Showing papers on "Piezoelectricity published in 1976"

Electromechanical properties of polarized polyvinylidene fluoride films as studied by the piezoelectric resonance method

Abstract: The piezoelectric resonance was observed in free vibrators of uniaxially oriented and biaxially oriented polyvinylidene fluoride films polarized at high electric fields. Using the piezoelectric resonance method, piezoelectric and elastic constants, and electromechanical coupling factors of such films were determined at high frequencies (20 kHz–30 MHz) in the temperature range −170–100 °C. For the uniaxially oriented films, the coupling factors k33 and k32 are independent of temperature, while k31 increases noticeably above the primary dispersion temperature. The value of k33 is about 0.2, one of the largest values ever reported for piezoelectric polymers. Similar results were obtained for the biaxially oriented films. The temperature dependence of elastic and piezoelectric constants of the uniaxially oriented films is interpreted by a model in which the crystalline and amorphous phases are combined in series along the stretching direction and in parallel along the perpendicular directions. The origin of t...

Electromechanical Properties in the Composites of Epoxy Resin and PZT Ceramics

Abstract: The complex dielectric, elastic and piezoelectric constants were measured for the composites of epoxy resin and ferroelectric PZT ceramics at 10 Hz as a function of temperature, and the magnitudes and loss tangents of these constants were compared with the theoretical predictions. The piezoelectric constants for a two phase system with piezoelectric spherical inclusions were expressed in terms of the properties of the constituents by use of the known expressions of the dielectric and elastic constants. The observed values of the d-constant (electric displacement/stress) were about 3/4 of the predicted. In the local mode dispersion region of epoxy resin near -30°C, the g-constant (electric field/stress) showed a larger temperature variation than the theoretical prediction.

Theory of piezoelectricity in nematic liquid crystals, and of the cholesteric ordering

Abstract: A statistical-mechanical theory of the elastic constants of a liquid crystal based on the Onsager expansion is reexamined, with emphasis on the terms linear in the gradients of the director. This gives a microscopic theory of the piezoelectric effect in nematic liquid crystals, and of the spontaneous twisting of a cholesteric. Model cases of tapered rods, bent rods, and threaded rods are considered.

Piezoelectricity and Pyroelectricity of Polymers

Abstract: This article surveys theoretical and experimental work on piezo- and pyroelectricity of polymers in the 1970's with special emphasis on the origins of these properties. The origins are classified into three types: (A) internal strain (§2), (B) strain- and temperature-dependences of spontaneous polarization (§3), and (C) elastic and/or dielectric heterogeneity of a system with embedded charges (§4). The origin of piezo- and pyroelectricity of poly(vinylidene fluoride) is discussed as a typical example of electret (§5). Piezoelectric relaxations of polymers are discussed in some detail (§6). Methods of measurements of piezo- and pyroelectric constants of polymer films (§7) and applications of polymer films as new transducer materials (§8) are briefly reviewed.

Magnetoelectricity in piezoelectric-magnetostrictive composites

Abstract: In a composite material consisting of a piezoelectric and a piezomagnetic phase which are mechanically coherent, electric and magnetic fields are converted into each other by a two-step process involving mechanical deformation as the intermediate step. We have developed such a material on the basis of a Co ferrite-Ba titanate eutectic which is unidirectionally solidified so as to obtain an aligned two-phase structure. The maximum value of the magneto-electric effect obtained at present is 0.13 V/cm Oe at room temperature. The dimensionless quantity 4π(dP/dH) is 0.2 or a factor of 200 higher than the best single-crystal material known at room temperature (Cr2O3).

Piezoelectric driven Kelvin probe for contact potential difference studies

Abstract: A convenient piezoelectric driven Kelvin probe for the measurement of work function changes is described. The probe has a simple construction, is small, bakeable, and can be mounted on any 35‐mm‐i.d. UHV flange. As the piezoelectric device is inside the vacuum chamber, only one electrical feedthrough is needed for operating the probe. The distance between reference electrode and sample can be varied within ±0.5 mm simply by applying a dc voltage to the piezoelectric device in addition to the ac oscillator‐driving voltage, not requiring any mechanical driving and feedthrough provisions. The probe was tested studying the adsorption of O2 on Pt(111). The sensitivity for contact potential measurements is better than 0.1 mV at a response time of 10 sec.

Transducer having piezoelectric film arranged with alternating curvatures

Abstract: A transducer of the type converting between electrical and mechanical energy by means of the piezoelectric effect in a supported sheet of uniaxially oriented, electrically polarized thin high polymer film such as polyvinylidene fluoride, having surface electrodes thereon for connection to an electrical circuit. The transducer is characterized by an arrangement of the piezoelectric film into a series of elongate curved cylindrical segments of alternating sign of curvature, with the surface electrodes on the film being divided in selected locations between adjacent segments. A useful level of elastic stability is achieved without using a static pressure difference on the film, good electromechanical coupling is attained, and the individual transducer elements formed by the divided surface electrodes may be usefully interrelated electrically to substantially cancel even order harmonic distortion and enhance linearity of operation.

Zinc-oxide thin-film surface-wave transducers

Abstract: The piezoelectric film layer transducer represents the most efficient method for generating and detecting surface acoustic waves on nonpiezoelectric substrates. ZnO, which has a strong piezoelectric effect and can readily be sputtered as an oriented crystalline composite on a wide variety of substrates, is a natural choice as the piezoelectric film layer. This paper summarizes a body of knowledge which has been developed on the characteristics of transducer quality ZnO film layers, and focuses attention on those sputtering parameters and microstructural properties which characterize a superior surface-wave transducer film. Requisite sputtering conditions are high substrate temperatures (150-300°C), modest deposition rates (0.5-1.0 µm/h), low background vapor pressures (<5 µm Hg) and an ultraclean vacuum system. Transducer quality surface-wave films are characterized by their optical clarity, high density, smooth surface, small crystallite size, and well-oriented crystallite axes. Such ZnO films will play an important role in future surface acoustic wave device technology.

New piezoelectric crystal: Synthetic fresnoite (Ba2Si2TiO8)

Abstract: A fresnoite (Ba2Si2TiO8) single crystal was grown from the melt by the Czochralski method. Synthetic fresnoite has an electromechanical coupling factor in the thickness shear mode of k15=0.28, and a resonance‐frequency temperature coefficient in this mode of Tfr=−33 ppm/°C. Fresnoite is considered to be superior to Ba2Ge2TiO8 for various piezoelectric applications because of the absence of microtwins observed in Ba2Ge2TiO8.

Characterization and piezoelectric activity, of stretched and poled poly(vinylidene fluoride). Part I: Effect of draw ratio and poling conditions†

Abstract: A number of investigators have reported on the high degree of piezoelectricity manifested by oriented films of poly(vinylidene fluoride) (PVF2) To develop applications for this piezoelectric effect, our laboratory is involved in a systematic investigation of the factors responsible for this remarkable behavior of PVF2 In a unique high-speed process, commercial PVF2 film was uniaxially stretched to a series of draw ratios ranging up to 7/1 The resulting films were characterized by techniques involving infrared spectroscopy, density, birefringence, sonic modulus, X-ray diffraction, and dynamic mechanical response The films were then poled at various electric field strengths, temperatures, and times Correlations have been made between draw ratio, physical properties, poling conditions, and piezoelectric activity of the films It was found that the piezoelectric activity increased to limiting values with draw ratio, poling voltage, poling temperature, and poling time It was evident that for PVF2 film a significant amount of oriented phase I crystalline material is required for high degrees of piezoelectric activity The Appendix gives the apparent rate dependence observed for the piezoelectric effect when signal is measured with a voltage sensor of relatively low input impedance

Finite Element Approach for a Piezoelectric Circular Rod

Abstract: Absiracr-Circular rods and plates are widely used for ultrasonic transducers, resonators, and electromechanical filters. A finite element formulation is presented for the axisymmetric vibrations of a piezoelectric or electrostrictive circular rod of finite length. The computer program developed is capable of coping with composite resonators of arbitrary profile, The procedure is successfully used to evaluate the vibrational characteristics o f a uniform circular rod and plate, a tapered ring resonator, and a Langevin-type transducer. The natural frequency and the corresponding mode and the input admittance at the electrical terminals are demonstrated. The results thus obtained are compared with the analytical as well as the experimental results in cases where they are available. Reasonable agreement which supports the present technique is found.

Persistent polarization in poly(vinylidene fluoride). III. Depolarization and pyroelectricity of poly(vinylidene fluoride) thermoelectrets

Abstract: Persistent polarization in poly(vinylidene fluoride) thermoelectrets prepared under high electric field has been studied by measurements of depolarization and pyroelectricity. Various polarizations are examined in detail; the polarizations related to a characteristic molecular motion near 60°C and the polarizing temperature are not responsible for the major piezoelectric effect in β-form electrets. The piezoelectricity is attributed to a polarization appearing near the melting temperature. The persistent polarization corresponding to d31 of 2 × 10−11 coul/N is about 5 × 10−6 coul/cm2. The pyroelectricity of β-form electrets is linearly correlated with the piezoelectricity.

Piezoelectric Effect in Stretched and Polarized Polyvinylidene Fluoride Film

Abstract: The mathematical expressions for the piezoelectric stress-constant, the electrostrictive constant, and the dielectric constant, all as complex quantities, have been derived by means of non-equilibrium thermodynamics on the assumption that the dipole orientation produces a residual polarization. The temperature dependence of these quantities for electretized polyvinylidene fluoride films has been experimentally determined at a frequency of 20 Hz over the temperature range from -100°C to 100°C. The residual polarization calculated from these experimental data is of the order of 103 esu/cm2. This polarization presumably originates from the aligned dipoles associated with the crystalline region. Measurements during poling process show a gradual two-step increase of the residual polarization.

Piezoelectric study of poling mechanism in lithium niobate crystals at temperature close to the curie point

Abstract: Using a piezoelectric technique, we show that when cooling a lithium niobate crystal through its curie point, three different mechanisms may lead to the orientation of its spontaneous polarization: the first one is the well known effect of an applied electric field. The second is the effect of a thermal gradient and the third one is related to the existence of a composition gradient. These last two effects are reported for the first time. All these mechanisms are shown to be effective only in a very narrow temperature range, around the Curie point (of the order of 3° C). Possible explanations for the last two effects are finally given and discussed.

Ultrasonic ceramic microphone

Abstract: An ultrasonic ceramic microphone having a wide operating frequency range, including piezoelectric ceramic plates disposed on upper and lower surfaces of a metal plate, wherein the ultrasonic ceramic microphone is operated near two or three adjacent resonance frequencies and in a frequency band covering those resonance frequencies, of a fundamental wave and respective higher order harmonics of the deflection vibration of a transducer comprising the metal plate and the pair of piezoelectric ceramic plates.

Multi-layered substrate for a surface-acoustic-wave device

Abstract: This invention provides a multi-layered substrate for a surface-acoustic-wave device which substrate comprises a piezoelectric layer on a base, the temperature coefficient of a phase velocity of the surface-acoustic-wave in the piezoelectric layer being different from that of the base, the piezoelectric layer having a thickness less than a wavelength of the SAW. This multi-layered substrate can have a large electromechanical coupling and controlled temperature coefficient of the phase velocity.

Experimental broadband ultrasonic transducers using PVF2 piezoelectric film

Abstract: : Broadband ultrasonic transducers using PVF2 piezoelectric plastics films, combining efficient transduction with extremely wide and uniform passbands, have been fabricated using very simple procedures without any critical tolerances. Frequency spectra of impulsed transducers using films of 25 and 50 micron thickness, centered at 10 and 5 MHz, respectively, are shown.

The piezoelectric constant for disperse systems.

Abstract: A mathematical expression is derived for the piezoelectric constant of a disperse system in which piezoelectric, anisotropic, spherical particles are uniformly dispersed in a nonpiezoelectric, isotropic, continuous medium.For the case when the sphere has the face-shear-type piezoelectricity and the system is incompressible, the piezoelectric strain constant d14 for the disperse system is given as where φ is the volume fraction of spheres, d14II the piezoelectric strain constant of the sphere, e the dielectric constant, G the elastic constant, and the superscripts I and II refer to the medium and sphere, respectively.For the case when the sphere is extremely rigid and has length-expansion and thickness-expansion types of piezoelectricity, the piezoelectric strain constants d31, d32, d33 under the approximation φ<<1 are given as where KI is the bulk modulus of the medium and α=4GI/3KI.

Current developments in piezoelectric applications of ferroelectrics

Abstract: The major use of ferroelectric materials continues to be in piezoelectric devices. Furthermore virtually all piezoelectric applications, with the exception of the very large business in quartz filters and oscillators, involve ferroelectric materials, mostly in ceramic form. The use of ferroelectrics in piezoelectric devices is reviewed with emphasis on the newer developments, particularly those with business potential. Features of the ferroelectric material which are desirable for the application are discussed and areas of possible improvement noted. The largest application areas have remained essentially the same for the last few years, even though there has been considerable technical improvement. They are electric wave filters, fluid loaded transducers for sonar and ultrasonic cleaning, phonograph cartridges, force transducers and high voltage ignition devices, Of these only electric wave filter devices are discussed in detail here; the others are reviewed briefly. Among newer applications whi...

Photoelastic effect in piezoelectric semiconductor: ZnO

Abstract: The photoelastic tensor elements of the piezoelectric semiconductor ZnO were measured by the comparative acousto‐optic diffraction method (reference material, fused quartz) at an acoustic frequency of 250 MHz and an optical wavelength of 0.633 μm. Two crystals with different conductivities, one is highly conductive and the other is highly resistive, were used as samples. The measured photoelastic tensor elements for piezoactive strains are different between these two samples. The difference is explained by the electro‐optic contribution to the photoelasticity induced by the electric field accompanying the piezoactive acoustic wave in the highly resistive sample and its screening by free carriers in the highly conductive sample. The contribution of the rotation of the volume element to the photoelasticity has been also observed in photoelastic tensor elements for shear strains.

Wideband ink jet modulator

Abstract: A modulator for ink jet printers is provided for operation over a wide bandwidth of high frequency drop rates. The longitudinal dimensions of each part of the modulator are made small compared to the wavelength of the shortest standing longitudinal acoustic wave that may be produced in a structure of the same material as the part in question. A piezoelectric crystal is seated within a mount acoustically decoupled at the edges therof. An electrode is axially aligned with the crystal and placed in contact with the crystal. A short hollow cylinder forms an ink chamber axially aligned with the crystal. The end of the ink chamber opposite the crystal is closed by a front plate having a nozzle axially located therein. Plural nozzles may be utilized to produce parallel ink streams which break into droplets at substantially the same time and at a near uniform distance from the nozzles.

Crystal growth and properties of TI3BX4 crystals for acoustic surface-wave and bulk acoustic devices

Abstract: Crystals of Tl3TaS4 and T13Tase4 possess properties which indicate that they could be extremely useful for acoustic devices. They are piezoelectric, have low acoustic velocities (6.89 to 8.53 x 104 cm/sec), high effective values of electromagnetic coupling (k2 up to ~ 3%) and contain directions in which the thermal coefficients of delay are zero. Materials preparation and crystal growth and properties are described.

Pressure dependence of the piezoelectric polarization of LiNbO3 and LiTaO3

Abstract: Linear and nonlinear hydrostatic piezoelectric constants for lithium niobate and lithium tantalate are determined from measurements of the hydrostatic piezoelectric polarization at pressures from 0.05 GPa to 2.6 GPa. The nonlinear constants are found to be large and relatively easy to detect. In LiTaO3 the nonlinear constant is large enough to reduce the piezoelectric coefficient to zero in the vicinity of 2.2 GPa. The nonlinear constants are interpreted in terms of the pressure dependence of the electrostrictive constants. The linear constant measurements indicate that LiNbO3 should prove useful for a wide variety of piezoelectric stress transducers for impulsive loading measurements.