Search

The analysis of scientific publications for rotor systems on the elastic supports made it possible to develop a basic version of the design scheme of active elastic support with controlled quasi-zero stiffness based on adaptive piezoceramic elements. The main components of the mathematical model of the functioning of active elastic supports with controlled quasi-zero stiffness based on adaptive piezoceramic elements are substantiated, which will help create the foundations of a theory for solving the problem of effective vibration protection. Numerical results show the possibility of effective applying of the proposed solution to the problem of rotor vibration damping.

Polymer matrix composites with embedded ferroelectric and/or piezoelectric particles, constitute a novel and interesting class of engineering materials. The incorporation of ferroelectric and/or piezoelectric particles within a polymer matrix is expected to add functionality to the resulting composite, due to the variation of polarisation of the ceramic particles with temperature. In this work, an elastomeric matrix such as polydimethylsiloxane and BaTiO(3) nano and microparticles were used for the fabrication of composites at various concentrations and sizes of the reinforcing phase. Morphological and structural characteristics were investigated via scanning electron microscopy images and X-ray diffraction patterns. The dielectric behaviour of all fabricated specimens was investigated via broadband dielectric spectroscopy, in a wide frequency (10^−1 Hz–10 MHz) and temperature (30–200°C) range. In the dielectric spectra, two relaxation processes were detected, namely cold crystallisation and interfacial polarisation. Values of dielectric permittivity enhance with filler content, and particles’ size, while diminishes significantly with frequency. Finally, the ability of the prepared systems to store energy was examined by calculating their energy density. The higher energy-storing efficiency is exhibited by the micro-BaTiO(3) reinforced composites, while functional behaviour is induced via the thermally activated structural changes of ferroelectric particles.

Робота знайшла своє застосування при конструюванні малогабаритних літальних апаратів, де як рушійну силу використовують п’єзокерамічні пластини. При конструюванні малогабаритних апаратів на основі п’єзокераміки є вкрай важливим вплив співвідношення довжини та ширини п’єзокерамічної пластини на її резонансну частоту. В результаті досліджень отримано математичні залежності для прогнозування частоти коливань залежно від геометричних розмірів п’єзоелектричної пластини. Адекватність отриманих чисельних розрахунків підтверджено експериментальними дослідженнями. In the article the attention is paid to the peculiarities of the construction of small-sized aircraft flying into the air with the help of wings based on the bionic principle – copying movements birds or insects. Micro devices of such size and type have a wide range of applications and a number of tasks set before them, such as: pollination of crops, search and rescue operations, observation, as well as monitoring of weather, climate and environment with high resolution. The work has found its application in the design of small-sized aircraft, where piezoceramic plates are used as a driving force. The piezoceramics becomes much more relevant than that of an electric motor, since with the reduced design of a small-sized flying machine built on the basis of an electric motor, it will have to reduce the electromagnetic engine itself, that will lead to a loss in the efficiency factor of the engine and the aircraft in general. The piezoceramic engine is capable of converting electric energy into a mechanical one with a very high operating coefficient, which in some cases amounts to more than ninety percents. In addition, the use of piezoactuators has a number of advantages: operating speed, the development of large forces, the absence of a magnetic field, low energy consumption, no tendency to wear, the ability to work in extreme conditions. When constructing small-sized devices based on piezoceramics, the ratio of the length and width of the piezoceramic plate to its resonant frequency is extremely important. As a result of the research, mathematical dependences have been obtained for predicting the oscillation frequency, depending on geometric dimensions of the piezoelectric plate. The adequacy of the obtained numerical calculations is confirmed by experimental studies

The work is devoted to a numerical study of the behavior of vertically oriented eccentric (non-coaxial) electroelastic shells, containing a fluid in the gap between them. The solution of the problem is found in the framework of a three-dimensional formulation using the finite element method. The shells are made of the piezoelectric material polarized in the radial direction. Thin-walled structures are considered in the framework of the classical theory based on the Kirchhoff – Love hypotheses, as well as the equations of linear electroelasticity. The distribution of the electric potential through the thickness is assumed linear. The fluid is considered within the framework of a potential theory. The study of the low natural frequencies and vibration modes is carried out for different variants of the boundary conditions at the edges of the shells, the level of fluid in the gap and the eccentricity of the inner shell. The influence of the electric boundary conditions specified on the parts of the shells surfaces covered with electrodes is estimated.

Barium Titanate (BaTiO3) is one of the most promising lead-free ferroelectric materials for the development of piezoelectric nanocomposites for nanogenerators and sensors. The miniaturization of electronic devices is pushing researchers to produce nanometric-sized particles to be embedded into flexible polymeric matrices. Here, we present the sol-gel preparation of crystalline BaTiO3 nanoparticles (NPs) obtained by reacting barium acetate (Ba(CH3COO)2) and titanium (IV) isopropoxide (Ti(OiPr)4). The reaction was performed both at ambient conditions and by a hydrothermal process carried on at 200 °C for times ranging from 2 to 8 h. Doped BaTiO3 nanoparticles were also produced by addition of Na, Ca, and Bi cations. The powders were annealed at 900 °C in order to improve NPs crystallinity and promote the cubic-to-tetragonal (c⟶t) phase transformation. The microstructural features of nanoparticles were investigated in dependence of both the hydrothermal reaction time and the presence of dopants. It is found that short hydrothermal treatment (2 h) can produce BaTiO3 spherical and more homogeneous nanoparticles with respect to longer hydrothermal treatments (4 h, 6 h, 8 h). These particles (2 h) are characterized by decreased dimension (approx. 120 nm), narrower size distribution and higher tetragonality (1.007) in comparison with particles prepared at ambient pressure (1.003). In addition, the short hydrothermal treatment (2 h) produces particles with tetragonality comparable to the one obtained after the longest process (8 h). Finally, dopants were found to affect to different extents both the c⟶t phase transformation and the crystallite sizes.

Electromechanical actuation in piezoceramics is usually enhanced by creating chemically homogeneous materials with structurally heterogeneous morphotropic phase boundaries, leading to abrupt changes in ion displacement directions within the perovskite unit cell. In the present study, an alternative mechanism to enhance electromechanical coupling is found in both chemically and structurally heterogeneous BiFeO3−BaTiO3 lead-free piezoceramics. Such a mechanism is observed in a composition exhibiting core-shell type microstructure, associated with donor-type substitution of Ti4+ for Fe3+, and is primarily activated by thermal quenching treatment. Here, we describe the use of in-situ high-energy synchrotron X-ray powder diffraction upon the application of a high electric field to directly monitor the ferroelectric and elastic interactions between these composite-like components, formed as core and shell regions within grains. Translational short or long-range ordering is observed in the BiFeO3‒depleted shell regions which undergo significant structural alterations from pseudocubic Pm-3m relaxor-ferroelectric in slow-cooled ceramics to rhombohedral R3c or R3m with long-range ferroelectric order in the quenched state. The strain contributions from each component are calculated, leading to the conclusion that the total macroscopic strain arises predominantly from the transformed shell after quenching. Such observations are also complemented by investigations of microstructure and electrical properties, including ferroelectric behaviour and temperature-dependent dielectric properties.

Работа посвящена исследованию возможностей применения пьезокерамических актуаторов в малогабаритных летательных аппаратах. Определено рациональное отношение длины к ширине актуатора, что является крайне необходимым при конструировании малогабаритных летательных аппаратов. В результате исследований получены математические зависимости для прогнозирования амплитуды колебаний в зависимости от геометрических размеров пьезоэлектрической пластины. Адекватность модельных расчетов подтверждена экспериментальными исследованиями. The work is devoted to the investigation of the possibilities of using piezoceramic actuators in small-sized aircrafts. The rational relation of the length to the width of the actuator is determined, which is extremely necessary for the design of small-sized aircraft. As a result of the research, mathematical dependencies were obtained for predicting the amplitude of oscillations depending on the geometric dimensions of the piezoelectric plate. The adequacy of model calculations has been confirmed by experimental studies.

We report on a heterogeneity study, down to the atomic scale, on a representative multiple-element-modified ceramic based on potassium sodium niobate (KNN): 0.95(Na0.49K0.49Li0.02)(Nb0.8Ta0.2)O3&ndash, 0.05CaZrO3 with 2 wt % MnO2. We show that different routes for incorporating the MnO2 (either before or after the calcination step) affect the phase composition and finally the functionality of the material. According to X-ray diffraction and scanning electron microscopy analyses, the ceramics consist of orthorhombic and tetragonal perovskite phases together with a small amount of Mn-rich secondary phase. The addition of MnO2 after the calcination results in better piezoelectric properties, corresponding to a ratio between the orthorhombic and tetragonal perovskite phases that is closer to unity. We also show, using microscopy techniques combined with analytical tools, that Zr-rich, Ta-rich and Mn-rich segregations are present on the nano and atomic levels. With this multi-scale analysis approach, we demonstrate that the functional properties are sensitive to minor modifications in the synthesis route, and consequently to different material properties on all scales. We believe that detecting and learning how to control these modifications will be a step forward in overcoming the irreproducibility problems with KNN-based materials.

A steel strand is widely used in long span prestressed concrete bridges. The safety and stability of a steel strand are important issues during its operation period. A steel strand is usually subjected to various types of prestress loss which loosens the anchorage system, negatively impacting the stability of the structure and even leading to severe accidents. In this paper, the authors propose a wavelet packet analysis method to monitor the looseness of the wedge anchorage system by using stress wave-based active sensing. As a commonly used piezoceramic material, lead zirconate titanate (PZT) is employed with a strong piezoelectric effect. In the proposed active sensing approach, PZT patches are used as sensors and actuators to monitor the steel strand looseness. The anchorage system consists of the steel strand, wedges and barrel, which forms two different direct contact surfaces to monitor the tension force. PZT patches are pasted on the surface of each steel strand, corresponding wedge and barrel, respectively. Different combinations of PZTs are formed to monitor the anchoring state of the steel strand according to the position of the PZT patches. In this monitoring method of two contact surfaces, one PZT patch is used as an actuator to generate a stress wave and the other corresponding PZT patch is used as a sensor to detect the propagated waves through the wedge anchorage system. The function of these two PZTs were exchanged with the changing of transmission direction. The wavelet packet analysis method is utilized to analyze the transmitted signal between PZT patches through the steel strand anchorage system. Compared with the wavelet packet energy of received signals under different PZT combinations, it could be found that the wavelet packet energy increased with the increasing of anchorage system tightness. Therefore, the wavelet packet energy of received signal could be used to monitor the tightness of the steel strand during operation. Additionally, the wavelet packet energy of the received signals are different when the same PZT combination exchanges the energy transfer direction. With the comparison on the received signals of different combinations of PZTs, the optimal energy transfer path corresponding to different contact surfaces of the steel strand could be determined and the optimal experimental results are achieved.

Smart Materials are designed materials that have one or more properties that can be significantly changed in a controlled fashion by an externally applied field value such as stress, temperature and electric or magnetic fields. This behavior is reversible and consequently enables these materials to fulfill actuation and sensing functions in one component. Compared to conventional systems such actuators are rather high integrated. They can be applied not just to be a discrete part of the system; they are the system itself combining sensing, actuation and mechanical functions. Certain actuating properties of Smart Materials are far beyond the ones of conventional actuating principles. These advantages possess to use them in special application areas such as lightweight construction, active vibration control or the development of highly dynamic systems for instance. The design of Smart Materials in highly integrated components is technically more advanced and requires interdisciplinary knowledge. In this paper we present three groups of Smart Materials: piezoceramics, shape memory alloys and dielectric elastomers and their specific characteristics. That covers their physical working principle, their mechanical behavior, the actuation and sensing properties. Especially the interdisciplinary design approach required for developing highly integrated components is exemplarily clarified on Shape Memory Alloys. To enable designers to use Smart Materials without having this special knowledge smart tools for smart design are presented.

Made available in DSpace on 2020-12-12T02:04:05Z (GMT). No. of bitstreams: 0 Previous issue date: 2014-12-01 In this paper, we present an alternative method for assessing the sensitivity of lead zirconate titanate (PZT) piezoceramics for damage detection in structural health monitoring (SHM) systems based on the electromechanical impedance (EMI) principle. An assessment of the sensitivity is obtained experimentally using the pencil lead break (PLB) method, which is frequently used in acoustic emission (AE) systems. Tests were carried out on an aluminum beam, and the results show a clear relationship between the damage indices obtained from the electrical impedance signatures of the PZT patch bonded to the monitored structure and the power spectral density (PSD) obtained using the PLB method. Faculdade de Engenharia de Bauru UNESP Univ Estadual Paulista Departamento de Engenharia Elétrica Faculdade de Engenharia de Bauru UNESP Univ Estadual Paulista Departamento de Engenharia Elétrica

The effect of a constant electric field ([Formula: see text]) on the absorption of microwave electromagnetic energy ([Formula: see text]) by BaTiO3 crystals and the highly sensitive PCR-1 piezoceramic was studied. The field dependence of the absorption value [Formula: see text] at the maximum of the spectrum [Formula: see text] has the form of a “butterfly”, and the dependence of the frequency shift of the maximum on the field strength [Formula: see text] has a hysteretic character. The PCR-1 [Formula: see text] absorption spectrum at high [Formula: see text] is modulated by pulses in a wide frequency range. It is assumed that the cause of the amplitude–frequency modulation of the spectrum may be the electromagnetic radiation of incomplete local discharges at the surface of piezoceramics. The change in the magnitude and position of the resonance maximum in the absorption spectra and the appearance of amplitude–frequency modulation [Formula: see text] when exposed to a constant field is interpreted from the point of view of changes in the parameters and concentration of the domains walls, as well as the [Formula: see text]- and [Formula: see text]-domain wedges of mechanical twins resonating in the electromagnetic field.

A new approach for modeling hysteretic non-linear ferroelectric ceramics is presented, based on a fully ferroelectric/ferroelastic coupled macroscopic material model. The material behavior is described by a set of yield functions and the history dependence is stored in internal state variables representing the remanent polarization and the remanent strain. For the solution of the electromechanical coupled boundary value problem, a hybrid finite element formulation is used. Inside this formulation the electric displacement is available as nodal quantity (i.e. degree of freedom) which is used instead of the electric field to determine the evolution of remanent polarization. This involves naturally the electromechanical coupling. A highly efficient integration technique of the constitutive equations, defining a system of ordinary differential equations, is obtained by a customized return mapping algorithm. Due to some simplifications of the algorithm, an analytical solution can be calculated. The automatic differentiation technique is used to obtain the consistent tangent operator. Altogether this has been implemented into the finite element code FEAP via a user element. Extensive verification tests are performed in this work to evaluate the behavior of the material model under pure electrical and mechanical as well as coupled and multi-axial loading conditions.

Optimal control theory is formulated and applied to damp out the vibrations of micro-beams where the control action is implemented using piezoceramic actuators. The use of piezoceramic actuators such as PZT in vibration control is preferable because of their large bandwidth, their mechanical simplicity and their mechanical power to produce controlling forces. The objective function is specified as a weighted quadratic functional of the dynamic responses of the micro-beam which is to be minimized at a specified terminal time using continuous piezoelectric actuators. The expenditure of the control forces is included in the objective function as a penalty term. The optimal control law for the micro-beam is derived using a maximum principle developed by Sloss et al. [J.M. Sloss, J.C. Bruch Jr., I.S. Sadek, S. Adali, Maximum principle for optimal boundary control of vibrating structures with applications to beams, Dynamics and Control: An International Journal 8 (1998) 355–375; J.M. Sloss, I.S. Sadek, J.C. Bruch Jr., S. Adali, Optimal control of structural dynamic systems in one space dimension using a maximum principle, Journal of Vibration and Control 11 (2005) 245–261] for one-dimensional structures where the control functions appear in the boundary conditions in the form of moments. The derived maximum principle involves a Hamiltonian expressed in terms of an adjoint variable as well as admissible control functions. The state and adjoint variables are linked by terminal conditions leading to a boundary-initial-terminal value problem. The explicit solution of the problem is developed for the micro-beam using eigenfunction expansions of the state and adjoint variables. The numerical results are given to assess the effectiveness and the capabilities of piezo actuation by means of moments to damp out the vibration of the micro-beam with a minimum level of voltage applied on the piezo actuators.

Piezoceramic materials exhibit different types of nonlinearities depending upon the magnitude of the mechanical and electric field strength in the continuum. Some of the nonlinearities observed under weak electric fields are: presence of superharmonics in the response spectra and jump phenomena etc. especially if the system is excited near resonance. In this paper, an analytical solution (in 2D plane stress domain) for the nonlinear response of a rectangular piezoceramic slab has been obtained by use of Rayleigh–Ritz method and perturbation technique. The eigenfunction obtained from solution of the differential equation of the linear problem has been used as the shape function in the Rayleigh–Ritz method. Forced vibration experiments have been conducted on a rectangular piezoceramic slab by applying varying electric field strengths across the thickness and the results have been compared with those of analytical solution. The analytical solutions compare well with those of experimental results. These solutions should serve as a method to validate the FE formulations as well as help in the determination of nonlinear material property coefficients for these materials.

Piezoceramic materials exhibit different types of non-linearities depending on the magnitude of the mechanical and electric field strength in the piezoelectric continuum. Some of the non-linearities observed under weak electric fields are the presence of superharmonics in the response spectra, jump phenomena, and so on, especially if the system is excited near resonance. In this article, an analytical solution (in the two-dimensional plane stress domain) for the non-linear response of a rectangular piezoceramic slab has been obtained by the use of Rayleigh—Ritz method and perturbation technique. The eigenfunction obtained from the solution of differential equations of the linear problem has been used as the shape function in the Rayleigh—Ritz method. Forced vibration experiments have been conducted on rectangular piezoceramic slabs of two different materials (e.g. PIC 181 and PIC 255) by applying varying electric field strengths across the thickness, and the displacement and current responses have been measured. Experiments have also been conducted for the first two free in-plane modes in the case of the piezoceramic PIC 181. Analytical solutions have been obtained by using the current formulations and they are found to compare well with those of the experiment. These solutions should serve as a method to validate the finite-element formulations as well as to help in the determination of non-linear material property coefficients for these materials.

Piezoceramic materials exhibit different types of nonlinearities depending upon the magnitude of the mechanical and electric field strength within the body. Some of the nonlinear phenomena observed under weak electric fields near resonance frequency excitation are the presence of superharmonics in the response spectra and the jump phenomena etc. In this work, an analytical solution for the nonlinear response of rectangular piezoceramic slabs have been obtained by Rayleigh–Ritz method and perturbation technique in the 3-D domain using a generalized nonlinear electric enthalpy density function. Forced vibration experiments (excitation with electric field) have been conducted on a rectangular piezoceramic slab at varying electric field amplitudes and the analytical solutions have been shown to compare very well with the experimental results.

The dependence of the dielectric constant and its losses on the applied field is studied, as well as the correlation between the dielectric constant and dielectric losses. The results show that hard lead zirconate titanate cannot be described by the Rayleigh model, so the hysteretic response of those materials cannot be attributed exclusively to the contribution of the irreversible processes. The experiments reveal the existence of reversible processes that could be related to the bending of the domain walls, which contribute to the dielectric constant of those materials without producing dielectric losses. The dependence of the dielectric constant on the poling state and on ageing are also studied. It can be reasserted that there are two distinct mechanisms that contribute to the dielectric response. The results show that the reversible contribution is independent of the ageing processes suffered by the sample.

It has been intended to improve the description of the nonlinear dielectric behavior of piezoelectric ceramic PZT, by applying diverse external actions, in order to correlate it to the phenomena that occur due to its structure. By using a bridge built for this purpose, the current obtained by applying a harmonic high voltage of low frequency is analyzed. It is intended to do not use any previous model in the treatment of the data. It can be seen that the nonlinear behavior depends explicitly on the field amplitude. The nonlinear increment of the dielectric constant can be split into two parts. One of them, εα, does not depend on the instantaneous field, and its value is higher in soft than in hard materials. It is also higher if the ceramics has been deaged or if its polarization has been altered. None of these effects occurs to the other part of the increment of ε. Furthermore, losses are closely related to the term εα for all types of PZT. It is reasonable to expect that this term comes from the nonreversible movement of non-180º domain walls. The term εα depends on the amplitude E0 through a power function, with a fractional power that depends on ceramic type.Se pretende mejorar la descripción del comportamiento dieléctrico no lineal de cerámicas piezoeléctricas PZT, sometidas a distintas acciones exteriores, para correlacionarlo con los distintos procesos que se desarrollan en él debidos a su estructura. Mediante un puente, construido ad hoc, se analiza la corriente obtenida al aplicar una tensión sinusoidal de gran amplitud y baja frecuencia. Se intenta que en el proceso de datos no se presuponga la validez de ningún modelo. Se observa que el comportamiento no lineal depende explícitamente de la amplitud del campo. El incremento no lineal de la constante dieléctrica puede desdoblarse en dos fracciones. Una de ellas, εα, no depende del campo instantáneo, siendo mucho mayor en los materiales blandos que en los duros. Es también mayor en cerámicas no envejecidas , o cuya polarización ha sido alterada. Nada de ello ocurre con la fracción restante. Las pérdidas están relacionadas directamente con el término εα para todos los tipos de PZT. Es razonable suponer que dicho término aparece a causa del movimiento irreversible de las paredes de dominio. El término εα depende de la amplitud del campo a través de una función potencial, cuyo exponente fraccionario depende del tipo de cerámica.

The success of active vibration control in adaptronics decisively depends on the performance of the actuators used as multifunctional structural elements. DLR’s concept of impedance matched actuators proposes novel actuators in honeycomb design (Fig. 8.1). The partitions of their hexagonal cells are made of piezoceramic materials. The honeycomb geometry guarantees lightweight properties with nearly perfect load distributions in the plane perpendicular to the cell tubes. Furthermore there is a dynamic flexibility in this plane even when the static stiffness is very high. New fabrication methods are required to realize honeycomb actuators with very small cells, low wall thicknesses and perfect rounded corners. In order to fulfill the lightweight conditions self-organizing effects were used to guarantee optimal 3D geometries. In this context, a local thermal treatment of ceramic structures by employing lasers initiates self-organizing mechanisms via material flow. Experimental comparisons between piezoelectric honeycomb actuators and conventional monolithic actuators demonstrate a reduction of electrical power by a factor of 500. Honeycomb actuators seem to be the most promising candidate for technical applications that require low energy consumption. Open image in new window Fig. 8.1 Piezoceramic honeycomb actuator

Current models of non-linear electromechanical behaviours of piezoactuators are mostly intended for actuator configurations where the strain of the piezoelectric material is directly used as the linear output. On the other hand, in the design of piezoactuators, there exist non-trivial configurations where the internal strains of the piezoelectric materials manifest externally in the form of bending and curving rather than simple elongation or contraction, it is also important to predict the non-linear performance of the actuator based on the design parameters. Therefore, it is the intent of this article to present a model that enables calculation of the quasi-static mechanical response of piezoelectric multilayer actuators in non-trivial configurations. It is based on the polarization hysteresis loop and butterfly curve of its constituent piezoelectric material. Using an energy-based formulation, the model takes into account the non-piezoelectric sections as well as the mechanical boundary conditions of the actuator. Furthermore, a three-layer lead zirconium titanate bimorph with both ends clamped is considered in this study. Model calculation of its relationship between input voltage V and midpoint vertical displacement X is carried out based on ferroelectric hysteresis data of the bimorph material from the literature. The calculation results are then validated by measurements.

The determination of the characteristic frequencies of an electromechanical resonance is not enough data to obtain material properties of piezoceramics, including all losses, from complex impedance measurements. Besides, values of impedance around resonance and antiresonance frequencies are also required to determine the material losses. Uncoupled resonances are needed for this purpose. The shear plates used for the material characterization present unavoidable mode coupling of the shear mode and other modes of the plate. A study of the evolution of the complex material coefficients as the coupling of modes evolves with the change in the aspect ratio (lateral dimension/thickness) of the plate is presented here. These are obtained by Alemany et al. software. A soft commercial PZT ceramic was used in this study and a number of shear plates amenable to material characterization were obtained in the range of aspect ratios below 15. The validity of the material properties for 3-D modelling of piezoceramics is assessed by means of Finite Element Analysis (FEA), which shows that uncoupled resonances are virtually pure thickness driven shear modes., CSIC project #201060E069 and European Network of Excellence (NoE-MIND CE FP6 515757-2)

In the present paper, a review on piezoelectric sensing of mechanical deformations and vibrations of so-called smart or intelligent structures is given. After a short introduction into piezoelectric sensing and actuation of such controlled structures, we pay special emphasis on the description of some own work, which has been performed at the Institute of Technical Mechanics of the Johannes Kepler University of Linz (JKU) in the last years. Among other aspects, this work has been motivated by the fact that collocated control of smart structures requires a sensor output that is work-conjugated to the input by the actuator. This fact in turn brings into the play the more general question of how to measure mechanically meaningful structural quantities, such as displacements, slopes, or other quantities, which form the work-conjugated quantities of the actuation, by means piezoelectric sensors. At least in the range of small strains, there is confidence that distributed piezoelectric sensors or sensor patches in smart structures do measure weighted integrals over their domain. Therefore, there is a need of distributing or shaping the sensor activity in order to be able to re-interpret the sensor signals in the desired mechanical sense. We sketch a general strategy that is based on a special application of work principles, more generally on displacement virials. We also review our work in the past on bringing this concept to application in smart structures, such as beams, rods and plates.

Weight is a critical parameter in the design of any system launched into space. Current launch costs are on the order of 10,000 dollars per pound of payload capacity. Reducing weight and thus increasing payload capacity is always in the forefront of the design process. One method of increasing the payload capacity of launch vehicles is to reduce the acoustic environment in the interior of the fairing. A major problem is that passive methods currently used for noise suppression do not exhibit significant energy dissipation at low frequencies. This motivates the use of active noise control. Using active noise control for frequencies below 200 to 300 Hz in addition to the passive control means has potential to provide broadband noise suppression and thus a smoother, cheaper ride for any payload. The problem with this technique is that active noise control commonly uses electromagnetic speakers as the control element. The weight of the speaker adds more cost to the application due to the approximate cost per pound to send a launch vehicle and payload to space. At 10,000 dollars per pound of payload capacity, the added cost spent on protecting the payload can potentially reduce the amount of payload capacity a customer receives due to monies spent on non-payload mass. Therefore, necessity dictates a light weight noise control solution. This work investigates the feasibility of a transducer with less mass than that of a conventional loudspeaker which dissipates energy at the acoustic resonances of an enclosed cavity. The test setup involves using the transducer to lower the sound pressure levels of acoustic resonances which are excited by an external source, thus simulating the launch phase of a launch vehicle. The transducer is used as an actuator to add damping through feedback control. The transducer is comprised of three thin flexures that are actuated by piezoceramic material attached to both sides. The flexures actuate a speaker cone that is attached to the end of the flexures. The transducer can act as a sensor or an actuator due to the nature of the piezoceramics. The sound absorbing transducer is modeled to couple to the first acoustic resonance of a six foot cylindrical cavity. The cavity acts as a simplified model of a launch vehicle payload fairing. Equations of motion are derived to model actuator motion and the acoustic impedance of the cavity. A state-space model of the system was derived for two cases: a collocated sensor/actuator pair exciting the tube and an external source exciting the tube with the transducer acting as an absorber. The transducer is designed to affect the first mode, however damping is noticed in the next acoustic resonance. Analysis of the theoretical model indicated up to 70 percent reduction of the open-loop RMS values or a reduction of 10 dB. Experimental results with the optimized transducer produced a 35 percent reduction of the open-loop RMS value or 3.73 dB. The first acoustic resonance coupled well with the first structural mode of the transducer providing optimal noise suppression for the first mode. Damping was also noted in the second acoustic mode. Neglecting the inertia of the tip mass introduced errors in the predictions of the transducer resonances at higher frequencies. This problem limited the ability to control the higher modes of the cavity. Master of Science

Aircraft and satellite structures are exposed to a wide range of temperatures during normal operation cycles. These fluctuations in temperature may result in significant changes of the structural dynamics. Aircraft, automotive, and satellite structures are also subject to various vibration sources. Passive and active vibration suppression techniques have been developed to minimize acoustic noise and fatigue stress damage. Featuring low weight solutions and high performance, active control techniques are becoming increasingly common. Structures with varying dynamics require more sophisticated active control techniques, such as adaptive control. This research uses a special vibration test rig for evaluating the performance of different vibration suppression systems on a representative aircraft panel. The test panel is clamped rigidly in a frame and can be excited in various frequencies with an electromagnetic shaker. To simulate temperature fluctuations the temperature on the panel can be increased up to 65°C (150°F). Smart material based sensors and actuators are used to interface the mechanical system with the electronic controller. The active controller utilizes three positive position feedback (PPF) filters implemented through a digital signal processor board. This research develops two different adaptation methods to perform vibration suppression in the presence of thermally induced frequency changes of the representative panel. To adjust the PPF filter parameters an open-loop adaptation method and an auto-tuning method are investigated. The open-loop adaptation method uses a measurement of the plate temperature and a look-up table with pre-determined parameters to update the filters accordingly. The auto-tuning methods identifies the frequencies of the poles and zeros in the structure's collocated transfer function. From the knowledge of the pole and zero locations the optimal PPF parameters are calculated online. The results show that both adaptation methods are capable of reducing the vibration levels of the test specimen over the temperature range of interest. Three PPF filters with parameter adaptation through temperature measurement achieve magnitude reductions of the resonance peaks as high as 13.6 decibel. Using the auto-tuning method resonance peak reductions up to 17.4 decibel are possible. The pole/zero identification routine proves to detect the frequencies correctly. The average identification error remained at around one percent even in the presence of external disturbances. Master of Science

This study evaluates the effectiveness of actively controlled piezoceramics with positive position feedback (PPF) for reducing structural vibrations. A comparison is made between active control with PPF and a parallel resistor-inductor (RLC) shunt technique. The primary objectives of this study are to: 1. Explore the feasibility of using smart materials and fiber optics for simultaneous health monitoring and active damping of a representative aircraft panel. 2. Determine how optical fiber sensors may be used to detect vibration modes of an aircraft panel by investigating their use on a representative test article. 3. Determine how piezoelectric patches may be used to detect and counteract fundamental resonances of a representative test article. 4. Determine a control algorithm and hardware system to increase substantially the damping in the fundamental mode of the representative test article over a wide temperature range. 5. Develop a health-monitoring algorithm based on fiber optic sensors to detect impedance changes in a representative test article. 6. Make a comparison between active control with PPF and an RLC shunt technique. To achieve the objectives of this study, a special test rig was used to evaluate the performance of piezoelectric materials (PZTs) for vibration suppression. The test rig was used to rigidly clamp a flat 20-guage steel plate, and then excite the plate in various frequency ranges with an electromagnetic shaker. For each test, a data acquisition system was used to acquire the data to evaluate the performance of each PPF controller. Once the data was obtained, a comparison was made between active damping with PPF and passive damping with the RLC shunt technique. The active damping technique used for this study combined piezoelectric actuators with fiber optic sensors to achieve simultaneous active control and health monitoring of a test plate. The results of the active damping tests show that piezoelectric materials can provide substantial narrowband and broadband frequency reductions, while at the same time detecting damage on the test plate. More specifically, the test results indicate that smart damping materials can decrease the fundamental mode of vibration of the test plate by 23 dB and detect damage such as a loose bolt in the clamping frame, with the addition of only 0.04 lb of PZT on the test plate. The active damping technique reduced the plate vibrations at each mode within the frequency range of interest, with only one-third the amount of piezoelectric material needed for an RLC shunt circuit technique. Master of Science

The meso-scale surface roughness of piezoelectric fiber composites can be manipulated by applying an electric field to a piezocomposite with a polished surface. In the absence of an applied voltage, the tips of the embedded piezoelectric ceramic fibers are below the surface of the piezocomposite and a silicon wafer counter surface rests solely on the matrix region of the piezocomposite surface. When actuated, the piezoelectric ceramic fibers protrude from the surface and the wafer rests solely on these protrusions. A threefold decrease in engineering static friction coefficient upon actuation of the piezocomposite was observed: from μ 1.65 to μ 0.50. These experimental results could be linked to the change in contact surface area and roughness using capillary adhesion theory, which relates the adhesive force to the number and size of the contacting asperities for the different surface states. © 2013 AIP Publishing LLC.

During the last five years, the Dept. of Aeronautical Engineering of the University of Naples, has carried out a lot of work, especially on the experimental side, focused on assessing the feasibility of an active vibration and noise control approach, based on the use of piezoceramic actuators and sensors bonded to different structural elements. This paper concerns an application of this technique relative to a partially curved stiff frame of a medium civil transport jet aircraft. The general procedure, as previously assessed on different test articles, requires as first step, the dynamic characterization of the test article, to best point out the target of control procedure in terms of deformed shapes relative to the frequency of most interest. The use of PZT piezoactuators to be bonded on the structure guarantee at the same time high actuators forces in front of a low weight increment. The hearth of the MIMO (Multi Input Multi Output) feedforward control algorithm that is usually applied, is then represented by an ANN (Artificial Neural Network) control algorithm that use the evaluation of experimental FRF as measured by reference accelerometer, to calculate the optimum control forces to be applied to the actuators to minimize a target cost function. Experimental results provided over 32 dB of overall vibration level reduction in a single controlled mode shape, without any spillover effect.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In this work, the piezoelectric properties at high electric fields of dielectrophoretically aligned PZT—polymer composites containing high aspect ratio particles (such as short fibers) are presented. Polarization and strain as a function of electric field are evaluated. The properties of the composites are compared to those of PZT-polymer composites with equiaxed particles, continuous PZT fiber-polymer composites, and bulk PZT ceramics. From high-field polarization and strain measurements, the effective field dependent permittivity and piezoelectric charge constant in the poling direction are determined for dielectrophoresis structured PZT-polymer composites, continuous PZT fiber-polymer composites, and bulk PZT ceramics. The changes in dielectric properties of the inclusions and the matrix at high fields influence the dielectric and piezoelectric properties of the composites. It is found that the permittivity and piezoelectric charge constants increase towards a maximum at an applied field of around 2.5-5?kV/mm. The electric field at which the maximum occurs depends on the aspect ratio and degree of alignment of the inclusions. Experimental values of d33 at low and high applied fields are compared to a model describing the composites as a continuous polymer matrix containing PZT particles of various aspect ratios arranged into chains. Thickness mode coupling factors were determined from measured impedance data using fitted equivalent circuit model simulations. The relatively high piezoelectric strain constants, voltage constants, and thickness coupling factors indicate that such aligned short fiber composites could be useful as flexible large area transducers. Erratum published 5 March 2015: http://dx.doi.org/10.1063/1.4914113

This letter investigates the nonlinear response of a bimorph energy harvester comprised of lead zirconate titanate (PZT-5A) laminates. For near resonant excitations, we demonstrate significant intrinsic nonlinear behavior despite geometrically linear motion. Fourth order elastic and electroelastic tensor values for PZT-5A are identified following methods recently published concerning a PZT-5H bimorph. A response trend indicative of a nonlinear dissipative mechanism is discussed as well as the inadequacy of linear modeling. The PZT-5A bimorph exhibits an increased softening frequency response in comparison to PZT-5H. The results contained herein are also applicable to electroelastic sensor and actuator technologies. (C) 2010 American Institute of Physics. [doi:10.1063/1.3530449]

This letter investigates the power generation and shunt damping performance of the single crystal piezoelectric ceramic lead magnesium niobate-lead zirconate titanate (PMN-PZT) analytically and experimentally. PMN-PZT is a recently developed interface for energy harvesting and shunt damping with its large piezoelectric constant (-2252 pm/V) and coupling coefficient (0.95) for the transverse piezoelectric mode. A unimorph PMN-PZT cantilever with an aluminum substrate is tested under base excitation and its electromechanical response is predicted with a coupled distributed parameter model. The power generation performance of the device is 138 mu W/(g(2) cm(3)) at 1744 Hz, causing 84% tip vibration attenuation due to the resistive shunt damping effect. AFOSR MURI under Grant No. F 9550-06-1-0326

International audience; The ferroelectric, piezoelectric, and pyroelectric properties of Ba1−xNaxTi1−xNbxO3 with x=0.70 (BTNN0.70) lead-free ceramic were investigated. Polycrystalline sample with composition BTNN0.70 was prepared by using conventional dry ceramic technique. Sample was sintered at 1250 °C for 3 h under oxygen showed perovskite structure with high densities 4.92 g/cm3 (~96% as relative density). X-ray analysis confirmed the formation of single-phase compound with cubic crystal structure. Dielectric properties were studied in detail as a function of frequency and temperature. From temperature variation of dielectric constant, Curie temperature (TC) was determined. Discussion on hysteresis behavior for the sample at room temperature is presented. An essential relation between the piezoelectric properties and the ferroelectric nature of the ceramics was detected. The piezoelectric and pyroelectric coefficients of the ceramic were studied as a function of temperature.

11 pages, 16 figures, 1 table.-- PACS: 81.05.Je; 77.84.Dy; 81.40.Ef; 77.22.Ch; 77.22.Gm; 77.80.Bh; 72.80.Sk; 81.20.Ev; 61.50.Nw; 77.22.Ej, Ceramics of composition Bi3TiNbO9 (BTN) and perovskite-layered structure (Aurivillius type) [B. Aurivillius, Ark. Kemi 1, 463 (1949)] were processed by natural sintering and hot pressing from amorphous precursors. Precursors were obtained by mechanochemical activation of stoichiometric mixtures of oxides. These materials are in general interesting for their use as high-temperature piezoelectrics. Among them, BTN possesses the highest ferroparaelectric phase-transition temperature (>900 °C). The transition temperature establishes the working limit of the ceramic and the electric properties, especially the dc conductivity, affect on its polarizability. In this work, dielectric studies of BTN ceramics with controlled texture and microstructure have been made at 1, 100 KHz, and 1 MHZ and in the temperature range from 200 °C up to the ferroparaelectric transition temperature. Values of ~250 at 200 °C are achieved in ceramics hot pressed at temperatures as low as 700 °C for 1 h., The authors thank the research projects 07N/0076/2002 of Spanish CAM and MAT2001-0561 of Spanish MCyT for the financial support of this work.

In this work, the contribution of the extrinsic effect to the macroscopic properties in soft and hard lead zirconate titanate ceramics is directly evaluated. Close to the room temperature, poled hard ceramics show an anomalous behavior, which is notably different from that of soft ceramics, not only in dielectric but also in piezoelectric and elastic responses. Hence, at room temperature their properties are thermally stable and the losses are unusually low. It is suggested that two mechanisms are present, with one mechanism inhibiting the other.

The role of Fe as an acceptor and Nb as a donor in [0.94−x](Bi1/2Na1/2)TiO3–0.06BaTiO3−x (K0.5Na0.5)NbO3 (100xKNN) (x = 0.02 and 0.03) lead-free piezoceramics was investigated. X-ray diffraction analyses show that all the profiles are best-fitted with a cubic symmetry where Fe doping tends to induce a lattice expansion, while Nb doping does the opposite. The strain and polarization characteristics are enhanced and suppressed by the acceptor and donor dopants, respectively. The improvement in the electrical properties with acceptor doping is accompanied by the stabilization of a ferroelectric order. Electron paramagnetic resonance spectroscopic analysis suggests that the stabilization of the ferroelectric order by the Fe dopant originates from the formation of (FeTi′–VO••)• defect dipoles.

We report on the experimental investigation of a high-frequency (1 MHz-1.8 GHz) dielectric dispersion in unpoled and poled Pb(Zr,Ti)O-3 ceramics. Two overlapping loss peaks could be revealed in the dielectric spectrum. The linear dependence between the lower-frequency peak position and average grain size D, which holds for D/

The growth of Vicker´s cracks during the poling of piezoelectric ceramics was studied for two PZT based compositions with different tetragonal distortion of the perovskite structure. Studies on the two compositions with different poling electric fields and similar initial crack lengths showed that crack growth was not proportional to the induced stress free longitudinal strain by 90º domain reorientation. This observation is not consistent with the previously proposed mechanism of crack growth based on a strain mismatch between the material at the crack flanks and the rest of the ceramic. This mismatch was proposed to occur because of the reduction of the electric field within the crack flanks. The reasons for the disappearance of the mismatch are discussed here, and an alternative mechanism of crack growth consistent with our results is proposed, which takes into account the electrically induced stress gradient at the crack tip, produced by the piezoelectric effect. Cracks were also found to grow during a small number of subsequent polarisation reversals, the explanation of which must be due to some other additional effect.Se ha estudiado el crecimiento de grietas Vicker durante la polarización de cerámicas piezoeléctricas para dos modificaciones del PZT con distinta distorsión tetragonal de la estructura perovskita. Los resultados en función del campo eléctrico de polarización y la longitud inicial de la grieta muestran que el crecimiento no es proporcional a la deformación libre de tensión inducida por orientación de dominios de 90º. Esta observación no es consistente con el mecanismo de crecimiento de grieta propuesto anteriormente, basado en el desajuste de deformación entre el material a los flancos de la grieta y el resto de la cerámica. Este desajuste se producía por la atenuación del campo eléctrico en los flancos de la grieta. Se discute la causa de la desaparición de este desajuste de deformación, y se propone un mecanismo alternativo de crecimiento de grieta consistente con los resultados obtenidos, que tiene en cuenta el gradiente de tensión en la punta producido por el efecto piezoeléctrico. También se ha observado crecimiento de la grieta durante un pequeño número de conmutaciones de la polarización realizadas a continuación del polarizado inicial, fenómeno que debe estar relacionado con algún otro efecto adicional.