The continued development of a Froude-Scale helicopter rotor model featuring a trailing-edge flap driven by piezoceramic bimorph actuators for active vibration suppression is discussed. Block force and stroke of the current actuators are evaluated using two theories and compared with experimental results. Dynamic performance of the actuator as well as the actuator-flap assembly are examined. Earlier hover tests have shown severe degradation in flap deflections with increasing rotor speed, and flap deflections were too small to be effectively utilized for significant vibration control. To investigate the causes of the performance degradation, new blades are constructed and tested in-vacuo to isolate the effects of centrifugal loading on the actuator-flap system. A beam model of the piezo bimorph including propeller moment effects is formulated to better illustrate the physical mechanisms affecting the system in a rotating environment. The cause of the reduced deflections is traced to frictional forces created at the junction where the flap is supported during rotation of the blades. The use of a thrust bearing was found to alleviate this problem and subsequent tests on a hover stand showed a dramatic increase in flap detection at high excitation frequencies.

An individual blade controller designed to attenuate the aeroelastic response of helicopter rotors in forward flight by tailoring the blade root attachment conditions is developed. A feasibility analysis indicates that the open-loop controller which incorporates both passive and active design techniques is energy efficient and may be realized by available adaptive structures.

The main theme of this research project has been to analytically develop a proof-of-concept design to demonstrate the effectiveness of a smart material actuator employing ETREMA TERFENOL-D^TM for helicopter rotor servoflap control. This design enables the control of the rotor blade flap with an actuator embedded in the blade itself. By moving the control to the rotor blades, the swashplate system could be eliminated. Requirements such as applied load and motions were the key issues that needed to be accounted for in order to achieve a successful design employing the `giant' magnetostrictive material. A series of loading conditions characterized by an additive process of Steady-State. Cyclic, and Active control functions were considered for Sustained flight. Optimization of the overall system gave rise to a system gain of 3.7 for Sustained motion. At this same optimal gain value, and using an ETREMA TERFENOL-D^TM rod length of at least 22.7 inches, a net peak-to-peak displacement of as high as 42 mils (1.07 mm) was obtained.

The purpose of this paper is to design an active control system for flutter suppression of laminated plate wing model by using the segmented piezo actuators. It describes the investigations pertaining to the optimal size, thickness and locations of piezo actuators on laminated plate-wing structure for flutter suppression. The analysis for laminated composite wing model is conducted by Ritz solution technique, which represents the displacement on the plate in terms of the power series in spanwise and chordwise directions. The active control system design for flutter suppression requires the equation of motion to be expressed in a linear time-invariant state-space form. Doublet lattice method is used to compute unsteady aerodynamic forces, which are approximated as the transfer functions of the Laplace variable by Minimum State method combined with optimization technique. To design control system, linear quadratic regulator theory with output feedback is considered in this study. The feedback control gains are obtained by solving coupled nonlinear matrix equations via numerical optimization routines. The optimal geometry of piezo actuators which minimizes the control performance index is determined by optimization technique referred to as the sequential linear programming method. Numerical results shows a substantial saving in control effort compared with the initial model.

A new type of subsonic missile flight control surface using piezoelectric flexspar actuators is presented. The flexspar design uses an aerodynamic shell which is pivoted at the quarter-chord about a graphite main spar. The shell is pitched up and down by a piezoelectric bender element which is rigidly attached to a base mount and allowed to rotate freely at the tip. The element curvature, shell pitch deflection and torsional stiffness are modeled using laminated plate theory. A one-third scale TOW 2B missile model was used as a demonstration platform. A static wing of the missile was replaced with an active flexspar wing. The 1' X 2.7' active flight control surface was powered by a bi-morph bender with 5-mil PZT-5H sheets. Bench and wind tunnel testing showed good correlation between theory and experiment and static pitch deflections in excess of +/- 14 degree(s). A natural frequency of 78.5 rad/s with a break frequency of 157 rad/s was measured. Wind tunnel tests revealed no flutter or divergence tendencies. Maximum changes in lift coefficient were measured at (Delta) C_L equals +/- .73 which indicates that terminal and initial missile load factors may be increased by approximately 3.1 and 12.6 g's respectively, leading to a greatly reduced turn radius of only 2,400 ft.

Bending a thin flat panel on an aerodynamic surface using piezoelectric actuators has been proposed to control phenomena such as flutter, sing divergence and transonic drag. Such smart material applications are not feasible unless actuators can produce larger panel bending deflections than are presently predicted. The objective of this study is to maximize bending deflection of a flat, rectangular panel by attaching a thin piezoelectric actuators to one side of the panel. Two optimization cases are considered: (a) the rectangular actuator is mounted in the center of the panel surface and has area and thickness as design variables; (b) the rectangular actuator is composed of two stacked layers, each having an independent design thickness and area. Studies are presented for different panel aspect ratios for simply supported and clamped (fixed) boundary conditions, and for aluminum and steel host panels. The results show that, for a simply supported aluminum panel with an aspect ratio of 1.5, the best single thickness PZT actuator has a thickness of 0.634 of the host panel and covers 64.7% of the panel. For the two layer stacked actuator, one PZT layer has a thickness ratio of 0.391 and covers 70.6% of the panel, while the other layer has a thickness ratio of 0.313 and covers only 35.7% of the panel. Both of these configurations create nearly identical panel center deflections, but the two layer design weighs slightly less. This study also indicates that formal optimization is a necessary tool for actuator design and that shaped actuators can save weight.

This paper presents an experimental-analytical study on the active tuning of composite beams using Shape Memory Alloy (SMA) wires. Composite beams with fused silica tubes and `dummy' wires were manufactured first using autoclave molding techniques and then the `dummy' wires were replaced by pre-strained SMA wires. The beam and SMA wire were independently clamped at both ends. The SMA wires were activated using electrical resistive heating and a large tensile recovery force developed in them due to the mechanical constraints provided by the clamps. The influence of this recovery force on the vibration behavior of composite beams was determined by conducting vibration testing. Analytically, these beams with SMA wires inserted in embedded sleeves were examined as beams on an elastic foundation: the spring constant of the elastic foundation depended on the axial recovery force of SMA wire. Good correlation between analysis and experiment was achieved. A numerical parametric study of natural frequencies of composite beams with activated SMA wires was conducted. The parameters considered were the diameter, number of SMA wires and constituent of composite beam. The numerical study suggests that inserting 25 SMA wires of 20 mil diameter into a graphite-epoxy beam of 30 in. length, 1 in. width and 62 mils thickness increases its first frequency by 276%.

The results of a study to conceptually define an on-blade smart material actuator for primary and active control on a servoflap rotor are presented. Actuator design drivers, goals, and requirements are defined. For a previously developed hybrid actuator concept, the design of the cyclic and active (high speed) control actuator and feasibility of the collective (low speed) actuator and stroke multiplier are investigated. Sizing of actuator components based on AH-64 servoflap requirements shows that collective control using shape memory alloys is well within the capability of the material. Cyclic and active control using magnetostrictive material, leads to a reduced maneuver envelope due to weight and volume constraints. The promise of smart materials can be realized incrementally as the materials and actuator design approaches mature. Future improvements in smart material performance and actuator technology, and additional rotor system design changes to reduced load and motion requirements should provide the full AH-64 maneuver envelope.

General stiffness concepts for effective use of induced strain principles as they apply to quasi- static actuation of structures and devices are presented. The conventional induced strain actuator is first reviewed. The effect of structural elasticity is then added. Basic principles of displacement amplification are presented next. The influence of structural and amplification elasticity are then added. An example of effective induced strain actuator design with displacement amplification is provided.

A numerical study of electrorheological (ER) dampers is presented. Two models, the Newtonian and the Bingham plastic models are used to characterize the ER fluid behavior. Damping performance of two damper configurations, the Moving Electrode and the Fixed Electrode configurations, is studied. The effects of electrode gap sizes, the field strength and the ER fluid model used are quantified. The study provides a basis for design of ER-fluid based dampers.

Vibrations have long been a source of problems for space systems, with acoustic and aerodynamic excitations causing failures during launch and periodic disturbances degrading performance on-orbit. In exploring new solutions to such problems, research at The Aerospace Corporation has recently considered the applicability of piezoceramic based adaptive structures to space systems. A small-scale testbed has been developed comprised of active mounting brackets that can isolate payloads from disturbances and an active payload platform that can suppress vibrations generated by payload instruments. Various issues related to practical applications have been explored through this representative system, and in this paper the aspects of structural design and structural modeling are explored. Payload capabilities are bounded for realistic launch environments, and the accuracy of structural modeling techniques for the integrated system is considered. Through this effort, the feasibility and potential utility of space structures with integrated piezoceramic transducers is investigated. The paper concludes with a discussion of potential applications for such a system, and examines considerations for the transition to practical space systems.

The paper addresses the problem of satellite solar panel vibration. A multi-layer vibration control scheme is investigated using a flight test article. Key issues in the active control portion are presented in the paper. The paper discusses the primary control design drivers, which are the time variations in modal frequencies due to configuration and thermal changes. A local control design approach is investigated, but found to be unworkable due to sensor/actuator non-collocation. An alternate design process uses linear robust control techniques, by describing the modal shifts as uncertainties. Multiple modal design, alpha- shifted multiple model, and a feedthrough compensation scheme are examined. Ground and simulation tests demonstrate that the resulting controllers provide significant vibration reduction in the presence of expected system variations.

Inverse synthetic aperture radar (ISAR) uses target's motion to generate images on the range- Doppler plane. The conventional ISAR uses Fourier transform to compute Doppler spectrum for each range cell. Due to the target irregular translational and rotational motion, the Doppler frequency in fact is time-varying. By using Fourier transform, the reconstructed image becomes blurred. To represent time-varying Doppler spectrum, time-frequency transform should be utilized. Adaptive time-frequency wavelet transform is a very useful tool in analysis of signals with time-varying spectrum. We applied adaptive time-frequency wavelet transform to ISAR image reconstruction and developed a simulation procedure to describe the characteristics of the algorithm. By replacing the conventional Fourier processor with the adaptive wavelet processor, a 2D range-Doppler Fourier ISAR frame becomes a 3D time- range-Doppler wavelet ISAR cube. By sampling in time, a time sequence of 2D range-Doppler images can be viewed. Each individual wavelet ISAR image provides not only superior resolution but also the temporal information within each frame time. Both simulated and real ISAR data have been tested. The result from simulated ISAR data is illustrated in this paper.

We investigate the robust vibration control of an elastic robot arm. This robot arm, called the Elasticarm, is a new design that exploits the flexibility of a beam to generate motion that usually requires an elbow. Shape control is accomplished using a system of cables and motors. The resulting structure exhibits lightly damped, large-scale vibrations. The vibration control problem for the Elasticarm is challenging because the natural frequencies depend on the static shape of the beam. In this paper we compare two simple controllers that are designed to be insensitive to plant uncertainty and to offer satisfactory performance. The first controller is an H_(infinity ) design using an imaginary axis shift. The second controller uses direct strain feedback to increase vibration damping. Experimental results show that both controllers maintain adequate performance across a wide range of configurations.

An electrorheological (ER) fluid damper suitable for vibration and seismic protection of civil structures has been designed, constructed and is under testing. The damper consist of an outer cylinder and a piston rod that pushes the ER-fluid through a stationary annular duct. The design of the damper was based on approximate calculations based on the Hagen-Poiseille flow theory. It is found that the Hagen-Poiseille theory predicts satisfactorily the damper response at moderate values of the flow rate. Experimental results on the damper response with and without the presence of electric field are presented. The average fluid velocity in the ER-duct has to be kept relatively small so that viscous stresses do not dominate over `yield' stresses.

Composite materials are widely used in the design of pressurized gas and fluid vessels for applications ranging from underground gasoline storage tanks to rocket motors for the space shuttle. In the design of a high pressure composite vessel (P_i > 12 Ksi), thick-wall (R/h < 15) vessels are required. For efficient material use in composite material vessels, the radial dilation (expansion or swelling) of the composite vessel can often approach values nearing 2 percent of the diameter. Over long periods of internal pressure loading over elevated temperatures, composite material cylinders may also experience substantial creep. The short term dilation and long term creep are not problematic for applications requiring only the containment of the pressurized fluid. In applications where metallic liners are required, however, substantial dilation and creep causes plastic yielding which leads to reduced fatigue life. To applications such as a hydraulic accumulator, where a piston is employed to fit and seal the fluid in the composite cylinder, the dilation and creep may allow leakage and pressure loss around the piston. A concept called the adaptive composite cylinder is experimentally presented. Shape memory alloy wire in epoxy resin is wrapped around or within polymer matrix composite cylinders to reduce radial dilation of the cylinder. Experimental results are presented that demonstrate the ability of the SMA wire layers to reduce radial dilation. Results from experimental testing of the recovery stress fatigue response of nitinol shape memory alloy wires is also presented.

In order to meet the demands of simplicity and reliability in active control systems for flexible structures, an inexpensive active truss element and control law has been developed in this research. A decentralized switching control law is used along with a compressible fluid in the truss element in order to dissipate energy during the motion of the structure. However, the energy is not absorbed in the same manner as a conventional viscous damper. The truss element retains its maximum stiffness, but has a reset-able nominal unstressed length. Energy is absorbed in the working fluid of the truss element through heat transfer to the environment when the nominal length is reset at the proper switching times. The control law is insensitive to changes in structural parameters such as mass, stiffness, and damping. In this paper, a mathematical model for the system is presented along with a stability analysis and experimental results.

This paper describes experimental work on the semi-active control of structural modal energy by dynamically controlling structural stiffness. Stiffness adjustment of the structure is achieved by engaging or disengaging `relaxed' control elements, thus changing local stiffness and changing the global eigenstructure without the introduction of energy into the system. Experiments on a three story laboratory model are described. Control experiments when the model is subjected to sinusoidal and random excitations demonstrate feasibility.

High birefringence optical fiber embedded in composite laminates can be used for real time strain measurement. The use of such an embedded optical fiber for detection of damage in composites through strain monitoring has been investigated.

Described in this paper are the details of an automated real-time structure health monitoring system. The system is based on structural signature pattern recognition. It uses an array of piezoceramic patches bonded to the structure as integrated sensor-actuators, an electric impedance analyzer for structural frequency response function acquisition and a PC for control and graphic display. An assembled 3-bay truss structure is employed as a test bed. Two issues, the localization of sensing area and the sensor temperature drift, which are critical for the success of this technique are addressed and a novel approach of providing temperature compensation using probability correlation function is presented. Due to the negligible weight and size of the solid-state sensor array and its ability to sense incipient-type damage, the system can eventually be implemented on many types of structures such as aircraft, spacecraft, large-span dome roof and steel bridges requiring multilocation and real-time health monitoring.

A novel method of monitoring damage in structures is presented. The concept utilizes an electronically steered acoustic beam produced by an array of interdigital transducers placed in the structure. The acoustic beam is scattered by the damage, and therefore the scattered signal received by the array contains detailed information about the damage. A brief discussion of resolution and accuracy of the damage detection by acoustic waves is presented followed by the basic aspects of beam formation, array aperture and electronic beam steering. The description of cross-field interdigital piezoelectric transducers to produce bulk waves of sufficient strength is also included. The aspects that make the proposed concept different and desirable with respect to the prevalent nondestructive testing by external ultrasonic transducer are presented as the concluding remarks.

In this paper we have presented a sensor system capable of measuring two parameters on a surface mounted beam. We have used an In-Line Fiber Etalon (ILFE) and an Intrinsic Fabry- Perot (IFP) sensor to capture two parameters at a single point. This sensor with gage length of about 200 micrometers can be used to determine the axial strain and temperature on a beam or can be embedded in composite material to determine two strain components. The two sensor signals which travel in the same fiber are discerned using coherence based multiplexing schemes. Three tests are performed with the sensor mounted on a cantilevered beam to demonstrate the concept. In the first test, the beam is subjected to simple vibration and the phase strain model is used to calculate the strains from the two sensors. In the second test the beams is given only thermal loading, and in the third test, the beam is subjected to a combination of both thermal and mechanical loading.

A high-frequency-electrical-impedance-signature-based technique for structural integrity monitoring is presented. The technique which has been under investigation at the Center for Intelligent Material Systems and Structures at Virginia Tech for the last 18 months is unique and different from conventional non-destructive damage identification and structural integrity monitoring methods. It relies on tracking the high-frequency (typically > 50 kHz) point impedance of the structure to identify damage. At such high frequencies, the technique is comparable in sensitivity to sophisticated traditional NDE techniques, such as ultrasonics, and is capable of qualitatively detecting incipient-type damage by looking at changes in structural impedance. As yet, it can be implemented in a remote sensing scenario with small non- intrusive piezoelectric (PZT) materials. The structure's high-frequency electrical impedance signature, which is functionally equivalent to its mechanical impedance signature, is obtained through a bonded PZT functioning both as actuator and sensor. A statistic algorithm based on the difference in the electrical impedance of a healthy and a damaged structure, is then applied to extract an index of the health of the structure. High-frequency excitation, which is greatly facilitated by the electrically driven low-power compact PZT patch, assures a clearly visible change in the impedance/vibration signature even for very minor damage/changes. It also limits the actuation/sensing area to a small region, `local-area', close to the PZT patch. Because of the limited actuation/sensing area, the impedance signature is affected only by changes in the structural properties close to the sensor-actuator and is insensitive to changes in far-field boundary conditions, mass loading, etc., which may be part of the normal usage of the structure. As a case study, an application to a real complex aircraft structure is presented. Experimental proof that very minor alterations in the structure are easily identified and the fact that the detection range of the bonded PZT actuator/sensor is constrained to its immediate neighborhood is presented.

Significant progress in fulfilling the current joint Air Force/Navy `Smart Metallic Structures (SMS)' program primary objective, to demonstrate a viable structural health monitoring system (SHMS) for a large structural aircraft component, is presented. Structural health monitoring and its relation to current Force Management (FM) and Aircraft Structural Integrity Program (ASIP) procedures are first reviewed together with a brief status overview of the relevant sensor technologies (e.g. AE, fiber-optic, corrosion, etc.). Key features of the SHMS architecture are described for the selected F/A-18 bulkhead and T-38 wing spar structural demonstration articles, highlighting sensors, processors, data busses, hardware, and software. Results from acoustic monitoring of the program sub-element structural tests are presented in some detail along with a status review of the SHMS multiplex bus component hardware and software. Finally, structural requirements for an SHMS meeting minimum ASIP guidelines for damage detection are discussed along with foals for future testing and development of the SHMS under the SMS program.

A review of the evolution of the field of damage identification is presented. Trends of research and the present state of the field are discussed and directions of future research are postulated. Ideally, an automated damage identification method incorporated into the smart structure scheme would be able to detect damage as it is incurred by the structure, determine the location and extent of the damage, predict when and if catastrophic failure of the structure will occur, and alert the operator as to how the performance of the structure is affected in order for appropriate steps to be made to remedy the situation. Obviously, this is no easy task but it is essential that it is clearly defined how the research fits into the ultimate goal of developing an automated, noninvasive damage identification method. In attempting to quantify changes in response characteristics due to damage on a structure, it is very important to be aware of the inherent variabilities one might encounter in acquiring these response characteristics. These variabilities may come from computational algorithms, sensor error, or environmental effects. A method which assumes a priori ignorance to the manifestations of damage in the response characteristics of the structure is presented. This method uses inductive learning to statistically isolate changes in response characteristics due to damage from those due to the inherent variabilities. In order to validate the method, an example is presented which identifies the existence and location of a small test mass on an aluminum plate via the measurement of the structural impedance-response of the plate.

This work discusses the effects of inherent variabilities on the damage identification problem and the creation of a practical damage identification method. Variability is present any time there are factors which have the potential to change during the course of the damage identification process. There are many variabilities which are inherent in damage identification and can cause problems when attempting to detect damage. Manufacturing variability is one of these variabilities and is shown experimentally to be a `non-qualifiable' one. Inductive learning is a tool which has been proposed to be an effective method of performing damage identification. This method is modified to accommodate manufacturing variability and shown to successfully detect hole damage on aluminum plates.

This paper presents an investigation of the monitoring of cracks at the edge of fastener holes on plates using an ultrasonic pulse-echo technique. Our studies show that, if the surface of the plate surrounding the hold is free, an acoustic wave on the surface of the plate is able to detect the cracks located in an arc of 60 degree(s). When the inner surface of the hole is free, surface acoustic waves on the inner surface are alternate choices. For the case when all these surfaces are in tight contact with other parts, hence unavailable for mounting transducers, a particular type of Lamb wave mode is presented.

A refined higher order plate theory is developed to investigate the actuation mechanism of piezoelectric materials surface bonded or embedded in composite laminates. The current analysis uses a displacement field which accurately accounts for transverse shear stresses. Some higher order terms are identified by using the conditions that shear stresses vanish at all free surfaces. Therefore, all boundary conditions for displacements and stresses are satisfied in the present theory. The analysis is implemented using the finite element method which provides a convenient means to construct a numerical solution due to the discrete nature of the actuators. The higher order theory is computationally less expensive than a full 3D analysis. The theory is also shown to agree well with published experimental results. Numerical examples are presented for composite plates with thickness ranging from thin to very thick.

Fiber reinforced thermoplastics offer substantial advantages over fiber reinforced thermosets. Besides high specific stiffness and strength and excellent resistance to impact damage, especially with respect to the manufacturing process considerable cost reductions are possible. The reason is the reduction of the processing times from hours to minutes. However the higher process temperatures close to the Curie temperature in the range from 250 degree(s) C to 400 degree(s) C are expected to have a significant impact on the polarization of embedded piezoceramic patches. Active structures require by definition embedded actuators and sensors as part of the load bearing structure. The success of the design philosophy of active structures is highly dependent on the manufacturing costs. For that reason fiber reinforced thermoplastics are supposed to be the ideal material for the host structure. Different manufacturing processes were applied to manufacture active test structures which are specifically designed with respect to the manufacturing process used. The embedding process of the active elements include the electrical insulation and wiring. Moreover the coefficient of thermal expansion of a typical PZT type ceramic was measured over a wide temperature range to understand the thermomechanical loading of the piezoceramic due to the manufacturing process. Moreover the electromechanical parameters of the active elements before and after the manufacturing process were measured. For this purpose a special test equipment has been developed. Furthermore the problem of thermal depolarization is touched. Basically it turns out that in spite of high processing temperatures the embedding of piezoceramics in fiber reinforced thermoplastics is feasible. The repolarization process of embedded piezoceramics is optimized for a given type of piezoceramics.

Electrostrictors are often avoided in structural control applications due to the non-linearity and temperature sensitivity of the electro-mechanical coupling. This paper describes control techniques so that constant performance is obtained from an electrostrictor in a feedback control system at temperatures ranging from 5 degree(s)C to 57 degree(s)C and at field levels ranging from 90 V/mm to 950 V/mm. The control techniques are experimentally implemented on a cantilevered beam with a 0.9 MN - 0.1 PT electrostrictor. With output linearization and temperature-gain scheduling, the electrostrictive system reduces the RMS strain vibration by 61%. An identical system with a G-1195 piezoceramic controller is used for comparison. The piezoceramic system reduced the strain vibrations by 55% which was robust to temperature variation but not robust to variations in the bias field. Extensive unconstrained wafer characterization as a function of temperature is also presented in the context of relevant constitutive equations.

Although piezoelectric actuators are widely used in smart structure applications, they frequently can not generate directly both the force and deflection required. A new class of piezoelectric actuators, called C-blocks, have been developed that provide greater force than traditional bimorphs and greater deflection than stacks. C-blocks are piezoelectric bimorphs configured into a half circle shape and are fabricated on the mesoscale (10 - 10-3) mm). This paper describes how C-blocks can be used alone or combined in parallel and/or series, like building blocks, to form C-block actuator architectures to further improve force and/or deflection capabilities. This paper presents the derivation and experimental testing of force-deflection models for four common C-block architectures. These models predict the full static performance of C-blocks including the maximum performance characteristics. To test the models, force-deflection experiments were performed with a polymeric piezoelectric C- block. The experimental results are in close agreement with the behavior predicted by the model and demonstrate that a C-block has potential to generate approximately five times more force than an equivalent traditional straight bimorph and orders of magnitude greater deflection than an equivalent stack.

Continuum damage mechanics approach is used to predict the failure of piezoelectric ceramics which are widely used as actuators and sensors in smart structures. A continuum damage model is developed for piezoelectric ceramics, and the model is used to investigate the degradation of effective properties of the material due to damage growth. Effective properties of the material are obtained by extending the Mori-Tanaka method to piezoelectric materials. A damage evolution law is proposed to predict the growth of damage with respect to time, and the involved material parameters in the damage evolution law are obtained from the experiments of Tanimoto and Okazaki. The results are obtained assuming all the effective properties of the material degrade as the damage grow, and the degradation is independent of the load history. This degradation should be taken into account to calibrate the sensors, actuators and controllers for the better reliability, maintainability and controllability of smart structures. The effective properties of the material is related to some measurable electrical quantity such as capacitance. Therefore, the state of damage can be predicted just by measuring the capacitance of the embedded piezoelectric ceramics.

Using the fact that polyvinylidene fluoride polymer (PVDF) has the anisotropic property, a study on adaptive design of the integrated structure was carried out when the PVDF acts as distributed actuators on laminated composite plate. In this study, static, dynamic and control analysis of integrated structure were performed when directionality of both PVDF and composite materials was taken into account. In order to examine the static and dynamic behavior, an efficient finite element method was developed and various numerical verifications were performed. The appropriate combination layer angles of both PVDF and composite material which can induce desired deformed states of the integrated structure were found out. On the basis of results obtained from static and dynamic analysis, control of specific vibration mode of the structure was carried out when PVDF used as distributed actuators. In the paper, an index which can indicate the effectiveness of the actuator to a specific vibration mode of the structure was suggested. This index, named as apriori-modal controllability index, measures the directional cosine of the integrated structural vibration mode and the deformed shape induced by the actuator. To check the usefulness of the suggested index, linear optimal control law known as LQR was applied to control specific vibration mode and the closed, open-loop responses were examined. And the multimode control of the structure with single input was achieved.

When discrete piezoelectric actuator patches bonded on structures are used for active shape, vibration, and acoustic control, the desired deformation field in the structure is obtained through the application of localized line forces and moments generated by expanding or contracting bonded piezoelectric actuators. An impedance-based model to predict the dynamic response of cylindrical shells subjected to excitation from surface-bonded induced strain actuators is presented. The essence of the impedance approach is to match the actuator impedance with the structural impedance at the ends of the actuators, which will retain the dynamic characteristics of the actuators. A detailed derivation of the actuator and structural impedance is included. It is found that the actuator's output dynamic force in the axial and tangential direction are not equal. Various case studies of a cylindrical thin shell are performed to illustrate the capabilities of the developed impedance model. Out-of-phase actuation is shown to be the most efficient in exiciting the lower order bending modes of shell structures. The paper is concluded with a finite element analysis verification of the derived impedance model.

An expression for the mean and variance of a transducer array's modal coefficients is developed to quantify the effect of spatial errors on the transducer structural coupling, and on the transducer augmented plant's input/output frequency response. Transducer elements are modeled spatially via their position, aperture, and shading (e.g., spatial gain weighting). Each of these spatial parameters can be statistically modeled in terms of their mean and variance, assuming statistical independence. Modal coefficients are described via composition integrals of the transducer spatial kernel and the plant mode shapes. The probability density function of each parameter is then assumed to be unimodal, with characteristic scale smaller than any corresponding spatial scale of the modal coefficient's dependence on the parameter. Consequently, the mean values of the modal coefficients are the values of the corresponding integrals evaluated at the mean transducer position, aperture, and shading. The variance of the modal coefficients, derived via a Taylor series expansion to second order about their mean values, is expressed in terms of the partial derivatives of the modal coefficient with respect to the uncertain spatial parameters. This suggests that transducers whose shadings consist of low- order generalized function or modal expansions are less sensitive to spatial parameter variations. Variations in the modal coefficients are mapped to expressions for the mean and variance of transducer-augmented plant transfer functions. Simulation examples are presented that model variations in the input/output transfer functions characteristics of a flexible beam with a mis-registered point actuator, and a mis-registered modally-weighted piezo film sensor distribution. For even slight aperture mis-registrations--0.26% of the beam's length--the modal sensors no longer perfectly `sift out' non-targeted modes, and off-mode contributions grow by nearly an order of magnitude.

The need to be able to predict the self induced thermal heat rise of piezoelectric and electrostrictive stack actuators under AC dynamic operation motivated the research presented in this paper. First, an equation for the electrical admittance of an stack actuator that explicitly includes the effects of having the stack actuator in a host structure is provided. This equation is then shown to be critical when determining the apparent, reactive and dissipative power used by an actuator. With the theoretical predictions of the electrical admittance available, it is possible to calculate the contributions of the individual loss components to the total dissipative power. Using a simple heat transfer analysis, the internal heat rise of the actuator is predicted given the dissipative power input. A case study is used to illustrate how to apply the developed theories. This research provides a first step toward the ability to predict the temperature state of active materials in stack configurations. This would allow accurate prediction of actuator parameters and hence electro-dynamic behavior. Additionally, knowledge of the physics behind self induced heat rise can be used to avoid exceeding the active materials Curie temperature during operation and allow proper design of active isolation elements for temperature sensitive equipment.

An electromechanical elasticity solution is presented to evaluate the response of a piezoelectric linear motor at cryogenic temperatures. This model incorporates the pronounced coupling which occurs in these materials between temperature and piezoelectric strain coefficients. Results from experimental tests are presented for ceramic piezoelectric flat specimens to determine the linear and nonlinear properties required in the model; including thermal expansion coefficients, coupling terms, and piezoelectric strain coefficient functionally dependent upon electric and thermal fields. Test results indicate that depoling and saturation effects in this ceramic piezoelectric material are strain dependent and electric field independent. These results suggest that piezoelectric materials can operate as effectively at cryogenic temperatures as they do at room temperatures. Comparison between the analytical model and experimental results for a cylindrical material system yields reasonable correlation. Conclusions include that a linear motor can be designed to operate at cryogenic temperatures.

Dynamic interaction between an integrated induced strain actuator and its host structure depends on the driving point mechanical impedance of the host structure and the mechanical impedance of the actuator. For the case of several actuators, the individual actuator/structure impedance will not only depend on the driving point host structural impedance, but also on the electromechanical coupling with the other actuators. In this paper, a general dynamic model of a structure driven by multiple actuators is presented, as based on an impedance modeling approach developed for a single actuator. The basic formulation is provided in terms of structural admittance of an arbitrary structure and dynamic transduction relations of transducers. It can be easily applied to any form of structure and actuators, even an electromagnetic shaker, provided their dynamic transduction relations can be developed. The developed theoretical model has been used to predict the dynamic response of a simply- supported beam with several bonded piezoelectric actuators activated simultaneously. Experiments have also been conducted which validate the theoretical model.

A finite element modeling technique has been developed to accurately predict both the static and dynamic response of a structure containing embedded piezoelectric actuators. This process utilizes a commercially available and benchmarked finite element program and can be used with shell or solid elements in any static analysis, time-domain or frequency-domain dynamic analysis. It is possible to apply the piezoelectric loads while simultaneously applying other mechanical or thermal loads even though the induced strain of the piezoelectric actuators is modeled using thermal expansion. The technique uses superelements to apply the thermal loads at any frequency and magnitude and to incorporate a fine mesh near the actuator even if a course mesh is used over the remaining portions of the structure. The technique's generic and modular nature allows a complex actuator superelement to be used multiple times in multiple smart structure models. Experiments conducted on composite coupons with embedded actuators validate the current modeling technique and demonstrate the method's successful prediction of the dynamic response of the specimens. This process is one of several smart structure modeling techniques being developed under the Synthesis and Processing of Intelligent Cost Effective Structures program sponsored by the Advanced Research Projects Agency.

A new adaptive sandwich structure is constructed using the shear mode of piezoelectric materials. A comparative study of the sandwich structure and the corresponding surface- mounted actuation structure is performed using finite element analysis. The effects of actuator length and location on actuation performance of the structures are studied. The stress distributions under mechanical and electrical loads are investigated for both the sandwich beam and the surface-mounted activation beam. It is shown that the stress level within the actuators is more severe for the surface-mounted actuation beam than for the sandwich. Also, the interface-stress distribution between actuator and host structure is analyzed. It is shown that sandwich construction offers many advantages over conventional surface-mounted actuation constructions.

This paper studies the vibration control of a flexible beam using a constrained viscoelastic damping treatment and layered shape memory alloy (SMA). The SMA layer is used as an actuator, which is capable of changing its elastic modulus and recovery stress. A linear control law is determined based on optimal regulator theory. The control results are discussed.

The influence function of an active optical system defines the relationship between commands to deformable mirror actuators and the changes in wavefront error that result from those commands. Accurate knowledge of the influence function is critical for stable closed-loop operation of the system. A recent program at Itek Optical Systems used a 2.6-meter-diameter, ULE deformable mirror with 144 lead-magnesium-niobate electrostrictive actuators. The influence functions of this mirror were measured under operational conditions over a period of fourteen months and no significant changes in the influence functions were found over that time. This is a very encouraging result for future applications of active optical systems where stable, closed-loop operation is required for many months between remeasurement of influence functions.

This paper deals with the identification of the dynamic characteristics of structural system. The relevant neural network characteristics of learning algorithm are discussed in the context of system identification. Because of self-learning nature of neural network the identified dynamic characteristics are strongly affected by the level of noise contained in the teaching signals. Using the Kalman filtering technique, a method to identify the dynamic characteristics of structural system proof against contaminating noise in teaching signals has been developed.

The active control of vibration using point actuators has received much attention especially for aircraft and aerospace structural applications. Presented here is a means by which acoustically excited panel vibrations may be controlled through the action of a single actuator. The actuator consists of a single-sheet piezoceramic embedded in a composite panel. A robust control algorithm is implemented to attenuate the dominant modes of the panel response. The sensing is provided by a second piezoceramic also embedded in the panel. Beside the system identification, special emphasis is given to the robust controller design based on H^(infinity ) methods. The presented results demonstrate the effectiveness of a parallel H^(infinity )- controller design procedure achieving significant attenuation levels in a broad frequency band.

A new form of recursive algorithm to estimate the transverse and angular displacement and/or velocity at any location along the length of a 1D cantilever beam using the strain/strain-rate data measured from a set of sensors distributed along the length of the beam is presented. This is based on the linear spline functions used to approximate the strain distribution in the beam. The main advantage of this algorithm is that it is independent of the structural parameters, viz., mass, stiffness and damping coefficient. Experimental results for both static and dynamic cases are furnished to validate the proposed estimation algorithm. In the case of static loading, strain gauges are used to measure the strain, while piezo-electric sensors are used in the dynamic case.

Active optical systems are complex systems that may be expected to operate in hostile environments such as space. The ability of such a system either to tolerate failures of components or to reconfigure to accommodate failed components could significantly increase the useful lifetime of the system. Active optical systems often contain hundreds of actuators and sensor channels but have an inherent redundancy, i.e., more actuators or sensor channels than the minimum needed to achieve the required performance. A failure detection and isolation system can be used to find and accommodate failures. One type of failure is the failure of an actuator. The effect of actuator failure on the ability of a deformable mirror to correct aberrations is analyzed using a finite-element model of the deformable mirror, and a general analytical procedure for determining the effect of actuator failures on system performance is given. The application of model-based failure detection, isolation and identification algorithms to active optical systems is outlined.

In this paper a new method of distributed adaptive control of vibration in flexible structures is presented. It is based on finite element approximation from which the auto-regressive parametric representation of the structure is obtained. This representation is used to estimate the structural parameters, viz., mass, stiffness and damping coefficient, using recursive least squares method. The finite dimensional model is then used to design a state-space controller based on the linear quadratic regulator principle. The on-line structural parameter estimation and the controller are then combined using certainty equivalence principle to obtain linear quadratic self-tuning controller for vibration suppression in flexible structures. The performance of the controller (without the self-tuning pat of the algorithm) in suppressing vibrations in an aluminum cantilever beam with surface mounted piezo-electric sensor and actuators is demonstrated experimentally. The spatial recursive algorithm to estimate transverse and angular displacement/velocity from the measured set of strain/strain-rate data, developed in the companion paper, is used as a state estimation algorithm for the state feedback controller.

Fiber optic sensors (FOS) for vibration monitoring of smart structures have certain advantages over conventional strain gage based sensors due to electromagnetic environment insensitivity and high response bandwidth. During the present study, a spatially integrating fiber optic sensor was used for vibration monitoring. It is based on the concept that the optimal placement of the sensing element can be sought by using a priori knowledge of the mode shapes of the structure. The applicability of this approach to polarimetric optical fibers is described. The acquired integrating FOS signal was used to sense and control the vibration of an electrorheological adaptive structure subjected to a random external excitation.

A technique for spatial compensator design is developed for the active vibration damping of interconnected flexible structures. Spatially gain weighted distributed transducers are utilized in order to `shape' the system's forward-loop transfer function, thereby increasing control effectiveness by increasing loop gain over a specified bandwidth. Colocated transducer locations and spatial distributions are chosen to shape the system's loop transfer function, making modal coefficients `large' within the control bandwidth, and `small' for higher frequency modes of vibration while remaining simple to implement in hardware. Temporal compensator design is linked to spatial compensator design by showing the dependency of the maximum velocity feedback gain on transducer modal coefficients. Closed-loop control experiments were performed in order to demonstrate the utility of the compensator design technique on a dynamically complex, interconnected structure: a 56' by 59' nine-bay aluminum grillage. A velocity feedback dissipative temporal compensator design was evaluated. For a band-limited transient disturbance exciting the first twelve modes of vibration (up to 40 Hz), the experiment showed a decrease in settling time from over 30 seconds to less than 8 seconds. For a band-limited stochastic input with a 2 - 22 Hz bandwidth, disturbance attenuation up to 8 dB was shown. In order to assess the model robustness of the compensator design, modifications were made to the experimental plant, changing plant natural frequencies up to 21.2%. Without changing the temporal compensator used in the previous tests, similar closed-loop vibration damping performance was observed, exhibiting significant compensator robustness to plant variations.

The mathematical model of a flexible beam covered with shape memory alloy (SMA) layers is presented. The SMA layers are used as actuators that are capable of changing the elastic modulus and recovery stress, thus changing the natural frequency of and adjusting the excitation to the vibrating beam. A linear control law is determined based on optimal regulator theory. The control results are discussed.

When large area piezoelectric sensors are used for structural control, they can exhibit a `hydrostatic' response due to external acoustic sources. This portion of the sensed signal leads to a response much like controller limit cycling if induced-strain actuators are used, because induced-strain actuators have no control authority over the hydrostatic response. Experimental results are shown for a large area PVDF sensor applied to a Bernoulli-Euler plate that demonstrate response to both the structure's strain field and an exogenous acoustic disturbance. Implications for structural and structural/acoustic control are discussed.

This paper first presents the methodology to design and optimize a feasibility demonstrator for low frequency active control of a composite plate. The demonstrator has been achieved and the experimental results are shown. The major steps to design a smart structure are described. A review of active control strategies with associated hardware requirements as well as different implementation methods shows that the final system is strongly related to the problem to be solved due to the complexity of the structure, the computer efficiency and the expected final response quality. The aim of the study is to prove the feasibility to control the low-frequency (less than 100 Hz) vibrations of a carbon/epoxy composite plate under various mechanical excitations. Experiments were driven to characterize mechanically the composite plate as well as the PZT piezoceramic actuators. An original approach with dual analog-digital controller has been designed and realized, resulting in a simple system: microprocessor programmable switched capacitor low-pass filters and a PC fitted with a timing and digital interface board were used for the controller. Performances using analog filters and a least mean square algorithm are presented.

One major problem in magnetic resonance image equipment is the high-level noise borne by the vibration of the cylindrical shell to support coils for gradient magnetic fields. The vibration of the shell is excited by the Lorentz force between the pulse current applied to the coils and the main magnetic field. In order to suppress the noise inside the cylindrical shell, it is aimed to control the vibration of the shell. In this paper, simulation is carried out on the vibration control of the shell by using distributed piezoelectric actuators. The actuators produce bending moment or in-plane force when pulse voltages are applied synchronously with the pulse current of the coils. Coupling of actuators and vibration modes, and parameter optimization are also discussed. The simulation results show that the vibration level is successfully reduced in the frequency range of 400 approximately 1200 Hz.

A finite element model for piezo-layer bonded beams, based on general finite element approach, has been developed. The modified model has been applied to the deflection controller design of a cantilevered beam supporting a distributed load q, by using piezoelectric layer as both sensors and actuators. The sensors generate electric voltages caused by the deflection of the loaded beam and the voltages through amplifiers apply to the actuators which generate control bending moments on the composite beam. A numerical examples for deflection control of a composite beam with seven elements is presented in detail in this paper.

In this paper, we use segmented piezopolymer and piezoceramic materials to impart control forces to structures for the purpose of annihilating undesired elastic motion. We use modal control techniques to generate the control inputs, particularly the Independent Modal-Space Control method. The actuators can be of any shape or size, making control implementation simpler than for modal actuators, which require that the actuators be cut into specific shapes. We analyze the performance of piezoceramic and piezopolymer actuators with regards to the size of the actuators and the maximum amount of charge that can be applied to these elements. The proposed control method is easy to implement and versatile. The control problem is formulated to have a similar form when traditional mechanical actuators are used. System simulations on 1D structural elements show that piezoceramic actuators are desirable for control of elastic motion.

Over the past several years Eastman Kodak Company has been developing technologies in the area of active vibration control for space structures. The basic goal is to keep the structure as still as possible during operation using active and/or passive damping and isolation. Inherent in these space structures are many of the qualities that make a system difficult to actively control. They are lightly damped, modally dense, and are sensitive to weight increases, as well as thermal loads that a powered actuator might apply to the structure. Further, any system must be fully space qualifiable. To overcome these hurdles, Kodak has investigated several schemes to apply in a multitier approach to achieve maximum benefit from an active system. This paper will present the theory of operation and test results for one of these technologies called `Self-Sensing Active Vibration Elimination'. We will elaborate on a collocated active damping technique using self-sensing piezo-ceramics. The term `self-sensing' is used to describe the phenomenon of simultaneous actuation and sensing using the same device, in this case piezo- ceramic wafers. This work is an extension of Dosch et al. (1992). The key differences lie in the geometry in which the self-sensor must operate. We parallel the theoretical development given in Dosch et al., but present the development in more of a tutorial form. Research in this area is plentiful, however, less than desirable results have often been reported on systems more complex than a cantilever beam. A strain-rate self-sensor with > 60 dB dynamic range and nano-strain sensitivity in the 10 to 200 Hz frequency band is detailed below, proving that self-sensing can be made to work on large structures. Closed loop results are presented that show performance improvements of over 30 dB reductions in the structural resonance response. It should be mentioned that the system described below could easily be applied to extremely small systems (such as a disk drive read/write arm). The self-sensor would allow an entire controller to be placed on a single 14-pin DIP chip, and since the actuator is also the sensor, less instrumentation loading will occur.

The reduction of sound radiation from vibrating structures is an important problem in acoustics. The sound power radiated from a structure can be reduced by altering the dynamic properties of the structure or by isolating the structure from the source of excitation. This is generally termed passive control. In some applications, notably aircraft, the weight penalty imposed by passive control techniques can be prohibitively large, especially at low frequencies. In these applications active control systems which use secondary control actuators can be used as an alternative technique for reducing the sound power radiation.2''1 It has been shown that the volume velocity of a surface is responsible for the majority of the sound power radiation at low frequencies.3 It has therefore been suggested that the cancellation of volume velocity is an appropriate strategy for reducing the sound power radiation from vibrating surfaces.7 In order to actively cancel the volume velocity of a surface an accurate measure of the volume velocity is required. Designs for volume velocity sensors have been suggested using piezoelectric material etched or cut into specific shapes.4'6"° In the experiments described in this paper such a sensor is tested and used to control the sound power radiation from a rectangular aluminium panel.

Analytical and experimental studies undertaken for controlling noise in the interior of a 3D enclosure with a flexible boundary are presented. The rigid boundaries are constructed from acrylic material, and the flexible boundary is constructed from aluminum materia. Noise generated by an external speaker is transmitted into the enclosure through the flexible boundary and active control is realized by using Lead Zirconate Titanate piezoelectric actuators bonded to the flexible boundary. Condenser microphones are used for noise measurements. For panel and cavity controller modes, analog controllers based on feedforward schemes using acoustic error signals are developed and discussed.

This paper describes analytical and computer tools for the analysis of the forced motion of a thin cylinder and of the resulting interior acoustic field. Examples are presented to illustrate the use of the tools in the design and placement of actuators to control the shell motion and the interior field.

Sensors are important components for any automatic process. Their function is to measure physical variables, and thus to allow automatic actions in a technical process, for example in a manufacturing sequence or a measurement. Selecting a sensor for a process, it is mostly overlooked that actuators used in a process also have sensory properties. The reactions of actuators to the state of a process give the possibility to extract relevant information out of the process with actuators. In using the sensory properties of actuators the costs for additional sensors can be saved. Even more important, under some circumstances it may not even be possible to place a special sensor directly at the location of interest: In that case the information about the physical variable is only accessible by analyzing the return signal of the actuator. An example of such a smart actuator combining active and sensory properties is demonstrated in a simple experiment. This experiment shows a steel ball supported as a pendulum. The steel ball can be pushed off, and on swinging back it can be caught in a single pass without any bounce. The actuator uses the piezoelectric effect which shows the underlying principle most clearly: Application of the reversibility of physical effects. In this case mechanical energy can either be produced or absorbed. This experiment is means as a demonstration model for students. It is also used for preliminary investigations developing a fast, actively damped tipping mechanism (optical scanner).

The design of a piezoceramic actuators which is to be embedded in a composite structure is examined. The actuator device must: (1) include a collocated accelerometer; (2) meet certain actuation authority (force, stroke) requirements; (3) be able to survive the embedding process; and (4) have a minimal effect on structural integrity. The need to accommodate an accelerometer limits the minimum thickness of the device. To ensure that the (brittle) piezoceramic material is not broken during the embedding process, it is encased within a frame which has been designed to protect the piezoceramic from short durations of high temperature and pressure. Additionally, the frame is used to apply a compressive prestress to the piezoceramic, ensuring that the piezoceramic is protected from tensile stresses encountered in the operating environment. The output strain levels of the piezoceramic are maximized by using a co-fired stack (178 layers) oriented such that the piezoceramic is excited in the 3 - 3 direction. Because the layers of the piezoceramic stack are to be driven at high voltages, a special high power amplifier was designed which can source the current required by the actuator. The performance of the actuator alone has been tested by driving it uniaxially into a known impedance and measuring the output force and displacement at low frequency. Results form the tests and associated models are presented, which demonstrate the performance capabilities of the actuator.

A general means of shading, or spatial gain-weighting, induced-strain distributed transducers is developed using spatially-tailored electrode patterns to facilitate the modally-structured measurement and control of structural components over a wide bandwidth. The electrode patterns consist of an array of parallel rectangular `line' patches of unequal width and spacing. For panels, the pattern is 2D. A numerical optimization procedure is described for selecting the number, width, and pattern of these electrodes given a specification of desired modal coupling over a bandwidth of interest. The design method may be used to develop electrode patterns for large-area piezopolymer transducers for ASAC sensing, or for designing piezoceramic chip actuator arrays. Beam and plate examples are presented.

This paper discusses the use of genetic algorithms (GA) as a global search technique to solve a loading bridge regulator control problem. The theory, design and implementation of the algorithm is discussed in detail. An improved selection scheme and two advanced genetic operators are introduced. Three different GA-based feedback controllers are designed: Simple GA (SGA), Improved GA (IGA), and Advanced GA (AGA). Their results performance results are compared. Among the three GA approaches considered, AGA is the most robust one for the design of feedback controllers.

Conventional model reference adaptive control (MRAC) requires perfect model matching condition as a prerequisite check for a successful controller design. Although such condition may be satisfied easily for some mechanical systems, it is extremely difficult for adaptive slewing control of a flexible beam with an unknown tip payload. The reason being, firstly, there must be as many actuators as the number of assumed vibration modes to be placed along the beam to provide bending moment. Secondly, if the first condition is satisfied, it would still result in very high feedback gains even for a very small variation of tip payload mass. Therefore the conventional MRAC scheme is physically unapplicable for such application. This paper addresses this issue and provides a solution to the general problem where the actuation power is limited such that the conventional MRAC scheme would not work. A new scheme called Adaptable Reference Model Adaptive Control (ARMAC) differs from the conventional MRAC in that the reference model of the ARMAC is not fixed. The ARMAC inheres infinitely many model gain sets which depend on the estimation of tip payload mass. As the controller/estimator is searching for the true tip payload mass, the working reference model is also trying to fit itself into the best reference model possible. The ARMAC employs the `steepest descent' method which the general MRAC uses to search for the true tip payload mass without any explicit parameter estimation process. This way the ARMAC avoids the stringent perfect model matching requirement while preserving the direct adaptation nature of MRAC successfully.

Our objective is the development of partition algorithms for active elements for multiperformance objectives. The approach is based on inner-outer neural network control designs such as the dynamic hill-climbing algorithm that have efficient outer loop that optimized the partition choice and focuses the inner loop to best implement a particular choice of control structure such as, LQG/LTR or PPF. The introduction of distributed array of actuation mechanisms for vibration suppression and drag reduction has been investigated at NASA Langley for the purposes of reduction of interior noise. In Ref. 3 it is poignantly shown that the process electronics dictates the control architecture for designs that use an array of high-bandwidth devices. The increasing number of actuator devices forces is beyond the multichannel capability of existing processors, forcing the partitioning of the actuators into 'ganged' subsets. With the advent of mesoscale technology, with large arrays of active elements, this will become increasingly the central issue. It was also demonstrated in Ref. 3 that when the partition choice is optimized for a particular performance objective (e.g., active control of interior pressure) it many have a deleterious effect on another performance parameter (structural vibration).

A study on the dynamics characteristics of a snap-action bistable microactuator that employs bimorph heating and residual-stress tension for switching behavior is presented. This study helps to characterize the device more completely and also provides valuable insights into the dynamic behavior of devices in micro-scale. The relation of bending moment and deflection during switching is numerically simulated by applying a simplified snap-through model. The model also takes air drag into consideration. The analysis shows that the switching time from one stable position to the other is less than 1 microsecond(s) , which is one thousand times shorter than the required cooling after each actuation. Hence, for the reported bistable microactuators that have overall lengths of about 200 micrometers and operate in air the maximum switching cycle time is expected to be in the kHz range that is based on thermal characteristics of the device.

In this paper, we discuss a smart motor concept, in which piezoelectric and magnetostrictive actuators forming a resonance electric circuit function together to produce bidirectional motion of a steel drum. Resonance frequency is set at 4 KHz, thereby enabling operation of the motor at reasonably high frequencies.

In this research, a synthesis methodology is presented for the development of a large- displacement piezoceramic actuator. The proposed designs combine piezoceramic actuation and large deflection of elastic members to bring about the required displacements. Configurations of series and parallel stacks of actuator elements and their options on excitation schemes for such actuators will be discussed. Bimorphial actions in these actuator layers are quantified via shell finite elements. A demonstrative prototype based on this concept has also been built and tested. Strokes up to 2.5 mm have been observed during the operation of this device. The level of performance of the prototype was found to be in good agreement with the theoretical calculations. Response of the prototype in the time and frequency domains have been studied. Both the analytical and experimental investigations are detailed in this paper.

The development of a rotary inchworm-motor using piezoelectric actuators is presented. The motor design has the advantage of a macro and micro stepper motor with high torque and speed. The design is capable of fast angular positioning with micro level accuracy. The rotary motor, as designed, can also be used as a clutch/brake mechanism. A constructed prototype motor along with its characteristics are presented. The motor consists of a torsional section that provides angular displacement and torque, and two alternating clamping sections which provide the holding force. The motor relies on the principal piezoelectric coupling coefficient (d₃₃) with no torsional piezoelectric elements used. The design eliminates bending moment and shear applied to the actuator elements, increasing its torque capability. An innovative flexure design has been introduced, and consideration has been given to contact elements which affect the performance of the motor; these issues are explored and discussed. Experiments are performed demonstrating a motor prototype based on the aforementioned design considerations.

Recently, much attention was paid to fabrication of vertical-cavity surface-emitting lasers. Similar structures but consisting of organic compounds may be made using the Langmuir- Blodgett technology of deposition of thin organic layers.

Langmuir-Blodgett films from p-terphenyl and anthracene with cetyl alcohol are fabricated on silicon substrates. A fluorescence decay kinetics of such films is studied. Fluorescence decay time at photoexcitation and at excitation by (alpha) -particles is determined. It is shown that a scintillator based on the Langmuir-Blodgett film is more fast-response than conventional scintillators based on single crystals.

We analyzed the measurement errors of a Shack-Hartmann sensor caused by two major factors. One is caused by the collimation lens aberration change which occurs due to the light path shift in the collimation lens. Another is the defocus of the collimation lens due to ambient temperature change. To obtain the aberration change caused by the light path shift, we apply the primary aberration to the collimation lens aberration at arbitrary light path. To obtain the defocus by ambient temperature change, we derived a formula as a function of the temperature dependence of the refractive indices and the linear expansion coefficients of the lens and the lens mount. Measurement errors of a Shack-Hartmann sensor are estimated by both methods of ray trace and the present error analysis to examine the performance. The results show good agreement with the measurement error of the light path shift and the temperature change. This analysis is effective for analysis of the measurement error of the sensor, which can be utilized for reducing the residual measurement error.

The results of an experimental study of the electrorheological sensitivity of dispersions based on a fibrous filler in a mineral oil are reported. A comparison is made with the powder analog-based ERS.

Transparent polymers are widely used in building test models and producing operation sensors. The diversity in the parameters of the modulated electromagnetic waves, when travelling through a polymeric medium in the form of a light vector, is the means of carrying information in most of the optical sensors. Therefore, the development of efficient operation sensing instrumentation relies basically on a solid understanding of the mechanical, chemical, and physical characteristics of the polymers involved. Optical anisotropy has been shown to prevail in commercially available polymers. This physical phenomenon may lead to erroneous results if not encountered while processing the acquired optical data. The presence of residing double refraction seem to be advantageous in numerous cases. The disadvantage of weak birefringence can be removed. Thus, a relatively cheap material, such as acrylic, may be upgraded to an excellent material for building optical strain gauges. This present contribution presents a brief review of the beneficial and adverse effects of the orientation of the chains in polymers, on the penetrating dielectric vector.

Computer simulations and experiments have show that active and semi-active (adaptive- passive) vibration compensators could be devised modifying the currently available fluidic vibration absorbers. These devices, despite their small size and weight, are currently used to isolate the low frequency high amplitude vibration of relatively massive devices such as engines. They consist of two chambers filled with an inexpensive fluid mixture such as water and anti-freeze which communicate through one or more orifices and an inertia track. The communication through the track is based on the concept of Helmholtz resonance. The lower chamber is separated from the upper chamber by a diaphragm called decoupler. Both semi- active (adaptive-passive) and active control mechanisms, for real-time adjustment of the Helmholtz resonance are discussed in this paper. Real-time manipulation of the inertia track inertance and the position of the decoupler result in semi-active and active control vibration, respectively. We call these novel controllable vibration compensators Intelligent Helmholtz Resonators, IHRs.

Carbon fiber-reinforced plastics (CFRP), as high strength advanced materials are often used as media for embedding sensors and actuators. Due to the properties of components and processing conditions they are electrically anisotropic, with coefficient of anisotropy sometimes exceeding several thousands. This may prevent elimination of static electricity and cause erosion of material due to micro discharges at contacts with fastenings and embedded sensors and actuators, causing their malfunction. For this reason, the investigation of electrical properties of CFRP may provide the solution to this problem. Distribution of electric current field in CFRP and related with it possible errors in measurements of longitudinal conductivity and anisotropy are analyzed. CFRP have been prepared from PAN or cellulose fibers with different heat treatment temperatures and conductivity anisotropy was measured as a function of filler volume fraction and processing conditions. With increasing loading coefficient of anisotropy (alpha) decreases. Lower values of (alpha) were observed when curing agents containing ionic complexes of metals were used. Modifications of fiber surface with hydrophobic agents results in increased anisotropy. Composites prepared with carbon fabrics are isotropic in the fabric plane. Coefficient of anisotropy decreases with increasing molding pressure and depends on the type of weaving of fabric. In hybrid composites with alternating layers of carbon fabric and complex fiber fabric anisotropy is higher due to partial decomposition of conducting layer on top of complex fibers. A method for reducing anisotropy by introducing conducting `jumpers', shorting individual fibers or layers of fabric is proposed. The change of anisotropy in the process of fabrication of carbon-carbon composite by passing electric current through fibers has been investigated. In conclusion, alternative uses of CFRP with reduced anisotropy for contact elements of electric current through fibers has been investigated. In conclusion, alternative uses of CFRP with reduced anisotropy for contact elements of electric machines and geological prospecting as imitations of rocks are discussed.

Engineering structures are designed to function within the elastic domain and designs are chosen based on their relative merits and capabilities to suitably address the specific requirements. The decision to monitor a structure to determine the long-term performance characteristics and operational stability involves many factors including, but not limited to, the objectives of the monitoring and the available resources to do so. One must choose between active monitoring systems, i.e., those that require real-time power supplies, and ancillary data acquisition, storage and monitoring systems and passive systems which, as the name implies, operate without any of these constraints. Passive techniques for structural health monitoring and materials damage assessment are reviewed. Data are presented to illustrate their application as related to structural health monitoring, crack detection and crack growth monitoring, and damage assessment in composite materials.

A number of tests have been conducted to evaluate the reliability of fiber optic sensors for use in health management of reusable space structures. Air gap Fabry-Perot sensors were embedded in a filament wound composite tank. Also, sensors were embedded in flat composite panels and loaded at cryogenic temperatures. At -423 F correlation between the fiber optic strain sensors and temperature compensated electrical strain gages was within 1%. Hydrostatic testing of the filament wound pressure tank at ambient temperatures produced similar results.

This paper presents a framework for the identification of the constitutive law for a class of nonlinear models of shape memory alloys (SMA) embedded elastomeric rods. Specifically, a formulation of the transient response of elastomeric rods with embedded shape memory alloy actuators that incorporate the inherent coupling between the dynamics of deformation at the structural level, the thermal response and the constitutive law describing the shape memory alloy is described. Previous work by the authors has shown that the incorporation of shape memory alloy actuation is distributed parameter systems can induce a large class of nonlinearities including hysteresis effects in the SMA constitutive law, nonlinear kinematics of large deformation, and, in some cases, local plasticity effects. To derive a methodology to control the dynamics for the class of SMA embedded elastomeric rods considered in this paper, it is essential that the system characteristics of the nonlinear distributed parameter system be identified accurately. This paper presents an identification theory applicable to the coupled system of partial differential equations. The results are validated using both numerical simulations and experimental results.

The model for the calculation of the thermal strain coeffitient of the compaund oriented composites with given fiber orientation is presented. The mutual sliping of layers are strained by the elastic law. The relations for the calculations of the axial and angular thermal strain coefficient depending on the thermal and elastic pro— perties of each layer are obtained and verified for carbonplastic specimens.