The rare earths, both in elemental form and in compounds, are widely known as possessing many extraordinary magnetic properties. In this paper, we focus on the huge magnetically induced displacements (magnetostrictions) based upon the element terbium. A proper balance of magnetic anisotropy and magnetostriction, plus a proper choice of crystal axes lead to materials which can switch large quantities of energy between the internal (magnetic) and external (mechanical) states with the application of small triggering magnetic fields. Power densities 2000 times those of conventional magnetostrictive materials and 10-20 times those of typical piezoceramics are available. These materials are particularly valuable for smart systems where large energy transduction is needed such as active structure stiffening and active vibration control.

As a promising candidate of advanced smart materials Tb-Dy-Fe system has been studied for many years. It is well known that the boundaries (which exist in polycrystal and grain oriented crystals of magnetostrictive materials) heavily hinder the motion of domain walls. Therefore to eliminating those boundaries will improve their magnetostrictive behaviors to a large extent. A single crystal growth method (which is called: growth with magnetic levitation cold crucible in CZ technique) has been successfully developed in our lab. since a few years ago. Now bulk cubic Laves phase RFe2 TbxDy1-xFe1.95–2.0 single crystals with boundary free structure can be prepared. Studies have been focused on comparing the performances of polycrystal, grains oriented crystal with a single crystal of the same composition. Some results indicate that λs and d33 performed by the single crystal are much higher than the two former materials under the same conditions.

This paper reports the results of detailed TEM observations on [211] oriented single crystal samples of Terfenol-D. Domain structures are interpreted in terms of recent micromagnetic models developed by James and Kinderlehrer. Lorentz transmission electron microscopy was performed on a JOEL 120CX equipped with a low field objective lens. We also report for the first time energy-filtered magnetic domain images, recorded using a Gatan Imaging Filter on a JOEL 40000EX high resolution TEM. This observational mode allows for enhanced resolution and improved image contrast.

The thermo-mechanical properties of Terfenol-D thin films deposited on Si substrates werestudied by static and dynamic measurements of film/substrate composite cantilevers. The Curie transition, δE effect and mechanical damping of the film were measuredsimultaneously. The stress in the film was controlled by annealing below the recrystallization temperature and determined to vary from -500 MPa, compression, in as deposited films to +480 MPa, tension, in annealed films. The Curie temperature shifts from 80ºC to 140ºC as the tension increases while the structure of the film remains amorphous. The stress change induced by annealing also drastically effects the film's damping characteristics. The δE effect of the amorphous material, about 20%, wasused to estimate the magnetostriction, λs≈4.10-3.

The outstanding feature of amorphous magnetoelastic alloys is the controllability of the magnetic anisotropy energy, Curie point, magnetostriction and magnetic moment. This control of material characteristics, achieved by magnetic and stress annealing plus changes incomposition, is impossible in crystalline materials. The control allows the design of tactile and magnetic field sensors with special features and very high sensitivity. The materials discussed are prepared by rapid solidification through melt spinning in ribbon and wire geometries and magnetron sputtering onto substrates. As an example of the advantagesof sputtered material, an accelerometer on silicon micro-cantilevers is shown. I-t has nocoils. The basic magnetoelastic theory that governs tactile sensors is shown. Low-noise magnetic field sensors with novel twist anisotropies and Barkhausen instabilities in wiresare discussed.

We have measured the magnetomechanical coupling coefficient of Metglas®2605SC (Fe81B13.5C2) ribbons that were annealed into 1.27 and 0.8 cm diameter cylinders. Lengths ranged from 0.6 to 5 cm. A novel furnace was constructed in which a cylindrical magnetic field was supplied by a current carrying copper rod. During the annealing, a 300 A current created a circumferential field of more than 6400 A/m. Annealing temperatures ranged from 380 to 420 ºC. Large shifts in both the optimum bias field and the coupling coefficient as a function of length and diameter were found due to demagnetizing effects. Impedance vs. frequency measurements show large numbers of modes, some of which are field dependent. Effective coupling coefficientsof the lowest order longitudinal mode were calculated from impedance measurements by using k2 = 1-f2r/f2a, where fr, and fa. are the resonant and antiresonant frequencies respectively. Coupling coefficients for 5 cm long cylinders were as high as 0.58. When the demagnetizing factor is taken into account, we find material coupling coefficients as high as 0.89.

Suitability of specific materials for use in magnetomechanical sensors more often depends on combinations of properties than on an outstanding value of a single property. These combinations include ratios and products of properties from different physical families. While magnetic, magnetoelastic, electrical and strength properties often play key roles in determining the performance of the sensor, non-physical characteristics such as manufacturability, available forms, environmental compatibility, toxicity and costs strongly influence the device design and may well dominate the final choice of material. The development of materials specifically for use in this class of sensors is encouraged by their already broad and growing range of applicability.

This paper begins with a review of the current problems associated with the application of conventional magnetic-head-type shaft torque sensors. These sensors were first proposedin 1954. Newly developed low-profile magnetic heads for torque sensors which address the problems of the older type of sensors are then presented. The torque sensor which uses the lowprofile pick-up heads is described in detail. Experimental results showing the basicperformance of the torque sensor with carburized nickel chromium molybdenum steel shafts (SNCM 420 in JIS) are then described. In this combination of the heads and the shaft, thehysteresis of the inputoutput relationship is generally small and shows that the direction of traversal around the hysteresis loop changes as the amplitude of the excitation current changes. It is shown that an optimum operating condition exists for the torque sensorin which the hysteresis achieves a minimum value yet the sensitivity remains high. In a particular combination studied in this paper, the optimum excitation current was 0.3 A at the excitation frequency 60 kHz, where the total power loss at the pick-up heads was 0.37W. Under this operating condition, the hysteresis was extremely small, and the linearity was better than 0.6%.

It has been proved that the saturation magnetostrictive constant λs of Tb0.2 7Dy0.73Fe1.95 single crystal is greater than the polycrystal and grains oriented crystal with the terfenol compositions, especially for its large linear magnetostrictive strain. Th0.27Dy0.73Fel.95 single crystal also can produce large force and fast, precision motion at high efficiency and power levels. A proto-type micro positioning actuator with the single crystal was designed inour lab. The structure and performances are discussed in this paper.

This paper reviews the history and present state of magnetostrictive devices capable of controlled motion over large linear distances. Magnetostriction imparts the most force perunit weight of any technology however, the successful development of practical devices requires a multi-disciplinary effort involving materials science, magnetics, innovative mechanical design, electrical power engineering, and system control engineering. Advances todate have included demonstrations linear motors capable of 115 Newtons of force at 2.54 centimeters/second.

Low temperature valves play an important role in many research and development applications. Conventional low temperature valves primarily use actuation mechanisms depending on either gas or mechanical pressure. These actuation mechanisms usually require inconvenientoperating procedures such as a gas handling system or manual operation. We developed a superfluid leak tight low temperature valve that can be activated by a magnetostrictive material. All that is required to activate this magnetostrictive valve is a magnetic field produced by a simple power supply and coil. This new valve consists of separate valve and actuator units. The valve unit is designed to be normally closed using a spring. The stemof the valve is made of a hard 440c stainless steel ball while the seat uses a softer 304 stainless steel.

Many of the innovations in ultrasonic technology make use of modem smart alloys and materials. As a result, the theory and application of ultrasonic energy have become extremely important in various disciplines such as ultrasonic surgery, deaning and imaging. However, despite the fact that most of these ultrasonic devices are based on widely known materials, there remains a class of materials which have not been fully explored as potential active components in ultrasonic designs. In this paper, the giant magnetostrictive smart material, ETREMA TERFENOL-D®, is discussed to illustrate its potential for such applications. Frequency analysis, reliability and advantages of ultrasonic mechanisms using ETREMA TERFENOL-D® are also shown for a general broadband ultrasonic device. Frequencies between 1 kHz and 30 kHz were obtained for these applications.

A previous study about the power limits of the magnetostrictive alloy called Terfenol-D, using a device biased by coils, showed the intrinsic superiority of this material compared to piezoelectric ceramics when used in high power sonar transducers. This fact was confirmed by another study where giant dynamic peak-to-peak deformations of 3500 ppm were measured with a transducer biased by permanent magnets.

Experience shows that the longitudinal functioning of magnetostrictive transducers is sometimes disrupted by interference caused by ‘flexure’ in the magnetostrictive rods. In fact, due to the shape of the rods, the flexure effects are strongly coupled to shear. Characterization of shear in Terfenol-D under conditions of magnetic bias and prestress is then necessary to control those effects. This was made possible by using a simple and original device that was designed totally with Computer Aided Design programs.

The recent development of actuators based on giant magnetostrictive materials in for instance hydroacoustic transducers has caused an increase in output forces from the drive elements used. The high stress levels make testing of the actuators with well defined mechanical loads difficult. The need for standards and improved evaluation methods has therefore become evident.

Based on experiences from earlier test facilities a new set-up has been designed with the intention to obtain

- higher resonance frequency

- facilitated assembly of test objects

- increased operating forces

- flexible choice of mechanical loads

- computer controlled measurement procedure

- controllable environmental conditions, for instance temperature.

In order to achieve the specifications, the test rig involves hydraulics for prestressing and clamping of the test object and the mechanical load. A method of mechanically disconnecting the prestress device from the fixture gives lower mass to stiffness ratio in the fixture and therefore a better high frequency performance.

The presented test rig is considered to have the prerequisites of serving as a platform for future evaluation and standardization of actuators.

Magnetic susceptibility measurements and Mössbauer spectra (MS) were performed on a series of NixFeyAlzB shape memory ribbons obtained by a melt spinning technique. The MS at room temperature show quadrupole splittings of two iron sites. At low temperatures (T<120 K) relaxed magnetic spectra begin to develop and, in one of the samples, a complete resolved magnetic spectrum at 13 K was observed. The overall magnetic susceptibility curves show non Curie-Weiss type behavior with peaks at around 60 K and 35 K. These curves also show magnetic hysteresis in the up-down temperature cycle used during the measurements. We relate our observations with a structural change occurring at temperatures between room temperature and 260 K, a second one around 200 K, and with the developing of spin-glass behavior at low temperatures, when the magnetic influences of Fe and Ni atoms almost compensate each other.

Thin film layers of shape memory alloys and ferroelectric ceramics can produce a family of ‘smart’ heterostructures capable of performing both sensing and actuating functions. The compatibility of sol-gel processed BaTiO3 (BTO) and SrTiO3 (STO) thin films with shape memory effect TiNi substrates were investigated. Important issues in the synthesis of these active structures are the ability to generate the appropriate crystalline phases of each material while producing defect-free homogeneous high quality films.

Sputter deposition of TiNi has been problematic due to the extreme reactivity of titanium. There are several advantages in depositing TiNi with other metals, such as Ti and Cu, as the Shape Memory Effect properties can be changed selectively, including coring of the thin film. Simultaneous co-deposition of cored material using sputter deposition becomes technically difficult as this implies that the sample to target distance increases. In this paper, we discuss a relationship developed so that a basic base vacuum pressure can be found with target-sample distance and correlated with the observed phases for both Ti and TiNi samples. Practical limitations imposed by the vacuum system on both devices and device quality are discussed

A crystal which can be in two possible phase states is considered. During tensile extension the crystal is deformed elastically. After a certain amount of elastic strain a phase transformation begins. For each fixed level of strain an equilibrium mesostructure is established, which corresponds to a minimum in the free energy of the crystal. The equilibrium mesostructure consists of plane, parallel layers of a product phase separated by layers of an initial phase. The product phase itself consists of two or more different domains (twins) forming plane, parallel alternations. The volume fractions of the phases and of different twin components in the product phase are functions of strain and temperature. Above a critical temperature the product phase is a single domain (untwinned). The stress-strain curve which reflects the evolution of the equilibrium mesostructure is calculated. For deformation under a strain control the calculated equilibrium stress-strain curve has a section with negative slope that corresponds to a negative Young's modulus. If deformation proceeds under stress control, hysteretic stress-strain curves on loading and unloading will result from a section with negative slope.

Electro-mechanical properties in the pseudo-ternary solid solution system of PbZrO3-PbTiO3- Pb(Mn1/3Sb2/3)O3 piezoelectric ceramics were studied by changing the vibration- level using a constant current / velocity driving method. The vibration velocity is proportional to the driving electric field under a relatively low field. The velocity, however, deviates from a linear relationship as electric field increases and converges on a certain value.

The increase of the vibration-level is accompanied by a large amount of heat generation as well, and this heat generation sets a practical upper limit of the vibration-level. The heat generation is caused by a dissipated-vibration-energy which is represented as a function of vibration velocity and the constants depending on the materials and transducers.

In these pseudo-ternary solid solution ceramics, the compositional ratio which shows excellent electro-mechanical properties under a relatively low vibration-level does not necessarily coincide with the compositional ratio which is excellent under a relatively high vibration-level.

Correlations between the strains induced by a unipolar-electric field and the strains induced by a bipolar-electric field were investigated for Pb(Mg1/3Nb2/3)O3 (PMN) and 0.9{Pb(Mg1/3Nb2/3)O3}-0.1PbTiO3 (0.9PMN- 0.1PT) relaxor ferroelectric ceramics in the temperature range of −50°C ∼ 150°C. The magnitudes of the unipolarly induced-strains are almost the same as the differences between the bipolarly induced-strains and the residual strains, which were attributed to the absence of change of spontaneous polarization direction when the unipolar-electric field is applied.