Bandwidth Of Vibration Energy Harvester Research Articles

Widening the bandwidth of vibration energy harvester by automatically tracking the resonant frequency with magnetic sliders

The mismatch between excitation and resonant frequencies, and the narrow bandwidth of the traditional vibration energy harvester, result in small amounts of generating power. This paper presents a novel automated resonant frequency tracking method by using a pair of cylindrical movable magnetic sliders. To increase the bandwidth, the slider can track the resonant frequency on the cantilever beam without manual intervention or additional energy input. The proposed method is validated experimentally by the sliding behavior of the sliders on a cantilever beam within magnetic slider vibration energy harvester (CBMS-VEH). The CBMS-VEH demonstrates 2.7 times increasing in bandwidth for low acceleration (<0.5 g) and low frequency (<10 Hz). Under different excitation frequencies, the relationship between the friction force on the slider and the tangential component of the slider gravity can be tuned to move the slider to specified positions for further widening the bandwidth. The comparative experiments with conventional cantilever beam-mass vibration energy harvester (CBM-VEH) indicate that the resonant frequency tracking method of CBMS-VEH works in the wider range of the energy-harvesting bandwidth (6–9 Hz). Finally, we have successfully demonstrated the great potential of this method in powering low-power electronics, such as digital clocks and LEDs.

A new approach to design electromagnetic transducers for wideband electrically-tuned vibration energy harvesting

This paper focuses on the opportunities offered by electrical tuning to widen the bandwidth of Vibration Energy Harvesters (VEH) based on electromagnetic conversion. The paper shows that some electromagnetic transducer topologies are more likely than others to take advantage of the wide bandwidth performance offered by electrical tuning. Using a general model including both a resonant electromagnetic VEH and a resistive-capacitive interface with electrical tuning, we highlight the parameters of interest influencing the bandwidth of the system. Based on these results, we develop an efficient optimization approach suitable for any electromagnetic transducer topology. The full optimization of different transducer topologies shows that the one that is based on variable reluctance is the best in terms of bandwidth-related performances.

Nonlinear Dynamic Analysis of Hybrid Piezoelectric-Magnetostrictive Energy-Harvesting Systems

To progress the proficiency and broaden the action bandwidth of vibration energy harvesters, this paper presents a cantilever piezoelectric-magnetostrictive bistable hybrid energy harvester with a dynamic magnifier. The hybrid energy-harvesting system comprises two vibration degrees of freedom and two electrical degrees of freedom. It consists of a composite cantilever beam made of three layers, in which the magnetostrictive and piezoelectric layers are attached to the top and bottom of the base layer. The electromechanically coupled vibration equations of the whole hybrid structure were established with the lumped-parameter model while taking into account the magnetic interaction of two magnets. The nonlinear frequency-response of vibrations for the hybrid harvester is calculated using the harmonic balance method, and the model has been validated by literature. The time response and phase portraits of oscillation for the cantilever harvester and its performance in generating electrical power under different magnet distances, dynamic magnifier features, and excitation levels are analyzed. Numerical results have shown that the hybrid structure can harvest additional electrical power and operates at larger bandwidth than routine bistable piezoelectric or magnetostrictive energy harvesters.

A continuous broadband electromagnetic energy harvester based on amplitude and phase adjustments

Broadening the bandwidth of vibration energy harvesters is a critical issue for their practical implementations. Although utilizing multi-degree-of-freedoms is a frequently used solution to widen the operating frequency range, the resultant effective bandwidth could consist of discrete peaks (existing local minimum points lower than the half-power level) if the modal amplitudes have large differences at different frequencies. To solve these problems, we designed a new electromagnetic multi-modal energy harvester, which works in a broad and continuous low-frequency bandwidth. This is achieved by attaching the magnet and the coil to a compliant frame integrated with two different kinked beams, respectively. In this way, the voltage can be generated in a continuous and wide frequency range by adjusting the amplitudes and phases of the magnet and the coil in different modes according to a proposed design requirement. Finite element results and experimental results are in good agreement with each other, which validate the performance of the proposed harvester. The experimental results demonstrate that the half-power bandwidth can be achieved in the range of 15.0 Hz and the maximum peak power is 1.56 mW at the center frequency of 40.5 Hz under base excitation of the root-mean-square acceleration of 0.24 g. The broadband and high power density feature are also validated in a random excitation test, so that this harvester has great potential for practical applications.

Stochastic Response and Bifurcation of a Two-Degree-of-Freedom Energy Harvesting System with Stoppers

It was shown previously that the synergy of the multi-degree-of-freedom (multi-DOF) and the mechanical stopper techniques is an effective way to further broaden the operation bandwidth of vibration energy harvesters. Considering the stochastic factor at the same time, this paper is devoted to developing a theoretical method for analyzing the dynamical characteristics of an impact-engaged 2DOF energy harvesting system under stochastic excitation, in which the impact is modeled as a nonlinear piecewise function. The existence of the impact and multi-DOF brings complexity in analyses, and the main theoretical method utilized in this paper is the stochastic averaging method which is suitable for multi-DOF quasi-nonintegrable systems. After that, the joint and marginal probability density functions of the system are derived, and numerical examples are shown to verify the effectiveness of the theoretical method. It is noteworthy that the theoretical method has the potential to be extended to more complex multi-DOF systems with stoppers. Subsequently, the stochastic response, bifurcations in the stochastic and corresponding deterministic systems, and the relationship between the D-bifurcation and the mean square voltage are discussed. Effects of crucial system coefficients, the impact stiffness and distance on the system are investigated as well.

Tuning and widening the bandwidth of vibration energy harvesters using a ferrofluid embedded mass

Widening the bandwidth and tunability are two of the major challenges associated with vibrational energy harvesting devices. This paper demonstrates a novel method involving embedding liquid into the mass which can be used to either widen the bandwidth or tune the frequency without significant decrease in power output. The paper builds upon previous research on using movable masses to widen the bandwidth. Various liquids including magnetic ferrofluid and Gallium-based liquid metal embedded masses were investigated. Ferrofluid location within the mass can be controlled using integrated hard magnet materials to tune and widen the bandwidth. Frequency tunability of 13.5% is demonstrated using ferrofluid with magnetic actuation. Bandwidth increase from 2.15 (non-movable mass) to 10.15 Hz with ferrofluid, and 17 Hz with liquid metal embedded mass was demonstrated without significant decrease in power output. Fill volume and applied acceleration significantly influence the bandwidth as they affect the percentage of movable mass as well as the force required to displace the liquid.

Experimental study on band merging of non-linear multi-band piezoelectric energy harvester into single broadband using magnetic coupling

The operational bandwidth of Vibration Energy Harvesters (VEH) is area of concern due to stochastic, time-varying, random and multi-frequency nature of available environmental vibrating sources. Most of the VEH have narrow bandwidth providing usable power at specific frequencies. Efforts have been made to increase the frequency range by introducing non-linear structures and techniques. In this paper, multi-band output of the non-linear Piezoelectric Energy Harvester (PEH) is transformed into single wider band output using additional non-linear phenomenon. Dual region operation of PEH results into two separate band output. First region is the outcome of beam resonance and Centre of Gravity (CoG) shift whereas second region is due to the non-linear behaviour of cylinders. In this work, these separate bands are merged to form a single wider band. For merging these two bands and enhancing the bandwidth of PEH, additional phenomenon is introduced using two permanent magnets. A varying magnetic field by changing the distance between magnets changes stiffness of the cantilever beam and that leads to a change in the resonant frequency of band-I. Thus, the overall process shifts band-I towards band-II. In this work, the two separate bands are merged to have one wider band providing 53.22% more frequency coverage than our previous work with a bandwidth of 47.5 Hz. This band includes vibrational frequency range of 25.65–73.15 Hz at 1.4 g acceleration. Cylinder material and its effect with magnetic interaction is also studied. The magnetic force between two permanent magnets is measured experimentally. Effect of magnetic force on centre resonant frequency of beam is compared with experimental and simulated results. Effect of magnetic force on bandwidth of the device is studied.

A Nonlinear Broadband Electromagnetic Vibration Energy Harvester Based on Double-Clamped Beam

The performance of vibration energy harvesters is usually restricted by their frequency bandwidth. The double-clamped beam with strong natural nonlinearity is a simple way that can effectively expand the frequency bandwidth of the vibration energy harvester. In this article, a nonlinear electromagnetic vibration energy harvester with monostable double-clamped beam was proposed. A systematic analysis was conducted and a distributed parameter analytical model was established. On this basis, the output performance was estimated by the analytical model. It was found that the nonlinearity of the double-clamped beam had little influence on the maximum output, while broadening the frequency bandwidth. In addition, the resonant frequency, the frequency bandwidth, and the maximum output all increased following the increase of excitation level. Furthermore, the resonant frequency varies with the load changes, due to the electromagnetic damping, so the maximum output power should be gained at its optimum load and frequency. To experimentally verify the established analytical model, an electromagnetic vibration energy harvester demonstrator was built. The prediction by the analytical model was confirmed by the experiment. As a result, the open-circuit voltage, the average power and the frequency bandwidth of the electromagnetic vibration energy harvester can reach up to 3.6 V, 1.78 mW, and 11 Hz, respectively, under only 1 G acceleration, which shows a prospect for the application of the electromagnetic vibration energy harvester based on a double-clamped beam.

Effect of Repulsive Magnetic Poles on the Natural Frequency and the Bandwidth of a Vibration Energy Harvester

Vibration energy harvesting has emerged as a promising source of sustainable power for wireless sensor networks. This paper describes the effect of alike magnetic pole repulsion on the natural frequency and operational bandwidth of a cantilever-based vibration energy harvester. Experimental result shows that the magnetic repulsive force produced by two horizontally oriented magnets was able to reduce the natural frequency of a cantilever by up to 35% as compared to a typical cantilever beam oscillated under normal conditions. Changing the orientation of one of the magnets to a vertical position reduces the magnetic repulsive force, resulting in a higher natural frequency, transmissibility and maximum amplitude than the horizontal orientation. The magnetic repulsive force effect also resulted in a significant increase in the operational bandwidth of the cantilever beam, recording different natural frequencies for different base acceleration magnitudes. For every 0.1 g increase in base acceleration value, the two horizontally oriented magnet configurations recorded an increase of 0.9 Hz in natural frequency, whereas an average increase of 0.6 Hz was recorded for the latter configuration.

A low-frequency piezoelectric-electromagnetic-triboelectric hybrid broadband vibration energy harvester

In practical applications, vibration-based energy harvesters are usually restricted by their output performance and operating bandwidth. Therefore, improving the performance and increasing the operating bandwidth of vibration energy harvester become to two significant and urgent research focuses in past years. In this paper, a low-frequency piezoelectric-electromagnetic-triboelectric hybrid broadband vibration energy harvester is presented and investigated. It consists of flexible PET picking-up vibration structures which designed to achieve broadband behavior at low acceleration. In the meanwhile, integrate piezoelectric, triboelectric and electromagnetic mechanisms successfully enhanced the electric output of the hybrid energy harvester. As a result, the novel hybrid harvester can scavenge vibration energy at a wide vibration frequency. Under 0.5g acceleration at 20Hz, the novel hybrid harvester obtained maximum output power 41.0μW at a load resistance of 800.1kΩ for one PEH unit, 66.5μW at a load resistance of 343.1Ω for one EMEH unit, and 4.6μW at a load resistance of 1.4MΩ for one TEH unit, and the piezoelectric, electromagnetic and triboelectric EH units can reach 3.5Hz, 10.0Hz, and 18.1Hz operating bandwidth under 0.5g acceleration, respectively.

Widening the bandwidth of vibration energy harvesters using a liquid-based non-uniform load distribution

Vibration energy harvesters typically have a narrow bandwidth, which allows them to generate high amounts of power, but only at a specific frequency. This paper presents a novel method of increasing the bandwidth of a cantilever beam by creating a non-uniform load. The concept uses a liquid filled mass, which causes the structures overall centre of gravity to shift as the beam bends. The overall centre of gravity shifts due to the mass change caused by the dynamic behaviour of the fluid. This paper validates the concept both numerically and experimentally by using a custom manufactured fluid filled mass on a piezoelectric cantilever. A water filled mass demonstrated a 2.8x increase in bandwidth for low acceleration (<1g) and low frequency cantilever (27Hz) devices. The effects due to liquid density and liquid viscosity are also experimentally measured. The numerical estimations match well with the experimental results for low accelerations (<0.5g). Above 0.5g acceleration the liquid water used in the cavity became chaotic, which caused liquid droplets to separate from the bulk liquid, thus reducing the overall mass for given point in time. This non-linear liquid dynamic behaviour further increases the bandwidth by creating a larger variation in the resonant frequency. In addition, as the fluid viscosity increases, the acceleration from the vibration source required to cause movement in the fluid also increases. The measured open circuit peak to peak voltage demonstrated an increase in bandwidth without significant loss in voltage.

Investigation of energy harvesting from high frequency cutting tool vibrations

The continuous reduction in power consumption of wireless sensing electronics has led to immense research interests in vibration energy harvesting techniques for self-powered devices. Currently, most vibration-based energy harvesters are designed as linear resonators that only work efficiently with limited bandwidth near their resonant fre-quencies. Unfortunately, in the vast majority of practical scenarios, ambient vibrations are frequency-varying or totally random with energy distributed over a wide fre-quency range. Hence, increasing the bandwidth of vibra-tion energy harvesters has become one of the most critical issues before these harvesters can be widely deployed in practice.This paper presents the simulation results of high frequency harvester composed from circular piezoelectric bimorph. A high frequency piezoelectric generator is pro-posed, because that during material cutting excited high frequency vibrations could be useful for the excitation of circular piezoelectric transducer bimorphs. The broadband vibration energy harvesting possibility is achieved by changing circular plate shape and constraints conditions. Self-powered wireless sensor node is elaborated for smart cutting tools applications.DOI: http://dx.doi.org/10.5755/j01.mech.20.5.7902

Bi-stable frequency up-conversion piezoelectric energy harvester driven by non-contactmagnetic repulsion

This paper presents miniaturized energy harvesters, where the frequency up-conversiontechnique is used to improve the bandwidth of vibration energy harvesters. Theproposed and developed miniature piezoelectric energy harvester utilizes magneticrepulsion forces to achieve non-contact frequency up-conversion, thereby avoidingmechanical collision and wear for long-term working durability. A pair ofpiezoelectric resonant cantilevers is micro-fabricated to generate electric power. Asimplified model involving linear oscillators and magnetic interaction is deployedto demonstrate the feasibility of the device design. A bench-top harvester hasbeen fabricated and characterized, resulting in average power generation of over10 µW within a broad frequency range of 10–22 Hz under1g acceleration.