Galfenol Rods Research Articles

Shunted magnetostrictive devices in vibration control

Structural vibrations in rotating machinery may lead to imprecise motion control, excessive noise, or even structural damage. Magnetostrictive materials can dissipate unwanted vibrations via hysteresis, eddy currents, and joule heating while exhibiting an electrically-tunable elastic modulus. Harnessing this feature, this article presents a shunted magnetostrictive device that includes an iron-gallium (Galfenol) rod, a permanent magnet array, a flux return path, and shunt circuits. The stiffness tunability and damping of this passive device are measured under a 750 Hz sinusoidal axial compression for resistive, capacitive, and inductive shunt circuits. The effect of eddy currents stiffness and damping is investigated for the first time by comparing results from laminated and solid Galfenol rods. Solid Galfenol produces larger eddy current-based damping, while laminated Galfenol enables larger stiffness variation and total damping. This device demonstrates a power density of 19.83 mW cm−3 for vibration energy harvesting. The frequency-dependent behavior of the shunted device is tested from 5 Hz to 1 kHz for selected electrical loads.

Design and Output Characteristic Analysis of 3-D Micron-scale Actuator

A new type of 3-D micron-scale actuator is designed, which is mainly composed of four Galfenol rods, drive coils, base, magnetic yoke and output head. According to magnetostrictive model and structural dynamic model, the output characteristics of the actuator have been analyzed. The 3-D moving trail of the output head is controlled by the drive coils of the four rods. The actuator prototype is fabricated and experimental investigated. Good agreement is observed between the simulation and experimental results. The maximum output displacements of the X, Y and Z direction are 46 μm, 46 μm and 8.2 μm. Furthermore, when a pair of opposing rods works, the actuator has two modes of vibration under 1000 Hz. The resonant frequencies of the actuator are 522 Hz in Y direction and X direction. The results have proved that the actuator can realize varied 3-D displacement according to actual demands, and can be used in 3-D micron-scale field, such as surface mold polishing.

Design and analysis of a nested structure micro-displacement amplification mechanism for a galfenol-based actuator

In this paper, two galfenol rods are arranged in a nested structure to amplify the micro-displacement of an actuator. First, a finite element model of the actuator is developed to analyze the magnetization process of the actuator for different material of the sleeves. Secondly, the mathematical model of the actuator is established using the theory of magnetization, magnetostriction, and structural dynamics to describe the output displacement characteristics of the actuator at different frequencies; the hysteretic behavior of the actuator is taken into consideration and is modeled according to Jiles–Atherton hysteresis model. The experiments and results show that the output displacement of the dual galfenol rods-based actuator is significantly larger than that of a single galfenol rod-based actuator under the same experimental conditions, in addition to that, the proposed nested structure exhibits the advantages of occupying small volume and maintaining response dynamics even at high frequencies. Finally, using the established mathematical model, studies are carried out to analyze the feasibility of further amplification of the output displacement using more than two galfenol rods in a nested structure.

A hybrid Jiles-Atherton/Armstrong magnetization model considering uniaxial anisotropy for magnetostrictive alloy rods

A magnetization model for magnetostrictive alloy (Galfenol) rods with uniaxial anisotropy is established, based on the theory of the Jiles-Atherton model and the Armstrong model. The magnetization under different magnetic fields and applied stresses at different directions has been calculated by the constitutive model. The magnetic properties of a Galfenol rod were made and are consistent with the calculated results. The proposed model accurately describes the relationship between the magnetization and applied magnetic field under different stresses for Galfenol rods, in particular, and can be applied to general ferromagnetic materials with uniaxial anisotropy due to crystallography or shape.

Experimental Characterization of a Three-Rod Magnetostrictive Device for Energy Harvesting

Energy harvesting allows the conversion of environmental energy into electrical energy to feed low-power consumption electronics. In particular, this method can be exploited to supply wireless sensors nodes for structural health monitoring (SHM) when the electric network source is not present. Indeed, vibrations induced by vehicle traffic on a bridge could be converted into electrical energy, but suitable devices are needed. This paper presents experimental tests over a device based on three Galfenol rods, where electrical and magnetic parameters are changed and tested with different mechanical sources in order to seek the best performance.

Experimental evaluation of external and built-in stress in Galfenol rods

Magnetostrictive properties of Iron-Gallium alloys, such as the saturation of magnetic induction and magnetostriction can be derived from experimental measurements. It is known that, in order to exhibit the largest saturation magnetostriction, Galfenol requires the application of a suitable external compressive stress. In order to avoid a bulky system to provide such stress, a built-in stress could be added to the material through a technological process known as stress annealing. In this paper an experimental method to evaluate the stress applied to Galfenol rods is presented. Then, the method can be exploited either to evaluate the built-in stress or to develop a stress sensor. A concept device exploiting the method and its experimental characterization are presented.

Frequency-dependent, dynamic sensing properties of polycrystalline Galfenol (Fe81.6Ga18.4)

This paper presents the first measurement of Galfenol's frequency-dependent strain and magnetic flux density responses to controlled dynamic stress, from which frequency-dependent, effective material properties relating these quantities are calculated. Solid and laminated Galfenol (Fe81.6Ga18.4) rods were excited by 2.88 MPa compressive stresses up to 1 kHz under constant field and constant current conditions. Due to magnetic diffusion cut-off frequencies of only 59.3 to 145.7 Hz, the dynamic properties of the solid rod are found to vary significantly; this illustrates the inaccuracy of frequency-independent dynamic properties calculated via linear piezomagnetic models from experimental responses to electrical excitation. Conversely, the sensing properties of the laminated rod exhibit a weak dependence on frequency over the measurement range (i.e., a cut-off >1 kHz). The data are used to validate an existing model for mechanically induced magnetic diffusion. Loss factors and magnetomechanical energy densities are also presented and discussed in terms of loss separation, magnetic diffusion, and energy conservation.

Development of a Novel Miniature Shaftless Motor Using Iron–Gallium Alloy (Galfenol)

In this paper, we presented a novel miniature shaftless motor using the impact drive mechanism (IDM) that takes advantage of the friction and the inertia force to achieve the self-propelling motion. The proposed motor uses two U-shaped iron–gallium alloy (Galfenol) rods as the driving elements. Besides Galfenol, the motor consists of one permanent magnet that provides a bias magnetic field within Galfenol. This bias magnetic field helps the motor to generate the swing motion that can amplify the inertia force of the IDM motor. By controlling swing directions of two motor arms through the driving current, the consistent rotation of the motor is accomplished. The experimental result indicates that the proposed motor is able to achieve an angular velocity of 12.74°/s at 230 Hz. Because of the unique design of the motor, the motor can achieve a linear movement, and the result is briefly reported. The objective of future work is to realize an in-plane three-degree-of-freedom motor that can follow a designated trajectory.

Generalized Dynamic Modeling of Iron-Gallium Alloy (Galfenol) for Transducers

In this research, using the energy approach, a generalized dynamic model is derived for Galfenol (Iron-Gallium Alloy) based on the mechanical strain theory and the Jiles-Atherton model. Experiments have been conducted to measure the relationship between the strain and the magnetic field. Using experimental data, unknown parameters in the model have been identified by a developed optimization algorithm. Results show that the novel dynamic model with identified parameters is capable of describing the performance of the Galfenol rod. Simulation and experiment dynamic responses of Galfenol rods are derived. The simulation and the experiment both agree that the magnitude of the strain output decreases with the increase of the excitation frequency.

Finite element analysis of magnetostrictive vibration energy harvester

PurposeThe paper aims to analyze the behavior of the Galfenol rods under bending conditions that are employed in a vibration energy harvester by illustrating the spatial variations in stress and magnetic field.Design/methodology/approachThis paper describes a 3‐D static finite element model of magnetostrictive materials, considering magnetic and elastic boundary value problems that are bidirectionally coupled through stress and field dependent variables. The finite element method is applied to a small vibration‐driven generator of magnetostrictive type employing Iron‐Gallium alloy (Galfenol).FindingsThe 3‐D static finite element modeling presented here highlights the spatial variations in magnetic field and relative permeability due to the corresponding stress distribution in the Galfenol rods subjected to transverse load. The numerical calculations show that about 1.1 T change in magnetic flux density is achieved which demonstrates the effectiveness of the inspected vibration‐driven generator in voltage generation and energy harvesting. The model predictions agree with the experimental results and are coherent with the magnetostriction phenomenon.Originality/valueThis paper fulfils the behavior analysis of Galfenol rods under transverse load that includes both compression and tension. The compressive and tensile stresses contributions to change in magnetic flux densities in the Galfenol rods were calculated by which the effectiveness of the inspected vibration‐driven generator in voltage generation and energy harvesting is demonstrated.

Behavior of magnetic field–annealed Galfenol steel

An attractive feature of the Galfenol alloy system is the ability to impart enough uniaxial anisotropy into the alloy such that no pre-load mechanism is required to attain saturation magnetostriction. Stress annealing is typically employed to generate this anisotropy. Recent published results indicate that magnetic field annealing could generate sufficient anisotropy to provide full magnetostriction with no prestress, which will suffice for the majority of applications. The magnetic field annealing apparatus used in these experiments applies a constant 1 T magnetic field at a temperature between 300 °C and 700 °C in a 7.6 cm square × 15.2-cm-long cavity. The magnetic behavior of field-annealed Galfenol is compared to stress-annealed samples. Field-annealed Galfenol rods behave differently than stress-annealed rods. While the saturation strain values are equivalent, the magnetic field required to saturate the Galfenol is much less, 60 Oe versus 200 Oe, in the field-annealed state. This behavior is also exhibited in the flux density versus field. Both curves have a significant impact on device design. The type (mechanical or magnetic) and magnitude of stored energy largely determines the optimum magnetic bias point and impacts operational efficiency.

Verification of a method for measuring magnetostrictive parameters for use in transducer design modeling.

Previous studies have initiated an investigation into a new method of measuring the d33, μ33T, and s33H magnetostrictive constants of a given sample using a pair of Helmholtz coils, a laser vibrometer, and a sense coil. These parameters are calculated from measurements made as a function of dc magnetic bias and ac drive amplitude. This method contrasts with the traditional measurement technique which involves building the sample into a transducerlike device. The new method was demonstrated for laminated stress‐annealed Galfenol rods of high aspect ratio. Measurements obtained by this method appear credible and demonstrate good repeatability. For verification, the authors have returned to the established approach and designed a simple transducer using one of the measured Galfenol rods. The transducer was driven in air as a function of dc magnetic bias and ac drive amplitude. Data obtained from this transducer are compared to an analytical model that uses the material properties obtained experimentally with the new method. [This work was sponsored by the Office of Naval Research (Contract N00014‐06‐1‐0530) and by Etrema Products, Inc.]