Showing papers on "Piezoelectricity published in 1973"

Theory of interdigital couplers on nonpiezoelectric substrates

Abstract: This paper is concerned with the theory of excitation of surface acoustic waves on a nonpiezoelectric material, by using an interdigital electrode structure overlaid with a piezoelectric film The impedance and capacity of such transducers have been worked out The results are given in terms of Δv/v, the perturbation in acoustic wave velocity when a perfect conductor is placed in the position of the transducer A computer program which calculates surface wave propagation on a layered medium consisting of a film on a substrate, with arbitrary elastic and piezoelectric properties for both media, has been used to determine Δv/v, and hence the coupling coefficients and radiation resistance of the interdigital transducer As a function of piezoelectric film thickness, two peaks in coupling are observed The results for the interdigital couplers are in quantitative agreement with experiments employing single‐crystal materials Data for experiments using sputtered piezoelectric films also give qualitative agreement with the theory If high‐quality crystalline layers are used, the theory suggests that interdigital couplers on nonpiezoelectric delay lines with properties comparable to or better than the present piezoelectric delay lines may be achievable

dc triode sputtered zinc oxide surface elastic wave transducers

Abstract: A piezoelectric film layer in proximity to an interdigital metal electrode provides a simple means for the excitation and detection of surface elastic waves on nonpiezoelectric substrates. These film transducer structures can be effectively used for the study of the surface elastic wave properties of solids and the development of monolithic acoustic and electronic circuit assemblies. Theory predicts that high coupling efficiencies can be obtained using piezoelectric film transducer structures. The properties of dc triode sputtered zinc oxide film transducers on fused quartz and oxidized silicon have been investigated at frequencies near 16 and above 200 MHz. Quantitative data on coupling factor, capacitance, and phase velocity have been obtained on plated and unplated structures for film‐thickness‐to‐acoustic‐wavelength ratios from 0.01 to 1.0. The experimental data follow the functional dependencies predicted by theory but differ in certain quantitative aspects. The maximum coupling constants (k2) measur...

Curved piezoelectric elements

Abstract: A curved piezoelectric element comprises at least one piezoelectric piece of sheet formed into a wave shape which deforms when a voltage is applied thereto. The wave shape of the piezoelectric piece comprises essentially at least two half-waves connected contiguously and consecutively in one body.

Third‐order elastic constants of lithium niobate

Abstract: The third‐order elastic constants of lithium niobate have been measured by small‐amplitude ultrasonic waves as a function of applied stress, including the piezoelectric effects.

Dielectric, mechanical and optical properties of orthorhombic KNbO-3

Abstract: Dielectric, piezoelectric and elastic constants have been measured in single domain KNbO3, and electrooptic r-coefficients are estimated. Results allow a thorough verification of Devonshire's theory for the orthorhornbic phase. Good agreement is found for the dielectric and piezoelectric properties whereas fitting the elastic behaviour requires inclusion of terms coupling stiffness to spontaneous strain. The temperature dependence of clamped dielectric constants and elastic stiffness points to the importance of piezoelectric coupling for the low temperature phase transitions. Absorption measurements reveal a nearly isotropic polarization-induced band edge shift of 200 meV. Large anisotropy is observed in the polarized UV reflectance spectra measured up to 10 eV. Comparison of reflectivity in ferroelectric KNbO3 with electroreflectance in cubic KTaO3 gives further evidence for the unified nature of electro-optic effects in oxygen-octahedra compounds. Differences in e''-spectra derived from Kramers-Kronig a...

Monolithic piezoelectric wavefront phase modulator

Abstract: A wavefront phase modulator is disclosed which is formed from a monolithic piezoelectric medium which undergoes dimensional changes in response to an electric field impressed thereacross. A thin metallized sheet is cemented to one surface of the piezoelectric medium to provide a mirror surface. Means are provided to produce a plurality of discretely electrically addressable locations on the piezoelectric medium. Such means include a series of segmented electrodes and/or saw cuts or drilled holes. Means are also provided for addressing each of the discrete locations with a variable strength voltage in order to cause the piezoelectric medium to undergo controlled and continuous surface deformations. These surface deformations are calculated to provide distortion correction for wavefronts reflected from the mirror surface of the modulator.

Paraelectric, piezoelectric and pyroelectric crystals: I. Dielectric properties

Abstract: The dielectric properties of crystals are studied on the basis of the weakly anharmonic crystal model. Particular emphasis is placed on the low frequency behaviour of the dielectric susceptibility and on the possibility of a coupling between the dielectric properties and the fluctuations in the phonon density distribution. These fluctuations cannot be treated by low-order perturbation theory but can be discussed by solving the appropriate transport equation. The approximate solution to this equation is obtained following the techniques developed for ultrasonic attenuation.

A new piezoelectric crystal: Ba2Ge2TiO8

Abstract: A Ba2Ge2TiO8 single crystal is synthesized by the Bridgman method. The space group of Ba2Ge2TiO8 is determined to be C2v21‐Iba2, where the lattice constants a, b, and c are 12.30, 135.2, and 10.70 A, respectively. The crystal includes a wedge‐shaped domain structure which resembles those observed in Gd2(MoO4)3 and Rochelle salt. Both X and Y plates have a large electromechanical coupling factor in a thickness shear mode, k15 = 0.27 and k24 = 0.31.

Paraelectric, piezoelectric and pyroelectric crystals: II Phase transitions

Abstract: For pt. I, see ibid., vol. 6, 121 (1973). The response of a crystal in the neighbourhood of a structural phase transition is discussed. It is shown that the behaviour of the scattering cross section is very dependent upon the symmetry of the two phases. The weakly anharmonic crystal model is used within the framework of the Landau theory of phase transitions to discuss nonpiezoelectric/ ferroelectric, piezoelectric/ferroelectric and transitions involving an increase in the size of the unit cell both of the improper ferroelectric kind and otherwise. In every case it is shown that the theory gives rise to the possibility of quasi-elastic as well as inelastic scattering below Tc, but above Tc quasi-elastic scattering is expected in the piezoelectric/ferroelectric and improper ferroelectric phase transitions.

Piezoelectric waves on layered substrates

Abstract: A set of computer programs has been developed for calculating the velocity of acoustic surface waves on a substrate with or without a film overlay where both the film and the substrate may be arbitrarily anisotropic and piezoelectric. Several examples of practical significance are presented. These include (i) propagation around the curved surface of a wrap‐around delay line, (ii) power flow angles for Rayleigh waves on LiNbO3 and Bi12GeO20 substrates, (iii) enhancement in the performance of an interdigital transducer due to the deposition of a film overlay (values of Δν/ν as large as 5.45% have been calculated), (iv) Δν/ν curves for piezoelectric films on nonpiezoelectric substrates.

Single‐crystal growth and piezoelectric properties of lead potassium niobate

Abstract: Large single crystals of lead potassium niobate were grown by the method of pulling from a melt, and their piezoelectric properties were preliminarily investigated. The crystals have ferroelectric tungsten bronze structure with a Curie point of about 460°C. Spontaneous polarization lies perpendicular to the c axis as in ferroelectric PbNb2O6. Particularly large electromechanical coupling factors were measured; i.e., 0.69 ± 0.03, 0.73 ± 0.03, and 0.59 ± 0.01 for k15, k24, and kt, respectively. Temperature coefficients of the fundamental resonant frequencies in y‐ and z‐cut plates were found to be <30 ppm around room temperature.

Method of producing a matched parameter acceleration cancelling hydrophone

Abstract: A seismic cable having minimum response to speed changes is provided. The cable includes a plurality of miniature seismic pressure sensitive detectors coupled one to another in such a manner so as to minimize through cancellation undesired electrical disturbance resulting from speed changes. Each detector includes transducers of the ceramic piezoelectric crystal type having matched geometric and physical property parameters. Each ceramic piezoelectric crystal is provided with metal electrodes such as, for example, gold, nickel, platinum, or rhodium which, in addition to being corrosion resistant and inactive as to the constituents in the ceramic material, are insoluble in liquids encountered by the detector in its use environment to avoid dendrite type growth of the metal through minute cracks developing in the ceramic which causes short circuits in the piezoelectric element.

Angular rate sensor

Abstract: A multiple axis angular rate inertial sensor measures the flexing of vibrating piezoelectric cantilevers induced by Coriolis forces, when the instrument is turned about an axis, in a mechanically resonant system excited by similar piezoelectric cantilever elements.

SH-Mode Piezoelectric Surface Waves on Rotated Cuts

Abstract: If the sagittal plane of a piezoelectric surface wave is normal to a twefold axis of symmetry, the boundary condi- tion equations and the wave equations will decouple into two subsets. One subset pertains to an elastic Rayleigh wave, and the other pertains to an SH-mode piezoelectric surface wave. This is a necessary but insufficient condition for the existence of the SH-mode. Ths condition requires that the surface be parallel to the two-fold axis of symmetry, but its orientation is not otherwise constrained. Consequently, the orientation of the surface has a rotational degree of freedom about the axis of symmetry. In general, the SH-mode will only exist for a limited range of such angular orientations. The value of the smallest decay constant is a useful index of this range of existence. This article uses this index to report the range of surface orientations which are capable of sustaining the SH- mode on quartz, bismuth germanium oxide, Rochelle salt, ADP, barium sodium niobate, LiGa02, LiS04 H2 0, and NiS04 . 6H20.

Method and system for acousto-electric scanning

Abstract: A method and system for scanning conductivity perturbations in semiconductor films by using the piezoelectric fields of acoustic surface waves. In accordance with one embodiment, a piezoelectric substrate is situated adjacent to and spaced a small distance from a semiconductor film. A reading acoustic surface wave of relatively long pulse duration is propagated along the piezoelectric substrate in one direction and a relatively short scanning acoustic wave pulse is propagated in the opposite direction. The amplitude of the reading wave is modulated by the scanning pulse at the point where the two pass each other. In accordance with one embodiment, an optical pattern image on the semiconductor film produces conductivity perturbations through carrier-pair generation. These conductivity perturbations appear as amplitude variations in the reading acoustic wave pulse after its interaction with the scanning acoustic wave pulse, so that the electrical output from the piezoelectric substrate contains the optical information in the pattern image on the semiconductor film. Two dimensional scanning may be accomplished by successively mechanically displacing the optical pattern being scanned with respect to the semiconductor film.

On the electroacoustic waves guided by a cylindrical piezoelectric interface

Abstract: The characteristics of electroacoustic surface waves supported by a curved piezoelectric‐vacuum boundary are studied. A coaxial structure with a piezoelectric insulator as the inner cylinder and an electric conductor as the outer cylinder is considered. A dispersion relation for electroacoustic surface waves circulating around the periphery of the piezoelectric cylinder is obtained. Asymptotic solutions are compared with numerical solutions. Profiles for the mechanical displacement and electric potential for various modes are presented. Possible application as delay lines with long‐time delay is indicated.

Ferroelectric, piezoelectric, and optical properties of SrTeO3 single crystals and phase‐transition points in the solid‐solution systems

Abstract: Temperature dependences of dielectric, ferroelectric, elastic, piezoelectric, and optical properties of a new ferroelectric crystal, SrTeO3, have been measured. Ferroelectricity in this crystal is confined to the temperature range between 312 and 485°C. All the measured constants exhibit abrupt changes at 312°C, which shows the phase transition at this temperature to be of the first order. The electromechanical coupling factors k21 and k22 at 312°C are 0.34 and 0.37, respectively, which are large in spite of the small value of the spontaneous polarization; 0.037 C/m2. The temperature dependence of the piezoelectric constant d22 is well explained by the dielectric constant and the spontaneous polarization, while that of d21 seems to be peculiar; i.e., it monotonically decreases to nearly zero at the upper transition point. The elastic compliances S11D and S22D show no anomaly in the ferroelectric temperature range. The obtained value of 17.3 eV for the dispersion energy of the refractive index nb indicates...

Strain gauge apparatus

Abstract: A specimen or in-service structural member in which strain is to be measured is fabricated as a unit which generates a signal in response to strain occurring in a given region of its surface. A film of piezoelectric material is deposited upon the surface in a manner providing a strong molecular bond between the specimen or member and the piezoelectric film. The film material is chosen from the class having a 6 mm type crystal lattice structure and is formed as a crystalline deposit with the c-axis perpendicular to the surface of the specimen or member. An arrangement of electrodes is provided for direct electrical coupling between spatially separated portions of the piezoelectric film. The electrodes form an output coupling for an electrical signal generated by the piezoelectrically active properties of the piezoelectric film in response to strain mechanically coupled from the substrate surface to the piezoelectric film through the molecular bond. In constructions in which there is a possibility of the electrode arrangement becoming short-circuited through minute vacancies present as imperfections in the piezoelectric film, an ultrathin film of insulating material is deposited adjacent one or the other sides of the piezoelectric film.

High voltage generating piezoelectric igniter

Abstract: A static pressure type high voltage generating device of the kind in which a high voltage is generated by applying a static pressure to piezoelectric elements and which has simple structure, requires only a small operating force and moreover is excellent in durability.

Phase lock detection and control for piezoelectric fluid analyzers

Abstract: Phase lock detector for an analyzer employing piezoelectric elements in electrical circuits. In general the piezoelectric elements differentially absorb a particular constituent in an analyzed fluid. This weight change of the crystal induces a change in the oscillator circuit containing this piezoelectric element. A phase detector detects the resultant phase change between the electrical circuits containing the piezoelectric elements, and provides a measurement of the amount of the particular substance sorbed and, thus, within the fluid. The phase detector output also feeds back to one or more of the electrical circuits and forces them to oscillate at the same frequency.

Optical storage device using piezoelectric read-out

Abstract: Apparatus and methods are described which utilize the dimensional changes of a piezoelectric material in response to an electric field impressed thereacross to retrieve optically an information pattern. In a preferred embodiment, a crystal such as bismuth germanium oxide is used because it has both a photoconductive, field-storage capabiltiy and a large piezoelectric effect. Information can be read into such a material optically, stored by means of a spatially varying internal electric field impressed thereacross, and subsequently optically read-out using the piezoelectric effect. Read-out is accomplished by sensing the modulation of read-out light caused by surface deformations on the crystal due to the internal electric field.

Poling process for linear piezoelectric strain transducers

Abstract: A process for producing sufficient piezoelectric effect in plastic dielectric coaxial cable to obtain a highly sensitive linear strain transducer. The process combines a selected soak temperature profile with the application of high voltage DC to maximize sensitivity and uniformity. The plastic dielectric material exhibits a high level of piezoelectric activity when processed according to the invention so that, for example, the cable is sensitive to the passage of humans or vehicles when buried in the ground.

Elastic and piezoelectric properties of &#945;-HgS

Abstract: Elastic, piezoelectric, and dielectric constants of α-HgS (Cinnabar) were measured mainly by the resonant method. Piezoelectric α-HgS thickness transducers when coupled with bulk α-HgS would realize perfect matching in acoustooptical applications.