Showing papers on "Piezoelectricity published in 1971"

Temperature Dependence of the Elastic, Piezoelectric, and Dielectric Constants of Lithium Tantalate and Lithium Niobate

Abstract: The elastic, piezoelectric, and dielectric constants, and their temperature dependence within the range 0°–110°C, have been determined for single crystals of lithium tantalate and lithium niobate. For each material, the constants were extracted from a combination of many ultrasonic phase‐velocity measurements, the measured resonant and antiresonant frequencies of a single length‐extensional bar resonator, and the measured low‐frequency capacitances of two thin flat‐plate specimens. For lithium tantalate, the normalized first temperature derivatives of the elastic constants range from −0.4 to −6.7×10−4/°C, while the derivatives for the piezoelectric stress constants range from −1.3 to +1.5×10−4/°C. In the case of lithium niobate, the elastic constant temperature derivatives are all on the order of −2×10−4/°C, while the piezoelectric temperature derivatives are all positive in the range 0.8–8.9×10−4/°C. The dielectric or permittivity temperature derivatives are positive for both materials.

Piezoelectric Crystals and Ceramics

Abstract: Piezoelectric crystals and ceramics are used as detectors and radiators of acoustic power from very low frequencies to above 109 Hz. The lower frequency range is now covered almost exclusively by the piezoelectric ceramics which date from the late 1940’s, and the upper frequency range is covered by new piezoelectric crystals discovered in the 1960’s. The very highest frequency range has been opened up by oriented deposited films of several of the new crystals.

Piezoelectricity, pyroelectricity, and the electrostriction constant of poly(vinylidene fluoride)

Abstract: A new device for measuring the electrostriction constant of polymer films is described. Observed values for various polymers except poly(vinylidene fluoride) and poly(methyl methacrylate) agree well with those calculated from the Clausius-Mosotti equation. Elongational piezoelectricity, the pyroelectric current, and the electrostriction constant are measured for undrawn and roll-drawn poly(vinylidene fluoride) films. The piezoelectricity and pyroelectric current are attributed to space charges antisymmetrically distributed along thickness direction of the film for two reasons: (1) the polarity coincides between these two phenomena for all specimens, and (2) the piezoelectricity and the electrostriction constant have the same anisotropy for drawn films. Similarity of signs between piezoelectricity and pyroelectric current is observed also in poly(vinyl chloride) films. The electrical behavior of poly(vinylidene fluoride) is interpreted in terms of the ferroelectric nature of the β-form crystal.

A normal mode theory for the Rayleigh wave amplifier

Abstract: A Rayleigh acoustic wave traveling on the surface of a semi-infinite piezoelectric medium may be amplified by interaction with drifting carriers in an adjacent semiconductor. The gain and frequency response of this interaction is determined here by using a normal mode expansion of the Rayleigh wave piezoelectric fields. The configuration which uses a thin semiconductor film supported by a semi-infinite dielectric and separated from the piezoelectric by a small air gap is described in detail and the results are expressed in a form that clearly shows the effect of piezoelectric, air gap, and semiconductor parameters. Comparisons with experimental data for the lithium niobate-silicon film configuration show that acoustic gains on the order of 100 dB/cm can be obtained in the frequency range above 0.1 GHz.

Dual crystal resonator apparatus

Abstract: Algebraic combination of the frequencies of two or more selected modes of piezoelectric crystal resonator vibrations yields a total frequency signal output which has a substantially zero temperature coefficient of frequency.

The Strength of Piezoelectricity in Liquid Crystals

Abstract: Abstract A simple method combining macroscopic and microscopic features is proposed to calculate approximate values for Meyer's piezoelectric coefficients. The numerical result suggests that the piezoelectricity of liquid crystals is weak and its effect on alignment fluctuations mostly negligible.

Piezoelectricity in Polarized Poly(vinylidene fluoride) Films

Abstract: Piezoelectric films of poly(vinylidene fluoride) were prepared by applying a static electric field of about 500 kV/cm to seven-times elongated films at 80°C for a few hours. The tensile stress T produced the polarization P normal to the surface of the film. The real and imaginary components of the complex piezoelectric strainconstant d=d′−id″=P/T were determined at temperatures from −140 to +160°C. The relation between the piezoelectric constant d′ and the angle θ between the direction of stress and the orientation axis is given by d′=d31′cos2θ+d32′sin2θ, where the 1-axis and 2-axis are parallel and perpendicular to the direction of orientation and the 3-axis is normal to the film plane. The values of d31′ and d32′ at room temperature were approximately 6×10−8 and 1.5×10−8 cgs esu, respectively. The piezoelectric dispersions occurred at four temperatures at which the elastic dispersions also took place.

Perturbation Theory for Electromagnetic Coupling to Elastic Surface Waves on Piezoelectric Substrates

Abstract: Starting from the fundamental acoustic and electromagnetic field equations an approximate expression is obtained for the perturbation in propagation wavenumber of a surface acoustic wave in a piezoelectric crystal. The source of perturbation is taken to be a surface spaced an air‐gap distance h above the piezoelectric and is described in terms of an electrical impedance. The resulting perturbation is found in terms of the perturbing electrical impedance, an effective dielectric constant for the piezoelectric, the air‐gap spacing h, and a perturbation coupling constant defined in terms of the unperturbed electric potential at the piezoelectric surface and the average acoustic power flow per unit frequency. The theory is applied to the case of a short‐circuit perturbing surface and found to be in excellent agreement with certain numerical results for Y‐cut Z‐propagating LiNbO3 and several cuts of Bi12 GeO20. In the general case of a complex perturbing impedance, such as that exhibited by a semiconductor, the theory indicates that attenuation or gain and dispersion may be introduced by the perturbation, in close agreement with experimental observations.

Method of making a piezoelectric element

Abstract: The present invention relates to the instrument manufacturing industry and, more particularly, the invention relates to piezoelectric elements made in the form of a spiral, to the method of their making and to apparatus that make use of said elements, for example piezoelectric relays, piezoelectric trigger devices, a clock with a piezoelectric drive, piezoelectric step-by-step motors, measuring instruments with a piezoelectric element, piezoelectric transfilters, piezoelectric bells and piezoelectric dynamic loudspeakers. The double-layer spiral piezoelectric element includes a piezoceramic material (1), electrodes on the outer surface (2) and the inner surface (3) of the spiral, terminals (4) and (5), a support (6) for mounting the piezoelectric element, a massive base (7), an electrode (8) between the two layers of the piezoelectric material and an electrode (9).

Dielectric response in piezoelectric crystals

Abstract: Raman scattering measurements in KDA and CsDA are used to show that the soft mode in a piezoelectric ferroelectric may not be described as a classical damped oscillator. The discrepancy arises because of a contribution to the selfenergy of the mode at low frequencies which arise from the coupling of the mode with fluctuations in the phonon density.

Piezoelectric Surface Waves on LiNbO 3

Abstract: : This article presents the results of an analysis of a uniform Z-propagating piezoelectric surface wave upon a y-cut LiNbO3 substrate. Two cases are created: an infinite plane interface between the substrate and free space, and a lightly metallized surface where inertial loading and stiffness of the metal film are neglected.

Piezoelectric acoustic surface waves for a film on substrate

Abstract: A computer program has been written for calculating the dispersion curves of acoustic waves for the film‐on‐substrate problem where both materials may be arbitrarily anisotropic and piezoelectric. The electromechanical coupling factor Δv/v is calculated for nonpiezo‐electric films on LiNbO3 showing a marked increase over its value without the film. Velocity curves are shown for fused quartz on LiNbO3, and Δv/v is shown for ZnO on a sapphire substrate predicting a maximum value of 0.019.

Piezoelectric Effect in Oriented Polyvinylchloride and Polyvinylflouride

Abstract: The direct piezoelectric effect has been observed in roll‐elongated films of polyvinylchloride and polyvinylfluoride. The effect was produced by applying tensile stress to a clamped specimen at a fixed frequency of 20 Hz. The piezoelectric modulus g31 was determined to be 0.2 to 0.7 V m−1/N m−2 in polyvinylchloride; in polyvinylfluoride g31 ≃ 0.2 V m−1/N m−2 and g32 ≃ 1 V m−1/N m−2. The piezoelectric effect in these films is believed to be due to mechanical distortion of oriented dipoles, resulting from the tensile stress, and the orientation appears to differ in the two materials.

Piezoelectric Constant in Oriented β-form Polypeptides

Abstract: Piezoelectric constant and its temperature variation are determined in oriented films of poly-γ-methyl-L-glutamate with the β-form molecular conformation. Semi-quantitative calculation of piezoelectric constants is performed on the basis of a molecular model of pleated sheet structure. Shearing force in the plane of the sheet brings about slide between two adjacent extended polypeptides molecules. The plane of CONH dipole then rotates around the axis of the main chain, which produces an electric polarization. The estimated piezoelectric stress-constant for a single crystal of β-form poly-γ-methyl-L-glutamate is e14=-2.8×104 cgse.s.u.. If the degree of crystallinity Xc=5%, the degree of orientation \varPiα=70% and the symmetry due to uniaxial orientation of the molecules are taken into consideration, e14=-5×102 cgse.s.u. is obtained for the present specimen, which agrees with the experimental observation.

Use of Sodium Tetrachloromercuriate as a Substrate for the Determination of So2 on the Piezocrystal Detector

Abstract: An experimental glass-tight piezoelectric crystal cell has been developed for studying gas-solid reactions on piezoelectric quartz crystals and several substrates have been evaluated for the determination of SO2 in ambient air. Sodium tetrachloromercuriate adsorbs from 0.18 to 4.01 ug of SO2 in 15 minutes periods and shows the best results. A study of the effect of the voltage and temperature applied to the piezoelectric crystal has also been performed.

Electromechanical coupling effects on the dielectric properties and feerroelectrpc phase transition in lithium thallpum tartrate

Abstract: Dielectric, piezoelectric and elastic properties of LiTlC4H4O6 · H2O have been studied over the temperature range 4.2 to 300°K. It has been shown that at low temperature the dielectric constant K11 is very sensitive to the mechanical boundary conditions. At 10°K, close to the Curie point, the free dielectric constant Kx11 is ∼ 5 × 103, whilst the clamped constant Kx11 is only ∼ 30. Both the elastic compliance sE44 and the piezoelectric constant d14 become exceedingly large close to Tc and appear to have the highest magnitude yet measured in any ferroelectric. An analysis of the Helmholtz free energy shows that the unusually large electromechanical coupling effect plays an important role in stabilizing the ferroelectric phase at lower temperature.

Coated piezoelectric analyzers

Abstract: Piezoelectric and magnetostrictive materials coated with charge transfer complexes of halogens are effective detectors for materials capable of being halogenated, such as olefins

Deformation Potential and Piezoelectric Ultrasonic Phonon‐Charge Carrier Coupling in Indium Antimonide

Abstract: The interaction of ultrasonic phonons with charge carriers in nearly intrinsic InSb via deformation potential and piezoelectric coupling mechanisms has been investigated at 296 K in magnetic fields of 0 to 11 kOe and over a frequency range of 10 to 200 MHz. The single crystal InSb was p type with an average acceptor concentration of (1.45±0.05)×1016 cm−3. The experiment permitted an ultrasonic determination of the electron and hole mobilities. The values obtained were μn0 = (58 000±4000) cm2 V−1 sec−1 and μp0 = (720±80) cm2 V−1 sec−1. Values of the deformation potential and piezoelectric coupling constants obtained were | Cn+Cp | = (5.8±0.4) eV and e14 = | 0.076±0.010 | C/m2.

Piezoelectric generation of surface waves by interdigital array

Abstract: The paper shows how the variational principle can be used to analyse the generation of ultrasonic surface waves by an infinite interdigital array of electrodes on the surface of a piezoelectric material. The method is used to analyse the behaviour of such an array deposited on a piezoelectric ceramic. Representation of surface-wave generation by an approximate electrical equivalent circuit is discussed, and the variation of piezoelectric coupling factor with the electrode width/gap ratio is computed for the fundamental resonant frequency, and the third and fifth harmonics. Bulk-wave generation is also treated in some detail.

Surface waveguiding in ceramics by selective poling

Abstract: A surface waveguide structure and method of making same. A substrate material consisting either of a piezoelectric ceramic or ferroelectric crystal, is selectively poled by an electric field so as to form an elastic surface wave channel within the substrate structure. The electric field applied cross the substrate causes a polarization of the crystalline structure in those areas influenced by the electric field and has a negligible effect in those areas not exposed to the electric field. The free surface wave velocity is substantially increased in the polarized areas of the substrate and remains unchanged in the unpolarized regions. Poling of the substrate is accomplished by applying an electric field across a pair of electrodes which cover the upper and lower surfaces of the substrate except for a narrow region between the transmitting and receiving surface wave transducers. The process for manufacturing the surface waveguide structure is applicable to both acoustic and optical surface waveguiding devices. Also, the polarization of the substrate may be selectively altered by subsequent application of electric fields across the body of the substrate to make switchable waveguide regions.

Method and apparatus for controlling frequency of piezoelectric transducers

Abstract: The resonant frequency of a high Q piezoelectric transducer is selectively varied by adjusting the magnitude of the supply voltage for the said transducer. In one apparatus embodiment, the supply voltage to the transducer is automatically adjusted, so as to maintain the resonant frequency of the transducer nearly constant in the presence of external factors tending to shift the said frequency. The system is especially suited to transducers operating from a constant frequency supply system.

Piezoelectric phase detector

Abstract: A phase detector using crystal filters in two signal paths subject to signal phase detection with a single piezoelectric material unit common to and interconnecting the crystal filters of the two signal paths. A signal combining electrode also on the single piezoelectric material unit is connected to a following amplitude detection circuit section.