A smart structure involves distributed actuators and sensors, and one or more microprocessors that analyze the responses from the sensors and use distributed-parameter control theory to command the actuators to apply localized strains to minimize system response. A smart structure has the capability to respond to a changing external environment (such as loads or shape change) as well as to a changing internal environment ( such as damage or failure). It incorporates smart actuators that allow the alteration of system characteristics ( such as stiffness or damping) as well as of system response (such as strain or shape) in a controlled manner. Many types of actuators and sensors are being considered, such as piezoelectric materials, shape memory alloys, electrostrictive materials, magnetostrictive materials, electro-rheological fluids and fiber optics. These can be integrated with main load-carrying structures by surface bonding or embedding without causing any significant changes in the mass or structural stiffness of the system. Numerous applications of smart structures technology to various physical systems are evolving to actively control vibration, noise, aeroelastic stability, damping, shape and stress distribution. Applications range from space systems, fixed-wing and rotary-wing aircraft, automotive, civil structures and machine tools. Much of the early development of smart structures methodology was driven by space applications such as vibration and shape control of large flexible space structures, but now wider applications are envisaged for aeronautical and other systems. Embedded or surface-bonded smart actuators cn an airplane wing or helicopter blade will induce alteration of twist/camber of airfoil (shape change), that in turn will cause variation of lift distribution and may help to control static and dynamic aeroelastic problems. Applications of smart structures technology to aerospace and other systems are expanding rapidly. Major barriers are: actuator stroke, reliable data base of smart material characterteristics, non-availability of robust distributed parameter control stratgies, and non-existent mathematical modeling of smart systems. The objective of this paper is to review the state-of-the-art of smart actuators and sensors and integrated systems and point out the needs for future research.

In these several years, piezoelectric and electrostrictive materials have become key components in smart actuator/sensor systems such as precision positioners, miniature ultrasonic motors and adaptive mechanical dampers. This paper reviews recent developments of piezoelectric and related ceramic actuators with particular focus on the improvement of actuator materials, device designs and drive/control techniques of actuators. Developments will be compared among USA, Japan and Europe.

This paper reports the structural, dielectric and pyroelectric properties of PZT ceramics modified by 5% rare earths i.e. La³⁺, Ce³⁺, Nd³⁺, Sm³⁺, Eu³⁺ and Gd³⁺. Out of these PLZT and PGZT were in tetragonal phase. The lattice volume decreases as rare earths ionic radii decreases except PEZT and PGZT. Dielectric constant is found to increase with temperature but decreases with frequencies. The value of tan(delta) , however, decreases up to 80 degree(s)C and the increases slightly. The pyrocurrents (p) as well as pyrocoefficients (p_i) increase with temperature up to 50 degree(s)C and then remains constant up to 80 degree(s)C. Above 80 degree(s)C (p and p_i) increase linearly with temperature. The pyro coefficient (p_i) and figures of merit of these ceramics are comparable to other thermal IR sensor materials. The preparation of these ceramics is relatively simple, inexpensive and properties can be tailored according to the desirable characteristics of the sensors. The results of the studies have shown that these ceramics would be very useful for the development of thermal IR sensors.

The synthesis, characterization and evaluation of optical properties of a series of new copoly(ester-amide)s containing donor-acceptor amino-nitro functionality and a chiral building unit are reported. The poly(ester-amide)s are highly thermally stable, possess high Tg values and show liquid crystalline behavior over a wide temperature range. The optical purity of the polymers is maintained even at high temperature. High temperature stability of the second harmonic generation efficiency was observed for the copolymers.

We describe an experiment in which a ramped or step stress can be applied to a piezoelectric sample and the charge generated on the sample can be determined by measuring the short-circuit current with a very high impedance electrometer. The low frequency direct piezoelectric charge coefficient, d₃₃, can then be determined and is found to be substantially non-linear in stress up to pressures of 60 MPa for all the types of Lead Zirconate Titanate (PZT) that we have studied. When a step stress is applied, the generated current shows a time dependence after the application of the stress and we believe that this is due to the relatively slow movement of 90 degree(s) domain walls in the ceramic. Our results can be understood on the basis of an activation energy model and average activation energies for the PZT types studied ranged from 0.2 to 0.7 eV. The charge coefficient is thus a function of the applied stress and of the temperature and frequency of measurement.

This research focuses on the organized integration of biological receptors and polymers into thin film architectures for biosensing applications. Layer-by-layer electrostatic adsorption was used for the first time to form alternating protein-conducting polymer multilayers. The light-harvesting, phycobiliproteins and the enzyme, alkaline phosphatase were the bioreceptors investigated and sulfonated polystyrene, poly(diallyl dimethyl ammonium chloride) and a new enzymatically polymerized, water soluble, polyaniline were the polymer counterions used for deposition. Spectroscopic characterization was used to determine both multilayer formation and biosensing function of the final bioreceptor-polymer assemblies. These techniques have proven to be simple, chemically mild, and versatile and are expected to find application in the fabrication of ultrathin films for biosensors, opto- electronic devices and biomedical applications.

Fiber amplifiers have revolutionized telecommunication networks. Fiber lasers as well as fiber fluorescent devices operate in the wavelength range from 0.38 to 4 micrometers and have found numerous applications in fields from spectroscopy to medicine. Since there is a high degree of synergy between such technologies and fiber-optic sensors, fiber lasing devices will have growing importance for fiber- optic smart structures, too, namely in monitoring large artificial or natural structures and for OCDR. The state of the art of the various fiber lasing device technologies is reviewed and their potential for sensor applications is discussed.

This was an investigation into the development of liquid core optical fibers for the detection and self repair of cracking in cement or polymer materials generated by dynamic or static loading. Hollow glass fibers filled with liquid can act as a fiber optic. Volume and location of liquid released from the brittle fiber can be determined, thus revealing the matrix crack volume and matrix crack location. The liquid released in the matrix for the purpose of crack assessment, can also be used to repair these cracks. Further techniques for crack assessment and repair have been developed based on results from this research. This research was sponsored by NSF.

A set of thickness resonators of PVDF-TrFE copolymer have been characterized as a function of the frequency and DC bias. The first six resonance peaks in the impedance spectra were analyzed to determine the degree of frequency dispersion in the complex elastic, piezoelectric, and dielectric constants. Modeling the dispersion in the material constants as a polynomial in the frequency f produced an excellent fit to the data over the 1 - 30 MHz frequency range. The samples were then tested for non- linearity by analyzing the fundamental resonance as a function of a DC bias field. The field dependence of the PVDF-TrFE samples was much smaller than for comparable samples of a soft PZT.

A system architecture for rapid and reliable emergency response in consequence of suddenly occurring natural disaster is conceived and described throughout this paper. The final goal of the developed methodology is the integration, within a single user interface environment, of data access and standardization techniques, image processing tools, GIS technology, analytical modeling and communication tools. This would allow to sensibly reduce the effects of the earthquake disaster by providing an immediate estimate of the extent and location of the suffered area and making this knowledge available to the responsible agencies. In particular, attention is focused on the implementation of the above system architecture distinguishing between local and central nodes in order to gain effectiveness and to optimize the reaction time for an efficient and rapid emergency response. The local nodes are located in the single municipalities and consists of personal computers where the spatial and tabular databases are collected and stored. The central node consists of a Unix workstation where the GIS software and the image processing tools are resident.

A neural network-based approach is presented for the detection of changes in the characteristics of structure- unknown systems. The approach relies on the use of vibration measurements from a `healthy' system to train a neural network for identification purposes. Subsequently, the trained network is fed comparable vibration measurements from the same structure under different episodes of response in order to monitor the health of the structure. It is shown, through simulation studies with linear as well as nonlinear models typically encountered in the applied mechanics field, that the proposed damage detection methodology is capable of detecting relatively small changes in the structural parameters. The methodology is applied to actual data obtained from ambient vibration measurements on a steel building structure, which was damaged under strong seismic motion during the Hyogo-Ken Nanbu Earthquake of January 17, 1995. The measurements were done before and after repairs to the damaged frame were made. A neural network is trained with data after the repairs, which represents `healthy' condition of the building. The trained network, which is subsequently fed data before the repairs, successfully identified the difference between damaged story and undamaged story. Through this study, it is shown that the proposed approach has the potential of being a practical tool for damage detection methodology, which leads to smart civil structures.

The purpose of this project was to investigate the effectiveness of `self-healing' concrete in seismic situations. The concept of self-healing concrete involves the release and activation of an adhesive agent from within a given concrete member in order to fill and seal local cracks. It is possible that such a mechanism could enhance stiffness in the member, increase damping, or do both, thus reducing the structure's chances of failure in the event of an earthquake.

The use of embedded piezoceramic elements in composite structures provides a simultaneous sensing and actuation capability that has applications in the problem of damage sensing and mitigation. The present paper describes an approach wherein strain readings from embedded sensors can be used to determine the state of the structure. The sensor elements can also function as actuators, and once a loss in structural integrity is established, compensatory strains can be induced in the embedded elements through actuation to control the growth of damage by redistribution of loads around the critical region. Since real-time response is critical for both damage sensing and mitigation, the approach studied is one based on using trained neural networks to establish the desired functional relations. Both the sensing operation and any required actuation is shown to benefit from an optimal placement of the piezoceramic elements in the structure. This design problem is formulated as a nonlinear optimization problem, which includes a mix of continuous, integer, and discrete design variables. A genetic algorithm based optimization strategy is used, where computational expediency requires the use of global function approximations. The approach is implemented in the design of composite beam structures with delamination.

Vibration reduction possibilities in laminated composite with one of the plies as actuation layer, have been investigated. Magnetostrictive and piezoelectric actuation have been considered. A comparative assessment of the vibration suppression performance of piezoelectric and magnetostrictive actuation in laminated composite beam has been presented. Variation of closed loop frequencies and damping coefficients with respect to the changes in ply lay- up, active layer position and controller gain have been studied. A smart composite finite element for laminated beam analysis has been developed. Numerical results have been presented in typical cases, to indicate performance of the finite elements developed and also to indicate the variation of vibration reduction times with various geometric and control parameters.

The objective of this work is to develop a method for placement of a single shunted piezoelectric patch to dampen several modes of plate vibration. This goal is accomplished by maximizing the generalized electromechanical coupling coefficient while limiting eigenvalues for the modes under consideration. The variation introduced is the location of the center of a square piezoelectric patch. The difficulty in finding the optimal location of the patch is rooted in both the vastly different mode shapes of the plate in this study and the fact the piezoelectric stiffness is frequency dependent and the frequency is dependent on the location of the piezoelectric. A method based on determining the maximum objective function due to a user-specified relationship between the modes of vibration of a given plate is presented. A small plate and an electrical chassis box bottom plate are used as optimization examples. The method developed is highly adaptable to changes in structural design, material changes and changes in the relative importance of the modes of vibration.

Active vibration control systems are becoming essential and viable means for minimizing the structural vibrations of large flexible structures. Distinct among the presently available active control systems are those that make use of piezoelectric materials as sensors and actuators. Two approaches to active control namely the coupled control and the independent control are applied in controlling the structural vibrations of beams and plates. In coupled control all vibration modes are controlled at the same time, whereas in independent control a selected number of modes are controlled independently by equal number of actuators. The two commonly available piezoelectric materials namely the PZT and PVDF are used in the study. The bending vibrations of the structure alone are considered in the control. Various control algorithms like direct proportional feedback, constant-gain negative velocity feedback, constant-amplitude negative velocity feedback, Lyapunov feedback and optimal control are used in determining the feedback control forces in the closed loop control system. The natural damping of the structure is not included in all the analysis, in order to check the working of the control process. The structural vibrations are actively controlled for various types of loading such as impulse, harmonic and random.

Active control has become important in structural systems as an efficient tool for vibration suppression. A cantilever beam has been chosen as a flexible structure. The entire structure (beam with sensors and actuators) is modeled by Finite Element Method (FEM) by using two different elements. A special beam element, which includes sensor and actuator dynamics has been developed. This finite element is used to model the regions where piezoelectrics are bonded and the rest of the structure is modeled with regular beam elements. Since much of the flexible energy is contained by the first few modes, controlled is designed to suppress only the first two modes. The state-space model of the system is obtained by appropriate method from the FEM model. The significant structural vibrations have been suppressed by using State Feedback and Optimal Output Feedback control laws. The optimal sensor/actuator location for controlling the first two modes has been done.

Integrated MEMS together with signal-conditioning electronics on the same chip appears to be the ultimate solution to realizing smart computer devices integratable into larger systems. This in principle will lead to systems with decentralized intelligence leading to applications in numerous fields. It is conceived that such devices would be the product of merging two mature technologies, that of microsensors and that of IC manufacture which is enjoying a well established success. Using common and suitable materials it is reasonable to expect a high degree of compatibility with little modification to standard processes. The various aspects of this co-integration will be analyzed and factors critical to the viability of the process, that go beyond mere technical feasibility will be highlighted. Australian research in this area is strong and continues to grow. We will pinpoint opportunities and constraints to the promising prospect of smart electronics and MEMS.

Excellent mechanical properties of silicon together with the advantage of fabrication of the IC circuitary on the same chip make it a very viable material for sensors. Thin membranes and diaphragms generated in crystalline silicon form an integral part of many micromechanical systems. In this paper, comparison of various techniques for bulk micromachining of silicon to create new structures is discussed. A new technique based on porous silicon formation using selective anodization is presented which is useful for generating different patterns required for making sensor arrays.

Glass-to-silicon anodic bonding is a well known process for fabricating number of microelectromechanical components and subassemblies. Experiments have been carried out by varying bonding parameters, i.e. temperature and bias voltage, to get strong bond between silicon and 7740 pyrex glass pieces. Bias voltage in the range of 400 - 450 V at 420 degree(s)C appears to be appropriate for quality bonds between silicon and glass.

A new micromachining process, the application of an anisotropic conductive film (ACF) for micromechanical structures as well as interconnection both mechanically and electrically, is reported. The film acts as a spacer and adhesive as well as an electrical conductor in the vertical direction. The process provides very flexible design scheme and simple fabrication process. New micropump structure was proposed, and simple microstructures have been fabricated and tested successfully. The full details of experiment are reported, experiments where ACF type CP 7621 (Sony Chemical Co) was used to bond p type (100) silicon wafers.

Potassium hydroxide, water and isopropanol based etchants have been used to etch silicon anisotropically for fabricating microelectromechanical components and structures for various applications. For etching V and U grooves, <100> and <110> orientation silicon wafer are used. Proper orientation of the pattern to be etched is needed to be aligned with reference to the standard flat provided in the commercial wafer. A method has been developed, where proper orientation is experimentally determined on the given wafer for pattern delineation. Very smooth walls and bottom of the trenches have been obtained after controlling the etchant composition, temperature and orientation of the masking pattern. Process details are presented with experimental results.

The C-V measurement for MOS capacitor technique has been adapted to investigate the anisotropic electrochemical etching of silicon for bulk micromachining C-V characteristics of the etching cell have been obtained during the electrochemical etching process. The behavior of the characteristics has been explained on the basis of various layers at the etching interface.

Silicon-to-silicon bonding with an intermediate oxide layer is an important aspect of the fabrication of microsensors and actuators. In this work, we have developed a novel, two step, pressure-assisted fusion bonding process which has proved to be extremely successful in bonding two silicon wafers. Moreover, as this process does not require a very high degree of surface cleanliness and flatness, it is more suitable for practical applications. In the first step of the process, after making the two wafer surfaces hydrophillic, the wafer pair assembly is slowly heated to 100 - 300 degree(s)C while applying pressure and voltage across them in order to ensure intimate contact. In the second step, the partially bonded wafers are heated to 1050 degree(s)C. The bonds thus formed are extremely strong as shown by fracture strength measurements. The bond strength measured is of the order of 40 kg/cm². The bonded wafer pair has also been cleaved (without disturbing the bonding) to demonstrate that the bonding is indeed strong enough to withstand further processing.

This paper deals with the experimental investigations conducted with magnetic abrasive powder in Magnetic Abrasive Machining. This experimental study is concerned with the experimental setup, development of equipment and detailed experimental investigations for the improvement of work surface finish by Magnetic Abrasive Machining. Experiments were conducted on heat treated stainless steel (AISI 440C) material with silicon carbide as magnetic abrasive. By means of Orthogonal Array experimentation, the set of parameters that can improve the workpiece surface finish by at least 50% are selected. The influence of different process parameters apart from the work surface characteristics on the process results are highlighted.

In this paper, the concepts of `bulk' and `surface' micromachining are first presented. The fabrication techniques for realizing silicon microaccelerometer using these two approaches are next presented. In both the cases, the acceleration is measured by detecting the change in the capacitance due to the deflection of an inertial mass called seismic mass or proof mass with respect to fixed plates. The relative merits of the two approaches are presented to allow that in spite of the simplicity and low cost nature of bulk micromachining, the surface micromachining has gained popularity because of its versatility and suitability for integrating the surface micromachined sensors with the integrated circuits.

Micro-mechanical components become the basic need to the construction of micro-mechanical systems. The development of silicon micromachining and increasing diversity and sophistication of anisotropic and isotropic etching techniques make micro-mechanical structures and devices feasible in forms and scales that could not have been achieved by conventional machining. In this work a new and simple technology for the fabrication of micro air turbine by Bulk Silicon micromachining is presented. A micro air turbine with a radius of 2000 micrometers and thickness of 60 micrometers has been realized out of discrete, silicon rotor, stator and operated at speed of 40,000 rpm. Limitations to further size reduction are not the photolithographic or etching processes, but the difficulty in handling such small components without loss or damage. Moreover, the use of silicon processing technology makes possible the fabrication and integration of sensors, actuators and control circuitry on the same chip.

Float type micro valves can be employed in very high output pressure micropumps. They provide a very large forward to reverse flow ratio with a low leakage flow rate at high applied pressures. The valve described in this paper is a thick metal 3D structure having an excellent dimension match to the valve orifice. The valve having a thick truncated pyramid shape was successfully manufactured using an electroplating process and a silicon mould. The mould was made by anisotropic silicon etching, the truncated pyramid shape being defined by <111> crystal planes. A fine and uniform nickel structure was obtained using an agitated nickelsulphamate electrolyte, buffered with boric acid. Because of precise crystal orientations this process allows the valve to fit snugly into the valve orifice.

This paper describes the fabrication techniques and characterization of silicon dioxide micromechanical components with a layer of porous aluminum oxide which results in novel properties. An aqueous SOL process has been developed to obtain a layer of porous aluminum oxide on the silicon dioxide. The micro-porous surface, so realized, can be used as sensitive moisture and gas detectors. Various parts fabricated in silicon dioxide are cantilever, cross beam, spiral spring and resonator, coated with porous aluminum oxide, and micro-probes, coated with chromium-gold for electrical contacts. This paper also demonstrates the use of the trapezoidal pit etched in silicon during micromachining as a radiation concentrator. The results of derivation of the concentrator efficiency clearly shows the advantage of the reflections from the trapezoidal cavity.

Of the various types of fiber optic sensors, the polarimetric sensors provides reliability greater than intensity sensors and are more rugged than interferometric sensors. Thus from an engineering standpoint, they would be best suited for strain measurement and damage detection in smart composite materials. This article looks at the capabilities of the polarimetric strain sensor and demonstrates some of its potential for on-line monitoring in smart structure application.

The strain of an optical fiber, embedded in a composite laminated plate, was measured using radio frequency interferometry. While the response of a similar fiber glued to the plate was linear with the applied loading, the strain experienced by the embedded fiber exhibited significant fluctuations around the linear expected trend. This phenomenon is qualitatively described in terms of polarization mode dispersion associated with excess fiber birefringence, which was introduced during the manufacturing process of the laminated plate.

This paper reports on developments in the field of self- sensing fiber reinforced composites. The reinforcing fibers have been surface treated to enable them to act as light guides for short distances. The reinforcing fiber light guides were embedded in carbon fiber reinforced epoxy prepregs and processed into composites. The resultant composite was termed the self-sensing composite as any damage to these fibers or its interface would result in the attenuation of the transmitted light. The self-sensing fibers were capable of detecting a 2 J impact.

Thin films of SnO₂ when suitable doped are used for the detection of H₂S and H₂ gases. The results of the characterization showed that the gas sensing properties of the films are governed by the micro-structure, dopant used and the operating temperature of the film. For the H₂S gas sensors developed, the observed change in the conductivity for 10 ppm gas concentration was approximately 10⁴. By suitably altering the film resistance at ambient temperature, SnO₂ based sensors have been developed which can detect 100 ppb H₂S gas present in the environment.

Using the beat-length measurement technique an experimental method is described to determine the modal birefringence characteristics of fundamental type of elliptical core polarization maintaining fibers.

We report our investigations of polarization dependent recording of surface relief gratings on azobenzene containing polymer films. The experimental results indicate that the localized variations of magnitude and polarization of the resultant electric field and the existence of a nonzero component of the resultant electric field along the light intensity gradient direction in the film are essential to the formation of the surface relief gratings. Large surface modulation (> 6500 angstroms) were obtained under optimal recording conditions. It has been found that under optimal recording condition, the diffraction efficiency of the surface relief grating is dependent only on the total light energy incident on the film surface and the diffraction efficiency increase rate is proportion to the intensity of recording beams.

Development of new viscoelastic materials were attempted. New damping materials were developed starting from hydroxyl terminated liquid natural rubber prepared by photodepolymerization of coagulated natural rubber latex by reacting with 1,4:3,6-dianhydro D-Sorbitol (isosorbide) and terephthaloyl chloride/(bis-2-Chloroformyl, 4-nitrophenyl) terephthalamide. The copolyesters were characterized by spectral and thermal techniques. Inherent viscosity and optical activities were measured. The damping performance as studied using DMA technique, was found to be superior compared to starting natural rubber.

The application of chiral composites in the reduction of the radar cross section is now well established. In this paper, the extended T-matrix method and the modified MIE solutions are used t compute RCS reduction possible with chiral coatings. Several scatterer shapes including the sphere, cylinder and oblate spheroid have been taken up for illustration. The RCS reduction obtained using chiral coatings has been compared with conventional RAMs. In all cases an RCS reduction of around 10 - 15 dB better than RAM and over a wide frequency range has been observed. A brief discussion on the possible mechanisms that can be attributed to cause this reduction in RCS is also included.

When materials possessing long range magnetic order (e.g., ferromagnetism, antiferromagnetism and ferrimagnetism) are reduced in size they can show unique properties as compared with bulk materials. One of the ways to reduce the size of the ordered magnetic regions is to isolate them inside non- magnetic species. The present paper describes in-situ room temperature synthesis of composites of fine magnetic particles in the polymer matrix of aniline-formaldehyde and their characterization using Mossbauer spectroscopy.

Analytical and experimental investigations into active control of sound fields within a 3D enclosure are presented for tonal and bandlimited disturbances. Lead Zirconate Titanate patches mounted on the flexible wall of the enclosure are used as distributed actuators, and polyvinylidene fluoride film mounted on the flexible wall and condenser microphones are used as sensors. The sensors and actuators are used in a digital, adaptive feedforward control scheme to realize `local' noise and vibration control. For tonal disturbances, the developed analytical model is found to yield results that are in good agreement with the experimental observations. Different cases of bandlimited disturbances are considered in the experiments. These cases include multiple panel and/or enclosure resonances. For bandlimited disturbances, the control scheme is found to be effective in identifying the dominant resonances and realizing significant noise reductions at the dominant modes. However, the local noise reductions realized for bandlimited disturbances are not as high as those realized for tonal disturbances. Issues such as performance functions are also explored in the investigations.

An active decoupler pylon approach for wing/store flutter suppression is proposed which involves the use of a piezoceramic wafer strut as an actuator for isolating wing torsion modes from store pitch inertia effects. A two degree-of-freedom typical section of an airfoil is used to represent the structural model of the wing, while the circulatory incompressible aerodynamic loads are modeled using Jones' approximation to the Theodorsen function. The analytical model developed neglects store aerodynamics, aileron degree-of-freedom and other flutter critical flexible and rigid body moves. This paper presents some typical perturbation models used to represent such uncertainties and compares their robust stability margins obtained using controllers designed with Loop Transfer Recovery and H_(infinity ) control techniques. Singular value Bode plots are used to analyze the robust stability and nominal performance characteristics.

In recent years many exciting developments have taken place in the area of smart structures which are designed to react to their environment by the use of integrated sensors and actuators. At the same time, important advances in lasers, fiber optics, semiconductor optoelectronics, optical and thermal imaging, and optical processing have made possible the application of optical methods in many novel ways. Optical techniques and technologies have thus a major role to play in the development of smart sensors and structures. The purpose of this paper is to present a review of some recent developments in this direction.

Transparent Polyimide: LiNbO₃ and Polyimide1: BaTiO₃ films were prepared by insitu polymerization of PI and gelation of respective alkoxide sols of the ceramics. These films were characterized structurally by x-ray and SEM. The x-ray diffractograms clearly indicates the presence of crystalline ceramic phase in these films. The optical transmission spectra shows about 80% transmission in the visible range. SEM micrographs shows the presence of ceramics clusters in the polymeric matrix. Moreover the crystallites are distributed in an orderly fashion in these clusters. The dielectric constant at room temperature was found to be about 6 and 10 respectively for LiNbO₃ and BaTiO₃ composite films. Dielectric loss is very low. Optical phase conjugation using degenerate four wave mixing technique has been observed in PI:LiNbO3 film, while hologram was recorded and reconstructed in two wave mixing in the transmission grating mode.

The synthesis and characterization of a series of new copolyesters containing azo mesogenic groups and chiral building blocks are reported. The polyesters were prepared by the condensation of bis(4-hydroxyphenyl)azo 2,2'- dinitro(3,5,3',5'-tetramethyl)diphenylmethane, terephthaloyl chloride and 1,4;3,6-dianhydro-D-sorbitol. The polysters showed higher thermal and photochemical stability with high values of glass transition temperature. DSC studies showed liquid crystalline behavior over a wide range. High values of second order nonlinear susceptibilities were recorded as a function of the molar proportion of isosorbide units.

This study outlines the design principles, analytical models and testing procedures for a new type of solid state adaptive rotor (SSAR) which was specifically intended for use in mini and micro-unmanned aerial rotorcraft ((mu) UAR). This new SSAR employed a pair of torque-plates which were structurally integrated at the helicopter hub and connected to a two-bladed rotor assembly of 22' (55.9 cm) diameter. These plates were constructed from symmetrically oriented directionally attached piezoelectric actuator elements which were bonded to an aluminum substrate. As the electrical field was changed across the elements, the twist of the plate changed accordingly. Because this new arrangement may be controlled as a function of azimuth, both collective and cyclic commands were available. Unlike earlier designs, this new arrangement used a Hiller servopaddle configuration to achieve flight control. Analytical modeling of the torque- plate performance was accomplished through laminated plate theory and showed good correlation between theory and experiment. Rotor-dynamic models included propeller and aerodynamic moments. Rotor testing showed servopaddle deflection levels in excess of +/- 5.8 degree(s) at rates up to 2.5/rev. Not only is this system effective in achieving flight control, but it is also very simple and lightweight. Indeed, the torque-late, electrical leads and contacts weight 40% less, have a much cleaner hub and replace more than 94 individual components which are found on the conventional flight control system.

This paper is concerned with designing a composite wing structure with enhanced roll maneuver capability at high dynamic pressures using a control system to retwist and recamber the wing. The approach selected in this paper is a two step process. In the first step, minimum weight design satisfying requirements on strength, aileron efficiency and flutter for a specified set of fiber oritations was obtained. The control system was then designed to retwist and recamber the wing to counteract the detrimental twisting moment produced by the aileron. The distribution of control forces was obtained from a technique referred to as `Fictious Control Surfaces'. The technique of retwisting and recambering of a flexible wing demonstrated a full recovery of roll rate at all dynamic pressures.

This paper discusses the application of wave propagation analysis to detect damage in rotorcraft flexbeams in the form of cracks and delaminations. The approach used involves examining the local scattering properties of structural discontinuities in the frequency domains to assess the effect of damage on the modal response of the structure. A model using a simulated cantilevered beam is used to illustrate the performance of the wave model approach for dynamic detection of damage in the form of transverse cracks imparted to composite rotorcraft flexbeams. Experimental validation is carried out on a graphite/epoxy cantilever beam test specimen with (0/90)_s ply orientation in vacuum. Damage in the form of a transverse crack, which extends across the entire width of the specimen is imparted at depths of 25, 50 and 75% of the beam thickness to the test specimen. A piezoelectric actuator mounted near the root is used to excite the structure dynamically to help locate and determine the extent of damage. The resonant frequencies and scattering properties are used as performance metrics to compare the experimental behavior against the analytical predictions from the wave modeling. Composite beams with artificially induced midplane delaminations of lengths (1/2'), (1'), and (2') were also tested experimentally.

This paper describes the modeling, fabrication and characterization of a Carbon Fiber Reinforced Polymer plate with embedded fiber optic strain sensors and surface mounted piezoelectric actuators. The purpose of this study was to design a test article which could actively correct the induced thermal distortions of a composite using surface mounted piezoelectric actuators. The composite plate was modeled using finite element analysis to determine the optimum lay-up and actuator positions for the final composite design. A 30.5 cm composite plate was then constructed with embedded fiber optic sensors, and piezoelectric actuators were surface-mounted to the plate. Finally,k the shape of the plate was characterized by measuring the distortion produced by the piezoelectric actuators.

Recent developments in the field of smart motors in Germany are presented in this paper. The paper describes the different working principles of the motors. The most important working principles are the traveling wave principle and those of vibrating beams or plates. The motors may be designed for rotational motion as well as for a linear motion. The major purpose of present investigations is to get more theoretical insight into the different parts of the motors, for example the friction layer and to realize motors with improved efficiency, power and torques. Other theoretical research focus on developing models of the interaction between the electrical and the mechanical parts of these motors in order to use them directly in controlled systems.

An innovative actuation principle is introduced in this paper to make a rotary actuator. The driving element is a three layer laminated beam with piezoceramics sandwiched between two anti-symmetric composite laminae. By taking advantage of material anisotropy, a torsional motion can be induced from in-plane strain actuation. With this structural coupling, a rotary actuator can be implemented. In addition to conceptual design, a prototype was fabricated. A finite element analysis was performed as well to model the mentioned device. Both experimental observation and computational simulation confirm the proposed actuation principle.

The present state of development of an electrically adjustable linear motion device is reported. Design methodologies are indicated which will, when integrated with the characteristics of the electrorheological fluid engagement means, predict the performances of the traverse. Some proof of the techniques used is given for dynamic, thermal and electrical aspects of operation. Approximate sizing data are outlined. Potential turn round acceleration (approximately 100 g) and precision of position (<EQ 0.5 mm) control duty are highlighted.

Magnetostriction-based actuators are finding increased applications in the general area of smart structures. This paper deals with the design methodology of magnetostriction- based actuators that use magnetostrictive material in the bulk or particulate form emphasizing the interaction between various design parameters. The design methodology is discussed under two categories, viz., constant internal stress actuators and variable internal stress actuators with examples. The simulation plots show how the parameters such as volume fraction, stiffness ratio, curing field, and internal stress affect the overall performance of the actuators.

A general technique providing effective but approximate characterization of electro-rheological fluids as continua (as against their apparent device specific performance) is extended by relating data from cylindrical, sliding electrode induced shear flow, and fixed, plane electrode, pressure induced linear flow types of test rigs. The motion being laminar, use is made of the well known Buckingham relationships: the yield stress in the fluid is taken to vary at constant excitation whilst the well defined unexcited viscosity remains fixed. On the basis of experimental data, and within an acceptable error band (for engineering design purposes) the two modes of operation are shown to share common fluid characteristics in terms of Hedstrom and Reynolds Numbers at constant excitation, and when these are related to a Friction Coefficient, a technique of using `fluid alone' data is made available. This technique allows small sample, low shear rate fluid test results from Couette-type apparatus to be applied in user friendly fashion to the prediction of performance of parallel plate valves and cylindrical clutches operating in the engineering scale.

The development of miniaturized diaphragm structures is highly significant to the successful realization of many microengineered devices. Most industrial designs of physical sensors are now based upon detailed finite element modeling of the mechanical microstructures using software currently available for conventional mechanics. This paper investigates the effects of miniaturization on corrugated diaphragm structures through the use of advanced computer modeling and simulation techniques. By developing detailed models of the diaphragm structures using commercial finite element analysis software it is possible to investigate the effects on diaphragm performance when diaphragms are scaled from a macro level (eg. 10 mm diameter) down to a micro level (< 1 mm diameter). Case studies are presented and comparisons are made with research work published by other workers. With subsequent sensitivity analysis it is possible to explore the critical design parameters of the microengineered diaphragms, and parameterize the diaphragm such that its performance will be compensated to some degree from limitations imposed by processing parameters.

The demand for small, low-cost, and reproducible sensors and actuators has lead to the use of the silicon IC-technology for the realization of these devices. To include the required function of the sensor or actuator in the silicon, special processing is often required. Micromachining, thin film deposition and wafer-to-wafer bonding processes have been developed for the realization of sensor and actuator systems. By making these processes compatible to silicon integrated circuit (IC) processing, an additional advantage is obtained: the possibility of integrating electronic circuitry with the sensor or actuator on one silicon chip which allows the development of smart sensors. In this paper some special technologies for integrated sensors and actuators are reviewed. Special attention is given to the newly developed IC-compatible wafer-to-wafer silicon fusion bonding, because this process is expected to accelerate the commercial realization and application of smart sensor and actuator systems.

The influence of LPCVD process parameters on stress in polysilicon films has been investigated for surface micromachined structures. The as deposited films show a large strain which can be considerably reduced by post deposition annealing. The polycrystalline film deposited at 605 degree(s)C and 250 mTorr is found to have minimum residual stress. The rapid thermal annealing (RTA) at 1100 degree(s)C for 30 sec relieves the stress completely. Further, the RTA is shown to be a superior process compared to the conventional furnace annealing for obtaining stress free films.

We have developed a new type of compact optical cross- connector by silicon micromachining technique. Torsion mirrors (300 micrometers X 600 micrometers ) supported by thin poly silicon beams (16 micrometers wide, 320 micrometers long, 0.4 micrometers thick) are arranged in a 2 X 2 matrix (3 mm X 5 mm) and independently operated by electrostatic force to reflect the incident light in a free-space. Using collimated-beam optical fibers for optical coupling, we obtained small insertion loss (-7.6 dB), a large attenuation ratio (>=60 dB), and small crosstalk (<EQ60 dB). The fabrication yield was higher than 80% thanks to the newly developed releasing technique using a silicon oxide diaphragm as an etch-stop layer and as a mechanical support in the process. Holding voltage (50 V) was reduced lower than the voltage to attract the mirror (100 approximately 150 V) using the large hysteresis of the angle-voltage characteristic of electrostatic operation.

This paper describes new micro-magnetic actuators for self- moving (-walking, -flying, and -swimming) microrobots. Their actuation force is generated by the interaction between external magnetic fields and the magnetic materials used for actuators. Accordingly, they can move independently without power supply cables. The walking actuator, composed of magnetostrictive thin films and two inclined legs, is capable of a high velocity of 65 mm/s and a reversible motion with forward and backward. The flying actuator has a pair of hard magnetic film wings with two elastic hinges and a soft magnetic film wings with two elastic hinges and a soft magnetic wire body for attitude control. It can successfully fly without any cable or guide. Two kinds of swimming actuators, composed of a small magnet with an elastic fin or a spiral wire, can swim in viscous silicone oil with low Reynolds numbers.

This paper presents an overview on the smart structures research and development activities in Japan which were reported after 1992 to some time in 1996, including a brief description of the recent situation in the smart structures research circle. Mention will be made of investigations on the vibration, shape and motion controls of space structures, vibration suppression of substructural elements and smart reinforced composites, shape memory alloys, design approaches, etc., focussing on their new aspects and ideas.

Horseradish peroxidase catalyzed oxidative free radical coupling of phenols and anilines has been utilized in the synthesis of soluble polymers with interesting electronic and optical properties. The main chain azopolymers synthesized by this method are soluble in polar solvents and undergo cis-trans isomerization upon exposure to light. The photoinduced conformational changes in the polymers are influenced by the molecular weight of the polymer. Water soluble polyanilines have been synthesized by polymerizing monomers containing polar functional groups. These polymers are reversible redox systems and show interesting optical properties, which are dependent on the solution pH. A polymeric ligand has been synthesized following this reaction, which may be used in the fabrication of metal ion sensors. We further describe the potential of these polymers in sensing and other related applications.

There has been much interest in enzyme catalyzed organic synthesis because it allows the design and synthesis of new materials via chemically mild reaction schemes. This study reports on the horseradish peroxidase catalyzed polymerization of the amphiphilic, C10 alkyl monomer derivative of d and l isomers of tyrosine in micellar solutions. The methodology has been developed to improve the solubility and hence processability of these phenolic polymers. The technique involves the formation of emulsions or micelles of the amphiphilic tyrosines in aqueous medium through manipulation of the solution pH and subsequent enzymatic polymerization. The solution pH, concentrations of the tyrosine derivatives, hydrogen peroxide and the enzyme have been optimized for maximum conversion. The physico- chemical properties of the resulting polymers have been studied by various spectroscopic techniques. Limited stereo- specificity of the reaction has been demonstrated by kinetic methods. Thin films of these polymeric materials have been fabricated using the Langmuir-Blodgett film technique.

This paper describes an experimental study on the vibration suppression of rotary shaft using liquid crystal. A controllable rotary damper using liquid crystal with nematic phase is proposed and applied to the vibration suppression of a rotary shaft and a pendulum. Two disks were mounted inside a housing, which were attached to rotary shafts. These disks are free to rotate inside and relative to the housing. Damping is introduced by filling the space between housing and disk with liquid crystal, apparent viscosity of which can be controlled by the applied electric field. The results show that the torsional vibration of the rotary shaft, and the free vibration and parametric resonance of the pendulum are suppressed effectively.

Vibrations caused by cyclic loads acting on structures are, in general, undesirable as they lead to fatigue failure. However, there are situations in which vibrations of structures are desirable. An outstanding example of this situation is the myocardium, the heart muscle. When arteries that supply blood to the heart become occluded due to heart disease, the heart muscle around the occlusion suffers oxygen depletion and results in a myocardial infarct. The presence of an infarct in the myocardium makes the pumping action of the heart weak thus making the heart partially dysfunctional. To address this difficulty, the problem of the myocardium with bonded/embedded smart patch, which is subjected to an electric field, is formulated and the deformations of the myocardium are calculated. The smart patches considered in this study include poly-vinylidene fluoride and lead zirconate titanate. The deformed configurations are calculated using a finite element method. The electric field is applied in a cyclic fashion to create a volume change in the closed myocardial structure to simulate the pumping action of the heart. The calculated shell-like configurations appear to be compatible with biomedical requirements.

A new simple approach to active sound absorption is presented for the tube reciprocity calibration of electro- acoustic transducers. In the tube reciprocity method, a region is created inside the tube in which plane waves travelling in only one direction are present, by using an active absorption system at the end of the tube. In the approach widely used, the magnitude and phase of the voltage applied to the system are manually adjusted until the desired condition has been achieved. In the present approach, a model of the active termination is used to determine the voltage to be applied. The termination consists of a thin piezoelectric disk with a thin water- proof coating. First, a disk is used as a sensor and the steady-state open circuit voltage generated by it when it is excited by a harmonic acoustic wave is measured. When the same acoustic wave is incident upon it the second time, a voltage is applied to the disk such that there is no reflected wave. The voltage to be applied is determined by using a three port distributed parameter plane-strain model of the disk. The model is used to express the magnitude and phase of the voltage to be applied as a function of the generated voltage. It is shown, theoretically, that almost all the incident acoustic power is electrically absorbed when the wave is incident from water and the disk is backed by air. It is also shown that the reflected coefficient will be less than -20 dB even if the voltage actually applied differs from the exact voltage to be applied by 10% in magnitude or 5 degrees in phase. Experimental results are also presented showing that the reflection coefficient is less than -20 dB when the active absorber is used.

Installation of a small multi-element comb type ultrasonic transducer is proposed as a component of a smart structure. It can be used in either an active or passive mode in carrying out ultrasonic bulk or guided wave nondestructive evaluation. Theoretical methods are developed and experimental results are presented for guided wave generation and mode control with this very efficient and versatile novel comb type ultrasonic transducer. Excitation and probe design is crucial in mode selection. The comb transducer generates waves that are influenced by such parameters as number of elements, spacing between elements, dimension, pulsing sequence, and pressure distribution. The excited elastic field depends on the excitation frequency, plate thickness, and elastic properties. Techniques are studied to optimize the applied loading and the comb transducer design parameters so that only modes that are most sensitive to particular material characteristics can be generated. Complete understanding of the comb transducer parameters and their impact on the elastic field allows us to efficiently generate higher order modes as well as low phase velocity modes which are valuable in composite material characterization. Sample experiments are presented for various plate and tube like structures.

An accurate and efficient indirect boundary element method is presented to analyze the electroelastic fields in piezoceramics with defects in the form of voids or openings. Stress concentration around the void can be studied by using the present method for defects of arbitrary geometry and orientation. The case of multiple voids can also be analyzed without any complexity. The integral equation is based on 2D Green's functions for a piezoceramic solid under plane strain or stress conditions. Closed form solutions for Green's functions are used in this study to enhance both the numerical efficiency and accuracy. Selected numerical results for an elliptical cavity are presented. The present methodology is useful in estimating stress concentrations in piezoceramic components used in the fabrication of smart structures.

Liquid molding manufacturing techniques including vacuum assisted resin infusion molding (VARIM) and resin transfer molding (RTM) offer low cost alternatives for producing composites. The cure characteristics of these composites are monitored by dielectric tool mount sensors in an RTM process, however embedded inter-digitated electrode sensors (IDEX) are becoming popular in the VARIM process. The IDEX sensors remain an integral part of the composite after cure. In this paper, first the response of the dielectric IDEX sensors to various resin systems in neat resin stage as well as in the resin matrix composite is presented. The paper then investigates the mechanical performance of the composites containing IDEX sensors for various loading situations involving interlaminar shear strength, low velocity impact and high strain rate testing. Ultrasonic nondestructive evaluation conducted is also presented.

The energy dissipation characteristics of Active Constrained Layer Damping (ACLD) treatments, consisting of visco-elastic cores constrained by active piezo-electric layers, is optimized using rational design procedures. The optimal lengths and control gains of these ACLD treatments are determined when a globally stable boundary control strategy is utilized to control the longitudinal strain of the active piezo-electric layers in response to the structural vibrations. The optimal parameters are obtained such that the sum of the passive and active loss coefficients of the ACLD treatments is maximized. The effect of the visco- elastic loss factor on the performance and the optimal parameters of the ACLD treatments is determined. Comparisons with optimal ACLD is more effective in dissipating vibrational energy particularly for visco-elastic cores with low loss factors.

Deformation control of smart structures and damage detection in smart composites by magneto-mechanical tagging are just a few of the increasing number of applications of polydomain, polycrystalline magnetostrictive materials that are currently being researched. Robust computational models of bulk magnetostriction will be of great assistance to designers of smart structures for optimization of performance and development of control strategies. This paper discusses the limitations of existing tools, and reports on the work of the authors in developing a 3D nonlinear continuum finite element scheme for magnetostrictive structures, based on an appropriate Galerkin variational principle and incremental constitutive relations. The unique problems posed by the form of the equations governing magneto-mechanical interactions as well as their impact on the proper choice of variational and finite element discretization schemes are discussed. An adaptation of vectorial edge functions for interpolation of magnetic field in hexahedral elements is outlined. The differences between the proposed finite element scheme and available formations are also discussed in this paper. Computational results obtained from the newly proposed scheme will be presented in a future paper.

A generalized mixed variational formula based upon Hamilton's principle is obtained by using Legender's transformation and Lagrange's multipliers. It is generally used to deduce the governing equations for laminated composite structures. A rational higher-order displacement- based 2D theory for the analysis of laminated plates is presented. This theory is established using the generalized mixed variational formula to study the vibration behavior of symmetric laminated orthotropic plates subjected to normal traction fields. Fundamental frequencies are obtained according to the classical, first- and higher-order plate theories. The effects of boundary conditions, transverse shear, aspect ratio, and materials anisotropy on natural frequencies are investigated. Results are compared with other exact results available in the literature.

There are three inherent length scales associated with the shape memory phenomena. At the continuum length scale, we can describe the global response of a shape memory material in a phenomenological sense. At the other end, in the atomic length scale, the motion of atoms (diffusionless, in this case) causing the phase change can be studied by experiments (both physical and numerical). In between the two length scales lies the mesoscopic length scale wherein the microstructure is the dominating material feature. In order to study the phase transformation and the associated microstructure at this scale, we adopt a recently proposed technique called the quasicontinuum method. This technique marries the continuum and atomic length scales.

Dynamic damping analysis study of hybrid composite laminated plate structures and their tailoring aspects to enhance dynamic behavior have been discussed in this paper. The present analytical formulation is based on an integrated approach in which the lamina level micromechanics based theory is combined with a higher-order transverse shear deformable plate theory to predict the equivalent material specific damping capacity (SDC) of a general hybrid composite laminated plate structure. The micromechanical equations based on a self-consistent stress method are used for the calculation of elastic stiffness and SDC at the lamina level. As a typical example, the solution procedures of a steady state dynamic characteristics including the modal SDC of a rectangular laminated plate simply-supported on all the four edges have also been discussed. Specifically, our aim is to evaluate the effects of fiber orientation and the volume fraction of the hybridizing fiber on the dynamic behavior such as, flexural vibration frequencies and the modal SDC of the laminated plate. In order to get a basic understanding about the various tailoring aspects, a parametric optimization was done to get the appropriate fiber volume fractions of hybrid composite to achieve a balanced dynamic performance involving both resonance frequency and modal SDC. Numerical results are furnished for a typical Carbon/E-Glass fiber hybrid composite laminated plate to understand the above mentioned effects. It has been observed that the fiber orientation has a strong influence in controlling the SDC of laminated plate similar to those of the natural frequencies of the plate. The modal SDC of the first three modes indicates that the trend of the SDC variation with respect to laminate fiber angle is in a reversed manner as those of the natural frequencies.

A finite element formulation using first-order shear deformation theory is used for vibration control of plates with piezoelectric sensors/actuators. The geometric nonlinearity based on von Karman's assumptions and structural damping in the form of Rayleigh damping are introduced in the present work. The formulation presented here, in general, is applicable for laminated composite structure. The dynamic responses are obtained using Newmark method coupled with iteration technique. The results pertaining to plates are presented.

A modal dynamic model is developed for the active vibration control of laminated doubly curved shells with piezoelectric sensors and actuators. The dynamic effects of the mass and stiffness of the piezoelectric patches are considered in the model. Finite element equations of motion are developed based on shear deformation theory and implemented for an isoparametric shell element. The mode superposition method is used to transform the coupled finite element equations into a set of uncoupled equations in the modal coordinates. A robust controller is developed using Linear Quadratic Gaussian with Loop Transform Recovery (LQG/LTR) design methodology to calculate the gain and actuator voltage requirements. A neural network controller is then designed and trained offline to emulate the performance of the LQG/LTR controller. Numerical results are presented for a spherical shell showing the variation in initial conditions and structural parameters. The neural network controller is shown to effectively emulate the LQG/LTR controller with slightly improved performance over that of the LQG/LTR controller for some cases.

This micro flow meter does not only measure the flow of the gas but also controls the input of the gas in a automatic manner. A micro air turbine of 4000 micrometers diameter has been generated in the silicon chip by bulk micromachining technique. It can rotate up to a speed of 4000 rpm with a jet of air. An optical sensor of 400 micrometers diameter has also been generated in the cavity of the silicon under the turbine blades. The output pulses of the sensor due to the chopping of incident light, by rotation of rotor, can be correlated with the input flow. The control circuit controls the input flow based on closed loop system. This work also presents the effect of temperature on the performance of the micro flow meter. This micro flow meter has the response time in micro seconds in comparison to others having in milli seconds.

Smart MEMS (MicroElectroMechanical Systems) in the form of integrated sensors and actuators offer significant potential for many rotorcraft applications. Sensing of flex beam deflection and acceleration, ice formation and deicing are major candidate areas where smart conformal MEMS based sensors can be exploited by the rotorcraft community. The major technical barrier of the present day smart structures technology is the need for wired communication between sensors and actuators in the rotating system and controllers, data storage units, and cockpit avionics. Many proposed sensors and actuators are commonly distributed either along the blade length or, in the active flap devices, out near the 75% blade radial station. Also they are not conformal to the airfoil shape of the rotor blades. The communication between rotating and fixed systems is typically accomplished using complex slip ring assemblies transferring electronic information down through the rotor shaft. Although advances have been made in wired communication, these complex assemblies are essentially similar to test hardware and present numerous reliability and maintainability limitations when implemented on a production scale. Considering these limitations, development of a wireless means of communication through a new generation of conformal sensors with built-in antenna, akin to telemetry, could have a dramatic beneficial payoff for rotorcraft applications. In this paper, an integration of IDT (inter digital transducer) microsensors and MEMS sensors is presented.

Silicidation of field emission tips brings about many improvements in device performance and long term reliability. Here we investigate the merits of titanium silicide coating as compared to other silicides including chromium. The silicidation takes place in two steps, deposition and high temperature alloying technique. Surface morphology was inspected and electrical characteristics were measured and compared with bare-silicon tips. The results show marked improvements in terms of lower turn-on voltage, enhanced emission, reduced current fluctuations, and homogeneous arrays. Moreover, titanium-silicide protected tips were harder, thermally stable, and discharge resistant.

Measurement of acoustic intensity provides information not only on the sound intensity level at the point but on the direction of sound propagation also. Acoustic intensity calculation needs the pressure information and pressure gradient information at a point. Pressure gradient at a point is obtained using pressure measurements from two closely spaced microphones and employing finite difference technique. Presently, two condenser microphones placed at a small distance apart are used for acoustic intensity measurements. These transducers require a pre-amplifier and a signal processing unit making the assembly cumbersome and possibly interfering with the sound field in view of their size. Micromachined sensors are ideal under these circumstances in view of their miniature size, low cost, high reliability and the convenience of heaving the signal processing circuitry in the same microchip close to the sensor.

Planarization techniques such as chemical-mechanical polishing (CMP) have emerged as enabling technologies for the manufacturing of multi-level metal interconnects used in high-density Integrated Circuits (IC). An overview of general planarization techniques for MicroElectroMechanical Systems (MEMS) and, in particular, the extension of CMP from sub-micron IC manufacturing to the fabrication of complex surface-micromachined MEMS will be presented. Planarization technique alleviates processing problems associated with fabrication of multi-level polysilicon structures, eliminates design constraints linked with non-planar topography, and provides an avenue for integrating different process technologies. The CMP process and present examples of the use of CMP in fabricating MEMS devices such as microengines, pressure sensors, and proof masses for accelerometers along with its use for monolithically integrating MEMS devices with microelectronics are presented.

The design of the SPST switch provides an insertion loss less than 2 dB, isolation more than 40 dB and return loss better than 17.5 dB in the frequency range of 0.1 GHz to 10 GHz. The insertion loss is improved by treating SPST switch as a 50 (Omega) artificial transmission line with incorporation of inductor in series arm and the capacitance of MESFET in the shunt arm. High isolation is ensured by the lower value of `ON' resistance of MESFET in shunt arm. Also good return loss is achieved by paralleling a 50 (Omega) resistor with capacitance of MESFET in series arm. The absence of DC blocking capacitors and replacement of large value bias chokes with 5 K(Omega) resistors effectively improved the performance of SPST switch at low frequency and also reduced the chip size. The overall chip dimension is 2.2 mm X 1.7 mm.

Advances in application of MEMS to smart structures can be accelerated by implementation of CAD tools, optimization and parametric studies which will result in rapid prototyping and virtual design. Dynamical finite element models are ideally suited to capture the complexity of active sensor and actuator devices that make up a smart structure. MEMS are miniature electro-mechanical devices that can also be modeled by FE analysis. Recent advances in FE analysis allows us to zoom in and magnify the mesh at desired locations while maintaining the larger structural model. Thus we can achieve economy in computational time without sacrificing accuracy. In designing a smart structure, the active devices whether they be MEMS or larger devices must be modeled in detail, with special attention to the coupled fields present in these devices (electric, magnetic, elastic, thermal, etc.) and the accompanying additional boundary conditions. Lumped parameter approximations are usually insufficient to describe the observed behavior of these devices. During optimization procedures, one must have the ability to move these devices on the structure and hence one needs automatic remeshing procedures. This paper will review finite element models for smart structures as they have evolved over the last decade and summarize some of the more recent advances for dynamical modeling of MEMS and smart structures including closed loop modeling and design optimization. Practical examples as well as comparisons and code validation with experimental results will be provided wherever possible.

Continuum constitutive models of shape memory behavior share a common feature. They describe the martensitic phase transformation by a parameter representing the martensite volume fraction, and formulate an evolution law in terms of the parameter. Exploiting the similarity of these models to elastoplasticity, a finite element formulation of a micromechanics based constitutive model is described. Several other models can be formulated in a similar way, and the present work can be seen as a testbed approach to study and evaluate the constitutive models on a common platform. Numerical results are presented for Au-47.5at%Cd to validate the finite element formulation.

Modeling of piezoelectric smart structures applied in a cabin noise problem is studied. Cubic shaped acoustic cavity with flat plate which covers one side is taken as the problem. Noise source locates outside of the box and the noise propagates into the interior region through the plate structure. Disk shaped piezoelectric actuators are mounted on the plate and the actuators are excited. The actuators will generate a proper response to reduce the pressure fields at a certain region in the cavity. The plate structure is modeled using finite element method which is based on a combination of 3D piezoelectric, flat shell and transition elements. The transition element connects the 3D and flat shell elements. Acoustic cavity is modeled using modal approach which represents the pressure fields in the cavity as a sum of mode shapes of the cavity with unknown coefficients. By using orthogonality of the mode shapes of the cavity, finite element equation for the structure with the influence of acoustic cavity is derived. Once the structure response is found by solving the finite element equation, the pressure fields at the inside of the cavity are recovered directly. Numerical results show the pressure fields at the inside of the box. No activation results are examined at different frequencies to see the feasibility of the proposed modeling approach. When the actuators are activated, the results of pressure fields inside of the cavity show that the cabin noise at a certain zone inside the cavity can be reduced. Future works to improve cabin noise control performance are addressed.

Amorphous conducting carbon films are prepared using plasma assisted polymerization process. SEM and TEM shows random aggregate of globular clusters of micron size inside the samples. Electrical measurements indicate a near metallic nature. A tendency of saturation of resistivity at low temperature is observed. From spectroscopic analysis we find some unusual features. Based on these observations a structural model of this carbon is proposed.