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A robust passive high frequency high pressure micro check valve was developed for piezoelectrically actuated pumps. A novel cross-patterned microvalve flap is used to increase the valve’s structural stiffness with pressures up to 10 MPa. A mechanical valve stopper prevents valve-flap failure under extreme high pressure. The valve-flap is also designed to work at frequency larger than 10,000 Hz. The valve-flap was fabricated with electroformed nickel on silicon substrate. Deep RIE etching was used to fabricate the valve channels in the silicon substrate. The whole valve weighs 0.2 g including packaging. The microvalve flow rate (water) is measured to be 18 cm3/s under a pressure difference of 50 psi. The microvalve was integrated with a compact piezoelectric pump and produced pressure of 350 psi when operated at 10 kHz frequency.

Nickel microspheres were produced by the spark erosion technique under both liquid nitrogen and water conditions. Density measurements and Scanning electron microscope analysis revealed that a significant portion of the Ni particles produced under the liquid nitrogen conditions are hollow spheres with a density of 6.67(4)g∕cm3 while the particles produced in water are primarily solid spheres with a density of 8.40(1)g∕cm3, close to the bulk nickel value of 8.90g∕cm3. Nickel∕polymer composites incorporating the hollow and solid nickel microspheres were manufactured with volume fractions of 25% and 36%, respectively. The hollow and solid nickel composites exhibited saturation magnetostrictions of −24 and −28ppm, respectively. In addition, small quantities of Terfenol-D (Tb0.3Dy0.7Fe2) were spark eroded under liquid argon conditions with ∼10% by volume of the spark eroded particles being solid microspheres. Calculations indicate that aligned composites that incorporate these Terfenol-D microspheres could rea...

A method for both identification and localization of structural damage is proposed and implemented on a simply supported beam. The results are predicted with an analytical model and verified with an experimental test set-up consisting of an aluminum beam with one actuator and one sensor, both piezoelectrics. The method estimates the energy localized in bandwidth regions near resonance that are the most sensitive to damage. The energy is estimated by power spectral density analysis and quantified by means of its root mean square value. These values are combined with mode shapes to locate damage. The method is evaluated with small masses used to simulate damage and or small cuts to simulate damage and good agreement is obtained between experiments and analysis.

The frequency response of thin film nickel–titanium (NiTi) shape memory alloy (SMA) membrane in three fluid mediums (air, silicon oil, and de-ionized water) was investigated in the present paper. Operation was investigated at different power input and duty cycles. Results showed an operating frequency of 40 Hz could be achieved in de-ionized water with appropriate power input and duty cycles. Larger operating frequencies could be achieved by applying power over a short heating time to minimize the temperature rise in the surrounding fluid. Results demonstrated the extreme sensitivity of frequency to operating medium, power input, and duty cycle. That is, changing one of these parameters, the frequency response could be changed by an order of magnitude.

The design of a piezoelectric-hydraulic pump with innovative active valves is presented in this study. The pump structure consists of a piezoelectric stack actuator and two piezoelectric unimorph disc valves acting as inlet and delivery valves. The pump actuation mechanism is composed of a pumping chamber and a diaphragm attached to the piezoelectric stack actuator. Static and dynamic piezoelectric finite element analyses have been used to maximize the delivered fluid volume per stroke and to predict the dynamic behavior, respectively. A structural optimization technique has been employed to optimize the pump’s efficiency for specific geometrical dimensions. A transient computational fluid dynamics (CFD) model has been utilized to predict flow rates. Dynamic experiments have also been conducted and results are in good agreement with those obtained from simulations.

We investigated the dynamic behavior of 1-3 type magnetostrictive particulate composites as a function of both bias field (5-140 kA/m) and frequency (1-100 kHz). The composites consist of approximately 0.5 volume-fraction Terfenol-D particles embedded and magnetically aligned in a passive epoxy matrix. The measured properties include elastic moduli (E/sub 3//sup H/ and E/sub 3//sup B/), dynamic relative permeability (/spl mu//sub r33/), dynamic strain coefficient (d/sub 33/), magnetomechanical coupling coefficient (k/sub 33/), and the ratio of the dynamic strain coefficient to the dynamic susceptibility (d/sub 33///spl chi//sub 33/). We observed the dependence of these properties on bias field and explain it here in terms of domain-wall motion followed by saturation near 40 kA/m. The spectra of /spl mu//sub r33/, d/sub 33/, and d/sub 33///spl chi//sub 33/ indicate that the magnetization process is independent of frequency and that the effect of eddy-current losses is insignificant up to 100 kHz. The observations agree with predictions made by classical eddy-current theory and suggest that the composites can be operated at significantly higher frequencies than monolithic Terfenol-D.

This paper describes magneto-thermo-mechanical test results for 1–3 type magnetostrictive composites incorporating Terfenol-D (Tb 0.3 Dy 0.7 Fe 2 ) particulate in an epoxy binder. The purpose of this study is to evaluate the behavior of magnetostrictive composites under combined magnetic, thermal, and mechanical loading, and to determine fundamental properties used for design of sonar transducers that incorporate these materials. Two different tests were performed both at room temperature and under thermal loading: (1) constant magnetic field with cyclically varying mechanical load around a bias load, and (2) constant mechanical pre-load with cyclically varying magnetic field. Testing was performed on five different volume fraction ( V p ) composites, namely, 13%, 23%, 31%, 37%, and 50%. Parameters that were evaluated include strain output ( e 3 ) and elastic modulus ( E 3 H ). Detailed analysis, including relative permeability ( μ 33 σ / μ 0 ) and the piezo-magnetic coefficient ( d 33 ), is only presented for the composite with 50% V p . Results indicate that composite properties, as pertaining to sonar transducers, are comparable to monolithic Terfenol-D while reducing brittleness, providing higher operational frequencies and easier manufacturability. Moreover, results for composite Terfenol-D can be explained well using theory developed for monolithic Terfenol-D.

The dynamic magnetomechanical properties of Terfenol-D/epoxy 1–3 magnetostrictive composites with approximately 50% Terfenol-D volume fraction have been investigated under different combined magnetic bias ( H Bias =5–140 kA/m) and drive ( H 3 =1–9 kA/m) fields. These properties include elastic moduli ( E 3 H and E 3 B ), dynamic relative permeability ( μ r 33 T ), dynamic strain coefficient ( d 33 ), magnetomechanical coupling coefficient ( k 33 ), and the ratio of the dynamic strain coefficient to the dynamic susceptibility ( d 33 / χ 33 ). The changes in the composite properties with applied fields can be explained in terms of domain wall motion followed by saturation. At a low H 3 of 1 kA/m, the available non-180° domain state created by residual compressive stresses in the composites results in negative- ΔE, d 33 , k 33 , and d 33 / χ 33 maximizing near H Bias =40 kA/m. As H 3 is increased, domain wall motion occurs, decreasing the H Bias required to maximize the properties by reducing stress-induced anisotropy.

A magnetic dipole-coupled magnetoelectric heterostructure comprised of three closely spaced ellipse shapes was designed and shown to be capable of achieving deterministic in-plane magnetization rotation. The design approach used a combination of conventional micromagnetic simulations to obtain preliminary configurations followed by simulations using a fully strain-coupled, time domain micromagnetic code for a detailed assessment of performance. The conventional micromagnetic code has short run times and was used to refine the ellipse shape and orientation, but it does not accurately capture the effects of the strain gradients present in the piezoelectric and magnetostrictive layers that contribute to magnetization reorientation. The fully coupled code was used to assess the effects of strain and magnetic field gradients on precessional switching in the side ellipses and on the resulting dipole-field driven magnetization reorientation in the center ellipse. The work led to a geometry with a CoFeB ellipse (...

The effect of bias electric field on the nonlinear stress–strain response of a lead zirconate–lead titanate piezoelectric ceramic is studied. The material is subjected to various compressive stress amplitudes (25–300 MPa) under constant electric field (from −0.5 to 2.0 MV/m) along the original poling direction. Application of a positive electric-field bias results in closed stress–strain hysteresis loops absorbing significant amounts of mechanical energy. Increasing the positive electric field increases the specific damping and decreases the elastic modulus. The trend is reversed when the electric field becomes sufficiently high to inhibit the domain-wall motion by the mechanical stresses. Measured specific damping values vary from 0.18 to 0.46 depending on the stress amplitude and bias electric field. The corresponding secant modulus varies from 79 to 24 GPa. The coercive stress is found to approach zero as the negative electric-field bias approaches the coercive field value. The coercive stress increase...

In this paper we have examined compositional shifts in NiTi film sputter-deposited from a heated and a cooled target. Substrates were radially placed at 18° intervals to capture the semicircular sputtering profile. The composition of the film was measured using Rutherford backscattering spectroscopy (RBS). Film thickness values were measured and the atomic flux captured was calculated. Results indicate that the target temperature significantly influences the composition of the sputtered film. It was found that, for cold targets, Ni and Ti sputter at different angles, producing a compositional shift in the film when compared with the target. For hot targets the sputtering angle is influenced to a lesser degree, such that the compositional shift is negligible. Therefore, target temperature appears to represent an approach to alter the stoichiometry of films deposited.

This paper presents numerical and experimental data for dipole-dipole coupled Ni nanodots on a piezoelectric [Pb(Mg1/3Nb2/3)O3]0.68[PbTiO3]0.32 substrate. Simulation results show that the dipole coupling produces artificial ferromagnetic (parallel magnetization alignment in the nanodot arrays) behavior that can be modified to artificial antiferromagnetic behavior with an applied voltage. Experimental results show the trends in Mr and Hc predicted by the model, but discrepancies arise due to geometric defects present in the fabricated samples. Geometric defects are introduced into the Ni nanodot models, thus dramatically improving the correlation between experiments and analysis. This work shows, through numerical simulations, that artificial multiferroic nanostructures can be designed to produce switching from parallel (artificial ferromagnetic) to antiparallel (artificial antiferromagnetic) magnetization ordering by leveraging dipole coupling with voltage induced changes in magnetic anisotropy.

Piezoelectric polycrystalline ceramics consists of a large number of polarized crystallites (domains) oriented along random directions. When subjected to an excessive electro-mechanical load, each domain may undergo polarization switching resulting in a nonlinear macroscopic behavior of the piezoceramic. In this article a finite element code is developed to simulate this nonlinear behavior. The polycrystalline piezoceramic is modeled as an aggregate of finite elements with each domain represented by a finite element. Each element within this model is oriented in a random direction and is allowed to undergo polarization switchings when a criterion is exceeded. All domains are assumed to possess tetragonal structure. The dielectric, strain, and stress-strain macroscopic responses of the material are generated by the model. The analytical results are compared with experimental data and reasonable agreement is achieved.

A novel thin film (micrometer thickness) shape memory alloy (SMA) micro actuator is presented in this paper. The thin film SMA with composition of approximately 50:50 nickel titanium (NiTi) is sputter-deposited onto a silicon wafer in an ultra high vacuum system. Transformation temperatures of the NiTi film are determined by measuring the residual stress as a function of temperature. The transformation temperature is independent of the presence of chromium (Cr) used as an adhesion layer, or being exposed to air before annealing. A mixture of hydrofluoric acid (HF), nitric acid (HNO/sub 3/) and deionized (DI) water is used to etch the film. Different etch masks are evaluated to protect the NiTi film during the etching. Among the masks tested, a thick photoresist (AZ-4620) produces the best result. The NiTi membrane is hot-shaped into a three-dimensional (3-D) dome shape using a stainless-steel jig. Results indicate the membrane exhibits two-way effect. The performance of the SMA micro actuator is characterized with a laser measurement system for deflection versus input power and frequency response.

In this work, the frequency-dependent magnetic properties of sputtered Galfenol/Permalloy (Fe85Ga15/Ni81Fe19 or FeGa/NiFe) magnetic multilayers were examined to tailor their magnetic softness, loss at microwave frequencies, permeability, and magnetoelasticity, leveraging the magnetic softness and low loss of NiFe and the high saturation magnetostriction (λs) and magnetization (MS) of FeGa. The total volume of each material and their ratio were kept constant, and the number of alternating layers was increased (with decreasing individual layer thickness) to assess the role of increasing interfaces in these magnetic heterostructures. A systematic change was observed as the number of bilayers or interfaces increases: a seven-bilayer structure results in an 88% reduction in coercivity and a 55% reduction in ferromagnetic resonance linewidth at the X-band compared to a single phase FeGa film, while maintaining a high relative permeability of 700. The magnetostriction was slightly reduced by the addition of NiFe...

Micromagnetic simulations of magnetoelastic nanostructures traditionally rely on either the Stoner-Wohlfarth model or the Landau?Lifshitz-Gilbert (LLG) model, assuming uniform strain (and/or assuming uniform magnetization). While the uniform strain assumption is reasonable when modeling magnetoelastic thin films, this constant strain approach becomes increasingly inaccurate for smaller in-plane nanoscale structures. This paper presents analytical work intended to significantly improve the simulation of finite structures by fully coupling the LLG model with elastodynamics, i.e., the partial differential equations are intrinsically coupled. The coupled equations developed in this manuscript, along with the Stoner-Wohlfarth model and the LLG (constant strain) model are compared to experimental data on nickel nanostructures. The nickel nanostructures are 100???300???35 nm single domain elements that are fabricated on a Si/SiO2 substrate; these nanostructures are mechanically strained when they experience an applied magnetic field, which is used to generate M vs H curves. Results reveal that this paper?s fully-coupled approach corresponds the best with the experimental data on coercive field changes. This more sophisticated modeling technique is critical for guiding the design process of future nanoscale strain-mediated multiferroic elements, such as those needed in memory systems.

This study reports on signal recovery of optical fiber Bragg gratings embedded in a carbon fiber composite overwrapped pressure vessel's (COPV) structure which have become chirped due to microcracks. COPVs are commonly used for the storage of high pressure liquids and gases. They utilize a thin metal liner to seal in contents, with a composite overwrap to strengthen the vessel with minimal additional mass. A COPV was instrumented with an array of surface mounted and embedded fiber Bragg gratings (FBGs) for structural health monitoring (SHM) via strain sensing of the material. FBGs have been studied as strain sensors for the last couple decades. Many of the embedded FBGs reflected a multi-peak, chirped response which was not able to be interpreted well by the current monitoring algorithm. Literature and this study found that the chirping correlated with microcracks. As loading increases, so does the number of chirped FBGs and microcracks. This study uses optical frequency domain reflectometry (OFDR) to demultiplex the array of FBGs, and then sub- divide individual FBGs. When a FBG is sub-divided using OFDR, the gratings' strain along its length is recovered. The sub-divided chirped FBGs have strain gradients along their length from microcracks. Applying this to all chirped gratings, nearly the entirety of the embedded sensors' readings can be recovered into a series of single peak responses, which show very large local strains throughout the structure. This study reports on this success in recovering embedded FBGs signal, and the strain gradient from microcracks.

The authors recently reported on a hybrid rotary-translational vibration energy harvesting approach using a spherical permanent-magnet and employing cycloidal motion as a mechanical amplifier. The rotary-translational harvesting approach, which is resonant in nature, can yield approximately twice the e.m.f. compared with a similar translationalonly device. This paper explores the analytic and numerical modelling of the rotary-translational harvester with the goal of finding an efficient method for design optimisation.

The effect of prestress on the nonlinear dielectric (polarization) and piezoelectric (strain) response of lead zirconate–lead titanate (PZT–5H) piezoelectric ceramic is studied. The response to bipolar (−2/+2 MV/m) and unipolar (0/+2 MV/m, −0.4/+2 MV/m) electric field under constant prestress (up to 175 MPa) is experimentally evaluated. In the bipolar regime, prestress mainly influences the first non-180° process. In the unipolar regime, the dielectric and piezoelectric response achieve maximum values near 50–60 MPa because the prestress increases the number of available non-180° domains. A detailed description of the effect of the prestress on electro–mechanical response is provided in terms of non-180° domain wall motion. Based on rule of mixtures formulation, an analytical model is developed to estimate the optimum prestress value for the unipolar electric loading condition. It is found that the dielectric and piezoelectric response of the material is proportional to the volume fraction of the non-180°...

We present experimental results for [1–3] magnetostrictive composites containing a 20% volume-fraction of Terfenol-D coarse particles (≫1 μm) suspended in a nonmetallic binder. Results from magnetostrictive strain and magnetoelastic measurements are provided for particle distributions that differ in particle size and range of size distribution. Particle size and packing density are shown to effect strain response and are attributed to demagnetization and loading (prestress) effects. Both a decreasing and increasing ΔE effect are measured for low and high fields, respectively, and found to be independent of particle distribution. The response of an optimized bimodal distribution increases packing density and produces 15% larger magnetostrictive strains than the other widely dispersed (polydispersed) (

This paper analytically evaluates the strength of microcomponents fabricated using both wet and dry etching techniques. A finite element model (nanometer meshed) coupled with a macroscopically accepted energy criterion is used to predict the strength of four different microridge structures (geometries). Agreement between analytical predictions and experimental data on single crystal silicon is excellent and validates the use of macroscopic models to predict the strength of micromachined components fabricated with a wide range of processes. The model is used to evaluate design parameters such as the influence of height and ridge material on strength properties. The analytical portion of the study suggests that optimum ridge height exists to maximize the strength and by choosing tougher materials, the strength of the ridges may be improved by an order of magnitude. However, the significant strength improvement is not validated experimentally. The simulation results confirm that the geometries rather than etching flaws are critical issues when dealing with strength of micromachined components. Furthermore, standard macroscopic methods can be used to predict the strength of MEMS components at the micron size level.

Vibration reduction using blade root pitch control introduces a significant power penalty and may adversely affect the airworthiness of the flight control system. Comparable levels of vibration reduction can be achieved using considerably less power through an actively controlled trailing edge flap mounted on the blade. Such a device would have no effect on helicopter airworthiness since it is controlled by a loop separate from the primary flight control system which utilizes the swashplate. Control flap actuation using the magnetostrictive material Terfenol-D is studied in this paper by designing a minimum weight actuator, subject to a set of actuation and stress constraints. An important ingredient in this design process is the precise characterization of the constitutive relations for the magnetostrictive material which provides valuable guidelines on the practical implementation of magnetostrictive actuators. It is shown that the magnetostrictively actuated flap is capable of producing vibration reduction in high speed forward flight in excess of 90%.

The design, fabrication, and testing of a compact displacement accumulation device is presented in this paper. The piezoelectric device provides both large displacement (mm) and large force (100 N). The device is based on conventional inchworm motor design that produces large displacement. The device integrates piezoelectric stacks for large force output and high-speed operation with MEMS ridges as a new clamping system. The device should be able to push and pull 450 N at 11 mm/s in a relatively compact size. FEM analysis is used for the design, EDM is used for the fabrication of a prototype, and conventional test techniques are used to evaluate performance. Stress and modal analysis are used to confirm that the device has an infinite fatigue life and a first modal frequency at 1309 Hz. Experimental data for clamping strength of the ridges and blocking force of the device validate that the device transfers the required load of 450 N. The device is successfully tested over a wide range of operating conditions at speeds up to 11 mm/s using open loop control. The stall load of the device is measured to be exceeding 2250 N. For the dynamic loading test, the device pushes test weights up to 50 N with the open loop control approach.

A new, rechargeable, thick-film, polymer electrolyte, lithium battery using a high-energy density cathode material (vanadium pentoxide aerogel, 350 mAh/g) has been tested in a pulse-discharge mode of operation. Three separate 12 volt batteries were pulse-discharged through a piezoelectric stack actuator. Since motion rectification devices such as linear motors operate at elevated frequencies, the batteries were pulse-discharged at 10, 100, and 500 Hz. Multiple cycle, charge/discharge data is presented for the three batteries tested in this study. Additionally, a 6 volt battery was fabricated and used to power a piezoelectric actuator patch (chirp source) that was part of a damage detection system.

A parametric study was performed on NiTiCu shape memory alloy torque tubes. Four samples with varying wall thickness values were evaluated for their thermo-mechanical response. The torque against the angular displacement was measured for each sample when purely martensitic and purely austenitic. The recovery torque was measured as a function of the pretwist applied during loading in the martensite phase. The trends observed were compared to three models with relatively good agreement. The recovery torque for biaxial tension/compression-torsion tests were measured with values comparable to pure torsional loadings. During the biaxial loading, a time-dependent phenomenon was observed. To evaluate the time dependence, standard creep tests were performed to elucidate the influence of the load on the temporal response of the material.

In this paper we present a novel method for depositing NiTi thin film by DC sputtering. The film has transformation temperatures very close to that of the target. The new process involves heating the target and does not require compositional modification of the NiTi target. Results from X-ray diffraction, differential scanning calorimeter, four-point probe, Rutherford backscattering, and transmission electron microscopy are presented. These results indicate that compositional modification can be produced by varying the target temperature. Films produced from hot targets have compositions similar to the target while films produced from cold targets were Ti deficient. Films that were produced by gradual heating of the target have compositional gradation through the film thickness. The gradated films exhibit the two-way shape memory effect.

A summary of the influence of microfabrication processes (wet and dry etching) and crystal orientation on the effective shear strength of microridges is addressed in this paper. Test results indicate that both crystal orientation and geometry plays an important role in determining the strength. The largest shear strengths obtained were for triangular and rectangular ridges fabricated with wet etching and deep RIE respectively. Both of these structures had similar crystal orientations. These strength values were approximately 3.5 times larger than the lowest strengths measured for wet etching structures. Using Chlorine RIE, we were able to demonstrate the influence of crystal orientation on strength, with microridges of {110} sidewall made on a (100) wafer the largest. For wet etching, we found that the strength was concentration dependent. For example, a 45% KOH fabricated structure produced strength values 65% higher than 30% KOH fabricated ones (note crystal orientation the same). This was attributed to a geometric effect, that is the 45% KOH solution had a “V” shaped bottom while the 30% KOH had a flat bottom. EDP and TMAH values had similar strengths to the 30% KOH solution (note similar crystal orientation). Therefore, microcomponent strength is strongly dependent upon fabrication process as well as crystal orientation.

In this paper, we present the results of an experimental study focused on understanding the strain concentrations arising due to nonlinear phenomena associated with polarization switching. A moire interferometry technique is used to measure the normal and shear strains of a PZT-5H piezoceramic undergoing 180 and 90 deg switching. These results include the strain concentrations measured between polarized regions oriented 180 and 90 deg apart. The results show that very large strain mismatches (e.g., as large as 4500 microstrains) occur along the boundary of dissimilar oriented domains, suggesting a source of microcrack initiation and fatigue degradation.

Using ab initio electronic structure calculations, we have investigated the effect of an electric field and of a heavy-metal cap of Pd on the magnetocrystalline anisotropy (MCA) of FePd ultrathin film. Analysis of the energy- and $k$-resolved distribution of the orbital character of the minority-spin band reveals that the perpendicular MCA of the uncapped film mainly arises from the spin-orbit coupling (SOC) between unoccupied Fe ${d}_{xy}$ and occupied Fe ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ states. On the other hand, the SOC between the Pd- and Fe-derived $d$ states yields negative contributions to the MCA. We find that the sensitivity of the surface anisotropy energy to the applied electric field is 18 fJ/(Vm) and is due to changes in the occupation of the surface Fe atoms ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ and (${d}_{xz},{d}_{yz}$) orbitals. We demonstrate that the thickness of the Pd cap has a dramatic effect on the MCA and can even switch the magnetization from out-of- to in-plane orientation. The underlying origin is the change of the position and orbital character of the spin-polarized quantum well states induced in the Pd cap by varying its thickness. These results have important implications for exploiting heavy metals with large spin-orbit coupling (Ru, Pd, Ta, Pt, or Au) as contacts with ferromagnetic thin films to tailor the magnetic switching of spintronic devices by tuning the cap thickness.

Piezoelectric ceramics contain anomalies which give rise to localized stress concentrations when electric fields are applied. These stress concentrations cause microcracking which leads to electro-mechanical degradation and eventually to material failure. In this paper, a unit cell approach is presented to understand the relationship between material properties and electric field induced stress concentrations around a specific anomaly, i.e., circular void. An exact electro-elastic analysis verified with a finite element model is used to study the stress and electric field concentrations as a function of material properties. Parametric studies indicate that the electric field induced stress concentrations in the material are effectively eliminated for certain values of the piezoelectric coefficients. While a trivial solution to this problem is that the piezoelectric coefficients are zero, other “optimum” coefficients exist. These coefficients do not limit the deformation profile of the piezoelectric and are thermodynamically admissible. Results presented for PZT-4 and PZT-5H support the contention that optimal piezoelectric materials can be manufactured.

The dynamic magnetoelastic properties of a [112]-oriented magnetostrictive composite comprising 0.49 volume fraction of needle-shaped, [112]-oriented Terfenol-D particles and Spurr epoxy were investigated as a function of magnetic bias field. These properties included elastic moduli (E/sub 3//sup H/ and E/sub 3//sup B/), dynamic strain coefficient (d/sub 33/), and magnetoelastic coupling coefficient (k/sub 33/). A randomly oriented composite with 0.51 volume fraction of irregular-shaped, ball-milled Terfenol-D particles was also prepared and characterized for comparison. It was found that the [112] preferential particulate orientation increases non-180/spl deg/ domain-wall motion in the [112]-oriented composite, resulting in maximum negative-/spl Delta/E,d/sub 33/, and k/sub 33/ values of about 10%, 5.5 nm/A, and 0.34, respectively. These are the largest property values reported as yet for magnetostrictive particulate composites, being up to 67% larger than the randomly oriented composite and approach to 65% of the monolithic Terfenol-D.

We demonstrate in situ 90\ifmmode^\circ\else\textdegree\fi{} electric field-induced uniform magnetization rotation in single domain submicron ferromagnetic islands grown on a ferroelectric single crystal using x-ray photoemission electron microscopy. The experimental findings are well correlated with micromagnetic simulations, showing that the reorientation occurs by the strain-induced magnetoelectric interaction between the ferromagnetic nanostructures and the ferroelectric crystal. Specifically, the ferroelectric domain structure plays a key role in determining the response of the structure to the applied electric field, resulting in three strain-induced regimes of magnetization behavior for the single domain islands.

In this paper, we report a strain induced exchange-spring magnetic behavior in sputter deposited (TbDy)Fe2 amorphous thin films with phase-separated layers of (TbDy)-rich and Fe-rich at room temperature. The magnetic hysteresis loops at different strain levels were obtained with a magneto-optic Kerr effect set-up incorporating a mechanical four-point bending fixture. The unstrained film exhibits a typical ferrimagnetic hysteresis loop while the strained structure exhibits step-like hysteresis loops representative of an exchange-spring magnetic system. The mechanically strained film changes the coercivity/remanence values from positive to negative. The observed magnetic changes under strain are attributed to magnetic anisotropy modifications in the highly magnetoelastic TbDy-rich layer.

Controlling magnetization using piezoelectric strain through the magnetoelectric effect offers several orders of magnitude reduction in energy consumption for spintronic applications. However strain is a uniaxial effect and, unlike directional magnetic field or spin-polarized current, cannot induce a full 180° reorientation of the magnetization vector when acting alone. We have engineered novel 'peanut' and 'cat-eye' shaped nanomagnets on piezoelectric substrates that undergo repeated deterministic 180° magnetization rotations in response to individual electric-field-induced strain pulses by breaking the uniaxial symmetry using shape anisotropy. This behavior can be likened to a magnetic ratchet, advancing magnetization clockwise with each piezostrain trigger. The results were validated using micromagnetics implemented in a multiphysics finite elements code to simulate the engineered spatial and temporal magnetic behavior. The engineering principles start from a target device function and proceed to the identification of shapes that produce the desired function. This approach opens a broad design space for next generation magnetoelectric spintronic devices.

Here we demonstrate electric-field induced magnetic anisotropy in a multiferroic composite containing nickel nanocrystals strain coupled to a piezoelectric substrate. This system can be switched between a superparamagnetic state and a single-domain ferromagnetic state at room temperature. The nanocrystals show a shift in the blocking temperature of 40 K upon electric poling. We believe this is the first example of a system where an electric field can be used to switch on and off a permanent magnetic moment.

The feasibility of using piezohydraulic pumps in drivers for pediatric ventricular assist devices is presented in this article. In this study a 0.5 kg piezohydraulic pump is incorporated into a ventricular assist device driver to drive a pulsatile pediatric 30 mL stroke ventricular assist device (VAD). The driver consists of a piezoelectric-hydraulic hybrid actuator and volume amplification section. Mechanical tests were performed on the pump and the hybrid actuator and a maximum power output of 5.4 W and 1.6 W were recorded respectively. The driver was tested running at multiple heart rates from 50-80 beats per minute (BPM) in an in-vitro bench top mock circulation to characterize the performance of the driver under a circulatory load. The maximum drive pressure output by the driver was 35 kPa. Peak flow rate from the VAD driven by the new driver was 6 L/min against a 10 kPa back pressure. Mean flow rate from the VAD outlet was 2.35 L/min for 80 BPM operation.

A method to compare the thermal to magnetic transduction efficiencies of different thermomagnetic systems was developed. The efficiencies of operating about a spin reorientation transition and the alternative ferromagnetic to paramagnetic transformation at the Curie point were directly compared. A case study was performed comparing Gd operating about its spin reorientation temperature and its Curie point. Additionally, a case study on NdCo5 operating about its spin reorientation temperature using experimentally derived values of the materials' temperature dependent magnetic properties was conducted. Analysis suggests that choosing the appropriate material and operating it about its transition produces considerable efficiencies (∼22%) as well as large harvestable energy densities (∼2.6 MJ/m3), which is an order of magnitude larger than Gd single domains operating about their Curie point (∼100 kJ/m3).

High void content and delaminations are observed during the fabrication of thick carbon/phenolic composites due to the high percentage of volatile release which occurs during polymerization. In order to eliminate these imperfections and enhance product quality for thick carbon/phenolic composites, smart sensors are used to monitor the property changes during the processing and control of the component to minimize this effect. This paper describes a technique to monitor and collect sensor data during the curing process of a general material system. Data obtained from sensors are used to generate an expert processing knowledge base which automatically controls the composite cure state based on direct sensor response, in lieu of classical time/temperature techniques. Microdielectric, ultrasonic, thermopile, thermal couple and extrinsic Fabry-Perot interferometer (EFPI) sensors are investigated as potential candidates to monitor and subsequently control the manufacturing process of a composite material. Microdielectric sensors are used to monitor resin property changes. Ultrasonic sensors are used to measure stiffness changes and porosity development in the composite material. Thermopile and thermal couples are used to monitor temperature variance and heat reaction rates within the material. EFPI sensors, historically used for monitoring structural integrity during service applications, are used to detect local strain changes caused by temperature, pressure, or process induced residual stresses. In addition to classical optical sensors, a modified EFPI thermal sensor is employed to monitor temperature variations.

The dynamic magnetomechanical properties of a Terfenol-D/epoxy 1–3 magnetostrictive particulate composite fabricated using 49% volume fraction of needle-shaped, [112]-oriented Terfenol-D particles were investigated as a function of magnetic bias field (HBias). A nonoriented composite with 51% volume fraction of irregular-shaped, ball-milled Terfenol-D particles was also prepared and characterized for comparison. It was found that the composites exhibit a similar qualitative trend in dynamic strain coefficient (d33) and dynamic susceptibility (χ33) with the oriented type possessing much higher values than the nonoriented type for all HBias. Data for the ratio d33/χ33 indicated that these increments in d33 and χ33 in the oriented composite are mainly attributed to [112] particulate crystallographic orientation.

In this paper we analyze the 3D modes of a linear homogeneous magnetoelectroelastic (MEE) material. We find that the behavior of the electromagnetic modes are strongly influenced by the mechanical coupling present in the MEE material system. A number of papers refer to the cross-coupling of laminated piezoelectric and piezomagnetic materials as magnetoelectric materials. We discuss here that the composite materials are MEE systems and that the constitutive relations need to reflect the mechanical coupling also. Further, we find that the mechanical coupling has a significant impact on the electromagnetic propagation modes of the composite material. Through examples of homogenized MEE materials we show possibilities for remarkable electromagnetic material characteristics which are not conventionally obtainable in single phase materials.

The ability to determine the state of strain within a plane is of great importance to the health monitoring of composite materials and structures. In this preliminary study, fiber optic strain sensors are arranged in a rosette configuration to study their effectiveness in monitoring arbi trary strain states within a neat resin and a graphite/epoxy laminate. The extrinsic Fabry Perot Fiber Optic Strain Rosette Sensor (FP-FOSRS) is very capable of measuring axial (0°) and transverse (90°) strains. However, discrepancies are noted between strain measured by the embedded Fabry Perot Sensors and externally mounted strain gages at 45°. Further, it is believed that the compressive strength of FP-FOSRS embedded composites is most affected by the sensors' presence. A com pressive strength reduction of 300% is measured. This reduction is compared with the result pre dicted by a micromechanical model.

Purpose Prior studies demonstrated the ability of a spring to lengthen intestinal segments. We made two innovations to this device. First, we employed a degradable capsule to control the deployment of the spring. Second, we decreased the spring force to allow slower expansion of the intestinal segment. Methods Nitinol springs with varying forces were compressed and placed in gelatin capsules. These capsules were coated with a degradable polymer and were placed in isolated segments of rat jejunum. Serial x-rays were used to determine the rate of spring expansion. Retrieved jejunal segments were analyzed histologically. Results Using the polymer-coated capsule, the spring was reliably deployed between 24 and 48 hours. Intestinal segments were lengthened from 1.0 cm to 3.6 cm after 14 days. The optimal spring for the gradual expansion of jejunal segments had a spring constant of 0.0010 N/mm. Villus height was preserved, but crypt depth was significantly greater in the lengthened intestine. Conclusion Use of a low-force spring resulted in a nearly four-fold lengthening of jejunal segments. The use of a polymer-coated capsule provided a reliable way to control the timing of spring deployment. This capsule may be useful for the endoscopic placement of the spring in patients with short bowel syndrome.

Wide-neck and giant cerebral aneurysms are difficult to treat with conventional endovascular or surgical means [1]. Recently, stand-alone stent treatment has been explored as a viable treatment option for these aneurysms. Two goals of standalone stent design are to permit flexible conformation of the stent through tortuous vessels and to provide sufficient coverage across the aneurysmal neck [2]. Stents that achieve those goals can facilitate the long-term physiological processes that exclude the aneurysmal sac from circulation. Thrombosis within the sac is an important intermediate step, which may begin with the elimination of aneurysmal inflow [3].Copyright © 2011 by ASME

A flexible, low profile, flow diversion stent could replace endovascular coiling for the treatment of intracranial aneurysms. Micropatterned-thin film nitinol (TFN) is a novel biomaterial with high potential for use in next-generation endovascular devices. Recent advancements in micropatterning have allowed for fabrication of a hyperelastic thin film nitinol (HE-TFN). In this study, the authors describe in vitro and in vivo testing of novel HE-TFN based flow diverting stents. Two types of HE-TFN with expanded pores having long axes of 300 and 500 μm were used to fabricate devices. In vitro examination of the early thrombotic response in whole blood showed a possible mechanism for the device's function, whereby HE-TFN serves as a scaffold for blood product deposition. In vivo testing in swine demonstrated rapid occlusion of model wide-neck aneurysms. Average time to occlusion for the 300-μm device was 10.4 ± 5.5 min. (N = 5) and 68 ± 30 min for the 500-μm device (N = 5). All aneurysms treated with bare metal control stents remained patent after 240 min (N = 3). SEM of acutely harvested devices supported in vitro results, demonstrating that HE-TFN serves as a scaffold for blood product deposition, potentially enhancing its flow-diverting effect. Histopathology of devices after 42 days in vivo demonstrated a healthy neointima and endothelialization of the aneurysm neck region. HE-TFN flow-diverting stents warrant further investigation as a novel treatment for intracranial aneurysms.

We report giant electrical control of magnetic anisotropy in a magnetoelectric polycrystalline Ni thin film and (011)-oriented [Pb(Mg1/3Nb2/3)O3](1-x)-[PbTiO3]x (PMN-PT) heterostructure. The (011) PMN-PT ferroelectric substrate exhibits both linear anisotropic piezoelectric response and unique giant hysteretic response. These important features can significantly tune the magnetization states via strain coupling. Reversible and permanent magnetization reorientation demonstrates an approach for developing magnetoelectric memory devices.

A novel hyper-elastic thin film nitinol (HE-TFN) covered stent has been developed to promote aneurysm quiescence by diminishing flow across the aneurysm's neck. Laboratory aneurysm models were used to assess the flow changes produced by stents covered with different patterns of HE-TFN. The flow diverters were constructed by covering Wingspan stents (Boston Scientific) with HE-TFNs (i.e., 82 and 77% porosity) and deployed in both in vitro wide-neck and fusiform glass aneurysm models. In wide-neck aneurysms, the 82% porous HE-TFN stent reduced mean flow velocity in the middle of the sac by 86.42±0.5%, while a 77% porous stent reduced the velocity by 93.44±4.99% (n=3). Local wall shear rates were also significantly reduced by about 98% in this model after device placement. Tests conducted on the fusiform aneurysm revealed smaller intra-aneurysmal flow velocity reduction to 48.96±2.9% for 82% porous and to 59.2±6.9% for 77% porous stent, respectively. The wall shear was reduced by approximately 50% by HE-TFN stents in fusiform models. These results suggest that HE-TFN covered stents have potential to promote thrombosis in both wide-necked and fusiform aneurysm sacs.

In this article we utilize a concentric cylinder model to analyze the stress state in a continuously reinforced coated fiber composite subjected to transverse loading. We incorporate this analysis into a methodical approach to determine an optimal inter phase coating for the fibers to maximize the composite's transverse strain to failure. The present study focuses on the effect of interphase Young's modulus on the stress state in the matrix material of a composite subjected to constant strain (displacement) boundary con ditions. We demonstrate, by analytically varying the coating modulus, that an optimum in terphase property exists which minimizes the maximum principal stress and the strain en ergy density in the composite material. The minimization of these quantities clearly indicates that failure initiation in a composite with an optimal fiber coating will occur at a significantly larger strain level. Therefore, we postulate (based on the current analysis) that the transverse strain to failure of a composite system can be increased with appropriate fiber coatings. Results and design curves are presented for an AS-4/Epon 828 composite system which suggest that for large fiber volume fractions (i.e., 60%) the optimum coating is an elastomeric material. The data presented on this composite suggest that the strain to failure can be increased as much as 6 times by coating the structural fibers with an optimal coating. A comparison between constant stress boundary conditions (i.e., optimizing strength) and constant strain boundary conditions (i.e., optimizing strain to failure) are also presented.