Topological metamaterial has become a research hotspot recently, owing to the unique features, including wave localization and topological protection. In this paper, we are motivated to introduce the topological metamaterial into vibration energy harvesting. The proposed topological metamaterial vibration energy harvester (topological meta-VEH) consists of two topologically different sub-metamaterials and a piezoelectric transducer mounted at the conjunction of these two sub-metamaterials. First, the governing equations of this electromechanical system are derived. Then, the band structure and dispersion relation of this topological meta-VEH is obtained by applying the Bloch theory. To obtain the transmittance response, the finitely long model of the proposed topological meta-VEH is formulated, the corresponding analytical solutions are obtained as well. From the theoretical analysis, it is found that the topological interface mode takes place at the first Brag band gap and it has the capability of concentrating elastic wave energy at the interface so that the piezoelectric transducer at the conjunction can generate large output power. Analytical results indicate that the topological meta-VEH is a novel and outstanding method to achieve high-efficiency energy harvesting.
One challenge in modelling a galloping piezoelectric energy harvester (GPEH) is the representation of the highly nonlinear aerodynamic force. The existing work in the literature employed various polynomial functions to fit the aerodynamic coefficient curve for simplicity, though their approximation capabilities are limited. In this paper, we propose to use the deep-learning technique to capture the aerodynamic force behaviour of a bluff body. Replacing the widely adopted third-order polynomial function by a welltrained artificial neural network (ANN) for aerodynamic force representation in modelling a GPEH, the feasibility of the proposed approach is preliminarily validated. To further improve the modelling accuracy, the electromechanical structure of the GPEH is then modelled using the finite element method. The trained ANN is integrated with the established finite element model to predict and update the aerodynamic fore applied on the bluff body in the real-time simulation. The aeroelastic motion and the electrical output of the galloping piezoelectric energy harvester are successfully predicted. Finally, based on a collection of experimental data, a welltrained artificial neural network (ANN) is proved to behave with a much better curve fitting performance than a third-order polynomial function. General procedures for using the deep learning technique to help model a general GPEH with complex geometric shapes are proposed.
The nonlinear beam-slider structure, which consists of a nonlinear cantilever beam and a free movable slider, can always obtain the high-energy orbit to achieve passive self-adaption in a wide bandwidth. The efficiency improvement of this structure has been demonstrated in energy harvesting application. In this work, the nonlinear beam-slider structure is applied as a vibration neutralizer. The behavior of the 2-degree-of-freedom (2-DOF) vibration system is investigated experimentally. The trajectory of the slider, time history response of the nonlinear beam and the linear primary structure are recorded simultaneously. The results show that the nonlinear neutralizer with appropriate parameters has broader bandwidth than the linear one. However, there are multiple solutions corresponding to different vibration states of the nonlinear neutralizer in the suppression frequency range. The vibration of linear primary structure can be suppressed only when the nonlinear neutralizer obtains the certain energy orbit at the given frequency range. The free movable slider can assist the nonlinear beam to obtain the high-energy orbit in multi-solution range (28 Hz-31 Hz). In the frequency range of 28 Hz-31 Hz, the nonlinear neutralizer on the high-energy orbit enhances the vibration suppression performance.
In the past decade, nonlinearity has been introduced into piezoelectric energy harvesters (PEH) for power performance enhancement and bandwidth enlargement. While a great emphasis has been placed on the structural design and the effect of electrical part on the nonlinear dynamics of the system, the maximum power and power limit, an important aspect for performance optimization of nonlinear PEHs, are rarely studied, especially their relationship with that of linear PEHs. To this end, this paper is motivated to investigate the maximum power and power limit of a representative type of nonlinear PEHs, i.e., monostable. An equivalent circuit is proposed to analytically study and explain the behaviors of monostable PEHs, and reveals the connection between linear and monostable PEHs. The effect of nonlinearity, e.g., due to the additional magnetic force, is modeled as a nonlinear stiffness element mechanically and a nonlinear capacitive element electrically, based on the harmonic balance method. Facilitated by this equivalent circuit and the impedance matching technique, clear closed-form solutions of power limit and critical electromechanical coupling, i.e., minimum coupling to reach the power limit, of monostable PEHs are obtained. Then the effect of excitation level and magnetic field on the power and electromechanical coupling of the system is investigated. Though this paper uses monostable PEHs as an example, the results and technique can be extended to other similar types of nonlinear PEH systems as well, for example, bistable.
This paper proposes a metamaterial beam with local resonators coupled by negative stiffness springs. First, a distributed parameter metamaterial beam model with the proposed configuration of coupled local resonators is developed. Due to the introduction of the negative stiffness springs, the system is prone to be unstable. The stability analysis indicates that the infinitely long metamaterial beam becomes unstable as long as the stiffness of the coupling spring becomes negative. For the finitely long metamaterial beam, the stability could be achieved for given negative coupling springs. A parametric study is then conducted to investigate the effects of the number of cells and the lattice constant on the system stability. The transmittance of the finitely long metamaterial beam is calculated. The result shows that due to the restriction on the tunability of the negative stiffness for the proposed metamaterial beam, a certain trade-off is needed for the appearance of the quasi-static vibration suppression region and the enhancement of the main vibration suppression region.
Snap-through oscillation has been widely utilized in nonlinear energy harvesting for power improvement and bandwidth enlargement. In this paper, the snap-through phenomenon of a bistable dual-beam vibration energy harvester (DB-VEH) when driven by harmonic and random excitations is investigated. First, the electromechanical model is established and the parameters are determined by experimental tests. Subsequently, the dynamic responses under different levels of excitation are simulated and the corresponding experiments are conducted. Results indicate that the bistable DB-VEH can achieve the inter-well and chaotic oscillations near the first and second resonances, providing two frequency bands of snap-through, which is helpful for enlarging the bandwidth. For the inter-well oscillation, the remarkably increased output of one beam is always in sacrifice of the efficiency of the other beam, resulting in an outperformed beam and an underperformed one. Finally, the performance when the bistable DB-VEH is under a random excitation is investigated in comparison with that of its linear counterpart. Results indicate that, thanks to the snap-through phenomenon, the standard deviation of voltage of a bistable DB-VEH is much higher than that of a linear DB-VEH for a certain range of intensity.
To enhance the output power and broaden the operation bandwidth of vibration energy harvesters (VEH), nonlinear two
degree-of-freedom (DOF) energy harvesters have attracted wide attention recently. In this paper, we investigate the
performance of a nonlinear VEH with magnetically coupled dual beams and compare it with the typical Duffing-type VEH
to find the advantages and drawbacks of this nonlinear 2-DOF VEH. First, based on the lumped parameter model, the
characteristics of potential energy shapes and static equilibriums are analyzed. It is noted that the dual beam configuration
is much easy to be transformed from a mono-stable state into a bi-stable state when the repulsive magnet force increases.
Based on the equilibrium positions and different kinds of nonlinearities, four nonlinearity regimes are determined. Second,
the performance of 1-DOF and 2-DOF configurations are compared respectively in these four nonlinearity regimes by
simulating the forward sweep responses of these two nonlinear VEHs under different acceleration levels. Several
meaningful conclusions are obtained. First, the main alternative to enlarge the operation bandwidth for dual-beam
configuration is chaotic oscillation, in which two beams jump between two stable positions chaotically. However, the
large-amplitude periodic oscillations, such as inter-well oscillation, cannot take place in both piezoelectric and parasitic
beams at the same time. Generally speaking, both of the magnetically coupled dual-beam energy harvester and Duffingtype
energy harvester, have their own advantages and disadvantages, while given a large enough base excitation, the
maximum voltages of these two systems are almost the same in all these four regimes.