While the concept of an adaptive aircraft wing, i.e., a wing whose shape parameters such as camber, wing twist, and thickness can be varied to optimize the wing shape for various flight conditions, has been extensively studied, the complexity and weight penalty of the actuation mechanisms have precluded their practical implementation. Recent development of sensors and actuators using smart materials could potentially alleviate the shortcomings of prior designs, paving the way for a practical, `smart' adaptive wing which responds to changes in flight and environmental conditions by modifying its shape to provide optimal performance. This paper presents a summary of recent work done on adaptive wing designs under an on-going ARPA/WL contract entitled `Smart Structures and Materials Development--Smart Wing.' Specifically, the design, development and planned wind tunnel testing of a 16% model representative of a fighter aircraft wing and incorporating the following features, are discussed: (1) a composite wing torque box whose span-wise twist can be varied by activating built-in shape memory alloy (SMA) torque tubes to provide increased lift and enhanced maneuverability at multiple flight conditions, (2) trailing edge control surfaces deployed using composite SMA actuators to provide smooth, hingeless aerodynamic surfaces, and (3) a suite of fiber optic sensors integrated into the wing skin which provide real-time strain and pressure data to a feedback control system.

The development of aircraft lifting surfaces that change shape to enable relatively shock-free performance throughout a range of design points in the transonic region is described. This type of reduced-drag airfoil can increase range, decrease fuel expenditure, increase cruising speed, increase lift, or accomplish a combination of these desirable effects. Preliminary payoff studies on a Gulfstream III aircraft with a hypothetical smart wing, show that if 1000 lbs. were added to the weight of the aircraft to incorporate smart-wing technology, and the coefficient of drag C_D could be decreased by 20 counts (0.0020), 5% less fuel would be required or the range could be increased by 5% with the existing fuel. Airfoil shapes are computed with a stochastic optimization method based on simulated annealing. Drag reduction is presented as a function of flight condition, region of surface control, and number of actuators. Design and development of an experimental TERFENOL-D actuator to provide the variable airfoil shape required for optimum performance are also discussed.

A survey of current literature was performed and vehicle designers from the aerospace industry were polled to examine how state of the art smart structural concepts could improve the design of hypersonic vehicles. Several types of hypersonic vehicles; including winged single stage to orbit, sub-orbital cruise aircraft, and supersonic/hypersonic missiles have demanding airframe and systems requirements which may not be sufficiently met with traditional structural designs. The use of smart structures is examined to improve vehicle performance in areas such as active vibration control, noise reduction, vehicle attitude control, structural cooling, and engine performance. The operating environment of hypersonic vehicles are examined and the capabilities of currently used structural materials and actuators are compared with those of smart materials and structures. Possible smart structures applications are presented as modifications to existing designs as well as new structural concepts. Conclusions are made on the suitability of various smart structures concepts for current and future hypersonic applications.

Damage identification of complex structures can be performed using an Active Structural Health Monitoring System (ASHMS) utilizing an array of piezoceramic (PZT) sensor- actuators and an electromechanical impedance analyzer. Based on the theory of electromechanical impedance for surface-bonded collocated sensor-actuators, the system provides the means of implementing effective Non-Destructive-Evaluation health monitoring to a structure at any point in its life cycle. When integrated into a structure, the ASHMS can identify the location and extent of damage through a statistical analysis algorithm which compares the electromechanical admittance of the structure's current condition with the structure's `baseline' condition over a defined frequency range. This paper presents a model independent method of structure damage identification based on statistical analysis of the changes in the electromechanical impedance of the structural response. Using a small section of an airplane fuselage with free-free boundary conditions as the test structure, a prototype system has been successfully developed which automatically measures and collects the electromechanical admittance data from an array of transducers. The measurement system developed can apply large voltages to the PZT transducers, while accurately determining the spectral and harmonic information of the frequency range of interest resulting in an increase in the measurement sensitivity and the area monitored by a single transducer. The system can accurately measure and collect large amounts of structural information with a limited number of transducers in a very short period of time. The post-analysis of the measured structural variation can be performed with the advanced signal processing algorithm presented herein within seconds of data collection. The results show a remarkable accuracy of damage location identification for a complex structure. The basic research conducted so far indicates that the ASHMS and associated processing techniques have a promising potential for health monitoring of real complex structures.

Variable stiffness is a new branch of smart structures development with several applications related to aircraft. Previous research indicates that temporarily reducing the stiffness of an airplane wing can decrease control actuator sizing and improve aeroelastic roll performance. Some smart materials like shape memory alloys (SMA) can change their material stiffness properties, but they tend to gain stiffness in their `power on' state. An alternative is to integrate mechanisms into a structure and change stiffness by altering boundary conditions and structural load paths. An innovative concept for an axial strut mechanism was discovered as part of research into variable stiffness. It employs SMA springs (specifically Ni-Ti) in a way that reduces overall stiffness when the SMA springs gain stiffness. A simplified mathematical model for static analysis was developed, and a 70% reduction in stiffness was obtained for a particular selection of springs. The small force capacity of commercially available SMA springs limits the practicality of this concept for large load applications. However, smart material technology is still immature, and future advances may permit development of a heavy-duty, variable stiffness strut that is small and light enough for use in aircraft structures.

Smart material actuator technology for operation `on the blade' is now becoming available and has the promise to overcome the size, weight and complexity issues of hydraulic and electric on-rotor actuation. However, the challenges of the limited output capability of the materials and the dynamic operating environment must be fully addressed and resolved. The present study covers the conceptual sizing and design of a full scale demonstration system to provide active control of noise and vibrations as well as inflight blade tracking for the MD-900 helicopter. Active control is achieved via a trailing edge flap and trim tab, both driven by on- blade smart material actuators. Overall, this ARPA sponsored program entails the design, development, and whirl tower testing of the full scale active control rotor system. If successful, an entry in the NASA Ames 40 X 80 foot wind tunnel and flight tests are planned for a follow on program.

Control of trailing vortex wakes is an important challenges for both military and civilian applications. This paper summarizes an assessment of the feasibility of mitigating adverse vortex wake effects using control surfaces actuated via Shape Memory Alloy (SMA) technology. The assessment involved a combined computational/design analysis that identified methods for introducing small secondary vortices to promote the deintensification of vortex wakes of submarines and aircraft. Computational analyses of wake breakup using this `vortex leveraging' strategy were undertaken, and showed dramatic increases in the dissipation rate of concentrated vortex wakes. This paper briefly summarizes these results and describes the preliminary design of actuation mechanisms for the deflectable surfaces that effect the required time-varying wake perturbations. These surfaces, which build on the high-force, high- deflection capabilities of SMA materials, are shown to be well suited for the very low frequency actuation requirements of the wake deintensification mission. The paper outlines the assessment of device performance capabilities and describes the sizing studies undertaken for full-scale Vortex Leveraging Tabs (VLTs) designed for use in hydrodynamic and aerodynamic applications. Results obtained to date indicate that the proposed VLTs can accelerate wake breakup by over a factor of three and can be implemented using deflectable surfaces actuated using SMAs.

This work is concerned with the development and testing of a foam-PVDF smart skin designed for active noise control. The smart skin is designed to reduce sound by the action of the passive absorption of the foam (which is effective at higher frequencies) and the active input of an embedded PVDF element driven by an oscillating electrical input (which is effective at lower frequencies). It is primarily developed to be used in an aircraft fuselage in order to reduce interior noise associated with turbulent boundary layer excitation. The device consists of cylindrically curved sections of PVDF piezoelectric film embedded in partially reticulated polyurethane acoustic foam. The active PVDF layer was configured to behave in a linear sense as well as to couple the predominantly in-plane strain due to the piezoelectric effect and the vertical motion that is needed to accelerate fluid particles and hence radiate sound away from the foam surface. For performance testing, the foam-PVDF element was mounted near the surface of an oscillating rigid piston mounted in a baffle in an anechoic chamber. A far-field and a near-field microphone were considered as an error sensor and compared in terms of their efficiency to control the far-field sound radiation. A feedforward LMS controller was used to minimize the error sensor signal under broadband excitation (0 - 1.6 kHz). The potential of the smart foam-PVDF skin for globally reducing sound radiation is demonstrated as more than 20 dB attenuation is obtained over the studied frequency band. The device thus has the potential of simultaneously controlling low and high frequency sound in a very thin compact arrangement.

The preliminary design of aeroelastically tailored adaptive missile fins for supersonic speeds is presented. Due to the extreme operating environment of supersonic flight including high temperatures and pressures, a successful supersonic smart missile fin design has been more difficult to develop than previously developed subsonic smart missile fins. Currently research at the University of Texas at Arlington is being conducted to develop a light-weight, low-cost, smart missile fin capable of surviving the supersonic operating environment while providing performance comparable to existing missile fins. Efforts are being concentrated on using aeroelastic tailoring to enhance the effectiveness of existing actuators using smart structures, allowing a lower total actuator weight with better utilization of missile internal volume. Previous work (Barrett) has used piezoelectric elements to apply span-wise twist to a fixed fin or deflect an all-moving fin around a fixed spar. This research attempts to identify improvements and alternative designs for the all-moving smart fin to enable it to be used at supersonic speeds. Various techniques to reduce the control surface hinge moment are presented and compared to attempt to reduce control forces which allow smaller actuators to be used. Future work will focus on improved analysis of the aerodynamic interactions and the elimination of fuselage mounted actuators by the use of a combination of smart fin technologies.

The development of control technology specifically for smart structures and materials has lagged substantially behind that of the base materials, transducers, and embedding techniques. Still, development of smart structures with ever-greater numbers of embedded elements continues, spurred by potential uses that require large arrays of sensors and actuators. For example, rather than implementing a control design that is sensitive to the particular device layout, a densely sampled array allows the controller to optimize the use of sensor information and actuator authority. No control technology suitable for such large arrays exists, however, and this presents a barrier to future applications. In this paper we report on recent progress in developing and demonstrating technology capable of controlling hundreds or thousands of sensors and actuators embedded in the base material. We have dubbed this the `KIKO control problem' (Kilo-Input/Kilo-Output) for smart materials. This paper focuses on a new multiscale/multirate theory of hierarchical design based on the wavelet transform. In the context of this theory, we develop efficient and highly scalable implementations of control systems using multiprocessor architectures. The paper describes our multiscale control approach and presents simulation results on a flexible plate.

Loading experiments have been carried out on a flat panel and C-channels fabricated by the Continuous Resin Transfer Molding (CRTM^TM) process. Arrays of fiber Bragg grating (FBG) strain sensors written during fiber draw were embedded in the structures, and the strains measured by these distributed sensors are compared with the results of surface-mounted resistance strain gages (RSG's) and FBG arrays. Reproducibility of the strains measured by an embedded FBG array was demonstrated during cyclical loading of a C-channel, and survivability and reliability of the array was established when the structure was loaded to failure. Discrepancies between the results reported by the embedded FBG's and surface- mounted RSG's and FBG's are attributed to deflections and/or distortions of the embedded FBG by the structural fibers during CRTM^TM processing.

Composite utility poles have significant advantages with respect to wooden utility poles that include superior strength and uniformity, light weight for ease of deployment, the ability to be recycled reducing hazardous waste associated with chemically treated wooden poles, and compatibility with embedded fiber optic sensors allowing structural loads to be monitored. This paper reports tests conducted of fiber optic grating sensors in combination with an overcoupled coupler demodulation system to support structural testing of a 22 foot composite pole.

Our laboratories have developed a measurement system called SOFO, based on low-coherence interferometry in singlemode optical fibers and allowing the measurement of deformations of the order of 1/100 mm. This system is especially useful for the long-term monitoring of civil structures such as bridges, tunnels, dams and geostructures. The SOFO system requires the installation of two fibers in the structure to be monitored. The first fiber should be in mechanical contact with the structure in its active region and follow the structure deformation in both elongation and shortening. The second fiber has to be installed freely in a pipe near the first one. This fiber acts as a reference and compensates for the temperature dependence of the index of refraction in the measurement fiber. This contribution presents the design process as well as the lab and field tests of a sensor responding to these requirements and adapted to the installation in concrete structures. The active region can be between 25 cm and 8 m in length, while the passive region can reach at least 20 m. While the reference is free, the measurement fiber (installed in the same pipe) is pre-stressed between two glue-points at each end of the active region. The glue was chosen in order to avoid any creeping problems even at temperatures up to 160 degree(s)C and elongation up to 2%. The sensor was tested in laboratory and field conditions. The lab tests included survival to concreting, high temperatures, freezing, thermal cycling, vibrations, cracking and corrosion; response to elongation and compression, measurement range and creeping of the glue points at high temperatures and high tensions. The field tests included installation of a number of these sensors in a bridge deck and in a tunnel vault. In these applications we tested the ease of use, the rapidity of installation and the survival rate.

We describe the use of first Bragg gratings for monitoring the tensile and compressive strains in a composite wrapped concrete cylinder subjected to load testing. Compressive strains of up to approximately 3.8% were measured using the system.

It is theoretically possible to place long fiber-optic displacement sensors on structures that are generally loaded and still maintain the ability to exactly discriminate signals of interest. The chief advantage of finite-length fiber-optic sensors is that the sensitivity of the measurement scales not only with the maximum strain along the path but the length of the sensor as well. One consequence of this scaling property is that `smart' structures incorporating such a measurement approach could be sensitive yet still have low maximum strains. In other words, the sensitivity of the measurement is partially decoupled from the stiffness of the structure. This theoretical result is true for simple prismatic structures composed of a linear elastic homogeneous material with arbitrary end loading, and with perfectly positioned displacement sensors. A model tail rotor torque tube has been constructed and verifies the essential elements of the analysis. Unfortunately, the use of long displacement sensors effectively integrates signals of interest along the measurement paths and is thus susceptible to accumulated manufacturing errors. These errors are evident both by a decrease in sensitivity to the load intended to be measured and a response of unintended loads. For a simple construction technique certain manufacturing errors were modeled and provide theoretical limits to the performance of a torque tube incorporating finite length sensor paths. Elements of the error model are confirmed by experiments on model torque tubes instrumented on the surface with various finite length sensor topologies. Finally, an extension of this work to sensors embedded in a composite structure is also discussed.

Because of the budgetary stridency, the future of long term Federal support for Smart Materials and Structures Technology is uncertain. Because of the near-term focus of commercial R&D industry is unlikely to invest large amounts of private funds without near term product sales. Therefore there is a need to accelerate the development of products from the Smart Materials and Structure research. The Advanced Research Projects Agency (ARPA) Advanced Materials and Processing Program endeavors to encourage productization through innovative government/industry programs. This paper discusses these issues in the context of the DoD dual-use technology strategy.

The Synthesis and Processing of Intelligent Cost Effective Structures (SPICES) program is comprised of a consortium of industrial, academic and government labs working to develop cost effective material processing and synthesis technologies to enable new products using active vibration suppression and control devices to be brought to market. Since smart structures involve the integration of multiple engineering disciplines, it has been the objective of the consortium to establish cost effective design processes between this multi-organizational team for future incorporating of this new technology into each members respective product lines. Over the twenty-four month program many new improvements in sensors, actuators, modeling, manufacturing/integration and controls have been realized. The paper outlines the four phases of development in the program and the impact some of the key technologies will have on the smart structure development process in the future.

The Synthesis and Processing of Intelligent Cost Effective Structures (SPICES) Program is a partnership program sponsored by the Advanced Research Projects Agency. The mission of the program is to develop cost effective material processing and synthesis technologies to enable new products employing active vibration suppression and control devices to be brought to market. The two year program came to fruition in 1995 through the fabrication of the final smart components and testing of an active plate combined with two trapezoidal rails, forming an active mount. Testing of the SPICES combined active mount took place at McDonnell Douglas facilities in St. Louis, MO, in October-December 1995. Approximately 15 dB reduction in overall response of a motor mounted on the active structure was achieved. Further details and results of the SPICES combined active mount demonstration testing are outlined. Results of numerous damping and control strategies that were developed and employed in the testing are presented, as well as aspects of the design and fabrication of the SPICES active mount components.

The final demonstrations of the ARPA SPICES (Synthesis and Processing of Intelligent Cost Effective Structures) program test the control of two active vibration mounts manufactured from composites with embedded actuators and sensors. Both mount demonstrations address wide band control problems for real disturbances, one at low frequency and the other at high frequency. The control systems for both are two-level hierarchies, with an inner active damping augmentation loop and an outer vibration control loop. We first review the control design requirements for the demonstration and summarize our control design approach. Then we focus on presenting the experimental results of the final demonstrations. For the low frequency demonstration, two alternative control approaches were demonstrated, one involving finite impulse response modeling and the other state space modeling. For the high frequency demonstration only the finite impulse response modeling approach was used because of computational limitations due to the complex system dynamics.

A new class of composite materials designated as the 1-3 piezocomposite is being investigated for potential use in underwater smart material structures. In-water acoustical properties of new 1-3 composite panels were examined experimentally as a function of temperature, pressure and frequency. The measured transmitting voltage response (TVR) showed the existence of parasitic modes in the composite panel in addition to the expected thickness mode. The effect of underwater explosive shock on the TVR showed no detrimental effects in mechanical structure or acoustical performance of the piezocomposite panel. The free-field voltage sensitivity was constant at -185 dB referenced to 1 volt per micropascal over the testing frequency range. Linearity with electrical drive level and pressure stability of the 1-3 piezocomposites have also been established with the present choice of ceramic-polymer components. These results demonstrated that this new material is potentially used for applications of both large-area actuators and sensors in forming active surfaces of new smart structures.

Finite element analysis was performed on the preliminary design of a multilayered composite panel for acoustic suppression. The panel design features a circuit board, alumina and circuit board base layer structure. An square array of 64 piezoelectric actuators is mounted on this base. These actuators are divided into 16 groups of four actuators by 16 alumina cap plates. A thin kapton layer is placed over the cap layer. The final top layer and the area between actuators are a polymer filler material. Unit cell analysis of the design was performed to evaluate the effectiveness of the embedded actuators in producing surface deformations, the stresses generated in the actuator during actuation and the role of a thin glue layer, between the actuator and alumina cap plate, in mitigating high stresses. The results show that the cap plates become curved during deformation. This deformation is transmitted through the top polymer layer to the surface. This suggests that the effect of this surface profile on acoustic fields generated by the actuator array motion should be understood. Stresses in the actuator are found to be high without the glue layer, compared to known critical fracture stress values. Inclusion of the glue layer significantly reduced the stresses and is therefore an important consideration in the design.

A cost-effective technology has been developed for producing 1-3 piezoelectric ceramic/polymer composites for active surface control. SonoPanel^TM 1-3 piezocomposite transducers consist of an array of piezoelectric ceramic rods in a polymer matrix. Stiff face plates are bonded to the composite for stress amplification when used as a sensor and to enhance surface response uniformity when used as an actuator. Many piezocomposite design variations have been produced for specific applications. The key technology in SonoPanel^TM manufacturing is the PZT ceramic injection molding process. Using this process, an entire array of piezoelectric ceramic rods are molded in one operation using specially designed tooling. Injection molded PZT preforms are formed at a rate of one per minute. Several thousand components with excellent piezoelectric properties and part-to-part reproducibility have been manufactured to date. The piezocomposite fabrication process has been scaled up for low volume manufacturing. More than thirty 250 X 250 mm SonoPanel^TM transducers have been produced and evaluated. The transducers show high receiving voltage sensitivity and transmitting voltage response as well as symmetrical beam patterns. Next generation SonoPanel^TM transducers, with materials and designs optimized for Navy systems, are under development, including advanced panels for active surface control. The devices incorporate actuators, pressure sensors, and velocity sensors--all made from 1-3 composite materials--into an autonomous smart panel.

The processing of Pb(Zr,Ti)O₃, or PZT, fiber and fiber/polymer composites for transducer applications is discussed. Green PZT fibers, 80 to 100 micrometers in diameter, were formed at Advanced Cerametrics, Inc., using the Viscous Suspension Spinning Process (VSSP). In this process, fine PZT powder is intimately mixed with polymer precursor by high shear mixing. The powder and precursor mixture is spun through a spinneret into a coagulation bath to form fibers. The fibers are washed, dried, and collected on a spool. Yarns containing between 10 and 500 individual fibers were collimated by applying a polymeric sizing to the yarns, and passing the yarns through sizing dies. Yarn bundle tightness and flexibility were controlled by the sizing chemistry. Continuous green yarns were cut to short lengths, or woven in different architectures to create composites with novel microstructures. The short yarns were fired to product PZT straight rods for `pick and place' piezoelectric composites. The woven structures were heat treated and backfilled with polymer to create composites with 1-3, 2-3, and 3-3 connectivity. After heat treatment, the diameter of the individual PZT fibers was 10 to 20 micrometers . Electromechanical characteristics of a number of composites were determined, and will be reported. The PZT VSSP fibers can be used to form fine-scale, large area piezoelectric fiber/polymer composites for use in hydrophones, transducers for medical ultrasonic imaging and non-destructive evaluation, and as sensors and actuators in vibration and noise control.

The paper presents a solution of the vibration problem for a sandwich panel with shape memory alloy (SMA) fibers embedded within resin sleeves and positioned at the middle plane of the panel. The fibers whose axial displacements are restricted, generate significant tensile stresses when working in the reverse transformation phase. The problem is formulated as follows: `Design such a system of SMA fibers that the fundamental frequency of the sandwich panel will not decrease below a prescribed value due to an increase of temperature within a specific range'. The solution of this problem that requires a minimum number of SMA fibers implies their nonuniform distribution. The design considered in the present paper is limited by the case where SMA fibers are oriented in one direction which may provide a better technological solution. The analysis is based on a new constitutive law proposed by the author. This law can accurately reflect the behavior of a constrained SMA fiber in the reverse transformation phase. It is shown that in SMA sandwich panels, the fundamental frequency can be kept equal or even higher than its room-temperature counterpart, in spite of the presence of compressive thermally-induced stresses.

Spacecraft require a variety of separation and release devices to accomplish mission related functions. Current off-the-shelf devices such as pyrotechnics, gas-discharge systems, paraffin wax actuators, and other electro-mechanical devices may not be able to meet future design needs. The use of pyrotechnics on advanced lightweight spacecraft, for example, will expose fragile sensors and electronics to high shock levels and sensitive optics might be subject to contamination. Other areas of consideration include reliability, safety, and cost reduction. Shape memory alloys (SMA) are one class of actuator material that provides a solution to these design problems. SMA's utilize a thermally activated reversible phase transformation to recover their original heat treated shape (up to 8% strain) or to generate high recovery stresses (> 700 Mpa) when heated above a critical transition temperature. NiTiCu alloy actuators have been fabricated to provide synchronized, shockless separation within release mechanisms. In addition, a shape memory damper has been incorporated to absorb the elastic energy of the preload bolt and to electrically reset the device during ground testing. Direct resistive heating of the SMA actuators was accomplished using a programmable electric control system. Release times less than 40 msec have been determined using 90 watt-sec of power. Accelerometer data indicate less than 500 g's of shock were generated using a bolt preload of 1350 kgs.

Sensor/Actuator coupling is a key parameter in the design of smart actuators (or systems) for sound and vibration control applications. To be practical, however, such a combination of transducers (actuator and sensors) must be available as an inexpensive ready-to-use electromechanical component with predictable well-behaved controllable characteristics. One approach NRL is currently pursuing toward reducing fabrication costs is to use the injection molding process developed by Materials Systems Inc. to co-form the accelerometer and actuator in one fabrication step. This results in an actuator with an imbedded array of accelerometers, where the inclusion of the accelerometer array adds little to the cost of the actuator. This low-cost fabrication approach is also applicable for aerospace vibration control or robotic sensing applications. This paper describes the design, and performance of prototype accelerometers and accelerometer/actuator systems formed using this process.

In an earlier SPIE paper, we described the development of a strain actuator consisting of a thin, co-fired, multilayered, PZT stack mounted within a titanium frame. The frame concept was designed to facilitate integration of the piezoceramic stack into a composite material during the fabrication process. The frame preloads the stack in compression, protects it during material fabrication and most importantly, provides an efficient shear transfer path to the surrounding host material. Because the piezoceramic stack power requirements are quite high, a special amplifier was also designed to meet the high current and voltage requirements. In this paper we focus on assessing the performance of the framed stack actuator for a variety of loading conditions. The calibration procedure uses a specially designed apparatus which loads the framed stack with a variety of impedances ranging from very compliant to very stiff. The mechanical power generated by the stack is measured directly in terms of the force transmitted to these loads along with their displacement. Electrical power is measured directly in terms of electrical current and voltage and is also computed in terms of the electrical admittance of the stack. Results show that the actuator is most efficient when a nearly matched impedance condition exists between the framed stack and its corresponding load.

In this paper we are concerned with Smart Materials that contain many actuators and sensors along with digital signal processing electronics that allow for the implementation of a control algorithm. Smart Materials have been proposed for the active control of sound from a vibrating structure. Here we investigate the design of structural control systems for these Smart Structures for noise suppression. First we model the radiated acoustic waves in terms of the velocity of the surface of the structure. Then we formulate an optimal control problem as a linear system that has a transmission zero in the path between the disturbance force and the shape that radiates best.

In this paper we report on the development of a high frequency switching amplifier for electrostrictive actuators. This amplifier is specifically designed for the capacitive loads that electrostrictive actuator present to them. One of the ultimate goals is to miniaturize these amplifiers so that they could be embedded into the material along with the actuators. Therefore, the configuration was chosen that would allow for miniaturization. The amplifier is also designed for high efficiency for thermal management. An integrated nonlinear model of the actuator and the electronics is also developed. A prototype Smart Material was fabricated consisting of sixty four actuators and sixteen amplifiers. Both experimental and simulation results of the Smart Material are reported.

Smart materials and structures are unknown to the medical community; therefore the opportunity exists to apply these new technologies to health care. A background of the emerging emphasis on advanced medical technologies and the information environment in which these technologies are based will provide a perspective that will enable designers of smart structures to envision new applications for products. A broad overview of the changes and new requirements for advanced medical technologies is presented, and a scenario-based illustration of the modern medical battlefield will provide insight for the application of smart structures to health care.

Magnetorheological (MR) fluids consist of stable suspensions of magnetic particles in a carrying fluid. The magnetorheological effect is one of the direct influences on the mechanical properties of a fluid. It represents a reversible increase, due to an external magnetic field, of the effective viscosity. Besides the variation of the rheological properties (viscosity, elasticity, and plasticity), the magnetic properties of the fluid (permeability and susceptibility), as well as the thermal and acoustic properties, are strongly influenced when an external magnetic field is applied. MR fluids have many appealing applications in the area of vibration control. The distinguishing feature of any MR fluid device is the absence of moving mechanical parts and the extreme simplicity of construction and technology. The most important element of any MR fluid device is an MR valve, which is functionally a controllable hydraulic resistance. As a demonstration of such devices, two commercially available pieces of exercise equipment, a cross stepper and a bench press, were modified to incorporate MR fluid and an external MR valve. As the magnetic field strength operating across the MR valve is adjusted, the viscosity of the flowing MR fluid changes and, accordingly, the needed force is adjusted.

Medical diagnostic capabilities have seen explosive growth over the past decade, as new techniques, such as MRI, have been taken from the laboratory setting into the clinical environment, with considerable benefit to the population at large. In this paper, we address another area of medical diagnostics which, we believe, stands on the verge of explosive growth, driven more by the emerging requirements for cost-effective diagnostic tools, and by the evolving needs of the defense medical community, with spinoff of those into the strongly related emergency care area of the civilian market. One of the factors that will drive this area of medical diagnostics is the development of smart materials and the sensors and sensor systems developed from them. In this paper we discuss some of the developments in the field of smart materials as they apply to development of new, low cost acoustic sensors for patient monitoring and medical imaging.

Current ultrasound images have relatively low contrast (high levels of clutter) and resolution. Image quality could be dramatically improved if 2D ultrasound transducer arrays were available to perform the scans. These improvements would come from reducing clutter by eliminating target echoes that the beam width of a 1D array causes to be superimposed on a scan plane, and enhancing resolution by enabling the use of algorithms which correct the wavefront distortion introduced by propagation through tissue. The advent of 2D arrays would also enable 3D images to be displayed--eventually in real time. The fabrication of 2D ultrasound arrays is, however, very difficult. This stems from the acoustic requirements of the array (aperture, pitch and element size) which combine together to dictate large numbers (> 1000) of very-low capacitance (< 10 pF) elements. The technology problems revolve around interconnecting the elements and reducing signal losses due to stray capacitance and impedance mismatch. This paper will show how the development of composite smart materials involving the integration of electromechanical elements with electronics is being extended to the development of relatively-inexpensive high-sensitivity 2D ultrasound arrays.

This paper describes a design study to determine the feasibility of integrating active control into a milling machine to enhance milling-process performance. The study described herein focuses on the active suppression of chatter instabilities in an Octahedral Hexapod Milling (OHM) machine. Structural dynamics contributing to chatter instabilities were described using calibrated finite element models, which were coupled with a tool-workpiece interaction model for purposes of determining, by simulation, machine performance enhancement due to active control. An active vibration control design to minimize vibration at the tool tip was also integrated into the simulation. Active control subcomponent and actuator size requirements were determined from the modeling and simulations. The study showed that active control is a feasible solution for suppressing chatter instabilities, allowing the metal removal rate of the OHM machine to be increased by roughly a factor of two.

Ingersoll's Octahedral Hexapod--a milling machine for the future--is described. The specific target applications and the performance goals for an enhanced version of the machine are illustrated. The approach to achieving the goals by incorporating of advanced composites and active chatter and vibration control using smart materials is discussed. The machine characterization performed on an existing machine, the FE models developed and the plans to use the characterization and the validated models in designing an enhanced machine are described.

Various structural control applications (e.g., high-precision machining) require high-force actuation. Actuators made by stacking and gluing plates are not suitable for many of these applications because, unless the plates are very thin (< 1 mm), the glued stack requires high voltages (> 1 kV) and stacks of very thin plates require extreme care in fabrication to avoid compliance due to the joints. This paper describes an effort to fabricate high-force, co- fired multilayer actuators. The actuator modules were designed to be approximately 50 mm X 50 mm X 20 mm (height), with 20 1-mm thick layers and a 12.7-mm diameter hole in the center for a prestress bolt. The modules were to be stacked together to form an actuator capable of delivering > 50 micrometers stroke at 5 degree(s)C under a load of approximately 10,000 lb. The major challenge in this task is fabricating the co-fired modules because of their size. It is exceptionally difficult to burnout and sinter such a large multilayer device without introducing flaws such as delaminations and, to the best of our knowledge, this had never been done successfully before. Three co-fired, high force actuator modules were fabricated and electrically and mechanically characterized. The capacitance of the actuator modules ranged from 1.5 to 9.4 (mu) F. Co-fired actuators gave modulus values of 12.2 X 10⁶ psi (at E equals 1 MV/m) which was close to the modulus of the material. The peak-peak strain of an actuator module at 0 prestress was 600 ppm (at a field of E equals 1 MV/m). At 2000 psi prestress, the strain measured was about 450 ppm (p-p).

A novel approach to mitigating chatter vibrations in machine tools is presented. Encountered in many types of metal removal processes, chatter is a dangerous condition which results from the interaction of the cutting dynamics with the modal characteristics of the machine- workpiece assembly. Tool vibrations are recorded on the surface of the workpiece during metal removal, imposing a waviness which alters the chip thickness during subsequent cutting passes. Deviations from the nominal chip thickness effect changes in the cutting force which, under certain conditions, can further excite vibrations. The chatter mitigation strategy presented is based on periodically altering the impedance of the cutting tool assembly. A cyclic electric (or magnetic) field is applied to the spindle quill which contains an electro- rheological (or magneto-rheological) fluid. The variable yield stress in the fluid affects the coupling of the spindle to the machine tool structure, changing the natural frequency of oscillation. Altering the modal characteristics in this fashion disrupts the modulation of current tool vibrations with previous tool vibrations recorded on the workpiece surface. Results from a simulated milling process reveal that significant reductions in vibration amplitude can be achieved through proper selection of fluid and excitation frequency.

An open-loop control method is presented for reducing the oscillatory motion of rotary crane payloads during operator commanded maneuvers. A typical rotary crane consists of a multiple degree-of-freedom platform for positioning a spherical pendulum with an attached payload. The crane operator positions the payload by issuing a combination of translational and rotational commands to the platform as well as load-line length changes. Frequently, these pendulum modes are time-varying and exhibit low natural frequencies. Maneuvers are therefore performed at rate sufficiently slow so as not to excite oscillation. The strategy presented here generates crane commands which suppress vibration of the payload without a priori knowledge of the desired maneuver. Results are presented for operator in-the-loop positioning using a real-time dynamics simulation of a three-axis rotary crane where the residual sway magnitude is reduced in excess of 40 dB.

The successful vibration reduction of machine tools during machining process can improve productivity, increase quality, and reduce tool wear. This paper will present our initial investigation in the application of smart material technologies in machine tool vibration control using magnetostrictive actuators and electrorheological elastomer dampers on an industrial Sheldon horizontal lathe. The dynamics of the machining process are first studied, which reveals the complexity in the machine tool vibration response and the challenge to the active control techniques. The active control experiment shows encouraging results. The use of electrorheological elastomer damping device for active/passive vibration control provides significant vibration reduction in the high frequency range and great improvement in the workpiece surface finishing. The research presented in this paper demonstrates that the combination of active and active/passive vibration control techniques is very promising for successful machine tool vibration control.

The surface finish of a turned part is primarily generated from process parameters such as feed, tool geometry, and cutting speed. A micropositioner system utilizing a magnetostrictive material, Terfenol-D, as a linear motor is presented as a means to actively control the process. The system has an actuator clamped in a flexor that is rigid in the feed and main cutting force directions, yet is flexible in the radial direction. Using control algorithms implemented on a digital computer, the system can provide a means to compensate for deleterious vibrations. The system has also been used to manipulate the tool position in the radial direction so that non-circular turning can be accomplished.

Solar collectors that are focused on a central receiver are designed with a mechanism for defocusing the collector or disabling it by turning it out of the path of the sun's rays. This is required to avoid damaging the receiver during periods of inoperability. In either of these two cases a fail-safe operation is very desirable where during power outages the collector passively goes to its defocused or deactivated state. This paper will be principally concerned with focusing and defocusing the collector in a fail-safe manner using shape memory alloy actuators. Shape memory alloys are well suited to this application in that once calibrated the actuators can be operated in an on/off mode using a small amount of electric power. Also, in contrast to other smart materials that were investigated for this application, shape memory alloys are capable of providing enough stroke at the appropriate force levels to focus the collector. In order to accommodate the large, nonlinear deformations required in the solar collector plate to obtain desired focal lengths, a torsional shape memory alloy actuator was developed that produces a stroke of 0.5 inches. Design and analysis details presented, along with comparisons to test data taken from an actual prototype, demonstrate that the collector can be repeatedly focused and defocused within accuracies required by typical solar energy systems.

Technologies developing in the smart materials and structures community might provide solutions to many challenges facing the electric power industry. Adoption of smart materials and structures would be facilitated if researcher knew more about power industry problems and about the changing nature of electric utilities. Accordingly, an overview of the utility industry is presented as an indication of the breadth and magnitude of problems facing the industry. Technical characteristics of some illustrative utility challenges are outlined and possible approaches for applying smart materials and structures are suggested.

The continuing development of the extrinsic Fabry-Perot interferometric sensor (EFPI) has led to a number of improvements to the original design. Manufacturing improvements have enabled the sensor to be employed in many diverse applications. This paper describes newly developed techniques used to manufacture the EFPI sensors and presents their use in advanced aerospace applications.

This paper reports on the results of a feasibility study concerning optical fiber Bragg grating sensors for vibration monitoring. The fiber grating sensors were embedded in glass-reinforced epoxy and graphite-reinforced PEEK active mount structures developed by the SPICES Consortium. The fiber sensors were interfaced to controllers by an acousto-optic tuned filter based instrument that provided simultaneous, real time, dynamic strain signals from 4 wavelength multiplexed sensors with a resolution of 0.002 microstrain per root Hz and a bandwidth of 4 kHz. The sensor interface design and performance are presented.

The processing of piezoelectric Pb(Zr,Ti)O₃ ceramic fiber/polymer composites via a modified lost mold process is discussed. In the lost mold process, plastic molds, which are negatives of the desired ceramic structure, are created. Each mold is filled with a slurry containing fine Pb(Zr,Ti)O₃ powders. After drying, the mold is burned out under controlled atmosphere, and the ceramic is sintered. The sintered ceramic structure is backfilled with polymer, polished, electroded and poled. In the modified lost mold process, several different sacrificial mold were investigated. One type of mold was plastic or wax sheets with precisely punched holes. A second was hollow polyester fibers. The modified mold forming procedure allows rapid prototyping of composites with a variety of connectivities, as well as novel spatial scale and periodicity. Composites with a ceramic fiber as fine as 50 micrometers in 1-3 connectivity have been demonstrated. A variety of rod shapes, including triangles, hexagons, and diamonds have also been demonstrated. Electromechanical characteristics of a number of composites were determined, and will be reported. The modified lost mold process can be used to form fine-scale, large area piezoelectric ceramic/polymer composites for use in hydrophones, transducers for medical ultrasonic imaging and non-destructive evaluation, and as sensors and actuators in vibration and noise control.

In this paper, an integrated identification and control procedure is studied. This integrated procedure seeks to find a high performance controller for real world systems. The procedure, which is inherently iterative, involves three steps in each iteration: (1) closed loop identification; (2) system model extraction from the closed loop experiment data; (3) controller design. The algorithm proposed in this paper uses weighted closed loop identification for deducing a model. The weight used for identification is obtained from the control design step and it provides a measure to evaluate the relative importance of each output channel in the closed loop behavior. Hence the weighted identification can capture models which are good for control design so as to achieve better closed loop performance. The procedure is demonstrated by controlling a smart structure under development at Purdue.