Prompt efficiency of energy harvesting by magnetic coupling of an improved bi-stable system

In order to improve the transform efficiency of bi-stable energy harvester(BEH),this paper proposes an advanced bi-stable energy harvester(ABEH),which is composed of two bi-stable beams coupling through their magnets.Theoretical analyzes and simulations for the ABEH are carried out.First,the mathematical model is established and its dynamical equations are derived.The formulas of magnetic force in two directions are given.The potential energy barrier of ABEH is reduced and the snap-through is liable to occur between potential wells.To demonstrate the ABEH's advantage in harvesting energy,comparisons between the ABEH and the BEH are carried out for both harmonic and stochastic excitations.Our results reveal that the ABEH's inter-well response can be elicited by a low-frequency excitation and the harvester can attain frequent jumping between potential wells at fairly weak random excitations.Thus,it can generate a higher output power.The present findings prove that the ABEH is preferable in harvesting energy and can be optimally designed such that it attains the best harvesting performance.     

利用二次型求解n模耦合谐振子能量本征值精确解

利用二次型理论构造一个幺正矩阵进行坐标和动量变换,把n模动量耦合谐振子体系的哈密顿量化为标准的二次型,进而得到n模动量耦合谐振子体系的能量本征值.对n模坐标耦合的情况也进行了类似求解,并提供了解决该类问题的一般数学方法.     

Linear and nonlinear electromagnetic coupling models in vibration-based energy harvesting

This paper investigates the response of an energy harvester that uses electromagnetic induction to convert ambient vibration into electrical energy. A unique aspect of the present study is the comparison of the system's response behavior when either a linear or a physically motivated form of nonlinear coupling is applied. The motivating hypothesis for this work was that nonlinear coupling could be used to improve the performance of an energy harvester by broadening its frequency response. Combined theoretical and numerical studies investigate the harvester's response for both single and multi-frequency base excitation. Our investigations unveil regions in the parameter space where nonlinear coupling is better than linear coupling and regions where the opposite is true. The meaningful conclusion is that nonlinear coupling can sometimes be detrimental, but it can also be beneficial if properly designed into the system.     

Broadband energy harvesting via magnetic coupling between two movable magnets

Harvesting energy from ambient mechanical vibrations by the piezoelectric effect has been proposed for powering microelectromechanical systems and replacing batteries that have a finite life span. A conventional piezoelectric energy harvester （PEH） is usually designed as a linear resonator, and suffers from a narrow operating bandwidth. To achieve broadband energy harvesting, in this paper we introduce a concept and describe the realization of a novel nonlinear PEH. The proposed PEH consists of a primary piezoelectric cantilever beam coupled to an auxiliary piezoelectric cantilever beam through two movable magnets. For predicting the nonlinear response from the proposed PEH, lumped parameter models are established for the two beams. Both simulation and experiment reveal that for the primary beam, the introduction of magnetic coupling can expand the operating bandwidth as well as improve the output voltage. For the auxiliary beam, the magnitude of the output voltage is slightly reduced, but additional output is observed at off-resonance frequencies. Therefore, broadband energy harvesting can be obtained from both the primary beam and the auxiliary beam.     

Synchronization in chaotic oscillators by cyclic coupling

We introduce a type of cyclic coupling to investigate synchronization of chaotic oscillators. We derive analytical solutions of the critical coupling for stable synchronization under the cyclic coupling for the Rössler system and the Lorenz oscillator as paradigmatic illustration. Based on the master stability function (MSF) approach, the analytical results on critical coupling are verified numerically. An enhancing effect in terms of lowering the critical coupling or enlarging the synchronization window in a critical coupling space is noticed. The cyclic coupling is also applied in other models, Hindmarsh-Rose model, Sprott system, Chen system and forced Duffing system to confirm the enhancing effect. The cyclic coupling allows tuning of two coupling constants in reverse directions when an optimal control of synchronization is feasible.     

Theoretical investigations of energy harvesting efficiency from structural vibrations using piezoelectric and electromagnetic oscillators

Conversion of ambient vibrational energy into electric power has been the impetus of much modern research. The traditional analysis has focused on absolute electrical power output from the harvesting devices and efficiency defined as the convertibility of an infinite resource of vibration excitation into power. This perspective has limited extensibility when applying resonant harvesters to host resonant structures when the inertial influence of the harvester is more significant. Instead, this work pursues a fundamental understanding of the coupled dynamics of a main mass-spring-damper system to which an electromagnetic or piezoelectric mass-spring-damper is attached. The governing equations are derived, a metric of efficiency is presented, and analysis is undertaken. It is found that electromagnetic energy harvesting efficiency and maximum power output is limited by the strength of the coupling such that no split system resonances are induced for a given mass ratio. For piezoelectric harvesters, only the coupling strength and certain design requirements dictate maximum power and efficiency achievable. Since the harvesting circuitry must "follow" the split resonances as the piezoelectric harvesters become more massive, the optimum design of piezoelectric harvesters appears to be more involved than for electromagnetic devices.     

Controlling chaotic oscillators by altering their energy

We developed the control technique for nonlinear oscillators when simple feedback alters the oscillation energy. The control does not require any computation nor knowledge of the system equations. Depending on the control perturbation parameters, two scenarios take place: (i) changing (linearly or nonlinearly) the oscillator damping, and (ii) suppressing (enhancing) the driving force. In the case of large deviations between phases of the chaotic oscillator and the driving force, only first scenario holds. Generalization of the technique to the case of oscillator networks is considered.     

超混沌振荡器的混沌耦合同步

提出了两种应用单变量单向混沌耦合同步超混沌振荡器的同步方案。首先给出了混沌耦合同步方案的数学证明，然后通过数值仿真证实了该混沌耦合同步方案的正确性和有效性。最后通过计算条件李雅谱诺夫指数，比较了不同耦合强度下，两种混沌耦合同步和典型的连续耦合同步的同步性能。计算表明在一定的耦合强度下，混沌耦合比典型的连续耦合同步速度快。     

Snap-through piezoelectric energy harvesting

Snap-through mechanism is employed to harvest electricity from random vibration through piezoelectricity. The random excitation is assumed to be Gaussian white noise. The snap-through piezoelectric energy harvester possesses the bistability. For small-amplitude vibration in a potential well, the Ito stochastic differential equation of the electromechanical coupling system is derived from the Taylor approximation at a stable equilibrium point. The method of the moment differential equations is applied to determine the statistical moments of the displacement response and the output voltage. The effects of the system parameters on the output voltage and the output power are examined. The approximate analytical outcomes are qualitatively and quantitatively supported by the numerical simulations. For large-amplitude interwell motion, the effects of the parameters on the output voltage and the output power are numerically investigated. Nonlinearity produced by the snap-through improves energy harvesting so that the snap-through piezoelectric energy harvester can outperform the linear energy harvester in the similar size under Gaussian white noise excitations.     

Interferometric output coupling of ring optical oscillators

We demonstrate the successful deployment of an antiresonant ring (ARR) interferometer within a ring optical resonator and its use for absolute optimization of output power. The integration of the ARR interferometer in a folded arm of the ring oscillator provides continuously variable output coupling over broad spectral range and under any operating conditions. We demonstrate the technique using a picosecond optical parametric oscillator (OPO), where we show continuously adjustable output coupling and optimization of the output power for different pump power conditions, from 3.5 W to 13.5 W. By operating the OPO under an optimized output coupling at 14 W of pump power, we obtain >5 W of extracted signal power, more than 2.6 times that with a ~5% conventional output coupler. We also show that the inclusion of the ARR interferometer has no detrimental effect on the spatial, temporal, and spectral characteristics of OPO output.     

Enhancing stationary entanglement between two optomechanical oscillators by Coulomb interaction with Kerr medium

We theoretically study the stationary entanglement of two charged nanomechanical oscillators coupling via Coulomb interaction in an optomechanical system with an additional Kerr medium. We show that the degree of entanglement between two nanomechanical oscillators is suppressed by Kerr interaction due to photon blockade and enhanced by Coulomb coupling strength. We also show other parameters for adjusting and obtaining entanglement, such as the driving power and the frequencies of the two oscillators, and the entanglement is robust against temperature. Our study proves a way for adjusting stationary entanglement between two optomechanical oscillators by Coulomb interaction and Kerr medium.     

Amplitude death in nonlinear oscillators with indirect coupling

We investigate the effect of frequency mismatch in two indirectly coupled Rössler oscillators and Hindmarsh–Rose neuron model systems. While identical systems show in-phase or out-of-phase synchronization states when coupled through a dynamic environment, mismatch in the internal frequencies of the systems drives them to a fixed point state, i.e., amplitude death. There is a region in the parameter space of the frequency mismatch and coupling strength where system shows amplitude death. The numerical results of Rössler system are also experimentally verified using piece-wise Rössler circuits.     

Mixed synchronization in chaotic oscillators using scalar coupling

We report experimental evidence of mixed synchronization in two unidirectionally coupled chaotic oscillators using a scalar coupling. In this synchronization regime, some of the state variables may be in complete synchronization while others may be in anti-synchronization state. We extended the theory by using an adaptive controller with an updating law based on Lyapunov function stability to include parameter fluctuation. Using the scheme, we implemented a cryptographic encoding for digital signal through parameter modulation.     

Determination of a coupling function in multicoupled oscillators

A new method to determine a coupling function in a phase model is theoretically derived for coupled self-sustained oscillators and applied to Belousov-Zhabotinsky (BZ) oscillators. The synchronous behavior of two coupled BZ reactors is explained extremely well in terms of the coupling function thus obtained. This method is expected to be applicable to weakly coupled multioscillator systems, in which mutual coupling among nearly identical oscillators occurs in a similar manner. The importance of higher-order harmonic terms involved in the coupling function is also discussed.     

Photorefractive mode coupling between two unidirectional ring oscillators

We consider the coupling between two photorefractive unidirectional ring resonators. The first resonator is driven by an external laser beam via photorefractive two-wave mixing. The internal oscillating beam is then employed to drive the second ring resonator via the same mechanism. Closed form solutions for the oscillation intensities and frequencies are given, and their numerical results are presented and discussed.     

Eliminating amplitude death by the asymmetry coupling and process delay in coupled oscillators

Coupling mode plays a key role in determining the dynamical behavior and realizingcertain system’s rhythm and function in the complex systems. In this work, the effects ofthe asymmetry and process delay in the coupling on the dynamical behavior areinvestigated. We find that both the asymmetry and process delay effectively reduce theregion of the frequency-mismatch-induced amplitude death in the parameter space, and makethe system to recover oscillation in the amplitude death regime so as to retain sustainedsystem’s rhythm function. Furthermore, we show the asymmetry and process delay can destroysynchronization. Our results suggest that the asymmetry coupling and process delay are ofcrucial importance in controlling amplitude death and synchronization, and hence thattheir considerations are vital for modeling real life problems.     

On energy harvesting for augmented tags

In this paper, the harmonic signals generated by UHF RFID chips, usually considered as spurious effects and unused, are exploited. Indeed, the harmonic signals are harvested to feed a supplementary circuitry associated with a passive RFID tag. Two approaches are presented and compared. In the first one, the third-harmonic signal is combined with an external 2.45-GHz Wi-Fi signal. The integration is done in such a way that the composite signal boosts the conversion efficiency of the energy harvester. In the second approach, the third-harmonic signal is used as the only source of a harvester that energizes a commercial temperature sensor associated with the tag. The design procedures of the two “augmented-tag” approaches are presented. The performance of each system is simulated with ADS software, and using Harmonic Balance tool (HB), the results obtained in simulation and measurements are compared also.