Zhangxian Deng

Major and minor stress-magnetization loops in textured polycrystalline Fe81.6Ga18.4 Galfenol

Major and minor magnetization versus stress loops under different bias magnetic fields from 0.8 kA/m to 8.0 kA/m in 0.8 kA/m steps were measured in research grade, ⟨100⟩ oriented, textured polycrystalline Fe81.6Ga18.4. Both compressive and tensile stresses were applied from −63 MPa to 63 MPa for major loop analysis. Minor loops were generated by superimposing a 4.0 Hz, 2.8 MPa amplitude sinusoidal stress on different dc compressive stresses ranging from −40.7 MPa to −5.6 MPa in 7.0 MPa increments. Bias magnetic fields were applied in two ways, constant field in the sample obtained using a controller and constant current to the excitation coils. An energy-averaged model and related optimization method are presented to compare the experiments with simulations. The slope of magnetic flux density versus stress, i.e., the materials sensitivity to stress, is quantified from major and minor loop measurements. The peak sensitivity at constant field is about 75 T/GPa for constant-field major loops, whereas it is ...

Modeling and design of Galfenol unimorph 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.

Magnetostrictive Vibration Damper and Energy Harvester for Rotating Machinery

Vibrations generated by machine driveline components can cause excessive noise and structural dam- age. Magnetostrictive materials, including Galfenol (iron-gallium alloys) and Terfenol-D (terbium-iron- dysprosium alloys), are able to convert mechanical energy to magnetic energy. A magnetostrictive vibration ring is proposed, which generates electrical energy and dampens vibration, when installed in a machine driveline. A 2D axisymmetric finite element (FE) model incorporating magnetic, mechanical, and electrical dynamics is constructed in COMSOL Multiphysics. Based on the model, a parametric study considering magnetostrictive material geometry, pickup coil size, bias magnet strength, flux path design, and electrical load is conducted to maximize loss factor and average electrical output power. By connecting various resistive loads to the pickup coil, the maximum loss factors for Galfenol and Terfenol-D due to electrical energy loss are identified as 0.14 and 0.34, respectively. The maximum av- erage electrical output power for Galfenol and Terfenol-D is 0.21 W and 0.58 W, respectively. The loss factors for Galfenol and Terfenol-D are increased to 0.59 and 1.83, respectively, by using an L-C resonant circuit.

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

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 / s 2 amplitude sinusoidal base excitation is 0.45 W and 6.88 mW / c m 3 , 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 validated using impulsive responses. A buckled unimorph beam is experimentally investigated. The proposed bistable system is shown to extend the harvester’s frequency bandwidth.

Experimental comparison of piezoelectric and magnetostrictive shunt dampers

A novel mechanism called the vibration ring is being developed to enable energy conversion elements to be incorporated into the driveline of a helicopter or other rotating machines. Unwanted vibration is transduced into electrical energy, which provides a damping effect on the driveline. The generated electrical energy may also be used to power other devices (e.g., health monitoring sensors). PZT (‘piezoceramic’) and PMN-30%PT (‘single crystal’) stacks, as well as a Tb0.3Dy0.7Fe1.92 (‘Terfenol-D’) rod with a bias magnet array and a pickup coil, were tested as alternative energy conversion elements to use within the vibration ring. They were tuned for broadband damping using shunt resistors, and dynamic compression testing was conducted in a high-speed load frame. Energy conversion was experimentally optimized at 750Hz by tuning the applied bias stress and resistance values. Dynamic testing was conducted up to 1000Hz to determine the effective compressive modulus, shunt loss factor, internal loss factor, and total loss factor. Some of the trends of modulus and internal loss factor versus frequency were unexplained. The single crystal device exhibited the greatest shunt loss factor whereas the Terfenol-D device had the highest internal and total loss factors. Simulations revealed that internal losses in the Terfenol-D device were elevated by eddy current effects, and an improved magnetic circuit could enhance its shunt damping capabilities. Alternatively, the Terfenol-D device may be simplified to utilize only the eddy current dissipation mechanism (no pickup coil or shunt) to create broadband damping.

Dynamic Characterization of Galfenol

A novel and precise characterization of the constitutive behavior of solid and laminated research-grade, polycrystalline Galfenol (Fe81:6Ga18:4) under under quasi-static (1 Hz) and dynamic (4 to 1000 Hz) stress loadings was recently conducted by the authors. This paper summarizes the characterization by focusing on the experimental design and the dynamic sensing response of the solid Galfenol specimen. Mechanical loads are applied using a high frequency load frame. The dynamic stress amplitude for minor and major loops is 2.88 and 31.4 MPa, respectively. Dynamic minor and major loops are measured for the bias condition resulting in maximum, quasi-static sensitivity. Three key sources of error in the dynamic measurements are accounted for: (1) electromagnetic noise in strain signals due to Galfenols magnetic response, (2) error in load signals due to the inertial force of fixturing, and (3) time delays imposed by conditioning electronics. For dynamic characterization, strain error is kept below 1.2 % of full scale by wiring two collocated gauges in series (noise cancellation) and through lead wire weaving. Inertial force error is kept below 0.41 % by measuring the dynamic force in the specimen using a nearly collocated piezoelectric load washer. The phase response of all conditioning electronics is explicitly measured and corrected for. In general, as frequency increases, the sensing response becomes more linear due to an increase in eddy currents. The location of positive and negative saturation is the same at all frequencies. As frequency increases above about 100 Hz, the elbow in the strain versus stress response disappears as the active (soft) regime stiffens toward the passive (hard) regime.

Modeling and design of Galfenol unimorph energy harvester

Magnetostrictive iron-gallium alloys, known as Galfenol, are a recent class of smart materials with potential in energy harvesting applications. Unimorph energy harvesters consisting of a Galfenol beam bonded to a passive substrate are simple and effective, but advanced models are lacking for these smart devices. This study presents a finite element model for Galfenol unimorph harvester systems. Experiments considering various design parameters such as pick up coil size, load resistance, beam thickness ratio, and bias magnetic field strength are conducted to guide and validate the modeling effort. If the free length of the Galfenol unimorph beam is considered as the effective length, the maximum average power density, peak power density, and open-circuit voltage amplitude achieved in experiments are 13.97 mW/cm3, 35.51 mW/cm3, and 0.66 V, respectively. By only considering the length of Galfenol surrounded by the pickup coil, the maximum average power density and peak power density are 23.66 mW/cm3 and 60.14 mW/cm3, respectively.

Characterization and finite element modeling of Galfenol minor flux density loops

This paper focuses on the development of a three-dimensional (3D) hysteretic Galfenol model which is implemented using the finite element method (FEM) in COMSOL Multiphysics. The model describes Galfenol responses and those of passive components including flux return path, coils and surrounding air. A key contribution of this work is that it lifts the limitations of symmetric geometry utilized in the previous literature and demonstrates the implementation of the approach for more complex systems than before. Unlike anhysteretic FEM models, the proposed model can simulate minor loops which are essential for both Galfenol sensor and actuator design. A group of stress-flux density loops for different bias currents is used to verify the accuracy of the model in the quasi-static regime.

Adaptive magnetoelastic metamaterials: A new class of magnetorheological elastomers:

This article reports means to significantly enhance the adaptation of static and dynamic properties using magnetorheological elastomers and demonstrates the enhancements experimentally. The tunability of traditional magnetorheological elastomers is limited by magnetic field strength and intrinsic magnetic–elastic coupling. This contrasts with recent efforts that have revealed large static and dynamic properties change in elastomeric metamaterials via exploiting internal void architectures and collapse mechanisms, although design guidelines have not been developed to adapt properties in real-time. Considering these benchmark efforts, this research integrates concepts from topologically controlled metamaterials and active magnetorheological elastomers to create and study magnetoelastic metamaterials that mutually leverage applied magnetic fields and reconfiguration of internal architectures to achieve real-time tuning of magnetoelastic metamaterial properties across orders of magnitude. Following detailed descriptions of the manufacturing procedures of magnetoelastic metamaterials, this article describes experiments that characterize the static and dynamic properties adaptation. It is found that by the new integration of internal collapse mechanisms and applied magnetic fields, magnetoelastic metamaterials can be reversibly switched from near-zero to approximately 10 kN/m in one-dimensional static stiffness and tailored to double or halve resonant frequencies for dynamic properties modulation. These ideas may fuel new research where geometry, magnetic microstructure, and structural design intersect, to advance state-of-the-art utilization of magnetorheological elastomers.

Quasi-static major and minor strain-stress loops in textured polycrystalline Fe81.6Ga18.4 Galfenol

The ΔE effect (Youngs modulus variation of magnetostrictive materials) is useful for tunable vibration absorption and stiffness control. The ΔE effect of iron-gallium (Galfenol) has not been fully characterized. In this study, major and minor strain-stress loops were measured under different bias magnetic fields in solid, research grade, ⟨100⟩-oriented, highly-textured polycrystalline Fe81.6Ga18.4 Galfenol. A 1 Hz, constant amplitude compressive stress was applied from −0.5 MPa to −63.3 MPa for major loop responses. Minor loops were generated by simultaneously applying a 4 Hz, 2.88 MPa amplitude sinusoidal stress and different bias stresses ranging from −5.7 MPa to −41.6 MPa in increments of about 7.2 MPa. Bias magnetic fields were applied in two ways, a constant field in the sample obtained using a proportional-integral (PI) controller and a constant current in the excitation coils. The ΔE effect was quantified from major and minor loop measurements. The maximum ΔE effect is 54.84% and 39.01% for consta...