Julie Slaughter

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.

A compact Terfenol-D vector projector

In active sonar applications, it is desirable to have a directional, steerable sound source to accelerate the target localization process. A narrow cardioid beam pattern with approximately 78° beam width and rear side lobes 25 dB down can be generated by combining monopole, dipole, and quadrupole beam patterns with appropriate amplitudes and phases. A cylindrical array composed of eight Terfenol-D Tonpilz transducers arranged in two rings with each transducer pointing radially outward from a common center mass has been developed to generate narrow cardioid beam patterns. Focus during the design process was on minimizing size, maximizing the bandwidth, and maximizing the duty cycle. The diameter of the source is 0.19 wavelengths at the lowest operating frequency and 0.76 wavelengths at the highest operating frequency. Bandwidth of the source is greater than two octaves. Lumped parameter modeling and finite element modeling are used to demonstrate the monopole, dipole, quadrupole, and narrow cardioid beam p...

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.

Magnetostrictive compacted sonar transducer design

A compact modular high power magnetostrictive sound source that is capable of producing scanning Cardioid beams every 45 degrees in the horizontal plane and operates over one octave has been fabricated. The device consists of 8 transducer elements in the form of a ring that radiates acoustic energy radially outward. This design uses the operation principles of a peizoceramic transducer of similar design [J. L. Butler and A. L. Butler, J. Acoust. Soc. Am. 119, 3409 (2006)], which operated in a higher frequency band. The sound source can be driven to form omni‐directional, dipole, and quadrupole beam patterns. By combining the measured electrical drive and acoustic pressure amplitude and phase coefficients of these beam patterns a narrower type Cardioid beam pattern is generated. The transducer elements are of a tonpilz type vibrator consisting of magnetostrictive Terfenol‐D drive rods sandwiched between radiating head mass and a tail mass that is common to all elements with tie bolts consolidating the part...

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...

Performance of a Terfenol‐D‐driven folded shell projector

The folded shell projector (FSP), U.S. Patent No. 5,805,529, is a compact flextensional transducer originally developed for low‐frequency naval sonar applications. The FSP design radiates sound from a one‐piece corrugated shell. Because the shell is inherently waterproof, the projector does not need a boot. This reduces cost, improves linearity, increases thermal conductance, and, most importantly, results in stable performance with depth. The folded shell projector is being evaluated for a number of applications including towed array and expendible sonar transducers, community warning sirens, and loudspeakers. A folded shell projector driven by the giant magnetostrictive material, Terfenol‐D, has been developed. This transducer was originally designed for use as a community warning siren, however, tests both in air and in water were performed to investigate its response to different acoustic loads. Experimental results of the transducer performance are presented and compared with performance estimates fr...

Investigation of eddy current losses in laminated TERFENOL‐D drivers

One of the most significant loss mechanisms in TERFENOL‐D is eddy currents. Performance of the active material is reduced both by heating of the magnetostrictive element, and thus decreased magnetostrictive capability, and also by reduced magnetic field intensities in the active material. Accurate predictions of eddy current losses in TERFENOL‐D are necessary to avoid too few laminations, which reduces performance, or too many laminations, which unnecessarily increases costs. Eddy current losses in TERFENOL‐D drivers of different configurations were investigated for realistic operating conditions. Drivers of the same size with different lamination configurations were tested at frequencies from 10 Hz up to 8 kHz. At each frequency, energy loss per cycle per unit volume due to eddy currents was calculated. Comparisons were made between the experimental data, theory for infinite sheets, and finite element analysis. Very good agreement was achieved between the FEA and the experiments. Poor agreement was shown...

Effect of thickness variations on the sound radiation from beams

The effect that spatial thickness variations of a beam has on the beam’s far‐field sound radiation was studied. The steel beams that were used in the initial tests show that at low‐frequency ranges (500–1500 Hz) the thickness variations acted as discontinuities along the beam that increased sound radiation. However, at higher frequency ranges (2000–4000 Hz) the thickness variations, when spaced at certain intervals, acted as global stiffness changes and decreased the sound radiation. This decrease occurred when the spacing of the variations corresponded to a structural wavelength. Composite beams with thickness variations have also been built and tested. The spatial thickness variations appear to have a similar effect on the sound radiation as in the steel beams. The two data processing techniques used to evaluate the influence of the spatial thickness variations were a phase‐speed tracking filter to quantify wave propagation in the structure and a wave‐number domain filter to quantify far‐field radiation...