Electromagnetic Vibration Energy Harvester Research Articles

Resonant Frequency Reduction of Vertical Vibration Energy Harvester by Using Negative-Stiffness Magnetic Spring

This work studies the resonant frequency reduction of vibration energy harvesters so as to adapt low-frequency ambient vibrations. In a typical electromagnetic vibration energy harvester, it is common sense that the resonant frequency decreases with the spring stiffness. However, the mass gravity will result in a large initial deformation of the spring with small stiffness when the energy harvester is vertically installed. To solve the problem, this work proposes a method of resonant frequency reduction by adding a negative-stiffness magnetic spring which is arranged symmetrically at the two sides of the equilibrium point. The theoretical expression of resonant frequency is derived based on magnetic field calculation. Comparisons between the energy harvesters with and without negative-stiffness magnetic spring are implemented through simulations and experiments. The results show that the resonant frequency of the vertical energy harvester can be reduced as expected without an increase of initial spring deformation by using the negative-stiffness magnetic spring. This work can provide an effective approach to designing energy harvesters for applications with low-frequency vibrations.

An Electromagnetic Vibration Energy Harvester with a Tunable Mass Moment of Inertia.

This paper presents a vibration-based electromagnetic energy harvester whose resonance frequency can be adjusted to match that of the excitation. Frequency adjustment is attained by controlling a rotatable arm, with tuning masses, at the tip of a cantilever-type energy harvester, thereby changing the effective mass moment of inertia of the system. The rotatable arm is mounted on a servomotor that is autonomously controlled through a microcontroller and a photo sensor to keep the device at resonance for maximum power generation. A mathematical model is developed to predict the system response for different design parameters and to estimate the generated power. The system is investigated analytically by a distributed-parameter model to study the natural frequency variation and dynamic response. The analytical model is verified experimentally where the frequency is tuned from 8 to 10.25 Hz. A parametric study is performed to study the effect of each parameter on the system behavior.

The full phase space dynamics of a magnetically levitated electromagnetic vibration harvester

We consider the motion of an electromagnetic vibrational energy harvester (EMVEH) as function of the initial position and velocity and show that this displays a classical chaotic dynamical behavior. The EMVEH considered consists of three coaxial cylindrical permanent magnets and two coaxial coils. The polarities of the three magnets are chosen in such a way that the central magnet floats, with its lateral motion being prevented by enclosion in a hollow plastic tube. The motion of the floating magnet, caused by e.g. environmental vibrations, induces a current in the coils allowing electrical energy to be harvested. We analyze the behavior of the system using a numerical model employing experimentally verified expressions of the force between the magnets and the damping force between the floating magnet and the coils. We map out the phase space of the motion of the system with and without gravity, and show that this displays a fractal-like behavior and that certain driving frequencies and initial conditions allow a large power to be harvested, and that more stable states than two exists. Finally, we show that at leasts fifth order polynomial approximation is necessary to approximate the magnet-magnet force and correctly predict the system behavior.

Design and analysis of a non-resonant rotational electromagnetic harvester with alternating magnet sequence

This paper proposed a portable non-resonant rotational electromagnetic vibration energy harvester using magnetic spring to scavenge kinetic energy from low-frequency human motion. Lagrange equations were established to study the dynamic characteristics of the harvester. MATLAB/Simulink was adopted to analyze the output performance at different excitation frequencies. A prototype has been fabricated for experiment, and the measured results are compared with the theoretical analysis. The energy harvester could respond to diverse vibration excitation. When external excitation frequency is 6 Hz, the output voltage and power density of the electromagnetic energy harvester are 2.2 V and 0.024 W·mm−3 respectively. Four LEDs are alight when external excitation frequency is 5 Hz. It is indicated that the electromagnetic energy harvester based on the magnet spring can efficiently harvest low frequency vibration energy at low frequencies. This work made a significant step toward energy harvesting from human motions. It has potential applications in self-powered portable electronics.

Analysis, design and testing of a rolling magnet harvester with diametrical magnetization for train vibration

Harvesting energy from ambient vibrations, particularly vibrations of a train, is very useful to build a transportation Internet of Things. This paper presents an electromagnetic vibration energy harvester (VEH) based on a cylindrical rolling magnet (RM) and one or three fixed magnets (FMs). This VEH can reach mono-stable and tri-stable potential energy states by changing the number of FMs, and enhance the nonlinearity of the system by reducing the vertical gap between the RM and FMs. Firstly, a theoretical model of the proposed VEH is established. During model construction, the commonly used dipole moment method (DMM) is found unsuitable for calculating the magnetic restoring force acting on the RM since the DMM cannot consider influences of magnet dimensions. Thus, the finite element method is applied. A position-varying factor is exploited to accomplish the electromagnetic coupling of the system. The occurrence of RM slip and the differences between its rolling and sliding effects are investigated. Then, frequency-sweeping tests are performed to understand the dynamical characteristics and energy harvesting capacity of the VEH. The experimental and simulated results under small-magnitude excitations exhibit similar trends, demonstrating the suitability of the theoretical model. The VEH with one FM achieves its maximum instantaneous power of 40.6 mW at 8.0 Hz (9.8 mW at 7.5 Hz for the VEH with three FMs). Finally, the application of this VEH for scavenging energy from the lateral vibration of a metro car body is explored in the laboratory, which suggests its high potential for powering a self-contained onboard monitoring node on a metro train.

Analysis of different cylindrical magnet and coil configurations for electromagnetic vibration energy harvesters

Electromagnetic vibration energy harvesting is a relatively new technology that transforms kinetic energy from mechanical vibrations into electrical energy, allowing the substitution of batteries or cables for powering ultra-low-power devices like wireless sensor networks for structural health monitoring. For this aim, different magnet and coil configurations have been proposed for the design of these harvesters by several researchers. In this paper, four cylindrical “Magnet in-line coil” configurations with back steel, which include a typical single-magnet, a double-magnet array, and two proposed cylindrical Halbach magnet arrays of three and five magnets, are analyzed using the finite element method and compared in terms of their magnetic flux linkage and transduction factor. The numerical simulations are conducted in all cases with the same materials properties, coil parameters, and geometrical boundaries, the latter consisting of the total cross-sectional area of the magnets and the coil, the air gaps, and the total volume of the transducer mechanism. Furthermore, the design that provides the best performance is analyzed with two different coil configurations. It is finally found that the proposed cylindrical Halbach magnet array with three magnets and one-center coil presents the best results, reaching an average transduction factor of 95.83 Vs/m and a normalized power density of 19.72 mW/cm3g2.

Analysis of different cylindrical magnet and coil configurations for electromagnetic vibration energy harvesters

Electromagnetic vibration energy harvesting is a relatively new technology that transforms kinetic energy from mechanical vibrations into electrical energy, allowing the substitution of batteries or cables for powering ultra-low-power devices like wireless sensor networks for structural health monitoring. For this aim, different magnet and coil configurations have been proposed for the design of these harvesters by several researchers. In this paper, four cylindrical “Magnet in-line coil” configurations with back steel, which include a typical single-magnet, a double-magnet array, and two proposed cylindrical Halbach magnet arrays of three and five magnets, are analyzed using the finite element method and compared in terms of their magnetic flux linkage and transduction factor. The numerical simulations are conducted in all cases with the same materials properties, coil parameters, and geometrical boundaries, the latter consisting of the total cross-sectional area of the magnets and the coil, the air gaps, and the total volume of the transducer mechanism. Furthermore, the design that provides the best performance is analyzed with two different coil configurations. It is finally found that the proposed cylindrical Halbach magnet array with three magnets and one-center coil presents the best results, reaching an average transduction factor of 95.83 Vs/m and a normalized power density of 19.72 mW/cm3g2.

Numerical research on a vortex shedding induced piezoelectric-electromagnetic energy harvester

To widen the operation wind speed bandwidth of a classic vortex shedding induced vibration piezoelectric energy harvester, a piezoelectric-electromagnetic hybrid energy harvester based on vortex shedding induced vibration is designed. The hybrid vortex shedding induced vibration energy harvester (HVSIVEH) includes a vortex shedding induced vibration piezoelectric energy harvester (VSIVPEH) and an electromagnetic vibration energy harvester (EVEH). The electromechanical coupled vibration model of the hybrid structure was established. By comparing the variations of the output power as a function of the wind speed of the HVSIVEH and the classic VSIVPEH, it is found that the power response curve of the HVSIVEH has two peaks. The hybrid structure can broaden the working wind speed range. The lower the requirement on the output power level, the more obvious the effect of widening the wind speed range. By the solution and analysis of the electromechanical coupled model, better values of related parameters of the HVSIVEH are obtained. The first and second peaks of the output power of the HVSIVEH show better values of 1.9 and 2.2 mW, respectively, under these parameters.

A Microtester for Measuring the Reliability of Microdevices in Controlled Environmental Conditions.

A miniaturized reliability test system for microdevices with controlled environmental parameters is presented. The system is capable of measuring key electrical parameters of the microdevices while controlling the environmental conditions around the microdevices. The test system is compact and thus can be integrated with standard test equipment for microdevices. By using a feed-forward decoupling algorithm, the presented test system is capable of generating a temperature range of 0–120 °C and a humidity range of 20–90% RH (0–55 °C), within a small footprint and weight. The accuracy for temperature and humidity control is ±0.1 °C and ±1% RH (30 °C), respectively. The functionality of the proposed test system is verified by integrating it with a piezo shaker to test the environmental reliability of an electromagnetic vibration energy harvester. The proposed system can be used as a proof-of-technology platform for characterizing the performance of microdevices with controlled environmental parameters.

A novel high-power density, low-frequency electromagnetic vibration energy harvester based on anti-phase motion

The paper proposes a novel electromagnetic vibration energy harvester based on the concept of anti-phase vibration. Anti-phase motion is desirable in electromagnetic vibration energy harvesting applications as it results in a higher power output due to the increase in the relative velocity between the coil and the magnet components. The proposed device achieves anti-phase motion at any driving frequency due to a developed new design. The harvester was experimentally tested under a base input of 0.49 g, 0.38 g and 0.36 g, recording a power density of 765.3 Wm−3, 420.8 Wm−3 and 587.2 Wm−3 respectively under a resonant frequency of 11.8 Hz. Although the device has not yet been optimised, these values obtained are already comparable, if not higher than the recent previous works on vibration energy harvesting. In addition, the observed experimental results have well agreed with the results obtained through the mathematical model, derived in this study. The original design was then optimised to determine the optimum load resistance, mechanical arm length and component dimensions that would result in the maximum power output. Considering a base input of 0.36 g and the same friction and damping forces as obtained from the experiment, a power density of 1708.5 Wm−3 could theoretically be achieved under the same natural frequency.

A novel electromagnetic bistable vibration energy harvester with an elastic boundary: Numerical and experimental study

This paper comprehensively investigates a novel electromagnetic bistable vibration energy harvester with elastic boundary (BEH_EB). The BEH_EB consists of an inclined-spring-based bistable vibration energy harvester (BEH) and a vertically attached elastic boundary. The BEH (which does not have the elastic boundary) is employed as a comparative counterpart. Owing to the vertically attached elastic boundary of the BEH_EB, the distance between the two equilibria are wider than that of the BEH, which could enhance the inter-well response. As a result, this can significantly enhance the performance. Firstly, the governing equations of the BEH_EB are formulated, which are experimentally validated. Moreover, the experimental comparison between the BEH_EB and BEH is presented to verify the benefit of the elastic boundary. Afterward, the parametric studies are conducted to demonstrate the response amplitude advantages of the proposed BEH_EB, and the advantage of the potential energy distribution is mathematically interpreted. It is found that the elastic boundary brings additional dynamic coupling to reduce the depth of the potential energy well, which makes the BEH_EB easier to realize large-amplitude inter-well responses. Finally, the basin-of-attraction maps are presented to show the initial condition influence. The results show that the BEH_EB could enhance the occurring probability of the favorable inter-well responses in the low-frequency band, where the occurring probability could reach 100% at 2 and 3 Hz.

Influence of vehicle body vibration induced by road excitation on the performance of a vehicle-mounted piezoelectric-electromagnetic hybrid energy harvester

In order to study the influence of vehicle body vibration caused by road excitation on the output performance of a vehicle piezoelectric electromagnetic hybrid energy harvester, the theoretical analysis of the energy harvester is carried out, and a corresponding electromechanical coupling model is established. The hybrid energy harvester includes a flutter piezoelectric energy harvester (FPEH) and an electromagnetic vibration energy harvester (EVEH). Sweep frequency experiments and wind tunnel experiments were carried out to verify the correctness of the coupling model. By establishing the road-vehicle coupling differential equations solving module, the vehicle body vibration under different road surfaces was simulated, and the influence of different roads on output performance is analyzed. The results show that when vehicle body vibration is not considered, the cut-in speed of the harvester is 32 km h−1. When the vehicle speed is higher than 32 km h−1, vehicle body vibration caused by road roughness will suppress the overall output performance. When the vehicle speed is less than 32 km h−1, the vibration of the vehicle body will cause the energy harvester to have no obvious cut-in wind speed. And the higher the road level, the stronger the body vibration, and the better the output performance when the vehicle speed is less than 32 km h−1. Under E-class road with vehicle body vibration considered, it has already power output at a vehicle speed of 20 km h−1. When the vehicle speed reaches 57 km h−1, the output power of hybrid FPEH and EVEH reach 1.74 and 2.51 mW under E-class road (2.88 and 3.25 mW under A-class road), respectively.

Nonlinear dynamics and parametric study of snap through electromagnetic vibration energy harvester using multi-term harmonic balance method

Abstract Vibration energy harvester (VEH) has proven to be a favorable potential technique to supply continuous energy from ambient vibrations and its performance is greatly influenced by the design of potential structures. A snap-through mechanism is used in an electromagnetic energy harvester to improve its effectiveness. It mainly comprises of three springs that are configured so that the potential energy of the system has two stable equilibrium points. In this work, a harmonically base excited snap-through electromagnetic vibration energy harvester is investigated by analytical and semi-analytical method. The approximate analytical outcomes are qualitatively and quantitatively supported by semi-analytical method using multi-term harmonic balance method (MHBM).The bifurcation diagram of response current shows that snap-through electromagnetic vibration energy harvesters exhibits periodic intrawell, interwell and chaotic motion when the system parameters are varied. The influence of system parameters on the response of snap-through electromagnetic vibration energy harvester are examined. Nonlinearity produced by the snap-through oscillator improves energy harvesting so that the snap-through electromagnetic energy harvester can outperform the linear energy harvester in the similar size under harmonic excitation. A fitness function was formulated and optimization of the selected parameters was done using genetic algorithm. The parametric optimization leads to a considerable improvement in the harvested current from the system.

Physical realisation of a nonlinear electromagnetic energy harvester for rotational applications

Control and structural health monitoring sensors are becoming increasingly common in industrial and household applications due to recent advances reducing their manufacturing costs, size and power consumption. Nevertheless, providing power for these sensors poses a key challenge to engineers, particularly in system locations where limited access renders regular maintenance infeasible due to high associated costs. In the present work, the design and physical prototype testing of a nonlinear electromagnetic vibration energy harvester is presented based on a previously reported concept of the authors. The harvester is activated by the torsional speed fluctuations of a rotating shaft. Experimental testing in a rig driven by an electric motor confirms the harvester’s properties and the modelled oscillatory behaviour. This novel rotational vibration energy harvester concept may generate over 10 mW of electrical power for a broadband speed range of approximately 400 rpm (in the examined rotational system with set fluctuating speed) for wireless sensing purposes on rotating shafts.

A silicone based piezoelectric and electromagnetic hybrid vibration energy harvester

This paper describes the investigation of a novel low-cost silicone-based hybrid vibration energy harvester (SHVEH) for converting machine vibrations into useful electrical power for wireless sensor nodes. Due to a novel fabrication technique, the harvester has the benefit of incorporating two transduction mechanisms (electromagnetic and piezoelectric) into a single silicone housing for improved output power. In the devised fabrication technique, water-soluble tablets are used to develop a cavity inside the silicone structure for an embedded magnet to vibrate in. The developed device was characterized inside the lab at different acceleration levels. The SHVEH was found to be capable of delivering a combined output power of 1.12 mW and a power density of 52 µW cm−3. The SHVEH was able to deliver maximum open circuit voltages of 3 V and 28 mV AC via the piezoelectric and electromagnetic portions, respectively, at a resonant frequency of 110 Hz. Furthermore, after connecting the SHVEH to rectifier circuitry, the DC voltage levels obtained were 3.5 V and 35 mV from the piezoelectric and electromagnetic portions, respectively.

Colored Lévy Noise-Induced Stochastic Dynamics in a Tri-Stable Hybrid Energy Harvester

Abstract The piezoelectric and electromagnetic hybrid vibration energy harvester (HVEH) has proven to be a favorable option to deal with the low power generation issue and overcome the drawbacks of each individual transduction mechanism. Besides, colored Lévy noise consisting of small perturbations, large jumps, and correlation time turns out to be a relatively suitable tool for describing the complex environments. For the purpose of enhancing the harvesting performance of HVEH, the stochastic dynamics induced by colored Lévy noise in a tri-stable HVEH is mainly investigated in this paper. The stationary probability density, the largest Lyapunov exponent, the signal-to-noise ratio, and the mean harvested power are calculated to explore the stochastic dynamics of system, such as the stochastic response, the stochastic stability, the stochastic resonance (SR), and the energy harvesting performance. The results show that the colored Lévy noise can induce stochastic P-bifurcation, D-bifurcation, and SR phenomenon. In particular, the comparisons between colored Lévy noise and colored Brownian noise in dynamics and harvesting performance are also discussed in detail. It is found that the colored Lévy noise can make a greater contribution than colored Brownian noise in the effective voltage and help to improve the mean harvested power through the SR effect.

Silicon-chip based electromagnetic vibration energy harvesters fabricated using wafer-level micro-casting technique

This paper reports a silicon-chip based electromagnetic (EM) vibration energy harvester that is fabricated with a wafer-level micro-casting technique to form on-chip integrated 3D metal solenoids and magnet sliding channels. Many solenoids of 150-turn coil are simultaneously formed by filling molten ZnAl x alloy into the pre-micromachined solenoid moulds in one wafer within 7 min. After saw dicing to obtain the solenoid chips, a sliding permanent magnet for responding to environmental vibration is inserted into the pre-etched silicon channel inside the solenoid. Excited by external vibration, the magnet can slide in the channel to generate electricity. The size of the micro electro mechanical systems (MEMS) harvester chip is only 10.5 × 2.5 × 1.7 mm3. The experimental results show that the energy harvester can efficiently collect vibration energy in the environment. Under excited acceleration-amplitude of 49 m s−2 (i.e. 5 g) at the frequency of 24 Hz, the normalized power density (NPD) generated from the harvester reaches 12.38 μW cm−3 g−2. By comparing with reported non-MEMS wire-wound EM harvesters and on-chip piezoelectric/electrostatic ones, this silicon-chip based EM harvester exhibits much superior NPD.

Investigation on Electromagnetic Vibration Energy Harvesting in Water Distribution Control Valves

Control stations of a water distribution system monitor several variables such as the pressure, the flow, and the quality of water. For these monitoring tasks, wireless sensor networks with ultra-low power consumption powered by vibration-based energy harvesters as an alternative to the usage of batteries or wired connections might be a suitable option in these facilities. This article investigates the potential applicability of an electromagnetic vibration energy harvester prototype in different control valves of a water distribution system in the province of Barcelona by means of experimental measurements and numerical simulations. The low-amplitude vibration with random excitation is measured with piezoelectric accelerometers in three control valves under normal operating conditions to process each signal and determine the dominant frequency in the complete spectrum, which is found to be in the order of magnitude of kHz, and the dominant frequency in the range of 10 to 100 Hz, where commercial harvesters normally operate. Numerical simulations of the harvester prototype are conducted in all cases with the same materials, geometries, and coil parameters, generating a maximum RMS load voltage and output power when the harvester's natural frequency matches the dominant frequencies of each vibration signal. The maximum output power estimated in these simulations is 1573.04 nW with a corresponding RMS load voltage of 53.6 mV and optimal load resistance of 1830 Ω.

On the Optimization of a Multimodal Electromagnetic Vibration Energy Harvester Using Mode Localization and Nonlinear Dynamics

In this paper we study a generic model of a nonlinear quasiperiodic vibration energy harvester (VEH) based on electromagnetic transduction. The proposed device consists of multiple moving magnets guided by elastic beams and coupled by repulsive magnetic forces. A system of two degrees-of-freedom (DOFs) with tunable nonlinearity and mode localization is experimentally validated. The validated 2-DOFs harvester is optimized using a multiobjective optimization procedure to improve its harvested power and frequency bandwidth. An efficient criterion using the modal kinetic energy of the finite element model is proposed to quantify the energy localized in the structure perturbed zones. Afterward, this concept has been generalized to a 5-DOFs VEH with two perturbed DOFs oscillators and the optimal performances are derived using a multiobjective optimization. This proposed model enables a significant increase in the harvested power and frequency bandwidth by 101% and 79%, respectively, compared to that of the 2-DOFs device. Moreover, it has been shown that harvesting energy from two perturbed magnets among five provides almost the same amount of harvested energy and enhances the frequency bandwidth by 18% compared to those of the periodic system. Consequently, the harvester can be improved by reducing the transduction circuits number and the manufacturing cost.

Fully Integrated Microsolenoid With Closed Magnetic Circuit for High Power Density MEMS Electromagnetic Vibration Energy Harvesters

This letter presents a highly efficient microsolenoid integrated with a closed magnetic circuit to enhance the power density of microelectromechanical systems (MEMS) electromagnetic energy harvesters. Compared with most MEMS electromagnetic energy harvesters adopting an air-cored planar coil, a high permeability closed magnetic circuit is specifically designed and integrated inside the microsolenoid with multiple wire turns for higher electromechanical coupling, which contributes to the effective increased power density of the MEMS energy harvester. Moreover, the wafer-level microsolenoid is compatible with nonlinear springs, which bring higher power output over a wideband frequency range. At an acceleration of 1 g , the prototype shows a load power of 265.2 µW and normalized power density of 5.9 mW·cm-3·g-2 with a load resistance of 40.1 Ω, accompanied with a half-power bandwidth of 30 Hz. The fully integrated solenoid is compatible with other soft magnetic-material and frequency-broadening mechanisms, providing adequate potential for comprehensive performance enhancement of MEMS electromagnetic energy harvesters.