The field of energy harvesting has grown concurrently with the rapid development of portable and wireless electronics in which reliable and long-lasting power sources are required. Electrochemical batteries have a limited lifespan and require periodic recharging. In contrast, vibration energy harvesters can supply uninterrupted power by scavenging useful electrical energy from ambient structural vibrations. This article reviews the current state of vibration energy harvesters based on magnetostrictive materials, especially Terfenol-D and Galfenol. Existing magnetostrictive harvester designs are compared in terms of various performance metrics. Advanced techniques that can reduce device size and improve performance are presented. Models for magnetostrictive devices are summarized to guide future harvester designs.

http://iopscience.iop.org/article/10.1088/1361-665X/aa8347/pdf

Review of magnetostrictive vibration energy harvesters

This article investigates the modeling and design of vibration energy harvesters that utilize iron-gallium (Galfenol) as a magnetoelastic transducer. Galfenol unimorphs are of particular interest; however, advanced models and design tools are lacking for these devices. Experimental measurements are presented for various unimorph beam geometries. A maximum average power density of 24.4 and peak power density of 63.6 are observed. A modeling framework with fully coupled magnetoelastic dynamics, formulated as a 2D finite element model, and lumped-parameter electrical dynamics is presented and validated. A comprehensive parametric study considering pickup coil dimensions, beam thickness ratio, tip mass, bias magnet location, and remanent flux density (supplied by bias magnets) is developed for a 200 Hz, 9.8 amplitude harmonic base excitation. For the set of optimal parameters, the maximum average power density and peak power density computed by the model are 28.1 and 97.6 respectively.

https://iopscience.iop.org/article/10.1088/0964-1726/24/12/125019/pdf

Modeling and design of Galfenol unimorph energy harvesters

Heavy haul trains used to transport commodities are generally very long and operated by a single individual. Owing to high noise levels from the rolling stock displacement, the driver cannot notice failures in the compartments. It is practically impossible to visually inspect the wagons located far from the locomotive. Sensors that can measure in-train forces may improve the train’s operation, indicating potential failures and preventing accidents and derailments. However, the freight cars employed in most of the railroads are not equipped with electric power sources, making inspections unlikely. Therefore, an energy harvesting system must be developed for the sensors to avoid the need for periodic battery charging or replacement. As a high level of kinetic energy is present in the rolling stock, a vibration energy harvester (VEH) system is an acceptable alternative. Among VEH devices, multi-beam piezoelectric materials used in planar zigzag (PZ) or orthogonal spiral outer fixed (OSo) configurations can be effective alternatives. These can be powered by low-frequency strains readily available in the freight cars. This study investigates the optimum geometries of PZ and OSo aiming to increase the generated power and minimize the structure mass with a focus on their application to ore wagons. Among the optimum solutions, the OSo geometry generates the maximum power, up to 20.93 mW, which is sufficient to feed some critical devices. Conversely, the PZ configurations present the highest energy density, up to 16.595 mW/kg(m s−2)2, which allows for a more suitable solution to be combined in serial and/or parallel pack configurations.

Optimizing strain energy extraction from multi-beam piezoelectric devices for heavy haul freight cars

Two-dimensional dynamic model for composite laminates with embedded magnetostrictive materials

A study on iron-gallium (Galfenol) unimorph harvesters is presented which is focused on extending the power density and frequency bandwidth of these devices. A thickness ratio of 2 (ratio of substrate to Galfenol thickness) has been shown to achieve maximum power density under base excitation, but the effect of electrical load capacitance on performance has not been investigated. This article experimentally analyzes the influence of capacitive electrical loads and extends the excitation type to tip impulse. For resistive-capacitive electrical loads, the maximum energy conversion efficiency achieved under impulsive excitation is 5.93%, while the maximum output power and output power density observed for a 139.5 Hz, 3 m/s2 amplitude sinusoidal base excitation is 0.45 W and 6.88 mW/cm3, respectively, which are 8% higher than those measured under purely resistive loads. A finite element model for Galfenol unimorph harvesters, which incorporates magnetic, mechanical, and electrical dynamics, is developed and v...

Influence of electrical impedance and mechanical bistability on Galfenol-based unimorph harvesters:

Design and modeling of a bi-laminate, Galfenol-driven composite beam is presented in which the elasticity of the adhesive layer is considered. The optimal thickness ratio necessary to maximize the tip deflection is found by minimization of the internal energy of the beam. Model simulations show that use of a substrate material with high modulus leads to larger tip deflections. Stainless steel was therefore utilized as substrate in the experiments. In order to reduce eddy currents, a laminated silicon steel frame was employed to magnetize the beam. A dynamic model is proposed by coupling the structural dynamics of the beam and adhesive layer with the magnetostriction generated by the Galfenol layer. The latter is described with a linear piezomagnetic law with uniform magnetic field distribution along the length of the beam. Galerkin discretization combined with Newmark numerical integration are employed to approximate the dynamic response of the beam. The model is shown to describe both the transient and s...

Optimization and Dynamic Modeling of Galfenol Unimorphs

This article presents a fully coupled, nonlinear model for the dynamic response of Galfenol-driven unimorph actuators in a cantilever configuration. The hysteretic magnetomechanical behavior of Gal...

Lu Quanguo

Papers

Optimization and Dynamic Modeling of Galfenol Unimorphs

Nonlinear model for Galfenol cantilevered unimorphs considering full magnetoelastic coupling