Eric Summers

Magnetostriction of ternary Fe–Ga–X (X=C,V,Cr,Mn,Co,Rh) alloys

Binary iron-gallium (Galfenol) alloys have large magnetostrictions over a wide temperature range. Single crystal measurements show that additions of 2at.% or greater of 3d and 4d transition elements with fewer (V, Cr, Mo, Mn) and more (Co, Ni, Rh) valence electrons than Fe, all reduce the saturation magnetostriction. Kawamiya and Adachi [J. Magn. Magn. Mater. 31–34, 145 (1983)] reported that the D03 structure is stabilized by 3d transition elements with electron∕atom ratios both less than iron and greater than iron. If D03 ordering decreases the magnetostriction, the maximum magnetostriction should be largest for the (more disordered) binary Fe–Ga alloys as observed. Notably, addition of small amounts of C (0.07, 0.08, and 0.14at.%) increases the magnetostriction of the slow cooled binary alloy to values comparable to the rapidly quenched alloy. We assume that small atom (C, B, N) additions enter interstitially and inhibit ordering, thus maximizing the magnetostriction without quenching.

Magnetic and mechanical properties of polycrystalline Galfenol

The Zone Melt Crystal Growth Method (FSZM) has been used to produce polycrystalline Galfenol specimens, Fe81.6Ga18.4, with preferred {100} orientation. This crystal growth technique has advantages over conventional Bridgman methods in that zone rates used were at least an order of magnitude greater; 350 mm/hr versus 2-4 mm/hr. This material had measured magnetostrictions ranging from 168 ppm to 220 ppm compared to 290 ppm for a single crystal with a similar composition. It was discovered that upon machining a large increase in magnetostriction occurred, ~15%. Using Orientation Imaging Microscopy (OIM) techniques it was shown that the magnetostriction increase is due to the removal of off-axis grains located on the circumference of the FSZM samples. The room temperature mechanical properties were measured to be 72.4 GPa-86.3 GPa modulus of elasticity, 348 MPa-370 MPa ultimate strength, and elongation values of 0.81% - 1.2% depending upon zoning conditions.

Investigation of magneto-mechanical properties of Galfenol for coil-less magnetic force control using inverse magnetostrictive effect

We have been proposing a magnetic force control method using the inverse magnetostrictive effect of magnetostrictive materials. With a parallel magnetic circuit consisting of iron yokes and permanent magnet, the magnetic force exerting on the yoke can be varied by the mechanical stress applied to the magnetostrictive material. The characteristics of the magnetic force, such as stress-sensitivity and range of the variation, are mostly dependent on the material properties of the magnetostrictive material. So far we have mainly investigated the magnetic force using Terfenol-D (Tb-Dy-Fe alloy) and demonstrated its usefulness in practical applications. Recently, Galfenol, Iron-Gallium is widely noticed for alternative for the Terfenol with several advantages. Even lower magnetostriction, it is superior to the Terfenol with high piezomagnetic constant, low hysteresis loss, high saturation and good machinability. In this paper, we investigate the potential of the Galfenol for the magnetic force control method which can enlarge the variation range of the magnetic force and increase the stress-sensitively. The formulation of the magnetic force and experimental results of fundamental material properties and magnetic force of the Galfenol and Terfenol clarifies the merits of the Galfenol inherited from high saturation and high piezomagnetic constant. The correlation between the piezomagnetic constant and bias field is verified, providing magnetic circuit design strategy to make full use of the material properties of the Galfenol for future applications.

Machining of iron-gallium for microactuator

We investigate the machining properties of Iron-Gallium alloy for microactuator. Iron-Gallium is ductile magnetostrictive material with moderate magnetostriction ranging from 100 to 300ppm. The microactuator of Fe-Ga is expected to have advantages of simple configuration, low voltage driving, high robustness against external force and high temperature environment, compared with that of PZT. Here the rod of Fe-Ga prepared by FSZM technique was machined to distributed pillars of 1mm square by milling process. The comparison of magnetostrictions of machined and non-machined parts by strain gage confirms the strains different in pillars are inherited from the grain distribution and the milling process does not significantly deteriorate the material properties. The measurement of displacements by LASER Doppler vibrometer supports the validity of strain measurement. The success of the fabrication of the distributed pillars of 0.7 and 0.5mm square exhibits the potential of the milling process for Fe-Ga with high aspect ratio suitable for practical micro applications.

Variable compliance split‐cylinder transducer using Galfenol for frequency control.

The size of conventional split ring transducers is much smaller than a wavelength at operating frequency leading to a high Q resonance and limited operating bandwidth. This work investigated modifying the split ring structure to allow its resonant frequency to be adjusted under active control so that it is always operated at or near its resonance. Because the transducer is operated at resonance, the phase of its input impedance is approximately constant, simplifying the design of the transmit power amplifier and reducing the size and weight of the system. A high Q system is desirable for an actively tuned system resulting in very high efficiency and allowing the use of less expensive shell materials. The two variable compliance designs studied involve the use of Galfenol stiffener bars located at the nodal point/hinge point of the shell. By activating all or a portion of these bars, the compliance (stiffness) of the shell can be varied with a corresponding shift in resonance frequency. Two methods of compliance control are being investigated, one that switches the stiffness “on” and “off,” and one that allows continuous control using the “delta‐E” effect in Galfenol.

Galfenol low frequency slotted cylinder transducer.

The ability of Galfenol to be readily formed into various geometries can be exploited by device designers in their efforts to create innovative sources and sensors. In this research forged Galfenol alloy is utilized as the active source actuating a slotted cylinder transducer (SCT). Analytical modeling was utilized to determine the geometry necessary to achieve the notional performance specifications: 210‐dB source level, 750‐Hz resonance frequency, and 200‐Hz bandwidth. The final form factor was a Galfenol SCT with overall dimensions of 7.75‐in. diameter × 12‐in. length with a graphite composite shell material and Galfenol drivers comprising a rib‐like structure within the shell. The advantages this device has over existing SCTs are reduced cost, ease in manufacture and assembly, and improved reliability. Magnetic and mechanical models were combined in order to conduct three dimensional FEA analysis. The magnetic circuit was modeled in COMSOL MULTIPHYSICS and the acoustic model was built in ATILA. This p...

Galfenol technology, state‐of‐the‐art.

Galfenol is a recently discovered magnetostrictive material containing iron (Fe) and gallium (Ga) in various ratios based on desired properties. This alloy system exhibits several unique advantages over legacy smart materials such as Terfenol‐D and PZT. Galfenol can be readily machined using conventional machining techniques, it can be formed into various geometries using standard metal working practices such as forging and rolling, alloys can be produced with large internal pre‐stresses negating the necessary presence of external pre‐load mechanisms, and Galfenol can be welded to other ferrous materials without issue. All of these attributes make Galfenol an attractive new material for the applications engineer. In this presentation, the current state‐of‐the‐art of Galfenol technology will be discussed along with future technology development. Static and dynamic magnetic properties will be presented for various Galfenol alloys; in addition, mechanical properties and available processing routes will be di...

A galfenol force‐based energy harvester.

A force‐based energy harvester utilizing the magnetostrictive material, Galfenol, has been developed. Energy harvesters currently available primarily utilize a mass‐spring concept where optimal energy harvesting efficiency occurs around a distinct resonance frequency. Deviation from the tuned frequency significantly degrades energy harvesting performance. Galfenol was engineered into a bolt‐like configuration with a Galfenol rod welded to threaded stainless steel end pieces and pickup coils wound around the Galfenol. Dynamic forces are applied axially to the Galfenol resulting in a change in flux inducing voltage in the pick‐up coils. Because dynamic force is the mechanism generating power, the energy harvester works across a broad range of frequencies. Two different electronic packages were developed; a voltage doubler and quadrupler, which provided efficient energy conversion based on the frequency range of interest. The configuration of the Galfenol bolt resulted in an energy harvester capable of harve...