Smart materials are expected to adapt to their environment and provide a usefulresponse to changes in the environment. Both the sensor and actuator functions with theappropriate feedback must be integrated and comprises the 'brains' of the material.Piezoelectric ceramics have proved to be effective as both sensors and actuators for a widevariety of applications. Thus, realistic simulation models are needed that can predict theperformance of smart materials that incorporate piezoceramics. The environment may includefluid loading, material damping, the effect of the backing structure and changes in both thestructure and the environment. In all cases, the smart material should sense the change andmake a useful response. A hybrid finite element method in conjunction with a boundaryelement technique is used to model the fields in and around a smart coating containingpiezoceramic elements mounted on an immersed structure. The properties of the backing andmatching layers as well as the host material in which the transducer elements are embedded areconsidered in the modeling. The effect of cross talk and influence of neighboring elements isstudied by taking into account the effect of neighboring elements in increasing order. Thecross talk is also studied as a function of element spacing and material properties. Numericalsimulation of the performance of several types of smart materials have been performed. Thesimulation is compared with experimental results to demonstrate the effectiveness of both thetheory and the dependable performance of piezoceramic elements as sensors and actuators.

Fiber optic sensor and communication technology have importantadvantages that can be expected to have a significant impact on future aerospaceplatforms. This paper provides a brief overview of the motivation and direction offiber optic smart structures for aerospace applications.

The development of intelligent materials and structures is anew and rapidly evolving field which is bringing together researchersfrom many diverse fields, such as medicine, aeronautics, materialsscience and computer engineering. The conceptual background ofintelligent materials is a combination of advanced aspects of materialsscience and computer engineering which seeks to create compositematerials systems which can sense and respond to environmentalchanges in ways which maximize their function. Several basic models ofpossible intelligent materials are discussed as well as the present status ofthis field in Japan.

New research has been initiated in the area of smart filters and opto- electronic materials, with an approach that is both evolutionary and revolutionary.Model molecular systems with controllable two-dimensional order are examined,such as siloxane-based liquid crystals, and their significance as a flexiblebackbone for the derivation of non-linear optical chromophores discussed.Advancements sought are through polypeptide-bound chromophores with hithertounrealizable properties, where the photomodulation of the helix-to-coilequilibrium of spiropyran-containing poly(L-glutamate) serves as a model system.The objective is to achieve an ordered three-dimensional network of nonlinear- optical chromophore-substituted polymer chains with controlled optical properties-- the so-called smart filter.s

Monitoring of buildings - especially of bridges- gets more and more important. The reasons for this arethe increase of the heavy goods traffic, of air pollutionand in precipitations, de-icing salts and the fact thatprices for traditional maintenance and repairs are goingup.The bridge Schiessbergstrasse in Leverkusen represents anew generation of building structures having a perfectsolution for this kind of problems: prestressing with"intelligent tendons", monitoring of the stress strainbehaviour of the concrete, chemical sensors, and - in thecase of the bridge Schiessbergstrasse additonally areinforcement with epoxy coating and foil sealing withpolyurethane of the bridge deck.

Approaches to creating distributed optical fibre sensors arecompared. Pump-probe architectures have potential for realising fully- distributed systems having fast response. Quasi-distributed systems usingfibre components based on photosensitivity are also attractive.

The development of the feed-forward polarimetricquasi-distributed concept for the recovering of theelastic curve of structures is shown. Anhigh-precision interferometric method permits toreach 1 due resolution in non-incremental strainmeasurement even with a polarimetric fiber-opticsensor. The method is applied to an feed-forwardinterrogated 8-segmented sensor embedded in acomposite sample.

We demonstrate a two-mode elliptical-core fiber strain sensorremotely interrogated over lead-insensitive single-mode fiber using pseudo- heterodyne demodulation. In addition, preliminary results obtaineddemonstrate FMCW multiplexing of two elliptical-core fiber sensors in a'single-fiber' configuration.

A multimode optical-fiber sensor-network for the simultaneous monitoring of heat andproximity is presented. The interrogation and processing system makes use of the short- wavelengths OTDR technique. The network topology is a hybrid configuration of reflective- tree and transmissive-ladder architectures, which are operative for temperature and proximitysensors, respectively.Temperature sensors are operative in the 20-80°C range with a best resolution of atleast 0.3°C. Proximity sensors can operate either as on/off devices or as analog sensors. Theranges of operation and resolutions can be varied according to the geometrical arrangementof the probes.

A prototype of a digital control system based on VME busArchitecture that is able to perform the automatic control of optical res- onators (Fabry-Perot cavites, Michelson Interferometers, etc..), has beenbuilt in Napoli, to ascertain the feasibility of the digital control techniquein the alignment of the mirrors of the Virgo Antenna, the italian-frenchproject of a very long baseline interferometric antenna for GravitationalWaves Detection. Its main features are the controlled band (0 -i- 5 KHz),12 and 16 bit ADC/DAC with a sampling rate of 40 kHz, error signal ex- traction by means of synchronous demodulation.

In this paper we propose a concept for a quasi-distributed fiber-optic strainand temperature sensor based on time division multiplexing (TDM) of in-line coupledFabry-Perot interferometers (FPI) with fiber Bragg gratings used as weak reflectors. A"differential" two core fiber is used for separate measurement of strain and temperatureand a dual-wavelength technique is used to perform absolute measurements over anextended dynamic range. Some advantages and limitations of this sensor system are dis- cussed. The system has been primarily designed to be embedded in composite structuresfor aerospace applications.

ABSTRACT:This paper describes a digital technique which may be used, ina homodyne interferometer, to recover both the shape and the amplitudeinformation of a measurand.

A technique for the detection of dynamic strain inducedwavelength shifts in fiber Bragg grating sensors which is capable of highresolution sensing is described. The scheme is based on the use of anunbalanced-interferometer wavelength discriminator to transpose thewavelength shift of light reflected from a strained fiber grating into thephase shift of an electrical carrier signal.

The series of transformations that allow one to infer dataindicative of structural performance from the scalar optical data provided byembedded sensors is discussed. Specific topics that are emphasized includeforward and inverse phase-strain-temperature relations, the difference betweenfiber and structure measurands, and the uniqueness and stability of inferredstructural data.

Fiber optic Bragg grating sensors have been built into glass fiber re- inforced polyester test specimens. The tests have shown good linearity and repro- ducibility of sensor data. A destructive test has demonstrated strain measurements onthe Bragg sensor up to 16000 ue.

We report the results obtained on cure and strain field monitoringof unidirectional Glass Reinforced Plastic (GRP) composites with bonded orembedded white light quasi distributed optical fibre polarimeters. The importance ofthe optical fibre coating is shown. When it buffers stresses generated duringfabrication a purely linear measurement is obtained versus strain either in extensionor compression without any hysteresis.

A fiber-optic double - polarization Michelson - interfero- meter is employed for remote sensing of the surface strain of platesmade from Carbon fiber composites. Simultaneous unambiguousinterferometric (incremental) and polarimetric (analog) readout isdemonstrated employing conventional single mode fibers. The allowsfor the additional sensing of the transverse stress field along theadhesive embedded fiber.

A spatial modulation technique applied to embedded fiber optic sensorfor real time monitoring of 3-D braided composites, is presented. Several 3-Dcomposite specimens with embedded fiberoptic sensor have been fabricated and tested.Optical fibers were incorporated into the structure during the braiding process. Thestudy shows that; (i) the spatial modulation technique is applicable to optical fibersbraided into 3-D composite structures, and (ii) it is preferable to use special geometricalconfigurations of the embedded optical fiber, to improve the sensor sensitivity anddynamic range.

The application of a three dimensional phase-strain-temperaturemodel is described for determining the total phase change as a function of variousstrain components and residual strains concerning the polarimetric fiber opticalsensors. The residual strains are determined experimentally using both bow-tie ande-core high-birefringent fibers. The procedure of predicting the total phase changeand the results obtained from both fiber types is presented.

The use of embedded fiber optic sensors for the impactdetection on woven-composite panels has been developped using interfero- polarimetric measurements. Preliminary results on the study of the process- induced birefringence properties modifications of two different types ofspecific optical fibers: Hi-Bi "Bow-Tie" fibers and Side-hole birefringent"FASE" fibers are discussed.

It has been only recently that research into smart structures and materials has beenidentified as an interdisciplinary area of activity in its own right. In spite of that, work that could quiteproperly be called smart structures and materials research has been carried out for a considerable period oftime. In particular, developments in the areas of designed materials, adaptive control of structures, andartificial intelligence have been of particular importance. In this paper, the recent evolution of a numberof fields will be described and their integration/fusion into the area of smart structures and materialsdiscussed. A specific example of a smart material combined with an integrating fiber optic vibrationsensor will then be provided. Finally, the implications of the success of ongoing research efforts will beconsidered.

Finite element analysis techniques have been used to predict the stress concentrationsaround optical fibres embedded transversely to the reinforcement in unidirectional and cross-plyCFRP laminates with thermoplastic PEEK matrices. The effects of applied transversecompression stresses and also thermal stresses resulting from fabrication have been analysed.The residual thermal stresses are affected by the dimensions of the fibre optic and the shape ofthe resin rich region which forms around the inclusion.

Smart materials/structures have embedded sensors to monitor theirown state. A novel sensor was synthesized by sputtering a piezoelectric film ontoa metal fiber. The piezo-fiber sensor, similar in configuration to an optical fiber,is active since an electric field is developed when strained. Thus the sensor candetect vibration as well as fracture in a manner similar to acoustic emission. Thesensor is well suited for use in fibrous composites, where it can be easilyincorporated into filaments and strands.

Sapphire optical fiber interferometric sensors have been developed anddemonstrated for the measurement of displacement, strain, ultrasonic waves andtemperature. The Fabry-Perot sensors use sapphire fiber waveguides to allowmeasurements up to 2000°C.

Future advanced aerospace vehicles such as next-generation aircraft, advancedlaunch system vehicles and spaceborne platforms will incorporate fault-tolerant smart acousticsensor networks to monitor structural integrity and initiate corrective actions. These smartstructures will be capable of assessing vehicle structural damage in real time and ultimatelyreconfiguring the flight controls to ensure mission success.

Accurate and fast strain measurements will be required by any resident sensing system to be used forSmart Adaptive Structures. We have developed a dual Fabry-Perot fiber optic strain sensor systemto be used with a controlled actuation structure in the form of a "Smartruss". This generic AdaptiveSmart Structure element will test many of the essential features of this technology and may serve asthe forerunner of systems that could be used for large flexible space structures or flexible roboticmanipulators.

The result of recent studies, performed in the ALCATEL CABLE Group in collaboration withFrench Authorities showed the feasibility of using fiber optic sensors in the aim to detect and to weight avehicle in motion on a road. This paper deals with the presentation and the evolution of the system from thestudy state to an industrial state.

Fluorescent, plastic fibers having a dye-doped polymer claddinglayer were fabricated and were used as a smart optical sensor fordetecting atmospheric humidity, breathing conditions and temperature.Under suitable light pumping, the fluorescence intensity of thesefluorescent plastic fibers changed by the above chemical and physicalparameters, and hence, they operaed as excellent fiber sensors withgood sensitivity and a fast response time.

An assessment has been made of the reliability of an optical-fibre crack- monitoring system for detecting the initiation and growth of fatigue cracks inaluminium alloys. The sensors are capable of detecting crack-width increases in therange 5 to 30 lam, in aluminium alloys subjected to cyclic loading, with a high degreeof confidence. The performance of the sensors is unchanged by large cyclic loadingcycles up to about 100 microstrain, over the temperature range -196° to +120°C, up to100% relative humidity conditions or immersed in normal or sea water.

A distributed temperature sensor is described that uses standard multi-modecommunications grade fibre as the intrinsic sensing element. The sensor employs anadaptation of optical time domain reflectometry (OTDR), a fibre analysis techniquewell established in the telecommunications industry. Spectral selection of the anti- stokes Raman side band provides a signal which is sensitive to temperature.A temperature profile is received along the entire length of an optical fibre whichmay be up to 10 km long. (A typical fibre length of 4 km would give 4000 pointsof information resolved to ±1°C and updated every 15 seconds).Among the advantages of this approach are the ease of installation andmaintenance, immunity to electromagnetic interference (EMI), safety in hazardousenvironments and the provision of not only temperature but also position data.The applications for distributed temperature measurements are very broad ranging,for example, from monitoring curing conditions in concrete structures and powercable hot spot detection to energy management and fire protection. Theperformance specification is discussed and a system configuration is suggested.

This paper discusses the complexity of wire hoist rope structure and describesresults of laboratory experiments using attached and embedded optical fiber sensors.These results are compared to those of similar research conducted at the U.S. Bureau ofMines using electrical conductors as embedded sensors. Both types of sensors wereembedded in order to investigate attachment procedures, and to determine sensorperformance and robustness. Results indicate that both optical fiber and electricalconductor sensors may have potential use in the evaluation of wire hoist ropes andsimilar applications.

Taking advantage of the sensitivity to temperature ofthe polarimetric sensors, the auto-measurement of theGrUneisen parameter of the fiber-optic silica wasexperimentally obtained. The first result is in goodagreement with the expected value.

Over the past decade, tremendous advancements have been made inthe development of structural control paradigms and in the necessary supportingtechnologies. The fundamental paradigm that has driven these advancements is thedesire to create "biologically inspired", controllable structures. In search of thesestructures with adaptive and lifelike features, modern-day alchemists have developedseveral approaches, based on natural systems, to incorporate adaptability intostructures. This paper will describe four specific examples of adaptive behavior andthe applications which might benefit from such lifelike functions.

In these several years piezoelectric and electro-strictive actuatorshave become very popular for micro-positioning in optical and precisionmachinery fields. Aiming at wide commercialization of these actuators, manyinvestigations have been made in the improvement of ceramic materials foractuators, designs of the devices and control and systemization of theactuators. This paper reviews recent applications of piezoelectric/electrostrictive ceramics from a viewpoint of "smart" actuators and systems.

This paper addresses some of the problems associated with the use of shape-memoryactuators in Smart structures. These problems include (i) prediction of the straintrajectories during partial actuation, and (ii) the long-term stability of actuation strain.These phenomena are discussed in the context of their implications for actuator control,and the design of structures containing shape-memory actuators.

The paper describes our experimental and theoretical investigations withNickel-Titanium(Ni-Ti) fibre-reinforced epoxy specimens and, the theoretically predictedactive vibration control possibilities for planar mechanisms with Ni-Ti-reinforced compositelinkages.

The SMAAC control surface concept is an adjustable camber foil which isactuated by shape memory alloy wires to control flight of hydrodynamic or aerodynamicvehicles. An operational model of a SMAAC control surface was fabricated anddemonstrated in a water tunnel. Lift measurements in the water tunnel indicated that theSMAAC foil produces 40% higher lift force than rigid foils at.the same angle of attack.Flow visualization showed that the wake behind a SMAAC foil was a factor of 3 smallerthan the rigid foil at equivalent lift. The next generation SMAAC design is presented.

Impulsive pressure applied on a thin plate coupled with fluid is measured bypiezoelectric disks. A pair of piezoelectric disks are put on the side of aplate in contact with fluid and the empty side. The outputs from each of thepiezoelectric disks are summed to cancel the effect of the plate-bendingdeformation. The summation of voltage histories is converted to impulsivepressure according to the calibration of the piezoelectric disk by thelongitudinal impact test. A generator of impulsive pressure is constructed toverify this method.

This paper introduces a novel concept of using semiconductor heat pumpmodules to heat and cool Nitinol shape memory alloy (SMA) wires in an effort to reducethe response time for complete thermal cycling. An analytical heat transfer model isdeveloped to provide a quantitative comparison between the effectiveness of semiconductormodules and other conventional modes of heating and cooling SMA wires. Results of theheat transfer modeling indicate that semiconductor heat pump modules can reduceheating/cooling cycle time by an order of magnitude compared to free or forced convectionalone.

An overview is presented of the recent establishment of a panel inthe United States under the auspices of the National Science Foundation to deal withthe field of active structural control. Information is given about the purpose of thepanel, its organizational structure, future plans, and some proposed internationalcollaborative efforts. Also provided is an overview of the state of-the-art of struc- tural control research with special emphasis placed on laboratory experiments usingmodel structures and on full-scale implementation of some active control systems.

The durability of bridges and the ability to permanently fulfilltheir initial function are topics of rapidly growing interest. For a long time,inspection programs have been carried out to follow up evolution of largestructures. To help managers in the decisions, an advanced metrology wasintroduced in sensitive parts of bridges to assess the structural aptitude. Thestructure was thus given a certain "intelligence". The paper presents newbridge bearings equipped with load measuring devices based on an opticalfibre method.

A technique for measuring reinforcement strains in reinforced concretestructures is described which uses electric resistance strain gauges installed in alongitudinal duct machined within the reinforcement to avoid degradation of the bondcharacteristic at the steel/concrete interface. Details of experimental work using thistechnique are given and typical results presented to demonstrate its performance.Possible developments for use in smart structures are discussed.

Laboratory experimental results obtained in five yearsof works with embedded and bonded Fiber OpticInterferometric Sensors (FOIS) in concrete specimens arepresented. The response of the FOIS in pure compressionand three point bending tests and observations regardingthe aging effects are discussed. The results confirm thegood characteristics of the FOIS in terms of sensitivity,reliability and aging for concrete applications.

This paper describes the installation and monitoring of structuralinstrumentation in a two storey building. The aim of the work was to evaluate the realbehaviour of the structure and compare this with analytical and experimental models. Theinstallation, monitoring and subsequent analysis of the results required careful thoughtand planning. The programme has led to critical observations of construction practice aswell as confirmation of the discrepancy between design and real behaviour.

Excessive displacements and/or deformations in engineeringstructures can lead to critical states in stability and to endangeringpublic security. To ensure a continuous and, at the same time, highreliable structure control fibre optic technique is used. In thispaper a description of two sensor applications in hydraulic works isgiven; firstly, an optical waveguide-compatible displacement limitsignaller for monitoring of dam's span joints; secondly, a fibre- optical deformability meter for a watertight core of a rock-fill dam.

Advances in the design, materials and constructiontechniques that provide buildings and structures with the capacity towithstand and resist natural and man-made dynamic forces have been theresult of civilian engineering research. In recent years the possibility ofusing passive and active control systems, new sensors and devices formonitoring structures behavior to control and reduce these structural andnon-structural damages has become an area of considerable interest.Existing research programs and a new initiative on structural controldeveloped in the Directorate for Engineering, National ScienceFoundation, will be described. The content, issues addressed and scopeof this initiative will be discussed together with a brief description of themain topics broached by the proposals received in the first year ofactivities.

A Cascade Hybrid Active Dynamic Vibration Absorber(CHADVA) is proposed, which is a cascade combination of an active and a passivedynamic vibration absorbers. CHADVA can avoid the influences of shock, noise, orcontrol spillover caused by ADVA on the buildings. Furthermore, a SwitchedCascade Hybrid Active Dynamic Vibration Absorber (SCHADVA) is presented,which not only possesses all merits of CHADVA, but also keeps a certainperformance of vibration control under large earthquake. The usefulness of them isverified through numerical calculations and computer simulations.

This paper presents an advance notification system which links smart structures in seismic regions and enables them to learn of impending earthquakes prior to the initial excitation. When an event occurs, the smart structure or sensor nearest the epicenter is triggered by the initial P wave and calculations are performed to estimate the earthquake's predominant frequency, epicentral distance, and magnitude. This information then is sent to the remaining smart structures via a networked telecommunications system where it is used to prepare active control systems and expedite emergency management procedures.

The use of extrinsic Fizeau fiber interferometric (EFFI) sensors attached to and embedded within concrete structures is described. The sensor heads consist of hollow tubes used to align the end surfaces of fibers which form the Fizeau cavities. Interrogation using two sensor heads allows determination of axial displacement and temperature. Three dimensional arrays of sensors were embedded in concrete to allow monitoring of the fabrication process and slippage between the matrix and internal reinforcement rods. Similar arrays have been attached to a reinforced concrete bridge and used to monitor dynamic strains.

A new closed-open-loop optimal control algorithm is proposed that has been derived by minimizing the sum of the quadratic time-dependent performance index and the seismic energy input to the structural system. We modify the developed algorithm as to be able to take into account the dynamic soil-structure interaction phenomena. Structural responses are well suppressed not only for the system with soil-structure interaction effect and also for that without one.

The paper summarises some modelling methods for use with civil structures containing active elements (in both differential equation and state-space form) and examines design optimization applied to these models. The optimization techniques are extended to give a means of making a quantitative relative assessment between different positions for the active element. Some results are presented, and the relevance of the technique in the context of an overall design methodology is discussed.

This paper presents the results of a preliminary study into the short term fatigue behaviour of a carbon/epoxide composite system containing embedded fibre optic sensors and NiTiNOL wire actuators. The high-load/low-cycle spectrum was addressed for both unidirectional and cross-ply laminates of different thicknesses. Fatigue loading applied through tension was maintained with constant force. Relationships are derived between the inclusion size and position, relative to the host reinforcement and the composite fatigue resistance. Failure modes have been discussed.

To monitor and control the stress profile in concrete bridges, a two-stage system is presented. The stress is first measured then monitored by the time-dependent pressure of an embedded flat jack, keeping the local strain variations constantly equal to those occurring at a sufficiently close but undisturbed point. When the flat jack clearly indicates a stress outside the allowable limits, external tendons then automatically re-adjust the pre-stressing force. This actively reactive system responds to significant irreversible stress variations but disregards minor fluctuations.

Smart composites contain inbuilt sensors which allow the material to be monitored during manufacture and service life. Whilst the technology is well established in the aerospace market, there are a number of factors preventing the widespread use of smart composites in other areas including the construction and offshore industries. A review of these problems is presented. In particular the influence of sensor implants on the mechanical performance of advanced composites is considered.

These problems are being addressed by Pera International's Advanced Materials Group, the objective, to develop a working strategy for the use of smart composites in critical structural applications.

Smart structures withstanding earthquake and high wind have emerged using complex systems such as Active Mass Driven (AMD) and Active Variable Stiffness (AVS) Systems. A simple alternative system is proposed where a system of auxiliary masses move in a prescribed fashion. The mass translation changes the dynamic characteristics to render the structure non-resonant during the external stimuli. The lower amplitude of vibration of a non-resonant system reduces the damage and disruption. The dynamic response is modeled by the analysis of a cantilever beam with auxiliary masses moving in a prescribed fashion.

A new method to optimize anisotropic fibre arrangements within composite material structures is presented in this paper. The so-called CAIO method (Computer Aided Internal Optimization) adapts biological fibre orientation methods for minimization of shear stresses within anisotropic or multi-layer composite material structures of engineering components to help avoid failure.

Biomaterials are defined as substances or combinations of substances, other than drugs, synthetic or natural in origin, which can be used for any period of time, as a whole or as a part of a system which treats, augments, or replaces any tissue, organ or function of the body. There are in general terms two types of biomaterials, those which are 'inert', accepting that this is not strictly possible in the way this is understood in chemistry, and those which are 'bioactive'. In both cases there must be a degree of acceptance by the body, expressed as the biocompatibility of the material, a very complex concept involving biochemical, cellular, and mechanical interactions between the implanted material and the living tissues. In most cases there is a response to the implanted biomaterial from the organism and the control of this is one of the major areas of research.

An overview is given on expectations in application of smart structures in aircraft with emphasis on Structure Health Monitoring and Active Structures.

This paper describes computer simulation analyses onapplication of a fuzzy logic and a neural network control to trackingand rendezvous of a moving target for docking by an adaptive spacestructure in order to examine the effectiveness and feasibility ofboth the controls. The example simulations have shown that theapplication of the fuzzy control/neural networks is very effectivein the tracking/rendezvous problem.

In this lecture we give fundamental well-posedness results for a variational formulation of a class of damped second order partial differential equations with unbounded input or control coefficients. Included as special cases in this classare structures with piezoceramic actuators. We consider approximation techniques leading to computational methods in the context of both parameter estimation and feedback control problems for these systems. Rigorous convergence results for parameter estimates and feedback gains are discussed.

A new control algorithm to improve a tuned mass damper is proposedand investigated. The feedback gain of the algorithm is linear to the response accel- eration of the primal system and it is optimized in the frequency domain under a har- monic excitation. The optimum feedback gain and the optimum parameters of thetuned mass damper are expressed in a closed form solution.

This paper is concerned with the control design for structures with spatially dis- tributed discrete sensor arrangements. Optimal controllers are derived which considerably increasesthe damping of the structure for a significantly large bandwidth. The control design is formulated as aconstrained optimisation problem and the sequential nature of the system is exploited to simplify thedesign procedure. The number and locations of sensors are determined in an iterative design procedureaimed at meeting a set of design specifications. The proposed technique is applied to an ideal Euler- Bernoulli beam of unity length with free ends. The result shows that high degree of damping can beachieved for a large bandwidth.

TRW is currently developing an adaptive structural damping system forspace structures based on real-time system identification algorithms. Simple recursiveleast squares (RLS) Auto Regressive Moving Average (ARMA) models are shown tobe suitable for structural identification. They have quick convergence rates and cantrack slowly time varying parameters. Real-time ARMA algorithms have beenimplemented on a Texas Instruments TMS320C30 Digital Signal Processor (DSP) chipand performance tested. Bandwidth limitations and code optimization are discussed.A hardware demonstration system utilizing these algorithms for real-time healthmonitoring is presented.

A computationally efficient procedure for the selection of placement of ac- tuators is described in this paper. This method is formulated in modal coordinates and isbased on a Progressive Collapse Analogy of adjoint structures made of a hypothetical brittlematerial and having the same shape as the eigenmodes of the structure to be controlled.

In order to minimize the control effort and the spillover energyof piezo-electric actuators in adaptive truss structures, optimal placementstrategies developed in conjunction with the Independent Modal Space Con- trol method are presented. Eigenvectors consisting not only of nodal dis- placements but also of electric potentials are used for the optimal actuatorplacement calculation. The method is illustrated by numerical examples.

The performance of a single input, single output, individual bladecontrol system, designed to attenuate the helicopter rotor vibration usingpiezoelectric crystals (PZT) embedded in the blade structure, is studied. Theresults indicate that an efficient control of the blade lower damped modes,which significantly contribute to the unpleasant vibration of helicopters,may be achieved with a "smart" adaptive controller.

The sound radiated from an electrically excited laminated piezoelec- tric plate is computed. Voltage distributions obtainable from an array of finite sizeelectrodes are used to examine the limitations of actively suppressing sound radi- ation at particular spatial wave numbers. The problem of active cancellation ofsound reflection at oblique incidence is investigated.

The paper reports on the integration in mechanical structures of piezopo- lymer films. Material properties were determined, technological and computational as- pects investigated. Typical functions such as vibration damping are demonstrated usingCFRP plates covered with several layers of piezopolymer films for bending and torsioncontrol. The test setup is described.

This paper presents the flutter suppression of a cantilevered pipeconveying fluid. The response of the cantilevered pipe is controlled by the torqueproduced by a pair of tendons attached to the pipe and a servomotor. The equation ofmotion is solved by means of the Galerkin method. To reduce the number of systemmodes, a suboptimal control law is used. The good agreement between the numericaland experimental results show that this method is effective for the flutter suppressionof the cantilevered pipe conveying fluid.

The independent structural design for stochastically disturbed activestructures, as part of the integrated structure/control design methodology, is the subjectof this paper. The methodology requires the consideration of a generic controller in or- der to guarantee the performances of the active structure resulting from the mechanicaldesign.An elastic 20 m long Extendable and Retractable Mast fitted with piezoelectric local ac- tuators and an offset rigid antenna illustrates the method.Configurations, values of modal dampings are investigated using modal analysis, analy- sis of disturbance and actuator effects, inclusion of modal shapes, choice of actuatorsand sensors, determination of final performances.

This paper outlines the design for a health monitoring system forgas turbine engines. Knowledge based techniques are emerging as useful toolsfor health and condition monitoring of high value engineering systems. Wedescribe a demonstrator system that uses these techniques, together withmodern signal processing methods, for monitoring the health and perfor- mance of a marine gas turbine engine.

A collection of diverse experimental investigations are presented herein which demonstrate theactive vibration control capabilities of macroscopically smart fibrous composite structures featuringelectro-rheological (ER) fluids, piezoelectric materials, and fiber optic sensing systems. Thiscollage of investigations demonstrates the ability of beam and plate-like structures fabricated in thisclass of smart laminated materials to tailor their elastodynamic characteristics in real-time.Furthermore, by judicious selection, the smart-materials designer can synthesize numerous classesof hybrid actuation systems from a variety of generic actuator systems in order to satisfy a broadrange of performance specifications that cannot be satisfied by embedding only a single type ofactuator systems within this class of composite structures.

A slewing frame configured with a piezoceramic strut is discussed. The slewing of aframe similar to a satellite solar panel induces both torsional and bending vibration in theframe. The torsional modes are relatively uncontrollable with the motor used to slew theframe. This provides a natural application of active structure technology. A frame elementis replaced with a dynamically equivalent element which contacts eight self-sensingpiezoceramic actuators. These actuators render the torsional modes controllable. Thisanalysis and experiment are then used to investigate various control laws for performingvibration suppression while slewing.

Smart structures withstanding earthquake and high wind haveemerged using complex systems such as Active Mass Driven (AMD) and ActiveVariable Stiffness (AVS) Systems. A simple alternative system is proposed wherea system of auxiliary masses move in a prescribed fashion. The mass translationchanges the dynamic characteristics to render the structure non-resonant during theexternal stimuli. The lower amplitude of vibration of a non-resonant system reducesthe damage and disruption. The dynamic response is modeled by the analysis of acantilever beam with auxiliary masses moving in a prescribed fashion.

B iomaterials are defined as substances or combinations of substances, other thandrugs, synthetic or natural in origin, which can be used for any period of time, as a whole or asa part of a system which treats, augments, or replaces any tissue, organ or function of the body.There are in general terms two types of biomaterials, those which are 'inert', accepting that thisis not strictly possible in the way this is understood in chemistry, and those which are'bioactive'. In both cases there must be a degree of acceptance by the body, expressed as thebiocompatibility of the material, a very complex concept involving biochemical, cellular, andmechanical interactions between the implanted material and the living tissues. In most casesthere is a response to the implanted biomaterial from the organism and the control of this is oneof the major areas of research.

This paper presents a theoretical model to predict the curvature of a rectangulargel which is subjected to a pH gradient. The curvature is formulated as a function of volumetricstrains. Experimental observations indicate a direct coupling between the electric field and the gelthat induces an immediate volume collapse independent of pH gradients. Additional deformationsoccur later due to a pH gradient evolving through hydrolysis.

The subject of this research is the sensing of damage such ascracking or corrosion in a settable material by a chemical or physical sensorwhich, in the process of sensing, starts the activation of a remedial orprevention process. It is a distributed system in which sensing and actuationrepair occur when and where they are needed.Materials containing various types of hollow fibers filled with a chemicalwhich releases into the matrix at appropriate times, or over time, are designedto address some of the major issues of material performance.

The distinguish features of superionic state ofsolids are considered as well as conditions need forthis state appearance. These features lead to uniquesmartness of the superionic materials to the differentimpacts. Possible areas of application of the super- ionic conductors are shown.

This paper describes the use of a numerical simulation topredict the dynamic behavior of a photorefractive crystal exposed tointerfering light waves at two different frequencies. Unlike staticrecording media, photorefractive materials allow for the simultaneousdiffraction from and generation of refractive index gratings. Thegrating properties are evaluated in terms of their effect on theperformance of a dynamic distributed sensor which uses the crystal as aholographic recording medium. Experimental results are presentedwhich support the behavior predicted by simulation.

Three methods of decoupling and one method of increasing actuator strain throughenhanced directional attachment (EDA) are presented. Directionally attached piezoelectric(DAP) elements are laminated to an uncoupled plate to generate 44°/m in bending without twistand 31°/m of twist without bending. The strains are enhanced 5 to 12% when the elements aretransversely stiffened. Analytical EDAP models are presented with experiment and theory inclose agreement. A comparison of EDA to current laminating techniques demonstrates 50 to 1000%higher strain rates in twist. Data from a wing using EDAP elements is also briefly summarized.

We discuss the design and analysis of an actuator system to deform awing over its entire cross section so that optimum aerodynamic shapes can be realizedfor more than one flight condition. Preliminary aerodynamic analyses indicate that thisconcept could reduce the drag coefficient of the JSTARS wing by at least 6% duringloiter; however, aerodynamic design optimization is required to quantify theimprovement. A test model of an active rib is being constructed. Finite-element analysisof this model indicates that the system will accurately produce desired deformed shapes.

In-situ fiber optic and acoustic waveguide sensors can monitorprocesses such as composite cure or microstrain in large aerospace structures. Thesimultaneous response to temperature and strain in optical fibers has been exploited tocreate a single-fiber dual sensor using a single light source that can measure bothtemperature and strain independently. With the use of lead-in/lead-out fibers, thesemeasurements can be performed over a localized region. The use of acousticwaveguides as sensors have shown their ability to monitor both graphite/epoxycomposite cure and post-process pressure-induced cross-ply strains.

The first on-line detection of cracks generated ina laser cladding process is obtained by a very-sensitiveoptical interferometer. The instrument is based on a homodyneMichelson-type configuration and uses an He-Ne laser assource. The instrumental performances (10 MHz bandwidth, 1Angstrom resolution) are maintained during the in-fieldtrials and confirm the feasibility of using opticalinterferometry in material processing diagnostic.

Electro-rheological fluids possess properties which render them particularlysuitable for inclusion as the controllable element in a variable stiffness or damping devicewithin an adaptive vibration isolation system. This paper reports on an experimentalinvestigation into the use of polymethycrylate based ER fluids, in particular in a dashpottype device, with the intention of studying their applicability for use in such a system.Initial effort was expended on dynamic modelling of the fluids using parameter estimationtechniques. The scope of this study was concentrated on variables related to fluidconstituent parts, forcing frequency and temperature.

Anisotropic materials are currently used in a wide variety of advanced engineer- ing applications. The most commonly used anisotropic materials are composites and.crystals. These materials are extensively used in aerospace, civil engineering construc- tion, electronic packaging etc. In recent years, transient wave propagation in anisotropicsolids has received increasing attention due to the relationship of this topic to fundamen- tal studies in the areas of smart structures/materials development and the modellingof ultrasonic non-destructive techniques for defect/flaw characterization in materials.This paper is concerned with the propagation of transient stress pulses in an anisotropicelastic solid. The anisotropy of the solid is presented by conventional orthotropy. Ini- tially, general solutions for transient wave propagation in 2-D problems are derived byusing Laplace-Fourier integral transforms. These general solutions are then used tosolve boundary-value problem corresponding to 2-D stress pulses applied at an arbi- trary location in the medium. Solutions are also presented for stress waves emanatingfrom a sudden fracture at an arbitrary location in the medium. Time history of theapplied stress and the displacement discontinuity is assumed to be arbitrary.

Organic dyes show strong absorption bands in UV-visible spectral region. In organicdyes, excited electrons generated by an incident radiation return to the initial groundstates without emitting any light. On the other hand, rare earth metal ions displayphotoluminescence when their electrons are excited, though their quantum efficiencies arerather small. Interestingly, it we could hybridize organic dyes with rare metal ions thenthe photoluminescent intensity will be significantly enhanced, in which the energygenerated by the photoexcitation of a dye will be transferred to the rare metal ion.Furthermore, if we could introduce noncentrosymmetry in the molecular assemblies andfabricate a cavity with a mirror and a grating mirror at both edges of a device, theluminescent light will be amplified in the cavity to permitting laser light. Therefore, asecond harmonic light is then generated due to the noncentrosymmetric molecularassembly in the cavity. The second harmonic light can be emitted through the gratingmirror. We can classify this newly designed laser emitting device as one of the intelligentmaterials because it manifests simultaneously three fundamental functions: as a sensorresponding luminescent intensity, and an actuator for emitting shorter laser light.Therefore, this hybridization of organic dyes with rare metal ions offers multifunctionalnew devices.

The University of Vermont is in the process of constructing a new major facility to housevarious biotechnology research laboratioes and offices. This five storey, 6000 squaremeter (65000 square foot) concrete structure, named the Stafford Building, has a reinforcedconcrete superstructure. During the construction, a number of optical fiber cables havebeen embedded into the concrete superstructure. They will allow monitoring of stressesincurred during the construction phase and concretr curing as well as vibration sensing andinternal crack detection. The sensors will also permit long term studies of the building'sin-service performance and overall health. A description of the sensor choices, physical

We present spatially-weighted optical fiber sensors that filter specific vibration modes from one dimensional beams placed in a clamped-free configuration. The sensitivity of the sensors is varied along the length of the fiber using two methods: 1) photo-induced refractive-index changes (gratings) in two-mode, e-core optical fibers, and 2) tapering two-mode, circular-core optical fibers. Selective vibration mode suppression on the order of 15 dB has been obtained using the weighted sensors. We describe experimental results and propose future applications for distributed sensors.