Showing papers on "Piezoelectricity published in 1978"

Piezoelectricity and pyroelectricity in polyvinylidene fluoride—A model

Abstract: A description is given of the molecular and morphological structure of polyvinylidene fluoride and from this description a classical model is proposed for calculating the piezoelectric and pyroelectric properties. The model consists of an array of crystal lamellae with a net moment from aligned dipoles in the crystals and compensating space charge on the crystal surfaces. The results for no compensation and complete compensation essentially bracket experimentally observed results and indicate that the largest contribution to the activity of this polymer arises from bulk dimensional changes rather than from changes in molecular dipole moments.

Piezoelectricity and pyroelectricity in polyvinylidene fluoride

Abstract: The piezoelectric, thermal expansion, and elastic coefficients of two different types of polyvinylidene fluoride film have been measured and used to calculate the secondary pyroelectric coefficient. It is found that secondary pyroelectricity can account for about half the pyroelectricity observed.

Corona charging and the piezoelectric effect in polyvinylidene fluoride

Abstract: Biaxially stretched PVF2 films were poled by corona charging over a range of surface potentials not exceeding 10 kV. Studies of x‐ray diffraction patterns are presented together with the measured values of the piezoelectric constant d31 of such films. The results indicate that the piezoelectricity in this polymer arises from the dipolar orientation of the polar crystallites.

The piezoelectric bimorph: An experimental and theoretical study of its quasistatic response

Abstract: Plates of the piezoelectric ceramic lead zirconate titanate of thickness approximately 150 mu m adhesively bonded to beryllium copper plates of comparable thickness form so-called bimorph elements. The electromechanical behaviour of such elements is studied under quasistatic conditions. Features dealt with include electrical poling, hysteresis behaviour, transverse and longitudinal mechanical strain. A theoretical treatment is given and used to interpret the measurements.

Analysis of surface waves using orthogonal functions

Abstract: A simple noniterative method using an orthonormal basis for expressing field distributions has been developed for obtaining surface‐wave solutions in piezoelectric crystals. Velocity and field distributions are obtained for YZ LiNbO3 that agree with earlier works. The boundary conditions are incorporated in a manner that is easily adapted to layered structures. Dispersion curves are obtained for surface waves in LiTaO3 with a SiO2 layer at the surface; the results are in good agreement with those published earlier.

Flexo-electric domains in liquid crystals

Abstract: 2014 The threshold characteristics of an instability in the form of longitudinal flexoelectric domains, arising in thin layers of liquid crystals exposed to a d.c. field were investigated for two nematic mixtures based on azoxy-and ester compounds. The experimental dependences of the threshold voltage and the domain period as functions of dielectric anisotropy were obtained. It was shown that maximum distortion of a homogeneously oriented layer corresponds to the central region of the layer. The difference of the flexo-electric moduli e* = e11 e33 was calculated for the mixtures by comparing the experimental data with the theory for two-dimensional flexo-electric deformation developed by Bobylev and Pikin. LE JOURNAL DE PHYSIQUE TOME 39, AVRIL 1978,

Elastic and Piezoelectric Properties of Potassium Lithium Niobate (KLN) Crystals

Abstract: The KLN crystal K2.89Li1.55Nb5.11O15 was pulled from the melt. Piezoelectric and elastic constants were measured from room temperature to about 120?C by observing resonant and antiresonant frequencies of bars and plates. The electromechanical coupling factors k15, k31, k33 and kt were 0.34, 0.18, 0.52 and 0.53 respectively. The temperature coefficients of elastic compliances Ts33E and Ts66E were fairly small and were -0.98 and 0.075?10-4/?C, respectively.

Monoaxially oriented piezoelectric polymer transducer for measurement of mechanical values on bodies

Abstract: A transducer comprising a piezoelectric measuring sensor element for measurement of mechanical values on hollow bodies, especially of the pressure distribution within pipes, the piezoelectric sensor element being a flexible piezoelectric film, the opposite surfaces of the film being in connection with electrically leading contact surfaces, and the measuring sensor element being at least partially and at least indirectly closely joinable to the surface of the hollow body.

Sensor device using piezoelectric coating subjected to bending

Abstract: A sensor device having a vibratable surface which can be exposed to variousmaterials and used to determine the presence thereof is disclosed. The device includes a sandwich structure comprising a substrate coated with a piezoelectric material, a pickup electrode joined to the piezoelectric and a drive electrode also joined to the piezoelectric. The piezoelectric material is applied to the substrate as a slurry and when dried forms a ceramic coating which is chemically bonded to the substrate. The sensor is electrically driven to vibrate and depending upon the absence or presence of the material to be detected a characteristic vibrational frequency or amplitude of the sensing surface is observed to indicate contact with such material. Various embodiments are discussed including a rectangular configuration which is cantilevered from a support base and a circular configuration which is held circumferentially by the support base.

Horn loaded piezoelectric matrix printer drive method and apparatus

Abstract: A method and apparatus for driving a matrix printer element is described which utilizes a piezoelectrically driven horn loaded driver. The horn is preferably tapered in the direction of the printing element and has a base area to which is attached a piezoelectric crystal excitation device. The piezoelectric crystal structure is driven by electric pulses which are coupled to the tapered horn to increase the impact velocity and stroke at the output end of the horn. The piezoelectric crystals may be controlled by the application of a particular pulse pattern to reduce resonance and insure an optimum deceleration of the crystal during rebound of the printing element.

Crystal symmetry of Ca2Sr(C2H5CO2)6 in the low temperature phase

Abstract: Crystal symmetry of a low temperature form (III phase) of Ca2Sr(C2H5CO2)6 was studied. X-ray, piezoelectric and pyroelectric evidences revealed that the III phase is not tetragonal but would be monoclinic C2.

Piezoelectric scanning of Fabry-Perot spectrometers: nonlinearities.

Abstract: Piezoelectric materials used in mechanical scanning of Fabry-Perot spectrometers are found to have measurable nonlinearities. Dynamic scanning has been used in the present investigation in order to decrease the effects of some of the variables, such as creep, of the piezoelectric material in static operation. The results show mainly a decrease in the distance between corresponding maxima, or apparent free spectral range, as the driving voltage increases to higher values. A relationship between this voltage and displacement (in terms of orders) has been derived, and it is given by νi = ln {1 − (xi − x0)/[a/(1 − b) − x0]}/ln b, where νi is the displacement in orders from an arbitrary starting point, xi is a quantity directly proportional to the voltage, while x0 is also a quantity proportional to the voltage at the arbitrary reference point, a is the distance between the arbitrary reference point and the next order, and b is the nonlinearity constant for a given piezoelectric material. Examples are given for emission and absorption measurements where the usually large effects of the piezoelectric material nonlinearities are derived, as well as schemes to minimize or altogether remove the effects by suitable handling of the data or by changing the experiment such that the scanning is forced to be linear.

Piezoelectric wavefront modulator

Abstract: A piezoelectric wavefront modulator employs a plurality of widely-separated posts, which are formed upon the upper portion of a monolithic piezoelectric medium and are affixed to the lower portion of a flexible mirror. The posts extend from the top surface of the piezoelectric medium a sufficient distance, so that the mirror floats. The posts are surrounded by moats formed within the medium, which are configured to produce a highly sensitive device, wherein the post mirror actuators are substantially electromechanically isolated from each other, but not from the piezoelectric material adjacent the moat.

Wave propagation in a piezoelectric two-layered cylindrical shell with hexagonal symmetry: Some implications for long bone

Abstract: Harmonic wave propagation is considered in a two‐layered cylinder of dissimilar but transversely isotropic materials such as bone. The model includes the approximate piezoelectric behavior of long bone and the frequency equation is shown to constitute a 16th‐order determinant. A frequency equation is also derived for the nonpiezoelectric case. Though the frequency equations are much too complicated to be treated analytically, they are shown to lead to simpler forms for the special cases of axial symmetry, very long and very short wavelengths. In the absence of established values for the piezoelectric moduli of bone and of the elastic constants of the inner spongy layer, a numerical solution to the model does not seem worthwhile at present.

Piezoelectric, electro-optic, dielectric, elastic and thermoelastic properties of hexagonal Cs2S2O6, LiClO4.3H2O, LiClO4.3D2O, and Ba(NO2)2.H2O

Abstract: Complete tensor sets of piezoelectric, electro-optic, dielectric, elastic and thermoelastic properties were measured on hexagonal Cs2S2O6, LiClO4. 3H2O, LiClO4. 3D2O, and Ba(NO2)2. H2O. The space-group symmetry of Cs2S2O6 and Ba(NO2)2. H2O has been definitely established, by X-ray work in combination with the measurement of polar properties, to be P63mc and P61 (P65), respectively, contrary to earlier X-ray determinations. LiClO4. 3H2O and LiClO4. 3D2O possess almost identical physical properties, with the exception of density and density-dependent properties. The very small differences correspond to those observed in other hydrates and deuterates. Most components of the piezoelectric and electro-optic tensors do not exceed the effective values of other crystals already in technical use. However, an exceptionally strong longitudinal piezoelectric effect is observed in Cs2S2O6 (d333 = - 41 e.s.u, dyn-1, electromechanical coupling coefficient kt = 0.25), which together with other favourable acoustic and optical properties supports the application of this new material for acousto-optical devices in the high-frequency range.

A study of piezoelectric properties of PLZT ferroelectric ceramics

Abstract: Piezoelectric properties of a wide range of compositions of hot-pressed mixed oxide PLZT ferroelectric ceramics, covering both the rhombohedral and tetragonal phases, have been investigated. The values of the electromechanical coupling constant, kp, were observed to range from 0.25 to 0.72. The values of the piezoelectric strain constant, d33, were observed to range from 76-710 × 10-12 C/N, Systemic variation of the Zr/Ti ratio and the La-concentration were discussed.

A new technique for excitation of surface and shear acoustic waves on nonpiezoelectric materials

Abstract: An interdigital transducer deposited on a piezoelectric substrate has been used to excite SAW on nonpiezoelectric materials by using a fluid couplant. The piezoelectric substrate is held at an angle to the nonpiezoelectric material so as to match the tangential k vectors of the surface waves. Experiments have been carried out with a LiNbO3 piezoelectric substrate and a ceramic such as SiC or Si3N4 with a fluid couplant. At a center frequency of 100 MHz, the estimated conversion efficiency of the surface wave from the piezoelectric to the nonpiezoelectric material is −3.5 dB. The results compare favorably with a normal mode coupling theory we have developed which predicts −2.7 dB efficiency.

Moulded piezoelectric transducers using polar polymers

Abstract: Polar polymer such as PVC, PVF and PVF2 show strong piezoelectric activity after being stretched and poled. They were used up to now in plane or cylindrical configurations. We show that such polymers can be moulded and poled, which constitutes a new generation of piezoelectric transducers. Example is given of a high range loudspeaker using a moulded PVC film.

Poly (vinylidene) fluoride used for piezoelectric coin sensors

Abstract: The usefulness of the piezoelectric polymer, poly(vinylidene) fluoride, for sensors in coin operated devices is demonstrated. Features such as high sensitivity, low cost, and ease of handling and processing make this material extremely attractive for these applications.

Second-order phenomena in α-quartz and the polarizing effect with plates of orientation (xzl)Ψ

Abstract: The change in series resonance frequency of piezoelectric resonators caused by a superposed dc electric field, known as the polarizing effect, is studied on the three thickness modes of thin plates made of α-Quartz. For cuts of orientation (xzl)Ψ, which operate in the fundamental frequency range between 2.7 and 5.0 MHzand at dc electric field intensities between ±106 Vm-1, the change in frequency is proportional to the intensity of the applied dc electric field and depends on the cut angle Ψ and on the mode of vibration. At the dc field of 106 Vm-1, the maximum change in frequency is found to be 16 parts per million. Quasilinear interpretation of the polarizing effect and the subsequent formula for its magnitude lead to determination of several components of the tensors of electroelasticity, second-order piezoelectricity, and second-order permittivity of α-quartz. The order of magnitude of these components is found to be 100 NV-1m-1, 10-10 NV-2, and 10-20 FV-1, respectively; the mean probable errors in the determined values are less than 4%, 30% and 30% in the same order. While an allowance must be made for the cumulative character of the determined values of the second-order constants, the available evidence indicates that the polarizing effect is caused mainly by the change in values of the elastic constants; with the polarizing effect exceeding 10-11 V-1m-1, the converse piezoelectric effect accounts only for multiples 10-12 V-1m-1, and typical contributions of the second-order piezoelectricity and the second-order permittivity are of the order of 10-13 V-1m. Based on these results, our experimental data are reproduced with an accuracy of better than 3% on the average. The potential of the polarizing effect for investigation of the second-order phenomena becomes evident and should be recognized.

Piezoelectric variable mirror or lens - of laminated structure including two piezoelectric ceramic layers

Abstract: In the variable focal length lens or mirror, the curvature of the element is determined by the flexing of a two layer piezoelectric transducer driven from a variable voltage source. The structure can vary from a simple two layer form having a reflective surface(21) directly laid on the surface of one layer to a five or six layer form both forms using the piezoelectric material(12, 13) as a ceramic. The radius of curvature of such an element can be changed from infinity to three metres by application of 500volts(15, 16, 17) to electrodes included between the ceramic layers and at their surfaces.

On the Temperature Dependence of the Velocity of Surface Waves in Quartz

Abstract: : The first temperature derivatives of the fundamental elastic constants of quartz are employed along with the thermally-induced biasing strains in the equation for the first perturbation of the eigenvalue for the linear electroelastic equations for small fields superposed on a bias to calculate the resulting change in surface wave velocity with temperature. Since the description employed is referred to a fixed reference state, the geometry does not change and the temperature coefficient of velocity is the negative of the temperature coefficient of delay.

Pyroelectric properties of dislocation-free ferroelectric Sr0.5Ba0.5Nb2O6 crystals

Abstract: Stress-free pyroelectric coefficient, dielectric constant, and volume specific heat of dislocation-free Sr0.5 Ba0.5Nb2O6 crystals were measured. Also measured were the elastic and piezoelectric properties and thermal expansion coefficients. The strain-free and partially clamped pyroelectric coefficient, dielectric constant and volume specific heat were calculated and discussed.

Mounting clips for thickness shear piezoelectric oscillator

Abstract: A support construction for a thickness shear piezoelectric oscillator such as a crystal oscillator or the like, which can improve oscillation characteristics thereof. The thickness shear piezoelectric oscillator is provided at its both ends with a so-called bevel portion which is supported at the upper and lower tapered portions thereof by a shaped guide so as to determine the horizontal position thereof.