Showing papers in "Smart Materials and Structures in 2004"

A piezoelectric vibration based generator for wireless electronics

Abstract: Enabling technologies for wireless sensor networks have gained considerable attention in research communities over the past few years. It is highly desirable, even necessary in certain situations, for wireless sensor nodes to be self-powered. With this goal in mind, a vibration based piezoelectric generator has been developed as an enabling technology for wireless sensor networks. The focus of this paper is to discuss the modeling, design, and optimization of a piezoelectric generator based on a two-layer bending element. An analytical model of the generator has been developed and validated. In addition to providing intuitive design insight, the model has been used as the basis for design optimization. Designs of 1 cm3 in size generated using the model have demonstrated a power output of 375 µW from a vibration source of 2.5 m s−2 at 120 Hz. Furthermore, a 1 cm3 generator has been used to power a custom designed 1.9 GHz radio transmitter from the same vibration source.

A synthetic time-reversal imaging method for structural health monitoring

Abstract: This paper presents an experimental and theoretical investigation of the applicability of the time-reversal concept to guided waves in plate-like structures, where the stress waves are dispersive and of multi-modes. It is shown that temporal and spatial focusing can be achieved through time reversal, although the dispersive behaviour of the flexural waves renders it impossible to exactly reconstruct the waveform of the original excitation. Based on the principle of the time-reversal concept, a digital imaging method suitable for distributed sensor/actuator networks has been developed. This new method, which overcomes the limitation of the conventional phased array method that operates under pulse-echo mode, provides an efficient imaging method for locating and approximate sizing of structural damages. In addition, it has been shown that signal strengths can be considerably enhanced by applying the present synthetic time-reversal method, thus reducing the number of sensors and actuators required to achieve a given signal-to-noise ratio.

Detection and monitoring of hidden fatigue crack growth using a built-in piezoelectric sensor/actuator network: I. Diagnostics

Abstract: A piezoelectric based built-in diagnostic technique has been developed for monitoring fatigue crack growth in metallic structures. The technique uses diagnostic signals, generated from nearby piezoelectric actuators built into the structures, to detect crack growth. It consists of three major components: diagnostic signal generation, signal processing and damage interpretation. In diagnostic signal generation, appropriate ultrasonic guided Lamb waves were selected for actuators to maximize receiving sensor measurements. In signal processing, methods were developed to select an individual mode for damage detection and maximize signal to noise ratio in recorded sensor signals. Finally, in damage interpretation, a physics based damage index was developed relating sensor measurements to crack growth size. Fatigue tests were performed on laboratory coupons with a notch to verify the proposed technique. The damage index measured from built-in piezoceramics on the coupons showed a good correlation with the actual fatigue crack growth obtained from visual inspection. Furthermore, parametric studies were also performed to characterize the sensitivity of sensor/actuator location for the proposed technique.

Modeling and analysis of micro piezoelectric power generators for micro-electromechanical-systems applications

Abstract: The extremely small size of the micro-electromechanical systems (MEMS) makes them widely suitable for some special applications. The simplicity of the piezoelectric micro-generators is attractive for MEMS applications, especially for remote systems. In this paper, a general concept of the piezoelectric energy conversion is first given. A simple design modeling and analysis of the ‘31’ transverse mode type piezoelectric micro-generator is presented. The output power is taken as the indicated parameters for the generator. The energy conversion efficiency of the generator, which is dependent on the operation frequency, is expressed in the frequency domain. A case study of laminated type micro-generators using PZT-PIC 255 for MEMS applications is given and the use of single crystal PZN-8% PT is also studied for comparison. Some design guidelines are presented based on the simulation results.

Ionic polymer–metal composites: III. Modeling and simulation as biomimetic sensors, actuators, transducers, and artificial muscles

Abstract: This paper, the third in a series of four review papers to appear in this journal, presents a number of descriptions of various modeling and simulation techniques and, briefly, the associated experimental results in connection with ionic polymer–metal composites and, in general, ionic polymer–conductor composites, as soft biomimetic distributed sensors, actuators, transducers, and artificial muscles.

Wavelet-based active sensing for delamination detection in composite structures

Abstract: In this paper a signal processing technique is developed to detect delamination on composite structures. In particular, a wavelet-based signal processing technique is developed and combined with an active sensing system to produce a near-real-time, online monitoring system for composite structures. A layer of piezoelectric patches is used to generate an input signal with a specific wavelet waveform and to measure response signals. Then, the response signals are processed by a wavelet transform to extract damage-sensitive features from the original signals. The applicability of the proposed method to delamination identification has been demonstrated by experimental studies of a composite plate under varying temperature and boundary conditions.

Dynamic properties of high structural integrity auxetic open cell foam

Abstract: This paper illustrates various dynamic characteristics of open cell compliant polyurethane foam with auxetic (negative Poisson's ratio) behaviour. The foam is obtained from off-the-shelf open cell polyurethane grey foam with a manufacturing process based on mechanical deformation on a mould in a temperature-controlled oven. The Poisson's ratio is measured with an image processing technique based on edge detection with wavelet methods. Foam samples have been tested in a viscoelastic analyser tensile test machine to determine the Young's modulus and loss factor for small dynamic strains. The same samples have also been tested in an acoustic impedance tube to measure acoustic absorption and specific acoustic resistance and reactance with a transmissibility technique. Another set of tests has been set up on a cam plastometer machine for constant strain rate dynamic crushing analysis. All the tests have been carried out on auxetic and normal foam samples to provide a comparison between the two types of cellular solids. The results from the experimental tests are discussed and interpreted using microstructure models for cellular materials existing in the literature. The negative Poisson's ratio foam presented in this paper shows an overall superiority regarding damping and acoustic properties compared to the original conventional foam. Its dynamic crushing performance is also significantly superior to the normal foam, suggesting a possible use in structural integrity compliant elements.

Structural health monitoring using scanning laser vibrometry: I. Lamb wave sensing

Abstract: Structural health monitoring using Lamb waves is based on guided waves introduced to a structure at one point and sensed at a different location. Actuation and sensing can be accomplished using various types of transducer. The paper demonstrates a non-contact method for low-frequency Lamb wave sensing. The technique utilizes a laser Doppler velocimeter. Lamb wave responses are enhanced using data smoothing and filtering procedures. The results are validated using classical piezoceramic-based sensing and numerical simulations. The study shows the potential of laser vibrometry for Lamb wave sensing.

Multiple-degrees-of-freedom electroelastomer roll actuators

Abstract: Electroelastomers (electroactive elastomers) such as the 3M VHB 4910 acrylic adhesive films have exhibited up to 380% strain in area expansion at 5?6?kV when they are highly prestrained. By rolling highly prestrained electroelastomer films around a compression spring, we have demonstrated multifunctional electroelastomer rolls (MERs, or spring rolls) that combine load bearing, actuation, and sensing functions. We extended the design to two-degree-of-freedom (2-DOF) and 3-DOF spring rolls by patterning the electrodes to align radially on two and four circumferential spans of the rolls, respectively. Multiple-DOF spring rolls retain the linear actuation of 1-DOF spring rolls with additional bending actuation. Mathematical equations are derived to correlate the bending angle and lateral force of the rolls with the actuated stroke in one of the electroded spans. Two-DOF spring rolls with a 1.4?cm outside diameter, 6.8?cm axial length, and 11?g weight have been fabricated; these rolls have a 90? maximum actuation bending angle, 0.7?N maximum lateral force, and up to 15?N blocked axial force. Three-DOF spring rolls with a 2.3?cm outside diameter, 9.0?cm axial length, and 29?g weight exhibit a 35? maximum bending angle and 1.0?N maximum lateral force. These specifications can be modified by variations in roll parameters according to the equations. Multi-DOF spring rolls are easy to fabricate, compact, multifunctional, and mechanically robust. They represent a radically new actuation technology and may enable a number of unique applications. We have demonstrated a small walking robot, MERbot, with one 2-DOF spring roll as each of its six legs. The robot's speed is as high as 13.6?cm?s?1 or two-thirds of its length per second. 'Sushi rolls' have also been fabricated: these consist of six 2-DOF springs connected in series and monolithic in structure. The sushi rolls can be driven so as to generate wavelike or serpentine motion.

Optimal placement of sensors for structural health monitoring using improved genetic algorithms

Abstract: The global optimization of sensor locations for structural health monitoring systems is studied in this paper. First, the performance function based on damage detection is presented. Then, genetic algorithms (GAs) are adopted to search for the optimal locations of sensors. However, the simple GAs can result in infeasible solutions to the problem. Some improved strategies are presented in this paper, such as crossover based on identification code, mutation based on two gene bits, and improved convergence. The analytical results from the improved genetic algorithm are compared with the penalty function method and the forced mutation method. It is concluded that the convergence speed with the proposed improved genetic algorithm is faster than that with the penalty function method and the forced mutation method, and the result of placement optimization is better.

Detection of cracks in plates using piezo-actuated Lamb waves

Abstract: In this paper, a comprehensive methodology for locating and determining the extent of linear cracks in homogeneous plates based on the time-of-flight analysis of Lamb wave propagation is proposed. Piezoelectric sensors and actuators (PZTs) placed on a square grid configuration are used to excite and receive direct and reflected waves. The actuation frequency, spacing of PZTs and length of the signal to analyze are first determined. The grid is used to sweep across the plate to identify the location of a crack, if there is one. Elliptical loci of possible crack positions are constructed based on the flight time of crack-reflected waves estimated using energy spectra from the Hilbert–Huang transform of the sensor signals. A detailed procedure for obtaining the ellipses is described, including the blind zones. After identifying the crack position, the crack orientation is determined by varying the positions of the PZTs and observing the strength of the energy peaks in the Hilbert spectra. This provides the basis for moving the PZTs to estimate the extent of the crack. Experimental results obtained using aluminum plates with through, half-through and concealed cracks showed that the proposed method is feasible and accurate.

Detection and monitoring of hidden fatigue crack growth using a built-in piezoelectric sensor/actuator network: II. Validation using riveted joints and repair patches

Abstract: A built-in diagnostic technique for monitoring hidden fatigue crack growth in aircraft structures has been developed in part I of the study. The technique uses diagnostics signals, generated from nearby piezoelectric actuators built into the structures, to detect crack growth. In this second part of the study, the proposed diagnostic technique was applied to monitor fatigue crack growth in riveted fuselage joints and a cracked metallic plate repaired with a bonded composite patch. A complete built-in diagnostic system for the tests was developed, including a sensor network, hardware and the diagnostic software. Predictions were correlated quite well with measurements from the eddy current test and the ultrasonic scan methods as well as visual inspection. The damage index successfully detected both crack growth and debond damage for the structures considered.

On the effects of moisture in a polyurethane shape memory polymer

Abstract: It was observed that the polyurethane shape memory polymer (SMP) loses its shape fixing capability after being exposed in the air at room temperature for several days. A significant indication for this change is the continuous decrease of the glass transition temperature (Tg) of polyurethane. Accompanying the decrease of Tg, the uniaxial tensile behaviour also changes. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) tests were carried out to find the cause behind this phenomenon. Moisture was concluded as the main reason. A mathematical expression was obtained for the relationship between Tg and the moisture. Moreover, the polyurethane shape memory polymer can fully regain its original properties after being heated at temperatures above 180 °C, which is the melting temperature of this SMP.

Structural health monitoring using scanning laser vibrometry: II. Lamb waves for damage detection

Abstract: Guided ultrasonic waves have shown great potential for structural health monitoring. Various types of transducer can be used for actuating and sensing of these waves. This includes non-contact approaches such as optical/laser techniques. Classical laser methods usually involve high energy interferometers. The paper demonstrates that a commercial laser vibrometer, designed for vibration/modal analysis, can be used for crack detection in metallic structures. The study involves a simple fatigue test in order to initiate and grow a crack. Lamb waves generated by one bonded piezoceramic transducer were sensed using a multi-point scanning laser vibrometer. The results demonstrate the potential of laser vibrometry for simple, rapid and robust detection of fatigue cracks in metallic structures.

A compact wireless gas sensor using a carbon nanotube/PMMA thin film chemiresistor

Abstract: The design and development of a compact wireless gas sensor with a surface modified multiwalled carbon nanotube (f-CNT) chemiresistor as the sensing element is presented in this paper. f-CNT/polymer composite sensing film is patterned on a printed circuit board and is integrated to the wireless system. The change in resistance of the CNT/polymer composite film due to exposure of different gases is utilized as the principle of this gas sensor. The response for different organic vapors are evaluated and it is observed that the f-CNT/PMMA composite film shows fast response and change in resistance of the order of 102–103 due to its surface modification.

Embedding damage detection algorithms in a wireless sensing unit for operational power efficiency

Abstract: A low-cost wireless sensing unit is designed and fabricated for deployment as the building block of wireless structural health monitoring systems. Finite operational lives of portable power supplies, such as batteries, necessitate optimization of the wireless sensing unit design to attain overall energy efficiency. This is in conflict with the need for wireless radios that have far-reaching communication ranges that require significant amounts of power. As a result, a penalty is incurred by transmitting raw time-history records using scarce system resources such as battery power and bandwidth. Alternatively, a computational core that can accommodate local processing of data is designed and implemented in the wireless sensing unit. The role of the computational core is to perform interrogation tasks of collected raw time-history data and to transmit via the wireless channel the analysis results rather than time-history records. To illustrate the ability of the computational core to execute such embedded engineering analyses, a two-tiered time-series damage detection algorithm is implemented as an example. Using a lumped-mass laboratory structure, local execution of the embedded damage detection method is shown to save energy by avoiding utilization of the wireless channel to transmit raw time-history data.

Position control of shape memory alloy actuators with internal electrical resistance feedback using neural networks

Abstract: The development of a position control system for a shape memory alloy (SMA) wire actuator using an electrical resistance feedback is presented in this paper. A novel control scheme is implemented to eliminate the need for a position sensor to achieve stable and accurate positioning by utilizing the actuator's electrical resistance feedback. Experiments are conducted to investigate the relationship between electrical resistance and displacement using an SMA wire test set-up. Due to the highly nonlinear behavior of the SMA actuator, a neural network is employed to model the relationship and to predict the position of the actuator using only the electrical resistance. Feedback control of the SMA is achieved by using a proportional-derivative (PD) controller. Experimental results demonstrate that the proposed position control system achieves good control performance without using a position sensor.

Vibration suppression capabilities of magnetorheological materials based adaptive structures

Abstract: This paper discusses the investigation of vibration suppression capabilities of magnetorheological (MR) materials in adaptive structures. Homogeneous three-layered adaptive beams with MR materials sandwiched between two elastic layers were considered. By varying the externally applied magnetic field level over the MR layer, the stiffness and damping properties of the adaptive beam can be varied. These variations in the damping and stiffness properties can be used to tune the vibration characteristics of the adaptive beams such as natural frequencies, vibration amplitudes, mode shapes and loss factors. In this study, theoretical investigation of the MR adaptive beams vibration behavior based on the energy approach is accomplished. Experiments were performed to observe the theoretically predicted vibration responses in real time. From both studies, vibration suppression capabilities of MR adaptive beams were observed in the forms of shifts in natural frequency values, variations in loss factors, and vibration amplitudes.

Quantitative health monitoring of bolted joints using a piezoceramic actuator-sensor

Abstract: The non-destructive evaluation technique using a piezoceramic (PZT) as an actuator–sensor has a potential to efficiently detect structural damage. In this technique, a PZT actuator–sensor patch is bonded on a structure. Through the measurement of its electrical impedance, which is related to the mechanical impedance of the structure being bonded, the change in structural properties due to damage can be detected. This paper presents the use of a PZT actuator–sensor in conjunction with numerical model-based methodology in structural health monitoring to quantitatively detect damage of bolted joints. The structure used in this study consists of two aluminium beams connected by a bolted joint. The damage was simulated by loosening the bolts. To quantitatively monitor the damage, a numerical model of the structure was formulated. A spectral element method (SEM), based on a wave propagation approach, was used to model the structure. A bonded-PZT beam and a bolted joint element were developed by using the SEM. The equations of motion were derived by using Hamilton's principle and then the spectral element matrices were formulated. Experimental results show the effectiveness of this method to detect the damage. By using the proposed model, the loosening of bolts can be quantitatively identified as the change in stiffness and damping at the bolted joint, indicating a high potential of this method in order to quantitatively monitor structural damage.

Deformation in magnetorheological elastomer and elastomer?ferromagnet composite driven by a magnetic field

Abstract: Magnetorheological elastomer (MRE) is a new class of smart materials, whose modulus can be controlled by the applied magnetic field. In this paper, using a white light speckle technique for deformation analysis, we present the real-time dynamic deformation progress (the vector diagram of the displacement or the whole-field quantitative displacement distribution) of the MRE and the elastomer?ferromagnet composite (EFC) while the magnetic field is turned on. The experimental results verify the prediction presented in a recently published paper, (Borcea and Bruno 2001 J.?Mech.?Phys.?Solids 49 2877?919), and reveals some interesting phenomena which will give us a deeper understanding for such smart materials.

Smart piezoelectric transducers for in situ health monitoring of concrete

Abstract: This paper presents the results of applying a non-parametric technique to the detection of the presence of damage and the monitoring of damage progression in concrete. The electromechanical impedance method using smart piezoceramic material is utilized in this study. The smart piezoelectric lead-zirconate-titanate (PZT) transducers bonded onto the structures are used to actively provide the local excitation and simultaneously sense the structural dynamic response in high frequency band. The frequency-dependent electric admittance signatures of the piezoelectric transducer are compared with the baseline signatures to determine the status of the health of structures. The damage is quantified by the root-mean-square deviation (RMSD) index. The correlation of the RMSD index with the location and extent of damage is investigated. In this paper, two sets of experimental tests are performed on the concrete beams instrumented with PZT transducers. The findings summarized from the experimental results are confirmed by a series of numerical simulations using finite element analysis. The experimental and numerical results demonstrate the suitability of using the smart PZT transducers for in situ health monitoring of structural integrity in civil infrastructures using concrete.

Passive damping of beam vibrations through distributed electric networks and piezoelectric transducers: prototype design and experimental validation

Abstract: The aim of this work is two-fold: to design devices for passive electric damping of structural vibrations by distributed piezoelectric transducers and electric networks, and to experimentally validate the effectiveness of such a damping concept. Two different electric networks are employed, namely a purely resistive network and an inductive–resistive one. The presented devices can be considered as distributed versions of the well-known resistive and resonant shunt of a single piezoelectric transducer. The technical feasibility and damping effectiveness of the proposed novel devices are assessed through the construction of an experimental prototype. Experimental results are shown to be in very good agreement with theoretical predictions. It is proved that the presented technique allows for a substantial reduction in the inductances used when compared with those required by the single resonant shunted transducer. In particular, it is shown that the required inductance decreases when the number of piezoelectric elements is increased. The electric networks are optimized in order to reduce forced vibrations close to the first resonance frequency. Nevertheless, the damping effectiveness for higher modes is experimentally proved. As well as specific results, fundamental theoretical and experimental considerations for passive distributed vibration control are provided.

Analytical design model for a piezo-composite unimorph actuator and its verification using lightweight piezo-composite curved actuators

Abstract: This paper describes an analytical design model for a layered piezo-composite unimorph actuator and its numerical and experimental verification using a LIPCA (lightweight piezo-composite curved actuator) that is lighter than other conventional piezo-composite type actuators. The LIPCA is composed of top fiber composite layers with high modulus and low CTE (coefficient of thermal expansion), a middle PZT ceramic wafer, and base layers with low modulus and high CTE. The advantages of the LIPCA design are to replace the heavy metal layer of THUNDER by lightweight fiber-reinforced plastic layers without compromising the generation of high force and large displacement and to have design flexibility by selecting the fiber direction and the number of prepreg layers. In addition to the lightweight advantage and design flexibility, the proposed device can be manufactured without adhesive layers when we use a resin prepreg system. A piezo-actuation model for a laminate with piezo-electric material layers and fiber composite layers is proposed to predict the curvature and residual stress of the LIPCA. To predict the actuation displacement of the LIPCA with curvature, a finite element analysis method using the proposed piezo-actuation model is introduced. The predicted deformations are in good agreement with the experimental ones.

Adaptive multi-mode resonant piezoelectric shunt damping

Abstract: Multiple-modes of structural vibration can be suppressed through the connection of an electrical impedance to the terminals of a bonded piezoelectric transducer. The so-called resonant shunts, one commonly used class of shunt impedances, provide good nominal damping performance but they are highly sensitive to variations in transducer capacitance and structural resonance frequencies. This paper introduces a new technique for the online adaptation of multi-mode resonant shunts. By minimizing the relative phase difference between a vibration reference signal and the shunt current, circuit component values can be optimally tuned online. Experiments on a cantilever beam validate the proposed technique and demonstrate the simplicity of implementation. The adaptive law converges quickly and maintains optimal performance in the presence of environmental uncertainties.

Development of a peristaltic crawling robot using magnetic fluid on the basis of the locomotion mechanism of the earthworm

Abstract: In the field of bio-engineering the aim of developing new machines which utilize the motion and control of organisms as a model is attracting attention. This technology is pursued by paying attention to various shapes and movements of organisms and autonomous system of organisms that act in response to the environment surrounding them, and by mechanically elucidating the locomotion mechanism, propulsive mechanism, nerve system and sensation system for these organisms. On the other hand, in the field of hydrodynamics, magnetic fluid that changes its apparent viscosity depending on the magnetic field has been developed, and its utilization is under trial in various fields. Attention has been paid to the peristaltic crawling of the earthworm as a transport function in place of wheels or ambulation, and based on these observations a micro-robot running inside a tube using magnetic fluid has been developed. In this micro-robot, individual cells corresponding to the earthworm's segment are composed of a natural rubber tube sealed with water-based magnetic fluid, and several cells are connected with elastic rods made of natural rubber. The feature of this micro-robot is that its structure is simply composed, and it can be controlled with external wireless force, by providing it with moving magnetism from the outside. This paper presents the analytical result on the peristaltic crawling of an actual earthworm and the evaluation result for the transport mechanism of a prototype micro-robot moved by an external magnetic field.

Giant magnetostrictive actuators for active vibration control

Abstract: Giant magnetostrictive actuators are designed and fabricated with home-made TbDyFe magnetostrictive rods. The corresponding static and dynamic characteristics are tested. The total output displacement can be obtained up to 100 µm and the output force up to 1500 N. The dynamic responses of input and output are accordant and have a small hysteresis. Experiments on active vibration control are implemented in single-degree-of-freedom (DOF) and six-DOF platforms in a flexible space structure. The excellent damping effect, up to 30 dB, proves the good performance of the actuators, the feasibility of the control algorithms, and the reasonable design of the six-DOF platform.

The influence of shape-holding conditions on shape recovery of polyurethane-shape memory polymer foams

Abstract: The thermomechanical properties of polyurethane-shape memory polymer (SMP) foams and the influence of shape-holding conditions on shape recovery were investigated experimentally. The results obtained can be summarized as follows. (1) By cooling the foam down to below the glass transition temperature Tg after compressive deformation above Tg, stress decreases and the deformed shape is fixed. By heating the shape-fixed foam up to above Tg under no load, the original shape is recovered. (2) The shape deformed above Tg is maintained for six months under no load at Tg− 60 K without depending on the maximum strain, and the original shape is recovered by heating thereafter. (3) If the deformed shape is held at high temperature, the original shape is not recovered. (4) The ratio of shape irrecovery increases in proportion to the holding strain, holding temperature and holding time.

Volume-constrained optimization of magnetorheological and electrorheological valves and dampers

Abstract: This paper presents a case study of magnetorheological (MR) and electrorheological (ER) valve design within a constrained cylindrical volume. The primary purpose of this study is to establish general design guidelines for volume-constrained MR valves. Additionally, this study compares the performance of volume-constrained MR valves against similarly constrained ER valves. Starting from basic design guidelines for an MR valve, a method for constructing candidate volume-constrained valve geometries is presented. A magnetic FEM program is then used to evaluate the magnetic properties of the candidate valves. An optimized MR valve is chosen by evaluating non-dimensional parameters describing the candidate valves' damping performance. A derivation of the non-dimensional damping coefficient for valves with both active and passive volumes is presented to allow comparison of valves with differing proportions of active and passive volumes. The performance of the optimized MR valve is then compared to that of a geometrically similar ER valve using both analytical and numerical techniques. An analytical equation relating the damping performances of geometrically similar MR and ER valves in as a function of fluid yield stresses and relative active fluid volume, and numerical calculations are provided to calculate each valve's damping performance and to validate the analytical calculations.

Piezoelectric thick bismuth titanate/lead zirconate titanate composite film transducers for smart NDE of metals

Abstract: Thick film piezoelectric ceramic sensors have been successfully deposited on different metallic substrates with different shapes by a sol?gel spray technique. The ball-milled bismuth titanate fine powders were dispersed into PZT solution to achieve the gel. The films with desired thickness up to 200??m have been obtained through the multilayer coating approach. These thick films were also effectively coated onto thin sheet metals of thickness down to 25??m. Self-support films with flat and shell geometries were made. Piezoelectricity was achieved using the corona discharge poling method. The area of the top silver paste electrode was also optimized. The center frequencies of ultrasonic signals generated by these films ranged from 3.6 to 30?MHz and their bandwidth was broad as well. The ultrasonic signals generated and received by these ultrasonic transducers (UTs) operated in the pulse/echo mode had a signal to noise ratio more than 30?dB. The main advantages of such sensors are that they (1) do not need couplant, (2) can serve as piezoelectric and UT, (3) can be coated onto curved surfaces and (4) can operate up to 440??C. The capability of these thick film UTs for non-destructive evaluation of materials at 440??C has been demonstrated.

Analysis of active vibration control in smart structures by ANSYS

Abstract: It is possible to model smart structures with piezoelectric materials using the product ANSYS/Multiphysics. In this study, the integration of control actions into the ANSYS solution is realized. First, the procedure is tested on the active vibration control problem with a two-degrees of freedom system. The analytical results obtained by the Laplace transform method and by ANSYS are compared. Then, the smart structures are studied by ANSYS. The input reference value is taken as zero in the closed loop vibration control. The instantaneous value of the strain at the sensor location at a time step is subtracted from zero to find the error signal value. The error value is multiplied by the control gain to calculate the voltage value which is used as the input to the actuator nodes. The process is continued with the selected time step until the steady-state value is approximately reached. The results are obtained for the structures analyzed in other studies. The active vibration control of a circular disc is also studied.