Magnetostrictive Iron-Gallium Research Articles

MEMS Package for an Iron–Gallium Nanowire-Based Acoustic Sensor

A novel nanowire-based acoustic sensor incorporating cilia-like nanowires made of magnetostrictive iron–gallium (Galfenol) alloy has been designed and fabricated using micromachining techniques. The sensor and its package design are analogous to the structural design and the transduction process of a human-ear cochlea. The sensor responds when nanowires shear against the fixed membrane, in response to the motion of the flexible membrane on interaction with the acoustic waves. This results in a change in the magnetic flux in the nanowires, which is converted into electrical voltage by a giant magnetoresistive (GMR) sensor. As the acoustic sensor is designed for underwater applications, packaging is a key issue for the effective working of this sensor. A good package should provide a suitably protective environment to the sensor, while allowing sound waves to reach the sensing element with a minimal attenuation. In this paper, design efforts aimed at producing this microelectromechanical (MEMS) bio-inspired acoustic transducer have been detailed along with the process sequence for its fabrication. Package materials including external enclosure and fluid medium have been identified based on their acoustic performance in water by conducting several experiments to compare their impedance and attenuation characteristics and moisture absorption properties.

Magnetostrictive Ultrasonic Waveguide Transducer for In-Pile Thermometry

Real-time and reliable temperature measurement on nuclear fuels is crucial for the safe operation of existing pressurized-water reactors and future advanced nuclear reactors. Magnetostrictive materials deform when subjected to a magnetic field or exhibit magnetization variation when stressed. Based on these properties, this study prototyped an ultrasonic thermometer (UT) consisting of a magnetostrictive waveguide, a dc coil providing appropriate magnetic biasing, and an ac coil generating an acoustic impulse and detecting the resulting acoustic echoes. By tracking the time of flight between the excitation pulse and the echoes, the UT can potentially detect nuclear fuel cladding temperature from a long distance. In this study, magnetostrictive iron–gallium alloys, or Galfenol, were selected as the waveguide due to their large magnetostriction, superior temperature survivability, excellent radiation resilience, and high mechanical robustness. A multiphysics finite-element model considering electrical, magnetic, and mechanical dynamics in the magnetostrictive UT was then developed. The model exhibited an error of 0.24% in time-of-flight simulation and, therefore, enabled computer-aided design and guided signal processing. Between room temperature and 120 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> C, the new Galfenol-based UT exhibits a linear sensitivity of 162.8 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\times 10{^{-6}} {^\circ }$</tex-math></inline-formula> C <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{-1}$</tex-math></inline-formula> , which is 51.7% higher than a previous magnetostrictive UT based on iron–cobalt–vanadium alloys.

Magnetostrictive iron–gallium alloy harvester with efficient two-mode AC–DC converting technology for effective vibration energy harvesting

A magnetostrictive vibration energy harvester based on an iron–gallium alloy composite cantilever beam is developed, and its capability is optimized from the aspects of bias magnetic field and the number of active layers. To solve the issue of low and irregular output voltage, it designs a converter suitable for a low-power harvester to make full use of the generated electric energy. A set of AC–DC converters with two working modes is designed by using the multiple voltage rectification method, which is able to directly drive low power load or store energy to supply power to higher power load. Through theoretical simulation and experiment, the converter’s characteristics, such as rectifier and filter characteristics, energy storage, and release process are systematically studied and tested. 1 V AC output voltage of the harvester is able to be converted into 5 V DC voltage after being processed by the converter. The proposed harvester provides an excellent vibration harvesting capacity that the AC normalized power density (power density per volume and acceleration) reaches 7.4 mW/(cm3/g). The harvesting system with the two-mode converter has achieved a high normalized DC output power vs AC input voltage of 630 µW/V. We have applied the harvester and converter for a low power electronic meter, which can work normally and display the time, temperature, and humidity in the laboratory. In addition, we have also applied the harvesting system for a higher power (1.2 W) electric fan with a universal serial bus (USB) port. After battery charging and IP5306 voltage boosting, the harvester meets the normal operation requirements of an electric fan with a USB port and it is able to operate normally.

Analysis of the Key Factors Affecting the Capability and Optimization for Magnetostrictive Iron-Gallium Alloy Ambient Vibration Harvesters.

The basic phenomena of a cantilever energy harvesting device based on iron-gallium alloy magnetostrictive material for low frequency were systematically studied. The results highlighted how the physical parameters, geometric structure and bias conditions affected the vibration harvesting capacity through a thorough experimental aimed at enhancing the vibration energy harvesting capacity through an optimal design. How the performance is affected by the configuration of the multi-layers composite beam, material and dimensions of the elastic layer, arrangement position and number of bias magnets, the matching load resistance and other important design parameters was studied in depth. For the first time, it was clearly confirmed that the magnetic field of bias magnets and electromagnetic vibration shaker have almost no effect on the measurement of the voltage induced from the harvester. A harvesting power RMS up to 13.3 mW and power density RMS up to 3.7 mW/cm3/g was observed from the optimized prototype. Correspondingly, the DC output power and power density after the two-stage signal processing circuit were up to 5.2 mW and 1.45 mW/cm3/g, respectively. The prototype successfully powered multiple red light emitting diode lamps connected in a sinusoidal shape and multiple red digital display tubes, which verified the vibration harvesting capability or electricity-generating capability of the harvester prototype and the effectiveness of the signal converter.

The Usage of Hydroextrusion for Plastic Deformation of Magnetostrictive Iron-Gallium Alloys

For the first time hydroextrusion process was chosen for Fe-Ga ingots deformation with a gallium content of 19 and 20 at.%. The samples were annealed at 950oC, followed by air cooling. Structure of deformation and primary recrystallyzation were investigated by the method of electron back-scattered diffraction (EBSD). The degree of hydroextrusion deformation achieved was 28 – 42 %. There was not found any crystallographic texture at such degree of deformation. The value of magnetostriction in recrystallization sample was about 100 ppm. Available in literature methods and approaches to creation of the Fe-Ga samples from the point of view of receiving high magnetostriction and also a possibility of machining of the samples are discussed.

A magnetostrictive biased magnetic field sensor with geometrically controlled full-scale range

A magnetic field sensor prototype is developed and tested in this work. The device exploits a Galfenol rod, i.e. a giant magnetostrictive Iron-Gallium alloy, integrated with a Fiber Bragg Grating. In particular, the full-scale range of the sensor can be modulated through the exploitation of the geometrically dependent effect of the demagnetizing field. Indeed, it pushes toward higher fields the magnetic saturation by producing a sort of magnetic shield in the material. As a consequence, the geometrical viewpoint is included into the frame of the entire design process, with the aim of investigate how it influences the detectability range and the performance of the sensor. Furthermore, a permanent magnet system providing a DC bias magnetic field has been designed and exploited to allow the device to be able to measure both negative and positive magnetic fields.

Dynamic Model for Magnetostrictive Systems With Applications to Damper Design

Magnetostrictive iron–gallium alloys are able to dissipate mechanical energy via eddy currents and magnetic hysteresis. The mechanically induced eddy current loss is determined by the piezomagnetic coefficient; the hysteresis loss is usually quantified by the phase lag. This study first characterizes these losses for research grade, -oriented, highly textured, polycrystalline $\mathrm{Fe_{81.6}Ga_{18.4}}$ within the structural frequency range (up to 800 Hz). The magnetic biasing is provided by applying a constant current of 500 mA on a pair of electromagnets; the mechanical excitation is a sinusoidal stress wave (3 $\pm$ 0.2 MPa) superimposed on a $-$ 20 MPa constant stress. As stress frequency increases, the piezomagnetic coefficient decreases from 32.27 to 10.33 T/GPa and the phase lag $|\Delta \phi |$ increases from 11.38 $^\circ$ to 43.87 $^\circ$ . A rate-dependent finite element framework decoupling eddy current loss and hysteresis loss is then developed. The model accurately reproduces the experimental results in both quasi-static and dynamic regimes. Guided by the knowledge of material properties and the finite element model, a coil-less and solid-state damper is designed which can attenuate vibrations before they propagate and induce structure-borne noise and damage. Modeling results show that the loss factor of this damper can be continuously tuned from 0 to a maximum value of 0.107 by adjusting the precompression on the magnetostrictive component.

Effect of hydrogen and magnetic field on the mechanical behavior of magnetostrictive iron–gallium alloy single crystal

Magnetostrictive Fe–Ga and other iron alloys are candidates for use in sensing, actuation and large-scale energy harvesting applications. Exposure to aqueous electrochemical environments is anticipated in some of these applications which could potentially introduce hydrogen into the alloy and cause severe ductility reduction due to the hydrogen embrittlement effect. In this work, the effect of hydrogen and magnetic field on the fracture behaviors of [100] oriented Fe–17.5at% Ga alloy single crystals are examined. Three-point bend test was used to measure the fracture stress. Hydrogen embrittlement was characterized by a change in fracture surface from a ductile fracture mode to a brittle cleavage type fracture. The cleavage fracture occurred along the (001) plane. Critical stress for the initiation of fracture was measured under different conditions and an upper bound for cleavage stress in these alloys is obtained. Applied magnetic field was seen to affect the fracture stress and strain of hydrogen charged sample. Acoustic emission signals collected during the test appear to be consistent with the fracture behavior.

Characterization of the magnetic properties of multilayer magnetostrictive iron-gallium nanowires

We investigate the magnetic properties of magnetostrictive iron-gallium (Galfenol, Fe100−xGax, 10≤x≤25 at. %) nanowires with magnetic force microscopy (MFM) and using micromagnetic modeling software (magpar). Wires with diameters of 150 nm were fabricated in alternating multilayered structures with Fe-Ga and Cu having aspect ratios of ∼2 and ∼0.5, respectively, with the goal of minimizing the relative contribution of shape anisotropy to magnetic domain alignment. Micromagnetic simulations of isolated Fe-Ga segments with these dimensions predict that (1) at remanence, two opposing vortex structures will form at the ends of a Fe-Ga segment, with a single domain wall in the middle of the segment and (2) traditional magnetic dipoles will form at the ends of the segment to align with a large (saturation) external magnetic field. MFM results are presented that support these models. At remanence, no contrast is observed in the MFM phase images. Magnetic poles become evident at the ends of the Fe-Ga segments when a magnetic field exceeding ∼300 Oe is applied along the length of the nanowire. The direction of the pole alignment is readily flipped by changing the direction of applied field by 180°. Additionally, MFM images show rotation of the magnetic poles in each Fe-Ga segment as they align with fields of ∼550 Oe applied at angles of ∼55° and ∼105° relative to the length of the nanowire. The MFM results support the simulation results and demonstrate that an aspect ratio of ∼2 will reduce shape anisotropy effects sufficiently in Fe-Ga nanowire that magnetization can lie off of the nanowire axis.

Modeling of Magnetomechanical Actuators in Laminated Structures

A magnetomechanical plate model (MMPM) has been developed to predict the elastic and magnetostrictive strains and mechanical stress in laminated structures with magnetostrictive and non-magnetic layers under the simultaneous effect of quasi-static mechanical stress and magnetic field. This model was obtained by combining an energy-based statistical magnetomechanical model with the classical laminated plate theory. The magnetomechanical plate model was used to study a unimorph structure having a magnetostrictive iron—gallium (Galfenol) patch attached to different non-magnetic substrates. The actuation response from the patch was obtained for in-plane axial magnetic field acting on the unimorph. The MMPM was used to predict the normalized tip displacement due to induced-strain actuation in a unimorph cantilever beam and the results were compared with existing modeling techniques. The model was used to study the effect of tensile and compressive axial pre-loads on the actuation response of the structure. A study was also performed to understand the effect of total thickness of the structure, the ratio of the active/ passive layer thickness and the effect of the mechanical properties of different substrate materials on the actuator performance. A non-dimensional parameter ST i (percentage strain transfer) was introduced to explain the behavior of the actuator in extension and bending dominated regimes and a critical thickness ratio (trc) was defined to demarcate these two regimes. The results demonstrate that the model captures the non-linearity in the magnetomechanical process and the different structural couplings.

The modeling of magnetomechanical sensors in laminated structures

A non-linear magnetomechanical plate model has been developed to predict the magneticinduction, elastic and magnetostrictive strain and mechanical stress in a laminatedstructure with magnetostrictive and non-magnetic layers under the simultaneous effect ofquasi-static mechanical stress and the magnetic field. This model was obtained by couplingclassical laminated plate theory to an energy-based statistical magnetomechanical model.The model was used to study a unimorph structure having a magnetostrictive iron–gallium(Galfenol) patch attached to a non-magnetic aluminum substrate. The sensingresponses from the patch were obtained for in-plane axial and shear forces as well asbending and twisting moments acting on the unimorph. The effect of the DC biasmagnetic field and the ratio of patch thickness to substrate thickness on the sensorperformance was studied. The results demonstrate that the model can capture thenon-linearity in the magnetomechanical process and the different structural couplings.