Showing papers on "Piezoelectricity published in 1988"

Domain wall excitations and their contributions to the weak‐signal response of doped lead zirconate titanate ceramics

Abstract: The ac field dependence of the polarization and strain responses of three different compositions of doped lead zirconate titanate ceramics were measured for samples in both the poled and the depoled states. The results indicate that a reversible domain wall excitation exists which contributes to the weak‐signal response of these materials. Irreversible domain wall motion can be excited within the frequency range measured by applying a field above a threshold field, which is much smaller than the coercive field. Therefore, the weak‐signal linear dielectric, piezoelectric, and elastic coefficients of these materials may not provide a suitable description of their behavior when the external applied field exceeds this threshold field. All the observed phenomena can be explained by thermally activated domain wall fluctuations and nucleations.

Surface acoustic wave propagation on lead zirconate titanate thin films

Abstract: Piezoelectric activity in reactively sputtered lead zirconate titanate [Pb(Zr,Ti)O3 or PZT] thin films has been confirmed through the fabrication of surface acoustic wave delay lines on poled polycrystalline films of PZT deposited on glass substrates. Films of varying thickness ranging from 3.4 to 6 μm show a dispersion in resonant frequency for interdigital transducers designed to resonate at 44 MHz on bulk PZT material. The electromechanical coupling coefficient k2 was in the range 0.57–0.79% for hk=0.21–0.37.

A Simple Way to Reduce Hysteresis and Creep When Using Piezoelectric Actuators

Abstract: We present a simple way to compensate for hysteresis and creep in piezoelectric actuators. By inserting a capacitor in series with the piezoelectric actuator, we find a reduction in the size of the hysteresis loop. For a suitable small capacity in series, creep is eliminated.

Analytical Uses of Piezoelectric Crystals: A Review

Abstract: I. INTRODUCTION Piezoelectricity was first discovered in 1880 by the brothers Pierre and Jacques Curie.1 They observed that when pressure is applied to the surface of a quartz crystal an electrical...

Air buoyant piezoelectric polymeric film microphone

Abstract: Piezoelectric polymer film, when conformably adhered to inner or outer surfaces of an inflated balloon, functions as a microphone when the pressure of sound waves causes the film to vibrate and generate an electrical signal. The film may be in the form of an helical strip, individual strips electrically serially connected, or may itself form the inflatable material. A receiving device is electrically coupled with the electrodes formed on the piezoelectric film for processing the electrical signals generated by the vibrating piezoelectric polymer film.

Mechanical Damper Using Piezoelectric Ceramics

Abstract: A piezoelectric ceramic mechanical damper with a controllable damping factor has been developed. Mechanical vibration energy is transformed through the piezoelectric effect into electrical energy which is dissipated through an external resistance. A significant variation in damping factor is realized when the external resistance is changed.

Effective elastic and piezoelectric constants of superlattices

Abstract: It is shown that the determination of a set of equivalent elastic constants for periodically layered anisotropic materials to predict the acoustic performance in the long wavelength limit can be extended on the one hand to include piezoelectricity of the component materials and on the other to allow multiple layers within each period. The necessary matrices are shown in a form which can be programmed easily. The validity of the use of these equivalent constants is shown by comparison of results obtained with them and with an exact layer‐by‐layer calculation both for bulk‐wave slowness surfaces and for surface‐wave propagation velocities in two quite different examples of material combinations.

PZT-based multilayer piezoelectric ceramics with AgPd-internal electrodes

Abstract: The advantages of piezoelectric actuators are often opposed by one decisive handicap: their high control voltage. Piezoelectric multilayer ceramics do not show this disadvantage. Their highest possible deflection can be gained with voltages between 5 and 15 V which are common in today's electronics.

Energy-trapping-by-frequency lowering-type piezoelectric resonance device

Abstract: An energy trapping type piezoelectric resonance device utilizing higher-order harmonics of the thickness extensional vibration mode comprising a body formed of a piezoelectric material and three or more electrodes arranged overlapping with each other and separated by the piezoelectric material layers in the direction of thickness of the body, wherein respective portions of the piezoelectric material layers interposed between the electrodes are polarized and at least respective portions of the piezoelectric material layers which are not interposed between the electrodes is polarized.

Piezoelectricity and pyroelectricity in polymers

Abstract: Piezoelectric activities of polymers arise from poling-induced orientation of dipoles (class 1) and uniaxial orientation of chiral molecules (class 2). The former accompanies pyroelectricity while the latter produces pyroelectricity if the spontaneous shear strain is incorporated. Strong activities have been found in class 1, namely, ferroelectric polymers, polar polymers having large dielectric relaxations, and composites containing a large amount of PZT. Poling conditions, factors that determine piezoelectric and pyroelectric activities, and their basic mechanisms are discussed. >

Method for electric field orientation of liquid crystal polymers and oriented materials of liquid crystal polymers obtained by the method

Abstract: This invention relates to a method for electric field orientation of liquid crystal polymers and oriented materials of liquid crystal polymers obtained by the method. This electric field orientation method comprises applying a pulsating electric field which is predominantly unidirectional and whose magnitude is varying periodically or non-periodically to a liquid crystal polymer capable of forming an optically anisotropic melt phase. The oriented material of liquid crystal polymer thus obtained has been unidirectionally oriented and polarized. This oriented, polarized material of liquid crystal polymer can be utilized as a piezoelectric material, pyroelectric material, electret material, non-linear optical element or the like.

Fiber-optic sensing of electric field components

Abstract: Symmetry properties of the converse piezoelectric effect are investigated for their use in fiber-optic sensing of individual electric field components. Three basic sensor designs are analyzed in detail. Suitable sensor materials are identified and relevant material properties are discussed. The sensitivity of the sensor to a specified field component is experimentally verified. A dynamic range of approximately 5 orders of magnitude is found for frequencies in the kilohertz range. The sensor concept is compared to electrooptic sensors.

Corona poling of PZT ceramics and flexible piezoelectric composites

Abstract: In the conventional poling method, piezoelectric ceramics and composites are poled by applying a large D.C. voltage directly to the sample. The poling of composites having a polymer matrix with 0–3 connectivity is especially difficult because the electric field within the high dielectric constant grains is far smaller than in the low dielectric constant polymer matrix. Therefore, very large electric fields are required to align the piezoelectric grains. Unfortunately, such large electric fields often cause localized dielectric breakdown of the samples which effectively prevents further poling.

Laminated piezoelectric keyboard

Abstract: The keyboard comprises piezoelectric crystal elements arranged between laminates provided with conducting strips. A voltage is generated when pressure is applied to the elements. The keyboard is tensionless in its rest state and contains no unwanted air spaces.

Development of Piezoelectric Technology for Applications in Control of Intelligent Structures

Abstract: This work presents analytical techniques, with experimental results for use with piezoelectric actuators as elements of intelligent structres. Mechanical models for the interaction of piezoelectrics with one- and two-dimensional structures are derived. In addition, a model coupling the electrical and mechanical properties of the piezoelectric is presented. This model is used to derive optimal resistive and tuned electrical circuits to maximize energy dissipation in the structure. These results are implemented on a prototype space-truss. Finally, a technique for embedding piezoelectrics inside laminated composite structures is presented.

Pressure sensor with a ferroelectric liquid crystal layer

Abstract: A new type of pressure sensor is disclosed here. The sensor is composed of a pair of glass substrates and a ferroelectric liquid crystal which is interposed between the substrates and exhibits piezoelectric effect. Because of crystalline property in liquid phase, the piezoelectric medium can be easily disposed and aligned between the substrates in light of the orientation of the surface contiguous to the liquid crystal layer.

Piezoelectric brake device

Abstract: A brake device for producing a braking force by pressing a friction member against a member to be braked in response to a deformation produced by applying a DC voltage to a piezoelectric element array including a stack of piezoelectric elements. A plurality of piezoelectic element arrays are coupled by a displacement transmission mechanism such that deformations produced by the piezoelectric element arrays are added together.

Energy-trapping-type piezoelectric resonance device

Abstract: An energy trapping type piezoelectric resonance device utilizing the mode of thickness extensional vibration comprises a plate-shaped body of a piezoelectric material and three or more electrodes provided to be opposed to each other through peizoelectric material layers in the direction of thickness of the body. At least one of the electrodes is provided to be smaller in area than the major surfaces of the body, to be capable of energy trapping.

Easy method to characterize a piezoelectric ceramic tube as a displacer

Abstract: We describe a useful method using a commercial linear variable differential transformer as a detector to characterize a piezoelectric ceramic tube as a displacer. Results show some inhomogeneity in the reduction of the voltage‐to‐displacement conversion of commercial piezoelectric tubes as a function of temperature from room to liquid‐helium temperature.

Development and experimental verification of a two-dimensional numerical model of piezoelectrically induced threshold voltage shifts in GaAs MESFETs

Abstract: The results of a combined experimental and analytical investigation of the effects of mechanical stress on DC electrical parameters, particularly threshold voltage, in MESFETs are reported. The theoretical aspect of this study involves a two-dimensional finite-element simulation of the device structure on which measurements were made. The substrate stresses and resultant piezoelectric charge distributions calculated in this study take into account the two-dimensional nature of the geometry of the gate. The experimental portion of this study involves measurement of DC parameters of devices using external mechanical loads that simulate mechanical stresses that arise during device processing. Measurements under applied loads of both signs and on devices of two different orientations confirm the existence of a piezoelectrically induced threshold voltage shift. A comparison between the approximate line load method of modeling substrate stress fields, and the finite-element method used in this study shows that the piezoelectric charge densities predicted by two models are substantially different. This results from the fact that the simplifying assumptions used to construct the line load model are inappropriate for accurately determining stress fields beneath micrometer and submicrometer gates. Good agreement was obtained between measured threshold voltage shifts and those predicted by the finite-element method model. The results show the need for accurate modeling of mechanical stresses when attempting to model piezoelectric effects. >

Ultrasonic lithotresis apparatus

Abstract: A large number of piezoelectric elements are arranged in a mosaic pattern on a spherical surface so that ultrasonic waves generated by the elements converge on a single point. The arrangement of the elements constitutes a transducer. With the transducer applied to a subject through a liquid bag filled with water, ultrasonic shock waves from each piezoelectric element are concentrated on a lithotresis object, or a calculus so as to break it. The ultrasonic shock waves are generated by applying driving impulses (voltage) to each piezoelectric element. In order to locate the calculus, the transducer is coupled to an ultrasonic diagnosis apparatus having a mechanical scanning type ultrasonic probe. The piezoelectric elements have resonance frequencies set such that the piezoelectric element positioned at the center of the transducer has the lowest resonance frequency and the resonance frequency of each piezoelectric element is increased in accordance with its distance from the center. Thus, the frequency range of vibration of the transducer is broadened so that the ultrasonic shock waves become low in negative sound pressure and narrow in pulse width at the point of convergence.

Determination of electromechanical coupling coefficients in transducer materials with high mechanical losses

Abstract: An important problem in transducer design is the accurate determination of electromechanical coupling coefficients for piezoelectric materials The authors report on novel methods for determining both k/sub t/ the thickness mode coefficient, and k/sub 31/, an important parameter for transducer arrays The coupling coefficients are computed near piezoelectric resonances using Krimholtz-Leedom-Matthaei (KLM) equivalent circuit models These models have been modified to account for the mechanical losses of the material through an effective attenuation coefficient which can be estimated independently of the coupling coefficient This measurement theory is applied to three different transducer materials: PVDF (polyvinylidene fluoride), PZT5A and a PZT (lead zinc titanate)/epoxy composite >

Compensating sensor device for a charge amplifier circuit used in piezoelectric hydrophones

Abstract: To compensate for the effect of external parameters on piezoelectric sensors connected to a charge amplifier, a small portion of this sensor is used to form the feedback capacitor of the amplifier. These parameters then have the same effect on the sensor and on the capacitor, thus making it possible to provide compensation to hydrophones made of piezoelectric polymer material.

Ultrasonic Motors Using Piezoelectric Ceramic Multi-Mode Vibrators

Abstract: The purpose of this paper is to report development of an ultrasonic motor using piezoelectric ceramic multi-mode vibrators of circular or annular plates, in which degenerate horizontal vibration modes of the same or different form are used. Some constructions of the motor and its experimental characteristics are presented. The ultrasonic motor investigated herein shows special merit in its thin construction.

Fiber-optic electric field sensor with piezoelectric body sensor

Abstract: A fibre-optic sensor for measuring a particular directional component of an electric field comprises a piezoelectric body (4) and a glass fiber (5a) which is rigidly connected to the piezoelectric body (4) in a given length section. A crystal class and a crystallographic orientation of the piezoelectric body (4) is selected in such a manner that only the directional component which is parallel to a given body axis (h) of the piezoelectric body (4) causes a change in a length of the glass fiber (a) by means of an inverse piezoelectric effect. The change in length is measured interferometrically. In a preferred embodiment, the piezoelectric body has the shape of a disk, of a plate or of a hollow cylinder.

Method of making piezoelectric composites

Abstract: A method of fabricating a piezoelectric composite comprising an array of piezoelectric elements and a reinforcement structure embedded in a material. The method includes the step of forming the reinforcement structure prior to assembly with the piezoelectric elements, the reinforcement structure defining an array of holes for receiving the piezoelectric elements.

Ultrasonic driving gear

Abstract: PURPOSE:To reduce the abrasion of a driven unit and drive it smoothly, by applying pressure to a piezoelectric unit strongly with long and short metallic blocks on both sides of the piezoelectric unit, and with a bolt. CONSTITUTION:On both the sides of ring-formed piezoelectric elements 1-2 consisting of piezoelectric ceramics and the like, electrodes 3-4 are respectively arranged, and the elements are placed between the long metallic block 6 and short metallic block 7 of circular truncated cones, and are fastened to be fixed to compose an asymmetrically bolted Langevin type piezoelectric oscillator 8. To the elements 1-2 of the oscillator 8, AC voltage is applied from an oscillating unit, and a travelling wave is generated. Because pressure is strongly applied to both the sides of the metallic blocks 6-7 with a bolt 10, torsional oscillation is generated on the traveling wave by the screws 11a-11b, and vertical oscillation and radial oscillation are combined with each other to form the traveling wave in the circumferential direction. Then, by permitting a driven unit to come in contact with the section of said oscillator 8, the driven unit can be driven.