaviour of a tensegrity-like unit. • Bistable response of the designed unit confirmed by experimental results. • Design procedure suitable to lightweight metamaterials with nonlinear behaviour. • Tessellation of units for multistable metamaterials and control of compact waves.

Design and Manufacturing of a Metal-Based Mechanical Metamaterial with Tunable Damping Properties.

In the present work, a novel concept for metallic metamaterials is presented, motivated by the creation of next-generation reversible damping systems that can be exposed to various environmental conditions. For this purpose, a unit cell is designed that consists of a parallel arrangement of a spring and snap-fit mechanism. The combination of the two concepts enables damping properties one order of magnitude higher than those of the constituting metal material. The spring element stores elastic energy while the snap-fit allows to absorb and dissipate energy and to reach a second stable state. Different configurations of single unit cells and connected cell assemblies are manufactured by laser powder bed fusion using Ti6Al4V powder. The dimensioning is supported by finite element modelling and the characteristic properties of the unit cells are studied in cyclic compression experiments. The metamaterial exhibits damping properties in the range of polymeric foams while retaining its higher environmental resistance. By variation of selected geometrical parameters, either bistable or self-recovering characteristics are achieved. Therefore, a metamaterial as an assembly of the described unit cells could offer a high potential as a structural element in future damping or energy storage systems operating at elevated temperatures and extreme environmental conditions.

Coarse-grained Stochastic Model of Myosin-Driven Vesicles into Dendritic Spines.

We study the dynamics of membrane vesicle motor transport into dendritic spines, which are bulbous intracellular compartments in neurons that play a key role in transmitting signals between neurons. We consider the stochastic analog of the vesicle transport model in [Park and Fai, The Dynamics of Vesicles Driven Into Closed Constrictions by Molecular Motors. Bull. Math. Biol. 82, 141 (2020)]. The stochastic version, which may be considered as an agent-based model, relies mostly on the action of individual myosin motors to produce vesicle motion. To aid in our analysis, we coarse-grain this agent-based model using a master equation combined with a partial differential equation describing the probability of local motor positions. We confirm through convergence studies that the coarse-graining captures the essential features of bistability in velocity (observed in experiments) and waiting-time distributions to switch between steady-state velocities. Interestingly, these results allow us to reformulate the translocation problem in terms of conditional mean first passage times for a run-and-tumble particle moving on a finite domain with absorbing boundaries at the two ends. We conclude by presenting numerical and analytical calculations of vesicle translocation.

Bistable sound insulator with an abrupt stiffness shift using magnetic-coupled dielectric elastomer actuator

Aiming at noise isolation in low frequency range, this paper presents a novel kind of membrane sound insulator featuring a bistable actuation, by combining magnets and multilayer dielectric elastomer actuator (DEA). With a critical applied voltage on DEA, it deforms and the magnets attract in terms of a bistable snapping, which leads to an abrupt stiffness shift, and consequently regulates the sound transmission loss peak frequency. An electromechanical model is established to reveal the bistable characteristics and to study the effect of voltage and structure parameters for design optimization. The sound-insulation measurement experiment verifies the tunable acoustic performance. The sound-insulation peak frequency has a maximum shift of 142, 130, and 141 Hz under voltages of 2000, 2500, and 3000 V, respectively, showing an advancing figure of merit compared with the existed acoustic metamaterial based on dielectric elastomer.

A Magnet-Coil-Type Bistable Vibration Energy Harvester for Random Wave Environment

In this study, a new bistable vibration energy harvesting system is developed by originally proposing a bistable vibration model comprising a spring and a mass block and then applying a vibration generator composed of a coil and a magnet. The nonlinear equations of motion for this vibration energy harvesting system are developed and the static potential energy distribution is analyzed. The bistable vibration characteristics and the method for prediction of the periodic excitation frequency at which stochastic resonance is likely to occur are investigated theoretically, and the electromagnetic induction-based bistable vibration energy harvesting system is then developed. We predicted the excitation value that the stochastic resonance phenomenon is most likely to occur at 1.543 Hz. We also conducted experiments at 1.15 Hz, 1.50 Hz, and 1.85 Hz, which are centered on the predicted value. As a result, stochastic resonance occurred in all experimental cases. The power generation efficiency was improved by 125.03%, 149.05%, and 95.39%, respectively.

Energy conversion mechanisms of a seesaw-type energy harvester

Vibration energy harvesters with bistable characteristics, which can convert mechanical energy to electric energy, are typically cantilever beams with magnetic repulsion. In order to enhance their low-frequency performance, a seesaw-type approach has been proposed, which can make the structure overcome the potential barrier more easily. In this paper, we establish electromechanical coupling equations of the whole system, and prove that the internal beam delivers mechanical energy to the primary beam based on time-domain analysis. Meanwhile, frequency-domain analysis and solutions are conducted to investigate the dynamical and electrical behaviors of the system based on the adjustment of different parameters. We find that both the mechanical and electrical responses are enhanced gradually with the decrease of the relative damping coefficient within the bounds of the discussion. And the maximum response amplitude can be increased by a factor of 11.3 just by adjusting the position of the internal beam. Furthermore, the length of the internal beam can affect the responses of the system visibly and regularly, and the maximum response amplitude remains unchanged when changing the length of the internal beam from 80 to 100 mm. All of this suggests that the mechanisms of a seesaw-type energy harvester will provide guidance for designing a more appropriate structure, depending on different applications.

Nonlocal nonlinear static/dynamic snap-through buckling and vibration of thermally post-buckled imperfect functionally graded circular nanoplates

The bi-stability characteristics of the post-buckled plates have demonstrated extensive potential applications for energy harvesting and vibration isolation. In this article, at first, thermal post-buckling, nonlinear bending, and vibration behavior of the functionally graded (FG) circular nanoplates in bifurcation buckling are investigated according to nonlocal elasticity theory. Then, the nonlinear static/dynamic snapping phenomena and free vibration responses of the thermally post-buckled nanoplate subjected to static and sudden types of mechanical load are presented. For this aim, the equations of motion in conjunction with the von-Kármán nonlinearity and geometrical imperfection are established in the framework of Hamilton's principle. In addition, two distinct cases of temperature distribution as well as two types of edge conditions are taken into consideration. The equations of motion are discretized using the Chebyshev-Ritz procedure along with three different numerical algorithms. To evaluate the nonlinear dynamic snap-through buckling, the Newmark time integration scheme is adopted. Next, by means of the Budiansky-Roth criterion and the phase-plane approach, the dynamic snap-through loads are identified. A set of parametric studies is presented to provide an insight into influences of the nonlocal parameter, geometrical imperfection, gradient index, and edge supports on the static and dynamic characteristics of the nanosystem.

Improving Energy Harvesting from Bridge Vibration Excited by Moving Vehicles with a Bi-Stable Harvester.

To monitor the health status of the bridge, many sensors are needed to be mounted on it. Converting bridge vibration energy to electrical energy is considered as a potential solution to the problem of providing reliable electric power to these sensors. The objective of this work is to present an operable strategy for improving the electric energy output of a piezoelectric energy harvester installed on a bridge by introducing bi-stable characteristics. A bi-stable harvester is proposed. By adjusting the tip and fixed magnets, different types of potential energy can be generated, and then the harvester can exhibit the linear, mono-stable and bi-stable characteristics. In the bi-stable state, the harvester triggers snap-through motions easily and generates large outputs. The corresponding prototype was fabricated, and the experiment was carried out to validate the advantage of the bi-stable energy harvester. The experiment results show that the bi-stable energy harvester outperforms the classical linear harvester over the whole range of vehicle speed. As the vehicle speed exceeds a critical one, the snap-through motion will happen, which is beneficial to enhancing the electricity output. This conceptual design may provide guidance for promoting the performance of bridge energy harvesting.

Light-driven Bi-stable actuator with oriented polyimide fiber reinforced structure

The unique feature of bi-stable structure is that it has the inherent ability to rapidly change between two stable configurations under external stimulations, and can maintain the equilibrium state without energy consumption. Herein, we reported a light-responsive bi-stable actuator which composed of functional and support layers. Firstly, the effect of oriented polyimide (PI) fiber-reinforced polydimethylsiloxane (PDMS) composites on thermal behavior was been studied. Then, this unique thermal performance of PI fiber-reinforced PDMS in combination with the laying method ensures the formation of a bi-stable actuator. Finally, a universal but straightforward strategy to generate a light-responsive actuator with fast deformation and bi-stable characteristics was developed based on photo-thermal expansion deformation mechanism. Moreover, the actuator was fabricated by using inexpensive materials and scalable methods. Overall we believe this work may open up a new perspective for the design of light-responsive actuators and enriches the design of fast-deformation flexible bi-stable actuators.

Numerical simulation and analysis of dual base transistor laser

AbstractIn this work, characteristics of dual base transistor laser are numerically analyzed for the first time. Active base region of the transistor laser is split into two unequal regions composing of shorter and longer sections, which are biased separately. Static characteristics of transistor laser are evaluated using a rate equation model, which reveals switching action in output optical power for a longer section base current of 9.2 mA with unpumped shorter section. Hysteresis behavior in the optical output is observed for the longer section input current till 1.6 mA. Optical bistable characteristics are studied for various values of gain (longer) and absorber (shorter) section currents. Further slope efficiency is evaluated using P‐I characteristics, before the onset of bistability, for gain lever features under common emitter (CE) configuration. A maximum gain lever of 4.5 dB is observed with the longer section bias current of 1.3 mA.

Cover Feature: Structural Insights into Hysteretic Spin‐Crossover in a Set of Iron(II)‐2,6‐bis(1H‐Pyrazol‐1‐yl)Pyridine) Complexes (Chem. Eur. J. 6/2022)

Bistable spin-state switching near room temperature: Two mononuclear iron(II) complexes showing technologically relevant abrupt and wide hysteretic, bistable spin-state switching characteristics in the vicinity of room temperature are reported. The large structural reorganizations from the Jahn–Teller-distorted high-spin state to the less distorted low-spin state and ethyl group conformational switching are proposed as the main contributing factors rendering the switching hysteretic. More information can be found in the Research Article by M. Schleberger, H. Wende, S. K. Kuppusamy, M. Ruben, et al. (DOI: 10.1002/chem.202103853).

Noise-induced transition in the Zeldovich–Semenov model with local and global bifurcations

The noise-induced transition of the Zeldovich–Semenov model in a continuous stirred tank reactor is investigated under small random perturbations. The deterministic model will exhibit mono- and bistable characteristics via local and global bifurcations. In the bistable zone, based on the Freidlin–Wentzell large deviation theory, the stochastic preference is explained by analyzing the required action of the fluctuational path. For the case of monostability, in the weak noise limit, the emergence of the switching line gives rise to the sudden switch of the optimal path and the sliding cycle will appear via the sliding bifurcation, which is verified by numerical methods. In addition, when there is no saddle in phase space, stochastic excitation with large-amplitude spikes is studied. On the quasi-threshold manifold, the point with the minimum quasi-potential plays the same role as the saddle, which means that the optimal path will undergo a large excursion by crossing this special point. These phenomena are verified by employing stochastic simulations.

Coupled Oscillator Dynamics in Brain EEG Signals: Manifestation of synchronization and Across Frequency Energy Exchange by Neutral Turbulence

Phenomenological models, involving coupled oscillators of both deterministic and stochastic nature, have been invoked to describe the behavior of the EEG signals, with experimental validation. These models derive justification from the fact that the basic electronic unit for potential generation, incorporating capacitive, inductive, and resistive components, as well as the source, is modelled as damped driven oscillator, which can behave independently and may also exhibit synchronized dynamics with others, that can manifest in spatially correlated behavior observed in brain dynamics. Here, using a phase-space approach, we show clear evidence of oscillator dynamics to wave packet collapse and revival in the brain EEG signals, with distinct differences in healthy individuals and epileptic patients. The low frequency components exhibit single oscillator type behavior in a phase-space description, with the potentials as coordinates and their instantaneous changes as the corresponding velocities. The closed paths reveal periodic motion, well described by one linear oscillator or possibly coupled ones with limit cycle dynamics and synchronization at the macroscopic level. The epileptic patients reveal dynamical features of bistability, originating from non-linearity, a prominent feature in the signals from the epileptogenic zone and much enhanced during the periods of seizure. Analogy from the phase-space of oscillator dynamics reveals dominance of potential energy in the signals from the epileptogenic zone, as also in the patients during occurrence of seizure. The acceleration, arising from the change of velocity, is found to be particularly strong in epileptic patients, when the phase space shows bi-stability and bursty behavior. Wave behavior with characteristics of superposition emerges in the frequency range corresponding to the observed unstable periodic orbits that appear at 8-14Hz, centered at 10Hz. A modulated carrier wave is observed for all subjects at 18Hz, higher in width for patients. Coherent wave dynamics, with interference playing a key role in the wave packet collapse and revival, is observed starting from 18Hz, with the coherence getting significantly enhanced around 40-45Hz. Mechanism of intra frequency energy transfer is shown to be neutral turbulence.

Unsteady aerodynamics over surface of a chambered airfoil at stall angle and low Reynolds number

The proposal of this paper is clear to reveal and understand the unsteady flow characteristics over the surface of chambered airfoil operating especially at low Reynolds numbers by detecting boundary layer separation and laminar separation bubble (LSB). Experiments including smoke-wire technique for flow visualization, velocity measurement via hot-wire sensor and quasi-wall shear stress measurement by means of the hot-film sensor have been performed over the suction surface of NACA 4412 airfoil at Reynolds number of 5x104 and angle of attack of 14°. Experiments indicate that the airfoil at a stall angle exhibits the bistable characteristics over the suction surface because of the unsteady bubble bursting at low Reynolds numbers. That is, either laminar flow separates from the leading-edge of the airfoil owing to a dominant adverse pressure gradient (APG) or it does not separate along downstream. It is also noted that unsteady boundary layer formation may affect the flow characteristics by changing airfoil’s stability appreciably, causing the periodic fluctuations with the occurring bubble bursting and the leading edge and trailing edge vortex merging. This may conclude undesirable problems such as noise, vibration and flutter for the flight vehicles and wind turbines.

Bow-type bistable triboelectric nanogenerator for harvesting energy from low-frequency vibration

Triboelectric nanogenerators (TENGs) are emerging, leading-edge, and promising devices for converting ambient vibration energy into electrical energy and power for low-power sensors. However, it is difficult to harvest energy from low-frequency ambient vibrations using conventional TENGs. To solve this issue, in this study, we propose a bow-type TENG with a bistable stiffness feature, which enables the conversion of low-frequency vibration energy into electrical energy with high efficiency. The dynamic model of the bow-type TENG was established based on extended Hamilton’s principle and numerically solved to obtain the dynamic responses. Subsequently, a prototype of the bow-type TENG was fabricated and tested to verify the design concept. Moreover, the dependencies of the energy-harvesting performance on the structural parameters were experimentally investigated. The average power had a maximum value of 0.64 mW at 5 Hz in the case of optimal load resistance. The bow-type TENG could power a number of light-emitting diodes (LEDs) to display the word “HNU” under low-frequency excitation. Hence, the bow-type TENG can substantially extend the function of harvesting vibration energy from high to low frequencies.