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SELF-HEALING PIEZOELECTRIC CRYSTAL Researchers from the Indian Institute of Science Education and Research in Kolkata, the Indian Institute of Technology Kharagpur, and RWTH Aachen University in Germany discovered a type [...]

Axisymmetric vibrations of a hollow piezoelectric sphere submerged in a compressible viscous fluid medium are investigated. The piezoelectric sphere is radially polarized. The differential equations governing the shell motion are obtained by the use of Hamilton's principle. Based on the classical bending theory of shells, it is shown that all the piezoelectric contributions can be included in the in vacuo natural frequencies and their corresponding mode shapes. As such, the previous theory on elastic shell vibration becomes readily extendable. The flow field, determined by the boundary layer theory, is coupled to the shell motion through no-slip and no-penetrating conditions. It is found that the contribution of the piezoelectric parameters in the thin shell's free vibration is of small order and is negligible. Natural frequencies and their associated vibration characteristics are numerically obtained and presented for a Polyvinglindene fluoride (PVDF) shell submerged in water Dynamic responses of a submerged piezoelectric sherical shell, and the associated radiation of sound are investigated. The oscillations are harmonically driven by an axisymmetrically applied electric potential difference across the surface of the shell. The vibrational fluid loading, and energy flow characteristics are derived and evaluated for a PVDF shell submerged in water The essential feature of the modal response is determined by various critical frequencies, such as resonant frequencies and vibration-absorbing frequencies. Viscous effect is found noticeable in several cases. [DOI: 10.1115/1.4001841] Keywords: piezoelectric spherical shell coupled vibration, dynamic response, viscous effect, compressibility effect, natural frequency, damping frequency, acoustic radiation, classical bending theory, boundary layer theory, normal mode method

Piezoelectric micro-actuators have been extensively studied and used in hard disk drive head positioning systems. In these cases, piezoelectric micro-actuators/sensors experience high frequency cyclic loading during their operations. The fatigue failure and the lifespan of such micro-actuators become a concern of researchers and engineers. However, the probability and statistics based reliability theory has not been well developed for piezoelectric micro actuators. In this paper, a probabilistic approach is presented to evaluate the reliability of piezoelectric micro-actuators. Based on the relationship between the lifetime degradation mechanism of piezoelectric actuators and the electric field strength, an interference model of electric load and strength is introduced for the reliability study of piezoelectric micro-actuators. Furthermore the reliability model is expanded into a 2-D case to take into account the effects of both driving voltage and temperature. A 2-D interference model incorporating the 2-D strength and load is proposed to obtain the relationship among the reliability, usage cycles, driving voltage and temperature. A case study of a piezoelectric micro-actuator used in a disk drive head positioning system demonstrates the application of the proposed approach. Index Terms--Electric strength, fatigue life, piezoelectric micro-actuators, probability distribution, reliability, temperature, 2-D strength.

A coupled mean field microelectromechanical model is developed as a predictive tool of the macroscopically observed piezoelectric material behavior. This model is used for studying the sensitivity of macroscopic foam behavior to various constituent material and void variables and it has improved the approximation of the true piezoelectret behavior.

Heterolayered Pb([Zr.sub.1-x][Ti.sub.x])[O.sub.3] thin films with different combinations of constituted layers are examined. The wake-up phenomenon is reduced at elevated temperatures, thus leading to fatigue degradation at a relatively lower number of switching cycles.

A constant voltage driving method was used for examining the high-power piezoelectric characteristics in (001) oriented ceramics of bismuth layer structured ferroelectrics (BLSF), Sr[Bi.sub.2][Nb.sub.2][O.sub.9] (SBN), [(Bi,La).sub.4][Ti.sub.3][O.sub.12] (BLT) and Ca[Bi.sub.4][Ti.sub.4][O.sub.15] (CBT). Constant resonance frequencies were observed in the SBN and CBT.

The study of the shear resonance behavior of rectangular-shaped samples of single-domain PZN-PT single crystal samples of 3m symmetry is discussed. Results suggest the unsuitability of sample geometries with inseparable resonance peaks for shear property characterization of piezoelectric single crystal of 3m symmetry.

An electromechanical model for a disk-type piezoelectric transformer (PT) is proposed and its optimal load resistance and maximum efficiency are calculated. The equivalent circuit model proposed predicts the PT's performance as a function of design parameters.

A modeling of the propagation of surface acoustic waves (SAW), leaky surface acoustic waves (LSAW), and surface skimming bulk waves (SSBW) in piezoelectrics is presented. A combined method of matrix Green's function and the finite element method (FEM) simulates propagation of SAW, LSAW, and SSBW.

A new stacked transducer structure, the 'super 1-3 connectivity device' and multilayered piezoelectric composites are analyzed. Results of the assessment indicate that the 3-1 plate devices offer no benefit over the conventional 1-3 connectivity arrangement.

Matrix algorithms for modeling acoustic waves in piezoelectric multilayers are presented. The algorithms that synergize both scattering and hybrid or impedance submatrices are superior.

An analytic solution for a piezoelectric bimorph plate with a central-attached mass operating in the flexural mode is derived and the performance of this bimorph plate in converting vibration energy to electric energy is evaluated.

The possibility of designing phononic crystal-based devices for telecommunication applications using commonly employed materials in microfabrication is discussed. The results suggest that the telecommunication device functionality might be significantly enhanced by integration of phononic crystals with radio frequency surface acoustic waves (SAW) devices.

The solutions for the Holland-EerNisse complex material-constant theory of lossy piezoelectrics are presented that provides a complex orthonormal set of eigenvectors and eigenvalues for the eigen coupling factor problem. Results state that the Holland-EerNisse theory shows that a crystal driven in the loss eigenstate tends to minimize the impact of the material losses.

The velocity shift of surface acoustic waves (SAW) caused by surface pressure and temperature variations of piezoelectric substrates are studied using the perturbation method. Results are derived considering the effects of pressures and temperatures on elastic, piezoelectric, and dielectric constants of piezoelectric substrates as well as the initial stresses and boundary conditions.

A basic eigenvector orientation approach has been used to evaluate the possibility of controlling the onset of panel flutter using a simple flat panel (wide beam) as an illustrative example. The use of the eigenvector orientation method for prediction of the flutter boundary (indicated by a gradual loss of orthogonality between two eigenvectors) was developed in a previous study and can thus provide a lead time for possible flutter control. As a first step, piezoelectric layers are assumed to be bonded to the top and bottom surfaces of the panel in order to provide counter-bending moments at joints between elements. The standard linear quadratic control theory is used for controller design and full state feedback is considered for simplicity. The controllers are designed to restabilize the system at the onset of flutter; as a result, flutter occurrence can be offset to a higher flutter speed. To illustrate the applicability and effectiveness of the developed method, several simple wide-beam examples are studied and presented. The effects of control moment locations are studied so as to fulfill the objective of adjusting the flutter speed to be within a desirable range. Potential applications of this basic method may be straightforwardly applied to plate and shell structures of laminated composites using the versatile finite element method.

A method is proposed for obtaining three dissipation factors of piezoelectric materials through equivalent circuit parameters. The results have shown that the elastic dissipation factor reaches its saturation over a stress level of about 10 MPa.

The 100th anniversary of Bernhard Gross was celebrated at the 12th International Symposium on Electrets in 2005. Gross has inspired and stimulated electret research since the 1930's when he entered this field as a young scientist. The following is, to a large part, a personal tribute to his contributions. In the first part, some of the seminal early work of Gross will be discussed. This is followed by reminiscences of the author to joint studies of radiation charging, carrier transport, and other aspects of eletrets at Bell Laboratories and at the Department University of Technology. In the last part, recent work in Darmstadt on charge storage, charge transport, and piezoelectricity of cellular electrets, still in part stimulated and accomapanied by Bernhard Gross, will be discussed. Index Terms--Cellular electrets, charge injection, charge transport, polarization, electrets, ferroelectrets, microphones, piezoelectric materials, radiation effects, radiation-induced conductivity.

A circular distribution is used to quantify certain domain properties and the hysteresis behavior of piezoceramic materials is modeled. The characteristics of microscopic domain distribution into the macroscopic behavior are bridged together for constructing the simple but physically based two-dimensional model.

The mode III interface crack problem is investigated for dissimilar piezo-electromagneto-elastic bimaterial media, taking the electro-magnetic field inside the crack into account. Closed form solutions are derived for impermeable and permeable cracks. The conventional singularity of [r.sup.-1/2] is found for the fields at the distance r ahead of the interface crack tip. Expressions for extended crack tip stress fields and crack opening displacements (ECODs) are derived explicitly, and so are some fracture parameters, such as extended stress intensity factors (ESIFs) and energy release rate (G) for dissimilar bimaterials. An approach called the 'energy method, 'finding the stationary point of the saddle surface of energy release rate with respect to the electro-magnetic field inside the crack, is proposed. By this method, the components of the induced electro-magnetic field inside the crack are determined, and the results are in exact agreement with those in the literature if the two constituents of the bimaterial media are identical The effects from mechanical and electro-magnetic property mismatches, such as differences in the stiffness, electric permittivity and magnetic permeability, between the two constituents of the bimedia on the mode III interface crack propagation are illustrated by numerical simulations. The results show that the applied electric and magnetic loading usually retard the growth of the interface crack and the directions of the combined mechanical, electric, and magnetic loading have a significant influence on the mode III interface crack propagation. [DOI: 10.1115/1.2073328]

The paper discusses an extension to the linear theory of piezoelectricity of the Rayleigh quotient used in the analysis of the properties and the approximate calculation of the natural frequencies of elastic continua. It is shown that for a piezoelectric continuum an infinite number of equivalent expressions can be obtained which generalize the classical Rayleigh quotient. The stationarity conditions of any of these quotients under additional constraints imposed by the Gauss equation of electrostatics and the prescribed natural electrical boundary condition are shown to result in the complete set of the governing equations of the free vibration problem of a piezoelectric continuum. The general results discussed in the paper are illustrated by the approximate calculation of the natural frequencies of a piezoelectric rod by the Rayleigh--Ritz method. Unlike in the case of elastic structures, no monotonic convergence of the approximate frequencies is guaranteed for a piezoelectric continuum, the property which can be explained using the introduced Rayleigh quotients. [DOI: 10.1115/1.2065667]

A theoretical study is performed of the acousto-electric waves guided by an air gap between two identical piezoelectric crystals of arbitrary anisotropy. The permissible number of such gap waves traveling slower than all bulk modes in the structure is established.

The use of finite element modeling, combined with optical generation and detection of Lamb waves in plate structures, was extended to encompass periodic ceramic-polymer materials typical of those encountered in 1-3 and 2-2 piezoelectric composite array transducers. Excellent agreement between theory and experiment was obtained using impedance measurements and laser scans of the surface displacement profile at selected frequencies.

An innovative method of hybrid vibration suppression using piezoelectric materials is proposed. It combines bang-bang active vibration suppression and energy-recycling semiactive vibration suppression. The piezoelectric materials are electromechanically coupled and convert mechanical energy into electrical energy and vice versa. With this method, a part of the electrical energy needed for suppressing vibration is obtained from the mechanical energy of the vibrating structures and is efficiently recycled. Furthermore, the actively supplied energy is stored in the transducers and is reused many times for vibration suppression. Therefore, the hybrid method has better performance than the case where the bang-bang active method and the energy-recycling semiactive method are both used, but independently. The hybrid method saves the actively supplied energy and is thus a low-energy-consumption vibration control. Its effectiveness in suppressing vibrations was proven in numerical simulations and experiments using a 10-bay truss structure. Moreover, a novel method to prevent undesired control chattering is proposed to further save energy supplied from the external source.

We propose a magnetic force control device consisting of laminate composites of magnetostrictive material and piezoelectric material. The magnetic force control is based on energy conversion in the composite, such that the variation of magnetization of the magnetostrictive material induced by the piezoelectric material is converted to the variation of magnetic force by magnetic circuits. Because of the capacitive property of the piezoelectric material, the device requires little current in order to maintain control of a constant force. The laminate composite can be fabricated easily and in small sizes. In this paper, we report the magnetic force control properties of a composite of Terfenol-D and piezoelectric material plates (PZTs) and discuss the design of the laminate composite. Our theoretical magnetic force formulation derived by an equivalent magnetic analysis and finite-element analysis of strain distribution in the Terfenol-D, and measurements with various thicknesses of PZT demonstrated that there are appropriate thicknesses to provide large variation of the magnetic force and energy conversion efficiency. Stacking the composites was found effective for increasing the effective area of the Terfenol-D. Index Terms--Laminate composite, magnetic force, magnetostrictive material, piezoelectric material.

We investigate the dynamic response of a magnetic force control device composed of a laminate composite of magnetostrictive/piezoelectric material. The device exploits the inverse magnetostrictive effect of a magnetostrictive material so that the variation in the magnetization of the material, and hence the magnetic force in a magnetic circuit, can be controlled with a voltage to the piezoelectric material. Here, we compare the voltage-induced frequency responses of the admittance and flux (magnetic force) between the new device and a conventional electromagnet in order to identify the factors that degrade the response of the device. A finite-element calculation of the modal shape of the composite supports the observed correlation between the vibration of the composite and the flux in the gap in dynamic response. Index Terms--Giant magnetostrictive material, laminate composite, magnetic force, piezoelectric material.

Piezoelectrically excited, resonant, elastic beams find wide use as piezoelectric fans, optical choppers, MEMS sensors, and piezoelectric motors. The devices consist of either one piezoelectric ceramic patch (piezopatch) bonded on one side (asymmetric configuration), or of two oppositely poled patches placed symmetrically on either side of a thin, flexible elastic beam (symmetric configuration). Field equations of the coupled structure governing the coupled longitudinal and bending motions of the resonator are derived using linear constitutive equations, slender beam approximations, and Hamilton's principle. Analytical solutions are found to the coupled eigenvalue problem. Eigenvalues and eigenfunctions for the short-circuited and open-circuited configurations are predicted analytically and are found to be in excellent agreement with results from three-dimensional finite element simulations. Electromechanical coupling factors (EMCF) are computed using the analytical and finite element model and optimal resonator geometries are identified for maximal EMCF. The EMCF predictions are also compared with experiments for an asymmetrically configured resonator. The analytical solution provides a convenient tool for the optimal design of such devices. [DOI: 10.1115/1.1857921]

Previous studies assumed that a crack is either impermeable or permeable, which are actually two limiting cases of a dielectric crack. This paper considers the electroelastic problem of a three-dimensional transversely isotropic piezoelectric material with a penny-shaped dielectric crack perpendicular to the poling axis. Using electric boundary conditions controlled by the boundaries of an opening crack, the electric displacements at the crack surfaces are determined. The Hankel transform technique is employed to reduce the considered problem to dual integral equations. By solving resulting equations, the results are presented for the case of remote uniform loading, and explicit expressions for the electroelastic field at any point in the entire piezoelectric body are given in terms of elementary functions. Moreover, the distribution of asymptotic field around the crack front and field intensity factors are determined. Numerical results for a cracked PZT-5H ceramic are evaluated to examine the influence of the dielectric permittivity of the crack interior on the field intensity factors, indicating that the electric boundary conditions at the crack surfaces play an important role in determining electroelastic field induced by a crack, and that the results are overestimated for an impermeable crack, and underestimated for a permeable crack. [DOI: 10.1115/1.1795219]

Experimental data on the structural features of nanorings and nanobows formed by bending single-crystal, PSD ZnO nanobelts is presented. The data exclusively support the electrostatic polar charge model as the dominant mechanism for bending.

Piezoelectric materials are used in electromechanical sensors, actuators among other applications and the vibration characteristics of piezoceramic disks with free boundary conditions are measured. Using theoretical analysis numerical simulation and experimental measurement it is found that finite element method calculations and experimental results agree well for resonant frequencies and mode shapes.

Piezoelectric polymers are widely used in sensor and actuator applications. Compared to ceramic materials, they have the advantage of mechanical flexibility and an acoustic impedance similar to those of water or air. Their electrical, electromechanical and mechanical properties can be investigated by analyzing piezoelectric resonances in their dielectric spectrum. Apart from its ability to reveal the high-frequency behavior of piezoelectric polymer films, this technique is appealing from a practical point of view because several important parameters can be measured with a single scan that only requires standard dielectric spectroscopy equipment commonly found in many laboratories. This article outlines the theoretical foundations of piezoelectric resonance, examines the experimental aspects, and reviews recent applications in the field of piezoelectric polymers. Index Terms--piezoelectricity, piezoelectric resonances, piezoelectric coefficient, coupling factor, polypropylene, polyvinylidene fluoride, polyvinylidene fluoride--trifluoroethylene, polyamide, thickness extension resonance, shear mode, voided polymer, cellular polymer, porous polymer, space-charge electret, corona charging, dielectric spectroscopy.

Poling conditions and resulting polarization and piezoelectricity in relatively thick ferroelectric films and cable layers are investigated and reported.

A wavelet neural network (WNN) control system is described. It is to control the moving table of a linear ultrasonic motor (LUSM) drive system for tracking periodic reference trajectories.

A method for characterizing a piezoelectric film that is sandwiched with two electrodes and deposited on a substrate to form a four-layer thickness extension mode composite resonator is described and discussed.

A description of a nondestructive quality evaluation and control procedure for large-area PZN-8%PT wafers is presented.

A laser-scanning vibrometer (LSV) is used to measure the longitudinal piezoelectric coefficient of thin films, based on the converse piezoelectric effect.

Interlaminar stress distribution in smart composite shells using a coupled thermal-piezoelectric-mechanical model is investigated. To maintain local accuracy of stress distributions, the trial displacement field is assumed layerwise higher order and Co continuous through the entire laminate thickness, accommodating zigzag in-plane warping and interlaminar shear stress continuity. The temperature and electrical fields are modeled using higher. order descriptions that can satisfy surface flux boundary conditions at structural surfaces and equipotential conditions at electrode surfaces. These assumptions ensure computational efficiency. A variational principle, addressing the interaction between thermal, piezoelectric, and mechanical fields, is used to derive the governing equations of equilibrium. The proposed theory is used to investigate the cylindrical bending problem of simply supported composite host structures with attached piezoelectric actuators, subject to a combination of mechanical, piezoelectric, and thermal loading. The interlaminar stress distributions under comprehensive loading are presented for different geometries and stacking sequences. The effects of two-way piezoelectric and thermal coupling on the stress distributions are investigated. The significance of the thermal mismatch effect on interlaminar stress distribution is also discussed. The results from present theory are validated with available exact elasticity solutions.

Two-dimensional (2-D), second-order approximate equations for extensional, thickness-stretch and symmetric thickness-shear vibrations of piezoelectric ceramic plates with electroded faces is derived from 2-D equations deduced in previously accomplished research.

Second-order equations of extensional vibrations for piezoelectric crystal plates are obtained. A new truncation procedure is used.

Resonant ultrasound spectroscopy (RUS) is used to investigate the electromenchanical properties of LGS and LGT.

Generalized surface acoustic wave (GSAW), pseudo-SAW (PSAW), and high-velocity PSAW (HVPSAW) propagation for langatate (LGT) are presented and discussed.

Two noncontact, real-time optical measurement techniques are proposed for evaluating the displacements, natural frequencies and mode shapes of a vibrating piezoelectric material.

A smart structural model is developed to determine analytically the response of arbitrary structures with piezoelectric materials and attached electrical circuitry. The equations of motion are formulated using the coupled piezoelectric formulations. However, rather than solving for strain and electric field, the proposed model solves for the strain and electric charge. The equations of motion are simplified for the case of a composite plate structure using a refined higher-order laminate theory; however, the model is applicable to most structural models. Additional degrees of freedom are then added to describe any attached electrical circuitry. A method is also presented for system simplification using the structural mode shapes and natural frequencies. Results are verified using experimental data for passive electrical shunt damping. The developed model results in a general framework that can be useful in solving a wide variety of coupled piezoelectric-mechanical problems addressing issues such as passive electrical damping, self-sensing, and electrical power consumption.

Piezoelectric coupling factors for thickness-vibration modes driven by lateral-field excitation are calculated using the Christoffel-Bechmann method. Results are presented and discussed.

A demonstration is described for feeding back results derived from line-focus-beam ultrasonic material characterization (LFB-UMC) of crystal growth conditions of optical grade LiTaO[subscript 3] crystals and for improving homogeneity of chemical composition.

A method is described for determining the acoustical physical constants of LiNbO[subscript 3] and LiTaO[subscript 3] single crystals. Leaky surface wave (LSAW) velocities are measured using line-focus-beam (LFB) acoustic micrscopy systems, with bulk wave velocities.

In this paper the problem of a finite crack in a strip of functionally graded piezoelectric material (FGPM) is studied. It is assumed that the elastic stiffness, piezoelectric constant, and dielectric permitivity, of the FGPM vary continuously along the thickness of the strip, and that the strip is under an antiplane mechanical loading and in-plane electric loading. By using the Fourier transform, the problem is first reduced to two pairs of dual integral equations and then into Fredholm integral equations of the second kind. The near-tip singular stress and electric fields are obtained from the asymptotic expansion of the stresses and electric fields around the crack tip. It is found that the singular stresses and electric displacements at the tip of the crack in the functionally graded piezoelectric material carry the same forms as those in a homogeneous piezoelectric material but that the magnitudes of the intensity factors are dependent upon the gradient of the FGPM properties. The investigation on the influences of the FGPM graded properties shows that an increase in the gradient of the material properties can reduce the magnitude of the stress intensity factor. [DOI: 10.1115/1.1467091]

The flexural vibration of an elastic beam with surface-bonded films, rotating about its axis, is examined. The beam can function as a gyroscope, detecting the angular rate of the rotation.