Search

Mechanical frequency up-conversion is a technique whereby a high-frequency oscillation is induced from a low-frequency source and aims to address inherent problems in low frequency vibration energy harvesting. This work presents a novel 1:2:6 internal resonances based frequency up-converting harvester in which the operation frequency is 6 times up-converted. Compared to traditional conceptual mechanisms (e.g. mechanical impact, mechanical plucking, impulsive acceleration), the proposed harvester can operate at much lower acceleration level, the missing of sound during the frequency conversion also reduces the energy consumption. Experimental measurements and theoretical simulations demonstrate that the proposed design can collect energy from ultra-low frequency (< 5 Hz) vibration sources. In addition, the harvester shows very high performance compared to the current state-of-the-art devices, a maximum 2.07 mW of average power is obtained from the fabricated prototype at the excitation frequency and level of 1.71 Hz & 0.19 g, respectively. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The harvester can scavenge energy from ultra-low frequency vibrations. • The harvester can capture vibration energy from any direction. • The harvester can up-convert the excitation frequency through internal resonance. • The harvester is designed with a novel piezoelectric spring based on binder clips. • A significant generated power of 13.29 mW (at 0.26 g, 2.03 Hz) is obtained. Abstract Low frequency vibration is a ubiquitous energy existing in our environment, but a large efficient harvesting of which remains challenging. This paper presents a simple piezoelectric spring architecture based on a common binder clip structure. The harvester with pendulum spring allows the energy of the dynamic mass to be converted into electrical energy in the piezoelectric transducer. Due to the basic characteristics of spring pendulums, the proposed harvester can efficiently scavenge not only ultra-low frequency but also multi-directional vibrational energies. Modeling and design are conducted and a normalized expression of the harvester behavior is given. Chirp and human motion excitations are used to evaluate the proposed harvester's performances. Simulation and experimental results are in good agreement. The proposed device could generate a high output power (13.29 mW) at a low operating frequency (2.03 Hz), which shows great application prospects in the power supply of wearable products, ocean buoys, etc. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a new self-powered vibration damping technique, which is an application of the enhanced synchronized switching harvesting technique. Compared with other self-powered vibration damping techniques, it not only shows its robustness (particularly facing environmental drifts), but also can harvest the energy and supply power to other electronic circuits, while does not simply dissipate the electrical energy. Experimental results show that a vibration damping of about 5dB is achieved as a result of energy harvesting, in good agreement with the theory. In addition, the vibration damping system can be not only self-powered, but also supply power to other electronic circuits. In other words, there is a good trade-off between energy scavenging and vibration damping. Along with experimental results demonstrating the effectiveness of the ESSH implementation, we discuss the design of a device aimed at bridging the gap between research in this area and practical application. [Copyright &y& Elsevier]

Abstract: In the paper, a vibration damping system powered by harvested energy with implementation of the so-called SSDV (synchronized switch damping on voltage source) technique is designed and investigated. In the semi-passive approach, the piezoelectric element is intermittently switched from open-circuit to specific impedance synchronously with the structural vibration. Due to this switching procedure, a phase difference appears between the strain induced by vibration and the resulting voltage, thus creating energy dissipation. By supplying the energy collected from the piezoelectric materials to the switching circuit, a new low-power device using the SSDV technique is proposed. Compared with the original self-powered SSDI (synchronized switch damping on inductor), such a device can significantly improve its performance of vibration control. Its effectiveness in the single-mode resonant damping of a composite beam is validated by the experimental results. [Copyright &y& Elsevier]

The energy conversion efficiency (ECE) of a piezoelectric generator can be denoted by its effective electromechanical coupling coefficient (EECC), which depends only on the geometry parameters with a certain boundary conditions. To obtain the optimal energy-harvesting device, the Raleigh Method was utilized to establish the analysis model of circular piezoelectric composite diaphragms. Simply supported and clamped boundary conditions were considered. The relationships between the performance parameters (EECC and natural frequency) and the structural parameters (diametric ratio β and thickness ratio α) of piezoelectric composite diaphragms were figured out. Given the correlative material parameters and boundary conditions, the performance parameters with the structural parameters as variables can be worked out. The simulation results show that the optimal structural parameters of a composite diaphragm in the case of the simply supported and clamped boundary conditions are different. A simply supported diaphragm generator tends to achieve higher effective electromechanical coupling coefficient and lower natural frequency, and is more suitable for the applications of energy harvesting. [ABSTRACT FROM AUTHOR]

The macro fiber composites (MFCs) with uniform and repeatable electromechanical performance have been a popular choice in various applications like structural actuation, vibration control, structural health monitoring, and energy harvesting. Herein, the strains of lead zirconate titanate based MFCs subjected to various driving signals were conducted via the strain-electrometry method. The formation mechanism of the strains was profoundly expounded, and the variation of the strains as a function of peak to peak value, frequency and superimposed DC bias voltage was further explored. The results demonstrate that both longitudinal and transverse strain-voltage curves with the voltage cyclic loading are closed "ellipse-like" hysteresis loops, in which the strain of ascending branch is smaller than that of the descending branch. Both strains increase with increasing the peak to peak value of driving signal and the increase is more remarkable at smaller bias voltage and lower frequency, while decrease with increasing the positive DC bias voltage and the decrease is specially obvious at larger peak to peak value and lower frequency. Besides, the dispersive effect of the strains induced by larger peak to peak value, particularly with smaller superimposed bias voltage, is more apparent than that induced by smaller peak to peak value. The longitudinal and transverse strains of MFCs with an active area of 40 mm × 30 mm range from 74.8 με to 1688.3 με, and 20.3 με to 488 με, respectively. This research indicates that through properly and carefully synthetical modulation of electrical parameters of driving signal, a notably enhanced strain can be achieved in MFCs for the specific applications such as actuation and high frequency structural control. [ABSTRACT FROM AUTHOR]

• An energy harvesting structure with compound ABH features is proposed. • Transducers are sliced into micro arrays to match the wavelength compression effect of ABH. • Fully coupled numerical models are built to assess the energy harvesting performance. • The compound ABH offers better harvesting performance than the reference beam. Acoustic black hole (ABH) effects can be obtained via proper structural tailoring to induce a gradual reduction of the flexural wave velocity, thus creating high energy density structural areas. The wave energy focalization effect shows promising features for establishing novel vibration energy harvester configurations in terms of the high energy level and broadband characteristics. In this study, an energy harvesting structure with ABH features which ensures the structural strength as well as enhances the harvesting performance is proposed and investigated. Considering the wavelength compression in ABHs, piezoelectric patches bonded on the surfaces of ABHs are sliced into micro arrays to convert the mechanical energy effectively, which make sure that the positive and negative electric charge generated on the surfaces of harvesters won't be neutralized. Each of the transducers is shunted with a resistor impedance. Fully coupled numerical models which consist of vibrational structures and electrical circuits are built to assess the energy harvesting performance of ABH-feature beam and uniform beam under both steady state and transient excitations. Experiments are also conducted to verify the significant performance enhancement in the ABH beam as compared that in the uniform beam. It is shown that the ABH structural tailoring can be used for broadband vibration energy harvesting and boost the harvested power by more than one order of magnitude. [ABSTRACT FROM AUTHOR]

In the field of piezoelectric energy harvesting from ambient low-frequency vibrations, frequency up-converting effect is a classical approach to improve the efficiencies of energy conversion and extraction. However, most of the frequency up-converting harvesters are implemented by either mechanical impacts or non-contact impulse-like accelerations, which needs high-level excitations and usually leads to reduced longevity or considerable noise. To address these limitations, this paper introduces and demonstrates a novel frequency up-converting energy harvester based on 1:3 internal resonance. The nonlinear harvester mainly consists of two asymmetric cantilever beams in which the ratio of their resonant frequencies is 1:3. The harvester features two vibrational degrees-of-freedom (DOFs) corresponding to the two cantilevers: The primary DOF picks up the ambient low-frequency vibrations and excites the secondary one to vibrate drastically at its resonant frequency. Because the secondary resonance is three times higher than the excited frequency, the harvester realizes the frequency up-conversion. The underlying mechanisms of this design are thoroughly analyzed in the numerical simulation and experiment. [ABSTRACT FROM AUTHOR]

This paper proposes a new energy harvesting architecture that optimizes the energy conversion under broadband vibrations, which is called adaptive synchronized switch harvesting (ASSH) technique. This technique is derived from the enhanced synchronized switch harvesting (ESSH) technique and based on a new and effective switch control law, which can prevent the switch in energy transferring circuit from over-frequent on-and-off and accordingly enhance the extracted power under multimode vibration. Compared with the ESSH technique, theoretical and experimental results demonstrate the new technique can improve electromechanical conversion efficiency when the piezoelectric energy harvester is excited under two-mode vibration, especially in the case of higher vibration amplitude of the second mode. The extracted power with the new technique is more than three times the ESSH technique in the case of the exciting signal of amplitude ratio (3:6). Furthermore, a self-powered circuit which implements the technique (ASSH) is proposed, which validates that the new technique can be truly self-powered, thus addressing the issue of harvesting environmental energy by autonomous devices. [ABSTRACT FROM AUTHOR]

Ultra-low frequency mechanical excitations are omnipresent in our surrounding environment, but the efficient exploitation of them is generally difficult because they normally drive the widely reported cantilevered harvesters to work under non-resonant conditions. Although the frequency up-conversion strategy has been proposed to mitigate this issue, it usually leads to complicated structures. This paper reports a novel energy harvesting approach based on the twisting vibration of a string-driven rotor. To examine the feasibility of this approach, an electromagnetic energy harvester is designed, which is composed of a lid, a rotor with embedded magnets, a pendant, and a tube with pick-up coils attached to the outer surface. The rotor is suspended between the lid and the pendant through a piece of string, and then actuated by the ambient excitations through the string. Under the excitations produced by a crank-slider mechanism, the designed harvester can generate useful electric outputs that are proportional to the excitation amplitude, the initial angle between the pendant and lid, and the excitation frequency. Moreover, the harvester can also provide 0.034 mW power when it is periodically pulled by the human hand at approximately 1 Hz. This study demonstrates the potential application of the string-driven rotor in collecting energy from ultra-low frequency excitations. [ABSTRACT FROM AUTHOR]

A micro-power-generator is developed with piezoelectric ceramics, which can convert the structural vibration energy generated by wind power into electricity to provide energy for micro-devices such as wireless sensor nodes. The vibration modes of the device are analyzed. The standard interface circuit for piezoelectric energy recovery and LTC3588-1 voltage stabilization circuit are selected, and the hardware circuit of the device is designed. The output voltage and power characteristics of micro-power-generator were analyzed under different loads, frequencies and amplitudes. The experimental results show that under the same wind speed, When the blunt body is a cuboid, the power generation effect of this device is the best under the optimal load, with the maximum output power of 350.7 μW. Under the same load with the same shape and structure, the load voltage and output power increase with the increase of wind speed. [ABSTRACT FROM AUTHOR]

Magneto Rheological Elastomers (MREs) are composite materials based on an elastomer filled by magnetic particles. Anisotropic MRE can be easily manufactured by curing the material under homogeneous magnetic field which creates column of particles. The magnetic and elastic properties are actually coupled making these MREs suitable for energy conversion. From these remarkable properties, an energy harvesting device is considered through the application of a DC bias magnetic induction on two MREs as a metal piece is applying an AC shear strain on them. Such strain therefore changes the permeabilities of the elastomers, hence generating an AC magnetic induction which can be converted into AC electrical signal with the help of a coil. The device is simulated with a Finite Element Method software to examine the effect of the MRE parameters, the DC bias magnetic induction and applied shear strain (amplitude and frequency) on the resulting electrical signal. [ABSTRACT FROM AUTHOR]

Energy harvesting methods that use functional materials have attracted interest because they can take advantage of an abundant but underutilized energy source. Most vibration energy harvester designs operate most effectively around their resonant frequency. However, in practice, the frequency band for ambient vibrational energy is typically broad. The development of technologies for broadband energy harvesting is therefore desirable. The authors previously proposed an energy harvester, called a flexible piezoelectric device (FPED), that consists of a piezoelectric film (polyvinylidene difluoride) and a soft material, such as silicon rubber or polyethylene terephthalate. The authors also proposed a system based on FPEDs for broadband energy harvesting. The system consisted of cantilevered FPEDs, with each FPED connected via a spring. Simply supported FPEDs also have potential for broadband energy harvesting, and here, a theoretical evaluation method is proposed for such a system. Experiments are conducted to validate the derived model. [ABSTRACT FROM AUTHOR]

Harvesting energy from wind to supply low-power consumption devices has attracted numerous research interests in recent years. However, a traditional vortex-induced vibration energy harvester can only operate within a limited range of wind speed. Thus, how to broaden the effective wind speed range for energy harvesting is a challenging issue. In this paper, a slotted cylinder bluff body is proposed for being used in the design of a wind energy harvester. The physical prototype is manufactured and the wind tunnel test is performed for evaluating the actual performance of the prototyped energy harvester. The effect of the orientation of the slot on the performance of the proposed energy harvester is experimentally investigated. As compared to the traditional counterpart without the slot at the lateral side of the bluff body, the proposed energy harvester demonstrates the superiority for realizing broadband energy harvesting. Due to the introduction of the slot, and by carefully tuning the orientation of the slot, both the vortex-induced vibration and the galloping phenomena can be stimulated within two neighboring wind speed ranges, leading to the formation of an extremely broad bandwidth for energy harvesting. [ABSTRACT FROM AUTHOR]

Acoustics Black Hole (ABH) effect shows promising features for potential vibration control and energy harvesting applications. The phenomenon occurs in a structure with diminishing thickness which gradually reduces the phase velocity of flexural waves. The coupling between the tailored ABH structure and the damping layer used to compensate for the adverse effect of the unavoidable truncation is critical and has not been well apprehended by the existing models. This paper presents a semi-analytical model to analyze an Euler-Bernoulli beam with embedded ABH feature and its full coupling with the damping layers coated over its surface. By decomposing the transverse displacement field of the beam over the basis of a set of Mexican hat wavelets, the extremalization of the Hamiltonian via Lagrange׳s equation yields a set of linear equations, which can be solved for structural responses. Highly consistent with the FEM and experimental results, numerical simulations demonstrate that the proposed wavelet-based model is particularly suitable to characterize the ABH-induced drastic wavelength fluctuation phenomenon. The ABH feature as well as the effect of the wedge truncation and that of the damping layers on the vibration response of the beam is analyzed. It is shown that the mass of the damping layers needs particular attention when their thickness is comparable to that of the ABH wedge around the tip area. Due to its modular and energy-based feature, the proposed framework offers a general platform allowing embodiment of other control or energy harvesting elements into the model to guide ABH structural design for various applications. [ABSTRACT FROM AUTHOR]

• A novel synchronized switch damping technique based on energy injection strategy is proposed. • The injection energy can be easily adjusted through changing the duty cycle of the corresponding switch control signal. • Low voltage source might lead to high piezoelectric driven voltage in the proposed technique. • Piezoelectric structural damping characteristic can be effectively enhanced or timely adjusted. • The stability problem of the controlled system can be easily solved and implemented. Synchronized switch damping (SSD) principle and derived techniques are a classical semi-active vibration control method based on piezoelectric elements. This paper presents a novel energy injection based SSD technique which has better effect of vibration reduction but with simpler implementation of electronic circuitry. The proposed circuit is composed of a flyback transformer, an ordinary low voltage source and two kinds of synchronized switches. Through controlling the synchronized switches, the electrical energy is extracted from the voltage source to the transformer, and then injected to the piezoelectric elements, increasing the piezoelectric voltage as needed. Moreover, this injection energy can be easily adjusted by changing the duty cycle of the corresponding switch control signal. The operation principle of this technique is introduced, the analytical expression of vibration attenuations is also derived for a typical electromechanical model. Finally, theoretical predictions confirmed by experimental results show that the proposed SSD technique provides an adaptive structural damping and enhances the effect of vibration attenuation. [ABSTRACT FROM AUTHOR]

[Display omitted] • The harvester can significantly up-convert the excitation frequency through 1:2:6 internal resonance mechanism. • The pendulum-like oscillator is designed as a key component to capture ultra-low frequency mechanical energy. • Elastic collision caused by mechanical stoppers can directly transfer the mechanical energy from the 1st swing DOF to 2nd vibration DOF. • The nonlinear harvester has advantages of ultra-low frequency and wideband vibration energy harvesting. The collection of ultra-low frequency mechanical energy that distributed in ambient environments remains challenging so far. This paper presents a frequency up-converting energy harvester based on a component pendulum, a pair of magnetic coupled cantilever beams, and two mechanical stoppers. The pendulum-like oscillator with ultra-low natural frequency can efficiently capture ambient mechanical energy and the designed 1:2:6 internal resonance mechanism can up-convert the frequency with a high conversion factor, presenting great potential for application in real-world systems with low vibration frequencies in the range of 1 to 5 Hz. Modeling and design are conducted, theoretical dynamic predictions are given and confirmed by experimental results. The proposed frequency up-converting harvester could generate a relatively high output power (about 2 mW) at a low excitation frequency and amplitude (around 2 Hz and 0.37 g). Moreover, the electromechanical coupling coefficient of the harvester can be further optimized, increasing the above-mentioned output power directly. [ABSTRACT FROM AUTHOR]

To date, the fabrication of high-performance flexible energy harvesters/nanogenerators based on piezoelectric poly(vinyldene fluoride) (PVDF) is of great concern due to their huge potential to realize full-flexible self-powered electronics. Herein, in this work, we report a flexible piezoelectric nanogenerator (PNG) based on a textured hybrid film consisting of PVDF and manganese dioxide (MnO 2) nanorods. It is found that the combination of MnO 2 and PVDF can notably facilitate the formation of piezoelectric phase, increase the crystallinity and promote the polarization level, inducing dramatically strengthened piezoelectric and output activity for PVDF. Additionally, the addition of MnO 2 has the effect of significantly enhancing the mechanical property while slightly increasing dielectric constant of nanocomposites, which are advantageous to further harnessing the output enhancement. With an optimal loading of 1.0 wt% MnO 2 , the piezoelectric coefficient (d 33 ≈ 38 pC/N) and correspondingly output response of hybrid films reached the peak. For instance, under the d 33 working mode, an output voltage of 3.2 V can be achieved in hybrid films while that of PVDF is only 1.7 V. Image 1 • A novel piezoelectric PVDF based composite with highly aligned MnO2 rods was developed for energy harvesting application. • MnO2 rods can effectively promote interfacial polarization within PVDF and boosting piezoelectric and output responses. • The superior mechanical property while low dielectric constant of composites can further harness the output enhancement. [ABSTRACT FROM AUTHOR]