Magnetostrictive Harvester Research Articles

Modeling and efficiency maximization of magnetostrictive energy harvester under free vibration

Vibration energy harvesting is becoming increasingly attractive in line with the development of wireless sensor technologies. Magnetostrictive materials inherently exhibit high mechanical strength and are thus suitable for various applications and mass manufacturing of energy harvesting devices. Many studies have been conducted to increase the output power of harvesters, and some utilized analytical methods. However, the optimization methods often take into account only the resonant frequency of the system under forced vibration. These models can produce correct predictions only when steady-state harmonic excitation inputs are considered.In this study, we propose the modeling and optimization method for a cantilever-type magnetostrictive harvester under free vibration. The cantilever has a double-beam structure composed of two parallel Fe-Ga beams with pickup coils. In the modeling, the shape function of the cantilever-type magnetostrictive energy harvester was derived based on the continuity of the internal force and magnetic flux. Hamilton’s principle for an electromagnetic-mechanically coupled system was derived from the virtual work principle. The equation of motion, magnetic circuit equation, and electric circuit equation of the system were respectively derived from the corresponding Euler–Lagrange equations. The harvestable energy of the magnetostrictive energy harvester was calculated by using the symmetric property of eigenvalues. In the efficiency maximization of the harvestable energy, we found that the optimal solution differs depending on the type of given energy. The optimal parameters to maximize the energy efficiency to potential energy and kinetic energy are respectively derived in the form of algebraic solutions. Experimental validation was conducted by measuring the energy harvesting efficiency at different loads.

Working characteristics of a magnetostrictive vibration energy harvester for rotating car wheels.

The practice of harvesting vibration energy from machine tools, windmill blades, etc., and converting it into electric energy to power low-power electronic circuits has attracted wide attention from experts and scholars. Abundant vibrations that exist in the moving vehicle can be harvested to power sensors in tire pressure monitoring. In this paper, for the first time, a device is proposed to harvest the rotational vibration energy with the iron-gallium alloy (magnetostrictive material) as the core material. Such a device utilizes the coupling characteristics of Villarreal effect and Faraday electromagnetic effect to convert the vibration energy generated by the moving vehicle into electric energy. Upon completion of the design of the magnetostrictive rotational vibration energy harvester, the influence law of key factors, including substrate material, substrate size, and pre-magnetization field arrangement on the harvesting capability of the device, was studied in detail through experiments. An electric motor and vibration exciter were used to apply varied excitation forms to the harvester, and the output patterns of the harvester under conditions of wheel rotation, road bumps, and random vibration were fully analyzed. In addition, the correlation between the deformation of the cantilever beam and harvester performance was also investigated. The results have shown that at the acceleration of 9.6 g and the rotational speed of 90 r/min, the harvester can reach the output voltage of 1.22 V. Consequently, it demonstrates the feasibility of employing the magnetostrictive harvester to gather rotational vibration energy and provides theoretical guidance for further and deeper research on the harvester.

Parameter optimization of magnetostrictive bistable vibration harvester with displacement amplifier

The vibration harvester can transform the ambient vibration energy into electrical energy for the use of microelectronic equipment. Currently, the introduction of bistable structure in magnetostrictive harvester makes the system have two equilibrium states, thus the output capacity of the system is improved. In order to further improve the working ability and its ability to harvest vibration of magnetostrictive bistable harvester with displacement amplification mechanism, the identification of the key parameters of the magnetostrictive bistable vibration harvester's mathematical model are first proposed in the paper. The accurate values of system damping, electromechanical coupling factor, piezomagnetic coefficient and permeability are obtained. On this basis, bistable structure and displacement amplification mechanism in the harvester are optimized, including the repulsive permanent magnets distance in the bistable structure, mass ratio and stiffness ratio between the bistable structure and the displacement amplification mechanism. Finally, the working ability of the optimized prototype is tested through experiments. The results show that the output voltage and electrical power of the optimized prototype are increased by 2∼4 times and 4∼15 times compared with the unoptimized prototype. Under the excitation amplitude of 7.84 m/s2, the voltage of the optimized prototype reaches 2.96 V, and the electrical power reaches146.032 mW.

Design and fabrication of rotary magnetostrictvie energy harvester for knee-joint wearable applications

PurposeThis paper aims to present the design and fabrication of a rotary magnetostrictive energy generator, using to harvest the rotation energy of human knee joint.Design/methodology/approachA rotary magnetostrictive energy generator is presented in this paper. The harvester consists of six movable flat Terfenol-D rods, surround by the picked-up coils respective, and alternate permanent magnet (PM) array fixed in the upper cover of the stator. The harvester rotates like as a stepper motor, which has rotary electromagnetic power generating effect and impacted magnetostrictive power generating effect in its rotation. Modeling and simulation are used to validate the concept. A prototype of harvester is fabricated and subjected to the experimental characterization.FindingsThe size of proposed structure is control as 77 cm3, and its mass is about 0.21 kg. Huge induced voltage generated in the short-time impact situation, and that induced voltage in the harvester can up to 18.6 V at 0.32 s stepper rotation. Also, the presented harvester has good harvesting effects at low frequency human walking situation, which is suitable to be used for future researches of wearable knee joint applications.Originality/valueA new concept of magnetostrictive harvester is presneted, which will be benefit for the application of human knee joint wearable. Also, this concept will give us more idea for collection of human movement energy.

Small-signal modeling and optimal operating condition of magnetostrictive energy harvester

Magnetostrictive energy harvesting has drawn attention in recent years for its high energy conversion efficiency and environmental durability. Magnetostrictive harvesters are mainly composed of giant magnetostrictive material, a magnetic circuit, and an electric circuit, which involves complex mechanical-electromagnetic coupled problems. Therefore, in many studies, the analysis of such device was implemented by finite element method. However, numerical calculation generally requires a great deal of time and does not provide adequate physical understanding of the effect of the design parameters on the harvester characteristics.In many previous studies, magnetostrictive harvesters have been operated under a small-signal vibration imposed over a constant prestress and magnetic bias. In such operating conditions, linearized small-signal models can be used to derive important analytical expressions for the harvester characteristics and their dependency on the design parameters. This paper presents the linearized modeling of a magnetostrictive energy harvester using linearized constitutive equations. The energy loss due to eddy currents is also considered for high-frequency application. The influence of parameter variation on the output power is investigated from the algebraically obtained output power, and the existence of an optimal value in resistance and capacitance of the electric circuit is discussed. These optimal design parameters are also presented in form of an algebraic solution. The obtained output power is finally proven to fit with experimental results when an appropriate permeability and magnetostrictive constant are given.

Modeling and Optimization Analysis for Base-Excited Magnetostrictive Vibration Harvester

Due to the low vibration frequency and weak vibration energy in natural environment, the vibration energy harvester is faced with the problem of low power and low adaptability and becoming particularly difficult in actual conditions. It is necessary to improve the harvesting capacity and efficiency by optimizing the parameters of the harvester, making full use of the energy of low and unstable atmospheric vibrations. In this paper, a mathematical model is established for the cantilever magnetostrictive vibration harvester under the base excitation, including the mechanical deformation of the composite beam, and the electromagnetic results produced thereof. The mechanical-magneticelectric energy conversion relationship is duly taken into account. The additional weight, coil parameters, external resistance and other parameters of the harvester are optimized and analyzed through numerical simulation. In addition, the theoretical results are analyzed and discussed via comparison with experiments. Finally, the effects of the above factors are assessed, which allows us to obtain the optimal winding length, number of turns of the coil, and optimal tip additional mass. The experiment result shows that the optimized magnetostrictive harvester can output 12.07[Formula: see text]mW power to the external resistor under the condition of 1[Formula: see text]g acceleration mechanical vibration, with normalized power density reaching 40.2[Formula: see text]mW/cm3/g. Moreover, the optimized magnetostrictive harvester can successfully supply power for the LED display screen of the temperature sensor and a low-power thermometer.

Analysis of a Magnetostrictive Harvester With a Fully Coupled Nonlinear FEM Modeling

A force-driven kinetic energy harvester, designed to be excited with impulse-like mechanical loads, is presented. Energy harvesting is a promising technique to feed wireless sensor networks. The proposed device exploits three rods of Galfenol and has been modeled through FEM COMSOL Multiphysics with nonlinear fully coupled characteristics. They consider the general behaviors of magnetostrictive materials and are compatible with thermodynamics. The preliminary results of the time-domain simulations, with an impulse-like force applied, have been compared with experimental results showing a good agreement. Moreover, the proposed nonlinear modeling has shown better performances with respect to software built-in magnetostrictive models. At the same time, further modeling improvements seem to be needed in the future to better fit the harmonic content of the free evolution of the device.

Enhanced the capability of magnetostrictive ambient vibration harvester through structural configuration, pre-magnetization condition and elastic magnifier

Vibration energy harvesting, which converts the mechanical vibrations that are commonly available in the surrounding environment to electrical energy, can realize self-power sensing, control and actuation, with the advantages of convenience, energy saving, eco friendliness and sustainability. However, it has some weakness, such as low output power, low efficiency, poor environmental adaptability and low reliability, which restrict its practical applications. It is necessary to optimize the harvester's structure, bias conditions and so on to adapt to the characteristics of ambient vibration, and then enhance the mechanical energy harvesting capability. This paper focuses on improving capability of the cantilever magnetostrictive harvester which is a new technology and still in the stage of proof-of working mechanism and concept prototype design. It systematically clarified the qualitative laws of the major factors affecting harvesting performance, including geometry, bias conditions, etc. Moreover, considering the low frequency characteristics of ambient vibration, it proposed an elastic magnifier with additional mass which can simultaneously enhance vibration harvesting, reduce resonance frequency and broaden effective frequency range. It was experimentally verified that the optimized magnetostrictive harvester can convert the mechanical vibration of 1 g acceleration into the voltage of 1210 mV. It was able to output 11 mW power to a load and the normalized power density reached to 18.3 mW/cm3/g. The magnetostrictive harvesting prototype successfully powered for multiple light emitting diode lamps, multiple digital display tubes and a low power electronic meter.

Modeling and characterization of permendur cantilever beam for energy harvesting

This article presents the development of a cantilever harvester made of permendur with tip excitation. In the beginning, the dynamic behavior of the tip-mass beam harvester subjected to a harmonic bending force at the free-end has been studied. Also, the magneto-mechanical model, rotating unbalance equations and Faraday's Law have been combined to present the general model for generated power. Furthermore, damping coefficients have been elaborately measured and considered in the modeling of magnetostrictive harvester and prediction of optimum load to generate the maximum power. Good agreement between analytical and experimental results shows that the model is able to predict the behavior of harvester under the vibration with tip excitation and can find the optimum external load to have maximum power. Experiment results show that the maximum output power is 6.81 μW/cm3 and this power happens when the harvester is connected to a 0.63 Ω external load. Compared to other magnetostrictive harvesters, Permendur shows lower power density. However, its harvested power is enough to energize μW electrical devices at a reasonable cost. The presented results in this paper can be utilized as a design guideline for future investigations to optimize vibration-based magnetostrictive energy harvesters with tip excitation.

Complexification-Averaging Analysis on a Giant Magnetostrictive Harvester Integrated With a Nonlinear Energy Sink

The present study aims to investigate the steady-state response regimes of a device comprising a nonlinear energy sink (NES) and a giant magnetostrictive energy harvester utilizing analytical approximation. The complexification-averaging (CX-A) technique is generalized to systems defined by differential algebraic equations (DAEs). The amplitude-frequency responses are compared with numerical simulations for validation purposes. The tensile and compressive stresses of giant magnetostrictive material (GMM) are checked to ensure that the material functions properly. The energy harvested is calculated and the comparison of transmissibility of the apparatus with and without NES–GMM is exhibited to reveal the performance of vibration mitigation. Then, the stability and bifurcations are examined. The outcome demonstrates that the steady-state periodic solutions of the system undergo saddle-node (SN) bifurcation at a certain set of parameters. In the meantime, no Hopf bifurcation is observed. The introduction of NES and GMM for vibration reduction and energy harvesting brings about geometric nonlinearity and material nonlinearity. By computing both the responses of the primary system equipped with the NES only and the NES–GMM, it is indicated that the added GMM can dramatically modify the steady-state dynamics. A further optimization with respect to the cubic stiffness, the damper of NES, and the amplitude of excitation is conducted, respectively. The boundary where the giant magnetostrictive energy harvester is out of work is pointed out as well during the process of optimizing.

Analysis of an operator-differential model for magnetostrictive energy harvesting

We present a model of, and analysis of an optimization problem for, a magnetostrictive harvesting device which converts mechanical energy of the repetitive process such as vibrations of the smart material to electrical energy that is then supplied to an electric load. The model combines a lumped differential equation for a simple electronic circuit with an operator model for the complex constitutive law of the magnetostrictive material. The operator based on the formalism of the phenomenological Preisach model describes nonlinear saturation effects and hysteresis losses typical of magnetostrictive materials in a thermodynamically consistent fashion. We prove well-posedness of the full operator-differential system and establish global asymptotic stability of the periodic regime under periodic mechanical forcing that represents mechanical vibrations due to varying environmental conditions. Then we show the existence of an optimal solution for the problem of maximization of the output power with respect to a set of controllable parameters (for the periodically forced system). Analytical results are illustrated with numerical examples of an optimal solution.

A Setup for the Performance Characterization and Traceable Efficiency Measurement of Magnetostrictive Harvesters

This paper addresses the assessment of the performance and the efficiency of direct force magnetostrictive harvesters. A suitable test rig is presented, and its characteristics are discussed. Moreover, this paper shows some harvester parameters able to influence the measurement results. The setup measures the electromechanical energy conversion properties of direct force harvesters, with a relative expanded uncertainty in the 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> range for the output power and 6 · 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> for the efficiency. The system has been employed to characterize a novel harvester having a maximum measured efficiency of ~32%.

Effects of hysteresis and eddy currents in magnetostrictive harvesting devices

The paper tackles the analysis of the magnetostrictive energy harvesting phenomena by formulating a model where the hysteretic static characteristic of the material and eddy currents induced by Villari effect are taken into account. The study aims to analyze the main loss mechanisms involved in this kind of devices, highlighting the impact of the hysteretic material behavior with respect to the linear and non-linear memoryless approaches.