Interwell Motion Research Articles

Snap-through piezoelectric energy harvesting

Abstract 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.

Novel piezoelectric bistable oscillator architecture for wideband vibration energy harvesting

Bistable vibration energy harvesters are attracting more and more interest because of their capability to scavenge energy over a large frequency band. The bistable effect is usually based on magnetic interaction or buckled beams. This paper presents a novel architecture based on amplified piezoelectric structures. This buckled spring–mass architecture allows the energy of the dynamic mass to be converted into electrical energy in the piezoelectric materials as efficiently as possible. Modeling and design are performed and a normalized expression of the harvester behavior is given. Chirp and band-limited noise excitations are used to evaluate the proposed harvester’s performances. Simulation and experimental results are in good agreement. A method of using a spectrum plot for investigating the interwell motion is presented. The effect of the electric load impedance matching strategy is also studied. Results and comparisons with the literature show that the proposed device combines a large bandwidth and a high power density.

An investigation of the plausibility of stochastic resonance in tubulin dimers

This paper considers the possibility of stochastic resonance (SR) in tubulin dimers. A formula for the signal-to-noise ratio (SNR) of tubulin as a function of temperature is derived. The effective potential experienced by a delocalized electron in such a dimer is postulated to be a symmetric bimodal well. Inter-well and intra-well motions are described by Kramers rate theory and the Langevin formalism respectively. The frequency-dependent expression for the SNR shows that the response of the electron-tubulin dimer system is enhanced by ambient dipolar oscillations in specific frequency regimes. This is a characteristic of SR. Biophysical implications of this property such as the relevance to 8.085 MHz microtubule resonance and the clocking mechanism are detailed.

Observation of Relaxation Mode in Ferroelectric Barium Dititanate by Micro-Brillouin Scattering

New ferroelectric single crystals of BaTi2O5 have been studied in detail by high-resolution micro-Brillouin scattering with focus on the central component of the relaxation mode over a wide temperature range (20–600°C). A relaxation mode has been clearly observed in these single crystals for the first time. In addition, the usual phonon features are also observed in the Brillouin shifts determined by selection rules for a monoclinic phase. The ferroelectric phase transition at Tc∼470°C, sharp anomaly has been observed from both the frequency shift and hypersonic damping. The relaxation time slows down and intensity of central peak increases markedly when temperature approaches Tc from above and below. Furthermore, the relaxation mode has an A(y) symmetry which implies that the relaxation mode involves interwell motion of Ti ions parallel to the polar axis. The temperature dependence of the relaxation time and integrated intensity of the relaxation mode are well reproduced by the extended semiclassical tunneling model in which the off-center ion in the octahedra tunnels between two sites of a double-well potential.

Quantum ratchets with few bands below the barrier.

We investigate directed motion in nonadiabatically rocked ratchet systems sustaining few bands below the barrier. Upon restricting the dynamics to the lowest M bands, the total system-plus-bath Hamiltonian is mapped onto a discrete tight-binding model containing all the information both on the intrawell and interwell tunneling motion. A closed form for the current in the incoherent tunneling regime is obtained. In effective single-band ratchets, no current rectification occurs. We apply our theory to describe rectification effects in vortex quantum ratchets devices. Current reversals upon variation of the ac-field amplitude or frequency are predicted.

Analysis of mechanisms inducing damping in dynamic force microscopy: surface viscoelastic behavior and stochastic resonance process

This work contains a short overview on two phenomenological models aiming to evaluate the loss of energy when a nanotip oscillates at the proximity of a surface. In one case, the surface is described as a continuous medium with a local stiffness k s and a local damping term γ s. The viscoelastic properties allows an easy evaluation of the energy loss as a function of the surface relaxation times τ s= γ s/ k s. The main purpose of the second approach is to evaluate the effect of large fluctuations on the dynamic properties of the oscillator. The surface is built of atoms, each of them lying in a symmetric double-well potential and the oscillating nanotip produces a stochastic resonance process. The linear response theory is applied to evaluate fluctuations of the particle corresponding to interwell motions. Then from the amplitude, fluctuation is calculated the loss of energy. The result shows that a stochastic resonance process can increase the amount of dissipate energy of two orders of magnitude at a forcing frequency much smaller than the usual ones corresponding to atom motions.

Study of stochastic resonance by method of stochastic energetics

Stochastic resonance (SR) is numerically analyzed by the method of the stochastic energetics that enable us to analyze the energetics of non-equilibrium processes described by the Langevin equations. The work done by the external agent which drives the potential to fluctuate periodically is shown to be a good quantitative measure of SR. If the phase lag of the inter-well resonant motion before the periodic force is investigated, the good measure of SR can be devised by extracting the inter-well resonant motion. Thus, we numerically investigate the phase lag of the Brownian motion. The value of phase lag at the optimal noise intensity is found to depend on the frequency of the periodic force.

Crossover from a displacive to an order-disorder transition in the nonlinear-polarizability model.

The dynamics of a two-dimensional shell model with a double-well potential in the core-shell interaction is simulated by means of molecular-dynamics techniques. Snapshots of the lattice displacement pattern reveal the presence of precursor regions in the high-temperature phase, while in the low-temperature phase the dynamical structure factor exhibits a quasielastic component in addition to the ferroelectric soft-mode peak. On the other hand, the local dynamics of particles are characterized by two different time scales corresponding to the coexistence of interwell and intrawell motions. In the vicinity of the structural-phase-transition temperature a crossover from a displacive to an order-disorder transition is observed, which may explain the experimentally observed discrepancies of the nature of the phase transition.