Several new materials capable of generating large strains under an electric field are being developed for applications as actuators and high-drive sonar projectors. These materials are capable of generating strains that are several times large than those produced by conventional lead zirconate-titanate ceramics. The first group of materials are the class of lead magnesium niobate-lead titanate (PMNPT) ceramics. These materials are electrostrictive and, therefore, are operated under dc bias fields. The largest strains are obtained when the temperature is maintained in the region of the order-disorder phase transition of the material. This, however, makes the properties of the material temperature dependent. An alternative material is the family of lanthanum-modified lead zirconate-titanate (PLZT) ceramics. These materials have been developed extensively for electro-optic applications. They can generate even higher levels of strain compared with the PMNPT ceramics with less temperature dependence. They, however, suffer from higher dielectric hysteresis and are more suitable for actuator applications because of dielectric heating. Results are presented for measurements on several compositions of PMNPT and PLZT.

Hysteresis is a form of nonlinearity that is present in piezoceramic microactuator systems. A methodology to predict influence of hysteresis on system performance is valuable when these actuators are employed as part of closed loop motion control systems. In this work, an existing phenomenological approach (Preisach models) is investigated for piezoceramic systems. Hysteresis in a piezoceramic system is experimentally documented initially for a bounding operating condition of a cyclic electric potential. The limiting hysteresis loop has a positive turning point of +100 V and a negative turning point of -100 V. Hysteretic behavior for various operating conditions within this bounding loop (i.e. minor hysteresis loops) is then predicted using a moving Preisach model. In addition, hysteresis effects are analytically predicted when a constant mechanical load and a cyclic electric potential are applied simultaneously, using two inputs Preisach model. Experimental data are also presented for the minor hysteresis loops at different positive and negative turning points. Predictions using Preisach models agreed well with the experimental results, particularly when the minor loops are closer to the bounding loop.

Heterostructure multilayers of ferroelastic TiNi coupled to thin film TiO₂ and ferroelectric lead zirconate titanate (PZT) produces a smart material capable of performing both sensing and actuating functions. An important issue is the ability to generate the appropriate crystalline phases of each of the materials and to minimize the chemical interactions from the surrounding material. TiO₂ and PZT thin films were deposited onto commercially available TiNi substrates by the sol-gel process. Minimum crystallization temperatures for the TiO₂ phases and PZT perovskite phases were determined and characterized by x-ray diffraction.

This paper concerns the mechanical and ferroelectrical properties of TiNi/TiO₂/PZT multilayers. As prototypes for `smart' materials, the TiNi and oxide ceramics must be capable of both sensing and actuation functions. For testing of the properties of these meso-scale structures to occur, the mechanical and electrical properties of the individual components need to be characterized. The mechanical properties of the PZT thin film were characterized by Scanning Electron Microscopy and optical microscopy. Cracking and defects in the PZT were observed for thick films, however thin PZT films of 1 micron or less showed better mechanical integrity. The ferroelectric properties of the PZT thin films were smaller than for bulk PZT; this was likely associated with leakage currents caused by the mechanical imperfections of the films.

An improved micromechanical model has been developed to predict the hydrostatic response of 1 - 3 piezocomposites. The influence of matrix stiffness, interlayer stiffness, rod aspect ratio, and rod volume fraction on the load transfer and the effective hydrostatic piezoelectric voltage coefficient was investigated. Model predictions treat the ceramic rods as transversely isotropic and relax plane strain assumptions by integrating over the non-uniform strains in the rod and matrix. Results of the current model are compared with predictions from a plane strain model. Optimal interlayer and matrix properties for maximum sensitivity are discussed.

The subject of this research in fracture mechanics is the enhancement of flexural toughening beyond the original hardened material by the release of liquid `healing' chemicals such as adhesives from hollow fibers into cementitious matrices in response to loading. These chemicals solidify in the cracks to impart an increased toughness and ductility. The mechanisms appear to be adhesive rebonding of the fibers and crack-filling with adhesives that behave more rigidly when bonded inside cracks. An investigation was made into the development of smart cement composites that can self-repair internal cracks due to mechanical loading. The research focused on the cracking of hollow repair fibers dispersed in a composite and the resulting timed release of chemicals that seal matrix microcracks and rebond any damaged interfaces between fiber and matrix. Fiber pull-out tests were performed to examine rebonding of fibers. The rebonding was successful.

Commercially, the shape memory alloy TiNi is produced by either vacuum induction melting or by vacuum arc remelting of the pure metal ingots. Powder metallurgy techniques provide an alternative fabrication route but problems arise achieving chemical homogeneity. In this study TiNi compacts were cold pressed from the blended elemental powders and sintered in vacuum for varying times at temperatures from 800 degree(s)C to 1000 degree(s)C. Two heating rates were used, 5 K/min and 10 K/min. A TiNi microstructure could be produced after annealing at 1000 degree(s)C for 6 hrs, although some TiNi₃ was still observed. This is likely to be difficult to completely remove as TiNi₃ is thermodynamically more stable than TiNi. Thus, homogenization is unlikely to be completed by solid-state diffusion processes. The martensitic B19' structure was observed to be highly oriented after processing.

This research reviews common implant materials and suggests smart materials that may be used as substitutes. Current prosthetic technology, including artificial limbs, joints, and soft and hard tissue, falls short in comprehensive characterization of the chemo-mechanics and materials relationships of the natural tissues and their prosthetic materials counterparts. Many of these unknown chemo-mechanical properties in natural tissue systems maintain cooperative function that allows for optimum efficiency in performance and healing. Traditional prosthetic devices have not taken into account the naturally occurring electro-chemo-mechanical stress- strain relationships that normally exist in a tissue system. Direct mechanical deformation of tissue and cell membrane as a possible use of smart materials may lead to improved prosthetic devices once the mechanosensory systems in living tissues are identified and understood. Smart materials may aid in avoiding interfacial atrophy which is a common cause of prosthetic failure. Finally, we note that advanced composite materials have not received sufficient attention, they should be more widely used in prosthetics. Their structural efficiency allows design and construction of truly efficient bionic devices.

We report our development of biomaterials for information processing and signal transduction by incorporation of photodynamic proteins into conducting polymer and sol-gel matrices. Our aim is to develop biomaterials with high optical quality, good thermal and mechanical stability, and superior opto-electronic characteristics for applications in biosensor, signal transduction, and information processing. A novel three-dimensional optical memory system based on a light transducing protein, bacteriorhodopsin, is designed and demonstrated.

We are investigating thin film and monolayer systems that involve conjugated conducting polymers and specific biological macromolecules. One class of conducting polymers, polyalkylthiophenes, are derivatized with biotin. These biotinylated polymers form the basis for a generic cassette system of attachment for any biological molecule through biotinylation or interaction with streptavidin. The high affinity of the biotin-streptavidin system, used in sequential steps, forms the basis of the cassette method. We have formed both monolayers and thin films (a few nanometers) of the cassette assembly in which phycobiliproteins are incorporated. We are investigating the optical signal transduction properties of specific phycobiliproteins (phycoerythrin, phycocyanin and allophycocyanain) using the cassette system on the inner surface of glass capillaries and on optical fiber surfaces. Phycobiliprotein photocurrent signals in conducting polymer matrices on microelectrodes are also being investigated. Our aim is to integrate the signal transduction mechanisms of the phycobiliproteins within monolayers or thin films of the conducting polymers to create biosensors and related smart materials for applications in biomedicine and biotechnology.

The preparation, characterization and electronic properties of three series of microphase separated mixed (ionic and electronic) conducting or MIEC block copolymers are reported. In these polymer systems the electronic and ionic conductivities are limited to separate microdomains. This work represents a new concept in the area of electroactive polymers and should impact the microelectrochemical device industry.

A novel design for a torsional spring-loaded pH indicator using ionic polymeric gel fibrous muscles is presented. The essential parts of the proposed self-powered pH indicator are a pair of co-axial and concentric cylinders, an assembly of fibrous polyacrylonitrile (PAN) muscles, a torsional spring, and a dial indicator. The two co-axial cylinders are such that the inner cylinder may pivotally rotate about the central rotation axis that is fixed to the inner bottom or side of the outer cylinder. The outer cylinder also serves as a reservoir for any liquid whose pH is to be determined either statically or dynamically. The internal cylindrical drum is further equipped with a dial indicator on one of its outer end caps such that when a pH environment is present the contraction or expansion of the PAN fibers cause the inner drum to rotate and thus give a reading of the dial indicator. The motion of the dial indicator may also be converted to an electrical signal (voltage) for digital electronics display and computer control. A mathematical model is also presented for the dynamic response of the self-powered pH indicator made with contractile PAN fiber bundle assemblies.

Polymer composite material, containing conducting filler particles (e.g., graphite) at concentrations above the percolation threshold should, as a conductor, exhibit certain magnetic-field-sensitive properties, such as Hall effect or magnetoresistance. These effects not only allow us to classify them as smart materials, but also help in establishing the mechanism of conduction in such complex disordered systems. The present paper reports the results of investigations on magnetoresistance in composite materials, prepared by direct polymerization of propylene on graphite particles. The method ensures grafting of polymer to the filler surface, imparting remarkable properties to the composite. For composites with graphite magnetoresistance is positive for filler volume fraction above percolation threshold. Maximum value of magnetoresistance exceeds 10%. Below the threshold the samples show weak negative magnetoresistance, characteristic of conduction through localized states in disordered systems. This result correlates with our model of double percolation over filler particles, surrounded by thin layers of injected charge. New magnetic effects have been found, such as oscillations of dark conductivity in magnetic field and resonance magnetic-spin effects.

Current military aircraft employ multiple single function antennas installed at different locations to provide communications, navigation and identification (CNI), electronic warfare and radar and weapon delivery in the .15 to 18 GHz frequency bands. The smart skins concept, wherein several antennas are integrated into one (or a few) multifunction apertures conformal to the outer geometry of the aircraft, promises considerable benefits. These include extended antenna coverage, efficient use of aircraft realestate, quick installation and replacement and structural weight savings. However, to realize these payoffs, several disparate technical and operational issues such as development of multifunction apertures, integration of the radiating elements and repackaging the electronics into load-bearing structure, antenna isolation and resource management, and tolerance to low velocity impact damage, need to be resolved. Potential payoffs and the technical challenges of smart skins implementation and avionics repackaging is discussed in quantized transitional states from black box avionics traditional packaging to structurally integrated avionics of the future. Qualitative assessments of related smart skin technologies and risk reduction approaches, which could transition the technology to current and future aircraft, are proposed, and preliminary cost estimates presented.

In this paper, electronically steerable microstrip and leaky wave antennas using tunable ferroelectric material are proposed. These antennas are lightweight, low volume, low profile, and conformal. They have low fabrication costs and are easily mass produced. They are thin and do not perturb the aerodynamics of a host automobile or aircraft. Linear, circular, and dual polarization are achieved with simple changes in feed position. Beam steering is accomplished by varying the relative phase between radiating elements. In planar array, both horizontal and vertical beam can be combined to provide full scanning capabilities. Tunable ceramic phase shifters are used in these antennas. In microstrip antennas, they are deposited as thin films on the feed lines whereas in the leaky wave antennas they have been used as a traveling waveguide with a ground plane on one side and metallic periodic grating on the opposite side. The dielectric properties of the ferroelectric material are changed by a bias voltage applied to the waveguide which in turn controls the leaky wave direction of the antenna. A simple experiment is presented which shows a good agreement with the theoretical prediction.

Specular reflection from airport buildings interferes with instrument landing systems. It is possible to eliminate these specular reflections by periodic strip grating techniques. These metallic strips, when painted over a dielectric sheet, are found to eliminate the specular reflections from a plane metallic surface and the surface behaves as a `non reflecting conducting surface.' These inexpensive surfaces are lightweight and have the added advantage of ease in fabrication. It is easy to apply metallic paint in a regularly spaced strip pattern. By a suitable choice of the period `d' and the thickness of the dielectric medium (the wall), it is possible to eliminate reflections at any desired angle. It may also be possible to eliminate the reflections from other targets like cylinders and corner reflectors.

Prediction methods for the proper positioning and optimal number of actuators are necessary for efficient structural vibration control. The method proposed can provide ideas on how to select the optimum positions and number of the actuators. Using the coupled mode optimal control algorithm and comparing the control results of each given system, these methods are implemented. As a control structure, an all-clamped thin square plate with proportional damping has been selected. Some possible control algorithms that can be applied to the distributed structural system are discussed. To decide the control gain, a steady-state quadratic optimal control algorithm and discrete-time control system have been used. Since 6 plate modes are considered in the control system, a 12 X 12 matrix form of the system equation can be set up. By changing the impulse and the actuator positions and the number of actuators, a series of mode control simulations have been tried, and on the basis of these results, optimal actuator number and positions can be obtained.

Microstructures can introduce significant dissipation to the signal propagation through the inhomogeneous media. We have demonstrated how to build up the proper microstructures to suppress vibration and noise in smart structures made of inhomogeneous media. We have shown that proper choice of the mismatch can become a very effective control of the structural damping.

The use of active noise control applied to an industrial machine is investigated. The control system consists of an analog controller, an optical synchronous sensor, an error microphone, and an actuator. The signal from the optical sensor, which is synchronized with the impacts, is compensated by the controller and then sent to the actuator. The controller automatically adjusts itself according to the error signal to get maximum noise reduction. Instead of the more traditional loudspeakers used in noise control systems, a piezoelectric actuator is developed to work in a harsh industrial environment. The actuator is basically a bending mode vibrator made of aluminum and PZT (lead zirconate titanate) plates and is able to work in the frequency range of interest. A computer program based on the finite element approach was developed to aid the design of the actuator. The predicted output and the measured one agree very well. The system is tested in a laboratory setup by replaying the noise recorded from the machine. A reduction of 10 dB(A) is achieved.

This paper presents a computer modeling and simulation of an active sound absorbing system with an optimal state-feedback controller. First, a state-space model is developed to describe one-dimensional sound reflection and transmission in the time domain. In the model derivation, the difficulty of discretizing the wave equation in an unbounded region is overcome by combining the finite-difference and analytical solutions. Numerical simulation of the open- loop model response is performed, which shows a good agreement with the well known frequency domain solutions. Second, a state-feedback controller including a linear quadratic regulator and a Kalman filter type state-estimator is designed using the optimal control theory. Numerical simulation of the closed-loop model response of an active sound control system containing two sensors and one actuator is presented. It is shown that a broadband attenuation of more than 30 dB over 2 octaves has been reached.

The unicellular ciliate, Stentor coeruleus, exhibits sensitive light-avoiding behavior. The photosensor stentorin showed a (M - H)^- at 591.1304, which is in accord with the formula C₃₄H₂₃O₁₀. Acetylated stentorin, when FAB-desorbed as (M + H)⁺, shows a series of ions indicating the presence of eight hydroxyl groups. Additional confirmation is a collisionally activated decomposition (CAD) spectrum of the (M + H)⁺ of the octaacetate. The NMR spectrum of stentorin shows characteristic signals of isopropyl groups. Similar studies indicate that photosensor blepharismin from Blepharisma japonicum is structurally different from stentorin. Time-resolved fluorescence decays indicated that a primary event occurs within a few picoseconds. The stimulus light signal absorbed/perceived by Stentor and possibly by Blepharisma, is apparently amplified by a transient calcium influx into the cell. Preliminary studies suggest that signal transduction in both organisms utilizes G-protein(s) as an initial transducer and a cGMP-phosphodiesterase as the effector system, analogous to the visual system of higher animals.

Based on the well known observation that refractive index changes can be induced with light and that such changes are often accompanied by density and length changes, we have demonstrated photomechanical effects (light induced length changes) in polymer optical fibers and have applied these effects to make all-optical devices that have a mechanical function. In particular, we report on the observation of the slower photothermal mechanism and the faster electrostrictive mechanism. These two mechanisms are applied to build an all-optical position stabilizer and digital positioner; and an ultrafast all-optical positioner.

A novel design for a helical spring-loaded ionic polymeric gel actuator is presented, specifically an encapsulated hermetically sealed, helical compression spring-loaded cylindrical linear actuator containing a counterionic solution or electrolyte such as water + acetone, a cylindrical helical compression spring and a collection of polymeric gel fibers. The proposed design is such that the helical spring not only acts as a compression spring between the two hermetically sealed circular end caps but contains snugly the polymeric gel fiber bundle and also acts as the cathode (anode) electrode while the two actuator caps act as the anode (cathode) electrodes. Electrical control of the expansion and the contraction of the linear actuator is possible. A mathematical model is presented for the dynamic response of contractile fiber bundles embedded in or around elastic springs that are either linear helical compression springs or hyperelastic springs such as rubber-like materials. The proposed model considers the electrically or pH-induced contraction of the fibers for the computer-controlled dynamic performance of the actuator.

An ionic polymeric gel is defined as a 3-D charged network of a cross-linked macromolecular polyelectrolyte capable of collapsing or swelling in an acidic or alkaline environment, respectively, purely due to pH changes. Fixed electrical charges reside at all cross-links in such macromolecular networks in the presence of wandering mobile charges that tend to change their spatial distribution within the gel network. In the presence of an electric field, the mobile ions redistribute themselves in the gel network and thus cause the network to deform accordingly. A microelectro-mechanical model is presented that takes into account such internal electric charge redistribution of fixed and mobile ions due to the presence of an electric field. Direct computer control of large expansions and contractions of ionic polymeric gels by means of a voltage gradient appears to be possible. A mechanism is presented for the reversible nonhomogeneous large deformations and in particular bending of strips of ionic polymeric gels in the presence of an electric field. Exact expressions are given relating the deformation characteristics of the gel to the electric field strength or voltage gradient, gel dimensions and other physical parameters. It is concluded that direct voltage control of such nonhomogeneous large deformations in ionic polymeric gels is possible.

Shape memory effect and pseudoelasticity due to phase transformation and reorientation are modelled by specifying the free energy function and the dissipation potential. The resulting equations account for combined isotropic and kinematic hardening, adiabatic transformation, and simultaneous, coupled transformation and reorientation. Adiabatic transformation results indicate `thermal hardening' that substantially increases the final transformation stress relative to isothermal transformation.

A new high temperature shape memory alloy system based on the Ni₅₀Ti_50-XHf_X has been successfully developed. The experimental results show that the martensite transformation temperature increases significantly with an increase in Hf content. The elevating effect of Hf on the phase transformation temperature is much higher than that of Pd. The A_f phase transformation temperature can reach as high as 503 degree(s)C when the Hf content is 25%. Examination of the one-way shape memory effect displays that the fully reversible strain decreases slightly as the Hf content increases, but the alloy also possesses a relatively high fully reversible strain even though the Hf content is 25%. It was also found that the new high temperature shape memory alloys demonstrate a very good two-way shape memory effect after proper training.

A preliminary investigation was made to study the possibility of training the newly developed TiNi-Pd high temperature shape memory alloys to posses the two-way memory effect, and characterize the various factors that affect the magnitude of the two-way memory effect. The experimental results show that all the newly developed alloys can demonstrate the two-way memory effect, even though the transformation temperature of the alloy reaches 280 degree(s)C. The permanent strain and phase transformation temperature are two important parameters to determine the magnitude of the two-way memory effect.

Mechanical tests have been conducted to characterize the shape memory effect and mechanical properties of a NiTi-20 at%Pd high temperature shape memory alloy. The experimental results show that the ratio of the Young's modulus of martensite to austenite is 0.58. The ratio of the yield stress of the martensite to austenite phase is 0.62 and the fully reversible strain is 3%. These values indicate that the shape memory properties of the NiTi-Pd alloys is not as good as those of the NiTi binary alloys. The mechanical properties of the alloy also demonstrate that the ductility of the alloy is significantly lower than that of the NiTi binary alloy. Further studies should be carried out to improve the shape memory effect and enhance the ductility of the alloy.

A great deal of attention has been devoted to the adaptive structure and composite materials constituting shape memory alloys (SMAs), especially for suppressing vibration. This requires a comprehensive understanding of the damping characteristics and other mechanical properties of SMAs. This paper focuses on the dynamic properties of various SMAs including NiTi, Ti(Ni-15at%Pd), and Ni(Ti-20at%Hf) higher temperature SMAs which have been systematically studied using a dynamic mechanical analyzer. The elastic modulus and damping characteristics have been measured as a function of temperatures during cooling and heating processes for Ni-51.0at%Ti, Ti(Ni-15at%Pd), and Ni(Ti-20at%Hf) alloys. The influence of dynamic factors, such as vibration frequency, ramp rate, and amplitude, on the damping and elastic modulus were systematically studied for Ni-51.0at%Ti alloy. The thermoelastic damping in the vicinity of the forward and reverse transformation also are discussed.

Several degradation mechanisms in ferroelectric ceramics are analyzed in this article. A ferroelectric crystal under cyclic electric field fatigues by forming a-domain bands. An energy based model is proposed, indicating that these bands are retarded by the electric field, but driven by the shear stress resolved onto the bands. The stress has been attributed to the misfit strain near the 180 degree(s) domain wall and the edge of the electrodes. A second problem is related to fracture of piezoelectric ceramics. A double-cantilever beam subjected to combined electrical and mechanical loadings is analyzed using finite elements. Also analyzed is electrode debonding, which is shown to decrease capacitance.

Closed form solutions for all three modes of fracture for an infinite piezoelectric medium containing a center crack and is subjected to a combined mechanical and electrical loading were obtained using the Stroh formalism. The strain energy release rate was derived and implication to fracture behavior was discussed. Mode I fracture experiments were conducted using compact tension specimens of PZT-4 piezoelectric ceramic. The results indicate that the use of the strain energy release rate as fracture criterion can accurately account for effects of the electric field on the apparent fracture toughness of the material.

This paper investigates the damping level trends of three-dimensionally braided composites as a function of matrix material, fiber-matrix interface, fiber braid angle, fiber volume, and axial fiber tow size. With knowledge of such trends, designers may increase the structural damping in a 3-D braided composite component, thereby reducing component vibration, shock response, and fatigue. The logarithmic decrements of the fundamental mode response of cantilevered, 3-D braided composite beam specimens were calculated for comparison. Although the logarithmic decrements of two specimens, differing only in their matrix materials (Tactix 123 and Epon 828), were essentially identical, both were considerably larger than that for steel. The value for the decrement of these two composite specimens' response was taken as a reference. Altering the nature of the fiber-matrix interface by lubricating the fibers before specimen consolidation greatly increased the damping relative to the baseline. Trends of increasing damping were measured with both increasing fiber braid angle and fiber volume. Finally, increasing levels of damping are reported for decreases in axial fiber tow size. Explanations for these trends, based on the possible microscopic and macroscopic nature of the braided composites, are offered.

An aerospace structural material with an intrinsic sensor system for monitoring characteristics such as temperature or strain has been the goal of many of today's research efforts. However, the anticipated anisotropy and interfacial conditions introduced by embedding sensors has traditionally resulted in conservative acceptance of smart materials. The present study has addressed the question of whether the addition of an embedded silica optical fiber compromises the mechanical properties of a polymer matrix composite. Three novel surface and subsurface imaging methods that may answer this question are presented which include scanning electron acoustic microscopy, scanning acoustic microscopy and strain stage electron microscopy. They have been found to have a realistic potential for applications such as imaging microstructural residual stress fields, mapping changes in elastic moduli across the fiber-matrix interface and micron-level observation of defect formation in real-time. The theory of each technique is discussed and preliminary results are presented.

Tape casting of ceramic materials offers the flexibility of gradually altering the electronic or structural properties of two dissimilar systems in order to improve their compatibility. This research outlines the processing and fabrication of two systems of functionally gradient materials. The systems are both electronic ceramic composites consisting of Ba_1-xSr_xTiO₃ (BSTO) and alumina or a second oxide additive. These composites would be used in phased array antenna systems, therefore, the electronic properties of the material have specific requirements in the microwave frequency regions. The composition of the tapes are varied to provide a graded dielectric constant, which gradually increases from that of air (dielectric constant equals 1) to that of the ceramic (dielectric constant equals 1500). This allows maximum penetration of incident microwave radiation as well as minimum energy dissipation and insertion loss into the entire phase shifting device.

We have measured the optical response speed of the semiconductor to metal phase transition in VO₂ films for excitation with femtosecond laser pulses at 780 nm wavelength. By probing at a wavelength of 780 nm on a time scale from 0 to 0.5 ns and at 633 nm for longer times, we have determined the dynamic response of the complex refractive index and the complex permittivity as determined from transmission and reflection measurements. The phase transition was found to be largely prompt with the final high-temperature metallic state reached in less than 5 ps.

The elasticity and anelasticity of Ni₅₀Ti₅₀ films deposited on Si substrates was studied yielding information on the damping and modulus softening. It was found that the transformation behavior strongly depends on the film thickness and approaches bulk Ni₅₀Ti₅₀ behavior as the film becomes a few micrometers thick. For the same film thickness, the transformation depends on the film/substrate adhesion. In films with good adhesion cross sectional transmission electron microcopy (TEM) reveals a thin parent phase layer which does not transform while the bulk part of the Ni₅₀Ti₅₀ film transforms. It is thus proposed that interface constraints stabilize the B2 structure. A microscopic interpretation in terms of transformation strains at the interface is given.

In this work, the preparation of PZT materials used for the fabrication of smart sensors and actuators is closely investigated. The sol-gel method is used for the processing of the PZT powder because of its potential for making fine, pure and homogeneous powders. Sol-gel is a chemical method that has the possibility of synthesizing a reproducible material. Microwave energy is used for the calcining of this powder and the sintering of the PZT samples. Its use for calcination has the advantage of reducing the total processing time and the soak temperature. In addition, the combination of sol-gel and microwave processing leads to smaller particles and a more uniform distribution of their sizes. Microwave sintering of sol-gel prepared PZT has been accomplished successfully and has been shown to yield improved microstructure and good properties.

In this study artificial neural networks were used to model the spray forming process. Networks were developed and trained using process parameter and product quality data collected from a series of five spray forming runs. Process parameters of time into run, melt temperature, and gas to metal ratio were used as inputs and the networks were trained to predict the corresponding values of exhaust gas temperature, preform surface roughness, and porosity in the product. These networks were then tested with actual and hypothetical data. The results of the study showed that the networks can determine relationships between process parameters and the end product quality. It was also shown that the networks can be used to predict the effect on product quality from changes in process parameters. Additional work is in progress to create a larger data set for training over a broader region of the operating envelope. The result of this ongoing work will provide greater reliability in network prediction.

This work outlines the material processing technique used to fabricate a multilayer ferroelectric material BST (barium strontium titanate). The composition and thickness of each layer can be controlled such that a tunable multilayer frequency-selective device can be fabricated. The BST materials can be processed by a combination of sol-gel powder processing, tape-casting and microwave processing to yield a multilayer composite material having variable and tunable dielectric properties. For thinner layers, microwave assisted plasma deposition is used to prepare thin film BST from a sol-gel slurry.

Some electrical properties were studied on potential responses of self-assembled bilayer lipid membranes (s-BLMs). Gramicidin doped s-BLM sensors responded to hydrogen ion concentrations linearly with the slope of 144 mV/decade in the range of 0.4 to 4 M; Monensin doped s-BLM sensors responded to sodium ion, which has a slope of about 40 mV/decade in the concentration range of 0.3 to 30 mM; Valinomycin doped s-BLM sensors have nearly Nernstian response in the concentration range of 1.0 to 30 mM/[K+]; Ferrocene doped s-BLM sensors responded linearly to the ferricyanide ion, whose slope is 146 mV/decade in the concentration range of 0.03 to 30 mM/[K₃Fe(CN)₆]. Many ions such as ferrocyanide, citrate, SCN^-, ClO_{4/$(superscript -}, etc. did not interfere with the sensor response characteristics. Factors influencing s-BLM sensors' reproducibility and stability also were investigated.

Composite materials were synthesized by direct polymerization of propylene on the surface of natural or synthetic graphite particles. The method ensures grafting of polymer to a part of filler particle surface, while the other part remains open to physical contact between the particles, the resulting properties of the material becoming favorably different from previously known composites. Coefficient of strain sensitivity K equals (Delta) R/R(epsilon) (R is resistance of the sample, (epsilon) is tensile strain) was measured at different concentrations of filler and different temperatures. There is a broad maximum of K around the percolation threshold (4.5 vol.% for natural graphite) with a peak value of 100 - 150, which is much higher, compared to conventional wire resistors. A slight hysteresis is observed at unloading due to plasticity of the matrix. Hysteresis disappears, when temperature is lowered by 20 - 50 degrees, or (epsilon) is less than 1%, but previously high value of K remains. Below the glass transition temperature K is very low. The results are explained by the change of current- carrying chains in loading-unloading cycles. Temperature dependence of resistance is presented, thermal conductivities were calculated for different models and compared with experimental values.

It has long been recognized that Ni-Ti shape memory alloys (SMAs) behave pseudoelastically above the austenite finish temperature (A_f) with an initially very weak strain-hardening character during the transformation. Under conditions of cyclic loading with a maximum strain, (epsilon) _max, the critical stress to initiate stress-induced martensitic (SIM) transformation decreases, the strain-hardening rate increases, residual strain accumulates and the hysteresis energy progressively decreases over many cycles of loading. Hence the hysteresis energy available for dissipation gradually decreases during cycling. In this paper, some modeling features are discussed to address the effects of dislocation arrays generated in the parent phase as well as the distribution of transformation product/interfaces. Several uniaxial experiments are reported on Ni-Ti to highlight the path dependence of the cyclic deformation behavior and progressive decrease of dissipated energy. Implications for multiaxial loading behavior also are discussed.