Showing papers on "Piezoelectricity published in 1990"

Crack Extension Force in a Piezoelectric Material

Abstract: A conservation law that leads to a path-independent integral of fracture mechanics is derived along with the governing equations and boundary conditions for linear piezoelectric materials. A closed-form solution to the antiplane fracture problem is obtained for an unbounded piezoelectric medium

Theory of laminated piezoelectric plates for the design of distributed sensors/actuators. Part I: Governing equations and reciprocal relationships

Abstract: A piezoelectric laminate theory that uses the piezoelectric phenomenon to effect distributed control and sensing of bending, torsion, shearing, shrinking, and stretching of a flexible plate has been developed. This newly developed theory is capable of modeling the electromechanical (actuating) and mechanoelectrical (sensing) behavior of a laminate. Emphasis is on the rigorous formulation of distributed piezoelectric sensors and actuators. The reciprocal relationship of the piezoelectric sensors and actuators is also unveiled. Generalized functions are introduced to disclose the physical concept of these piezoelectric sensors and actuators. It is found that the reciprocal relationship is a generic feature of all piezoelectric laminates.

Simulation of piezoelectric devices by two- and three-dimensional finite elements

Abstract: A method for the analysis of piezoelectric media based on finite-element calculations is presented in which the fundamental electroelastic equations governing piezoelectric media are solved numerically The results obtained by this finite-element calculation scheme agree with theoretical and experimental data given in the literature The method is applied to the vibrational analysis of piezoelectric sensors and actuators with arbitrary structure Natural frequencies with related eigenmodes of those devices as well as their responses to various time-dependent mechanical or electrical excitations are computed The theoretically calculated mode shapes of piezoelectric transducers and their electrical impedances agree quantitatively with interferometric and electric measurements The simulations are used to optimize piezoelectric devices such as ultrasonic transducers for medical imaging The method also provides deeper insight into the physical mechanisms of acoustic wave propagation in piezoelectric media >

In situ interfacial mass detection with piezoelectric transducers.

Abstract: The converse piezoelectric effect, in which an electric field applied across a piezoelectric material induces a stress in that material, has spurred many recent developments in mass measurement techniques. These methods commonly rely on the changes in the vibrational resonant frequency of piezoelectric quartz oscillators that result from changes in mass on the surface of the oscillator. The dependence of frequency on mass has been exploited extensively for mass measurements in vacuum or gas phase, for example, thickness monitors for thin-film preparation and sensors for chemical agents. Advances in piezoelectric methodology in the last decade now allow dynamic measurements of minute mass changes (< 10(-9) grams per square centimeter) at surfaces, thin films, and electrode interfaces in liquid media as well. Mass measurements associated with a diverse collection of interfacial processes can be readily performed, including chemical and biological sensors, reactions catalyzed by enzymes immobilized on surfaces, electron transfer at and ion exchange in thin polymer films, and doping reactions of conducting polymers.

Characterization of Terfenol-D for magnetostrictive transducers

Abstract: Measurements were made of the piezomagnetic d33 coefficient, the free permeability, μ33T, and the open-circuit elastic compliance coefficient, s33H, of grain-oriented Terfenol-D, Tb0.3Dy0.7Fe1.93, produced by a modified Bridgman technique. Prestress levels to 9500 psi (65 MPa) and magnetic bias fields up to 2200 Oe (175 kA/m) were applied with a laboratory electromagnetic modified so that one pole piece served as a hydraulically actuated piston. The results indicate that d33, μ33T, and s33H are dependent on stress and magnetic field, so that proper mechanical prestress and magnetic bias conditions are critical to the successful use of Terfenol-D in transducers and actuators. Radiated-power limits for underwater acoustic projectors are estimated and compared with those for projectors having lead zirconate titanate (PZT-4) piezoelectric drivers. Terfenol-D based transducers can be as much as 8 dB superior to PZT-4 under low-Q, field-limited conditions (Q=mechanical quality factor).

Electrostriction as the Origin of Piezoelectricity in Ferroelectric Polymers

Abstract: Electric-field-induced changes in thickness have been measured interferometrically for thin films of ferroelectric VDF/TrFE copolymers. For sinusoidal fields high enough to induce ferroelectric switching, the strain x in the thickness direction draws a hysteresis loop of butterfly shape while the electric displacement D draws a conventional square D–E hysteresis loop. The x is shown to be proportional to D2. Their ratio gives the electrostriction constant κ33 ranging from -2.1 to -2.5 m4/C2. Low-field measurements for poled samples with remnant polarization Pr yield a linear relationship between x and D. The piezoelectric constant given by the ratio x/D coincides with 2κ33Pr, implying that the piezoelectric activity of VDF copolymers originates from electrostrictive coupling as does that of traditional ferroelectrics. The role of the dimensional effect in both piezoelectricity and electrostriction is discussed.

Miniature ultrasonic transducer for plaque ablation

Abstract: Ultrasonic apparatus for clot dissolution and plaque ablation includes a radiator for coupling ultrasonic waves into plaque and a piezoelectric crystal, connected with said radiator, for the intravascular generation of ultrasonic waves; said ultrasonic waves being propagated along a longitudinal axis of said piezoelectric crystal and having an inertial node position within said piezoelectric crystal. The piezoelectric crystal is constructed in order to prevent significant power loss caused by a shifting of the inertial node of the generated ultrasonic waves to a position exterior to said piezoelectric crystal due to loading of the radiator caused by the coupling of ultrasonic waves into the clot or plaque.

Finite-element analysis of vibrational modes in piezoelectric ceramic disks

Abstract: The natural vibrational modes of axially symmetric piezoelectric ceramic disks have been calculated by the finite-element method. The disks are of the type used as active elements in compressional wave ultrasonic transducers, and are electrically polarized in thickness with full electrodes on the disk's major faces. To optimize disk geometry for ultrasonic transducer application, the dependence of the vibrational modes on the disk diameter-to-thickness ratio for ratios from 0.2 (a tall cylinder) to 10.0 (a thin disk) has been studied. Series and parallel resonance frequencies for each of the modes are determined through an eigenfrequency analysis, and effective electromechanical coupling coefficients are calculated. The modal displacement fields in the disk are calculated to determine the physical nature of each mode. An analysis of the complete spectrum of piezoelectrically active modes as a function of diameter-thickness ratio is presented for the ceramic PZT-5H, including and identification of radial, edge, length expander, thickness shear, and thickness extensional vibrations. From this analysis, optimal diameter-to-thickness ratios for good transducer performance are discussed. >

Method of making an integrated scanning tunneling microscope

Abstract: An integrated scanning tunneling microscope and an integrated piezoelectric transducer and methods for making both. The device consists of one or two arm piezoelectric bimorph cantilevers formed by micromachining using standard integrated circuit processing steps. These cantilevers are attached to the substrate at one area and are free to move under the influence of piezoelectric forces which are caused by the application of appropriate voltages generated by control circuitry and applied to pairs of electrodes formed as an integral part of the bimorph cantilever structure. The electric fields caused by the control voltages cause the piezoelectric bimorphs to move in any desired fashion within ranges determined by the design. The bimorph cantilevers have tips with very sharp points formed thereon which are moved by the action of the control circuit and the piezoelectric bimorphs so to stay within a very small distance of a conducting surface. The movements of the tip can be tracked to yield an image of the surface at atomic resolution.

Characterization of multiple piezoelectric actuators for structural excitation

Abstract: Past studies have been devoted to the application of surface mounted or imbedded piezoelectric elements for structural excitation and development of theoretical predictions for the response of the structure [E. F. Crawley and I. deLuis, AIAA J. 25 (10), 1373–1385 (1987)]. The thrust of the present work is to determine the range of linearity of structural response due to excitation by pieozoelectric actuators as well as to compare experimentally measured responses to theoretical predictions for the case of a simply supported beam. Emphasis was placed on illustrating distributed excitation, both experimentally and analytically, with multiple independently driven actuators. Results indicate that the theoretical model provides a viable means of determining appropriate locations of piezoelectric actuators for exciting desired modal distributions in the structure. [Work supported by ONR.]

Rectangular parallellepiped resonance method for piezoelectric crystals and elastic constants of alpha-quartz

Abstract: A theory is presented on the free osculations of a rectangular parallelepiped of piezoelectric crystal, by extending the theory of the rectangular parallelepiped resonance (RPR) method to determine elastic constants of crystals, as exemplified by an alpha-quartz specimen. The piezoelectric contribution to resonance frequencies was examined numerically on the specimen, and it was revealed that piezoelectricity causes approximately 5 kHz increase around 1 MHz. The resonance frequencies of the specimen were measured and inverted to elastic constants by least squares inversion. The inversion was by both the previous non-piezoelectric or elastic theory and by the present piezoelectric theory. The use of the non-piezoelectric theory resulted in an overestimate of 2σ or 0.6% in c 11 and underestimate of σ or 6% in c 12. These are the constants expected to be most affected by piezoelectricity. Errors are less than σ in the other constants. During measurement, it was found that the force applied to hold the specimen caused deviations from free oscillation and experimental errors of 5 kHz. The correction for this force is of some importance in RPR studies of piezoelectric crystals.

Fabrication and applications of piezo-and ferroelectric films

Abstract: Different thin film fabrication techniques of ferro- and piezoelectric materials is described with special emphasis on rf sputtering. The relative advantages and disadvantages of oxide and metallic targets, and the control of stoichiometry by adjusting the target substrate distance and composition of target is described. The possible applications of ferroelectric films in non-volative memories, pyroelectric detectors, electro- and acousto-optic devices is briefly presented. The applications of these films in the fabrication of integrated Surface Acoustic Wave (SAW) devices on Silicon is discussed in some detail. Theoretical calculations of SAW transduction in layered media is used to compare selected ferroelectric (PZT, PbTiO3. LiNbO3 and BaTiO3) and piezoelectric (ZnO, AIN and CdS) films on silicon for their use in SAW devices.

Ferroelectric thin films

Abstract: Summary form only given. A very wide range of both vapor- and liquid-phase deposition techniques were applied to produce crystalline films of composition in a lead zirconate:lead titanate solid solution system. At compositions close to the morphotropic phase boundary, a regimen which shows excellent piezoelectric properties in the bulk ceramic films with high permittivity ( epsilon /sub 33/-1350 epsilon /sub 0/) at room temperature and large switchable electric polarization (P/sub r/ approximately 35 mu C/cm/sup 2/) were fabricated by several groups. Progress toward the use of ferroelectric films, in combination with silicon micromachining, for a wide range of piezoelectric microsensors, micro-actuators and micromotors is reviewed. In view of the very high electric strength alternative electrorestrictive electromechanical coupling appears attractive. >

High frequency-high temperature ultrasonic transducers

Abstract: Ultrasonic testing is a promising NDE technique for ceramic structural components. The lifetime of such components is controlled by defects and flaws. The critical flaw sizes for high performance ceramics are 25 µm and to detect such small flaws, the frequency of the transducers has to be >30 MHz [1–4]. Such transducers are usually made from ZnO, LiNbO3, LMN composites [5], and PVDF piezoelectric materials However there are no reports of aluminium nitride (AIN) films being used for such applications In this paper the piezoelectric and dielectric properties of A1N films and their application to high frequency devices are discussed and compared with the conventional materials.

Analysis of piezoelectric bulk-acoustic-wave resonators as detectors in viscous conductive liquids

Abstract: An analytical solution for the resonance condition of a piezoelectric quartz resonator with one surface in contact with a viscous conductive liquid is presented. The characteristic equation that describes the resonance condition and accounts for all interactions including acoustoelectric interactions with ions and dipoles in the solution is obtained in terms of the crystal and liquid parameters. A simple expression for the change in the resonance frequency is obtained. For viscous nonconductive solutions, the frequency change is reduced to a relationship in terms of the liquid density and viscosity. For dilute conductive liquid, the change in frequency is derived in terms of the solution conductivity and dielectric constant. The boundary conditions for the problem are defined with and without the electrical effects of electrodes. Experiments were conducted with various viscous and conductive chemical liquids using a fabricated miniature liquid flow cell containing an AT-cut quartz crystal resonator. The results, which show good agreement with the theory, on the use of quartz crystal resonators as conductivity and/or viscosity sensors are reported. >

Material constants of new piezoelectric Ta2O5 thin films

Abstract: The first measurement of the material constants of Ta2O5 thin films is described. x‐axis‐oriented Ta2O5 thin films were deposited on fused quartz using the dc diode sputtering method. The material constants were determined from the phase velocity and the electromechanical coupling constant of the bulk waves and the surface acoustic waves propagating on the layered substrate.

Thin-film ZnO as micromechanical actuator at low frequencies

Abstract: A new model is proposed for the low-frequency piezoelectric activity of ZnO films grown on CVD SiO2. In this MOS structure, with ZnO as the semiconductor, a depletion layer is induced by means of a d.c. bias voltage. Using standard semiconductor theory, an expression is derived relating the electric field in this depletion layer with the driving a.c. and d.c. voltages. Due to the built-in charge at the ZnO-SiO2 interface, a depletion layer exists, even when no d.c. bias is applied. We measured the vibration amplitude at resonance of the tip of a silicon cantilever, upon which the MOS structure was deposited, as function of a.c. and d.c. voltages. The results show good agreement with calculated curves. Therefore, it can be concluded that thin-film ZnO can be used as a piezoelectric actuator for micromechanical devices working at low frequencies.

Ceramic particle size dependence of dielectric and piezoelectric properties of piezoelectric ceramic‐polymer composites

Abstract: Composites with 0‐3 connectivity were fabricated from barium titanate and phenolic resin powders. These composites were investigated for dielectric and piezoelectric properties with the active particle size. Under the condition of the same density and ceramic/polymer volume ratio, the dielectric constants and piezoelectric coefficients of composite increase as the ceramic particle size in composite increases. The surface layer model was used to explain these phenomena in our composite system and was confirmed experimentally. The thickness and dielectric constant of the surface layer of the powder prepared by grinding the sintered barium titanate ceramics were 1.59 μm and 105. When the ceramic particle size is larger than about 100 μm, the properties of the composite were nearly independent of size.

High frequency, high temperature ultrasonic transducers

Abstract: Piezoelectric films of 100% (002) oriented AIN were deposited on platinum-coated quartz, sapphire and LMN ceramics via a CVD process. The growth rate achieved was > 20 nm s −1 at 1020–1040 K. These films had the highest figure of merit (125) and dielectric strength ( > 2 × 10 7 V cm −1 ) of any known piezoelectric material. The relative dielectric constant is ∼8.6 and the thickness coupling coefficient, K t , 20%. The films exhibit ultrasonic response for temperatures ⩽1430 K. 30 MHz compressional-wave transducers were developed on quartz delay-rods with signal strength comparable to ZnO devices. Non-cooled, high temperature ultrasonic devices were developed using the oriented AIN films.

Modelling of piezoelectric actuator dynamics for active structural control

Abstract: The paper models the effects of dynamic coupling between a structure and an electrical network through the piezoelectric effect. The coupled equations of motion of an arbitrary elastic structure with piezoelectric elements and passive electronics are derived. State space models are developed for three important cases: direct voltage driven electrodes, direct charge driven electrodes, and an indirect drive case where the piezoelectric electrodes are connected to an arbitrary electrical circuit with embedded voltage and current sources. The equations are applied to the case of a cantilevered beam with surface mounted piezoceramics and indirect voltage and current drive. The theoretical derivations are validated experimentally on an actively controlled cantilevered beam test article with indirect voltage drive.

Optimizing ultrasonic transducers based on piezoelectric composites using a finite-element method

Abstract: A novel approach to understanding the vibratory behavior of composite piezoelectric materials is proposed. Elementary ceramic rods, and the effects of their width-to-thickness (W/T) ratio are studied. A model based on the finite-element methods is used. Some experimental results that agree well with the computed data are presented. Plots of resonant frequencies and coupling coefficients versus W/T are given that can be used in transducer design. >

A planar process for microfabrication of a scanning tunneling microscope

Abstract: With decreasing size, a scanning tunneling microscope (STM) becomes less sensitive to vibrations and thermal drift and easier to manufacture by batch fabrication techniques. An integrated-circuit-compatible planar process has been developed to fabricate arrays of STMs on Si wafers. Using planar technology, it is possible to integrate the tunneling tip, the actuation mechanism and (if desired) the counter electrode on a Si ‘chip’. The actuator mechanism is a cantilevered bimorph consisting of alternating layers of metal and piezoelectric zinc oxide. Each metal layer is divided into two electrodes that can be individually addressed, thereby enabling the cantilever to move in three orthogonal directions. The thin (3 μm) piezoelectric layers allow low voltage (< 30 V) operation. The theoretical response of the actuator is 2500 A/V in z, 104 A/V in y and 14 A/V in x. The device has been successfully fabricated and its operation has been demonstrated by imaging the surface of graphite with atomic resolution. A planar process for microfabrication of an integrated STM has been developed and operation of this ‘STM on a chip’ has been demonstrated by imaging the surface of graphite with atomic resolution. The devices are small (typically 8 × 200 × 1000 μm) and are fabricated in large batches of over 200 cantilevers per wafer. By utilizing the bimorph action of a cantilever made of metal and piezoelectric ZnO, it is possible to achieve three-dimensional scanning motions using low-voltage feedback circuits. Initial results show a z-sensitivity of up to 2500 A/V for the cantilever, which is sufficient to use the device as an STM and obtain atomic resolution images. Processes for growing a sharp tunneling tip on the cantilever are being prepared and we envision integrating onboard signal-processing circuitry with the device. The piezoelectric bimorph cantilever with three-dimensional motion is likely to have numerous and diverse applications in the field of microfabrication.

Electromagnetic radiation from doubly rotated piezoelectric crystal plates vibrating at thickness frequencies

Abstract: Exact solution of the three‐dimensional linear equations of piezoelectromagnetism is obtained for doubly rotated piezoelectric crystal plates surrounded by vacuum and excited by face traction. A generalized Poynting’s theorem is derived for general media in which electromagnetic and mechanical fields interact with each other. For linear piezoelectric crystals it is shown that the generalized theorem may still be interpreted as an energy theorem, and hence densities of energy stored in the electric, magnetic, and elastic strain fields can be identified. Radiated power, per unit surface area and averaged over the period, and induced strain and electric fields in the middle plane of the plate are calculated for doubly rotated quartz plates whose cut orientations follow the upper and lower loci of zeros of the first‐order temperature coefficient of frequency of the x1 ‐thickness‐shear mode. Quality factors and partition of stored energies are also examined.

Piezoelectric device and related converting devices

Abstract: A piezoelectric device includes a first electrode, a second electrode disposed in opposing, spaced relation to the first electrode, a ferroelectric liquid crystal interposed between the first and second electrodes, a first alignment layer formed between the first electrode and the ferroelectric liquid crystal, and a second alignment layer formed between the second electrode and the ferroelectric liquid crystal.

Measuring and controlling deposition on a piezoelectric monitor crystal

Abstract: The thickness and rate of growth of a deposited film is monitored using a piezoelectric crystal sensor such as an AT-cut plano-convex crystal. The frequencies of the fundamental frequency and another resonance mode are measured prior to deposition, and the change of these two frequencies is monitored during deposition. The areal mass density of the deposited material is determined from these two resonance frequencies for the uncoated quartz crystal and for the crystal during deposition. A frequency generator provides accurate sweeps of frequency which are applied to the crystal, and the crystal response is supplied to a phase detector to identify the positions of the resonance frequencies. The acoustic impedance ratio Z of the deposited material relative to the fresh crystal is computed from the resonance frequencies for the coated and uncoated crystal, by applying the modal equations for AT-cut plano-convex quartz crystal and Lu-Lewis relation. From the frequency shifts and acoustic impedance ratio, and areal mass density can be calculated. The same crystal can be used to control the growth rate of several successive layers.

Piezoelectric/electrostrictive film type actuator

Abstract: PURPOSE: To obtain a piezoelectric/electrostrictive film type actuator having the high speed of response and large generating force by laminating a first electrode film, a piezoelectric/electrostrictive film and a second electrode film onto a ceramic substrate. CONSTITUTION: A lower electrode film 4, a piezoelectric/electrostrictive film 6 and an upper electrode film 8 are laminated successively onto one surface of a ceramic substrate 2. The lower and upper electrode films 4, 8 are extended from the end section of the piezoelectric/electrostrictive film 6 respectively, lead sections 4a, 8a are shaped, and electricity is conducted through each electrode film 4, 8 through these lead sections 4a, 8a. The electric-field induced strain of the piezoelectric/electrostrictive film 6 is induced by conduction, and flexing displacement in the direction vertical to the board surface of the ceramic substrate 2 or generating force is developed by the transversal effect of the strain. Accordingly, large displacement is acquired at low driving voltage, and a piezoelectric/electrostrictive film type actuator, the speed of response of which is increased and the degree of integration of which can be improved, is obtained. COPYRIGHT: (C)1991,JPO&Japio