Showing papers on "Piezoelectricity published in 1969"

Piezoelectric Effects in Liquid Crystals

Abstract: A theory of the relationship between curvature strains and electric polarization in liquid crystals is developed in analogy to piezoelectric theory in ordinary crystals. The theory may explain some recently observed phenomena in nematic liquid crystals.

Linear Piezoelectric Plate Vibrations: Elements of the Linear Theory of Piezoelectricity and the Vibrations Piezoelectric Plates

Abstract: Linear piezoelectric plate vibrations: elements of the linear theory of piezoelectricity and the vibrations of piezoelectric plates , Linear piezoelectric plate vibrations: elements of the linear theory of piezoelectricity and the vib... , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Characteristics of Microwave Acoustic Transducers for Volume Wave Excitation

Abstract: Transducers which utilize acoustoelectric conversion in a piezoelectric film, plate, or surface have found wide application for generating planar volume-acoustic waves at microwave frequencies. A review is given of the electrical impedance, conversion loss, and bandwidth characteristics for piezoelectric film or plate transducers which vibrate in one-dimensional thickness extensional or shear modes. The transducer response is related to the electric and acoustic parameters that describe the transducer configuration, and experimental examples are given to illustrate the operation of typical transducer configurations. Methods for achieving low conversion loss and/or broad bandwidth are discussed and experimental examples given. Tables of bulk material constants are supplied for commonly used plate and film devices, and transducer fabrication methods are reviewed. Other types of volume wave transducers, such as those utilizing a single piezoelectric surface, a diffusion layer in a piezoelectric semiconductor, or mode conversion at a boundary are also briefly discussed.

Some Simple Modes of Wave Propagation in an Infinite Piezoelectric Plate

Abstract: Exact solutions of the equations of the fully coupled linear theory of piezoelectricity are obtained for some simple types of two‐dimensional waves in an infinite plate. It is shown that the coupling of the mechanical and the electrical fields can give rise to dispersion curves with complex branches and to waves that are largely confined to the region near the major surfaces of the plate.

Excitation and Detection of Surface Elastic Waves in Piezoelectric Crystals

Abstract: The amplitude of the surface elastic wave produced by the application of an alternating voltage to an interdigital arrangement of electrodes on the surface of a piezoelectric medium is determined. The electric field produced by the surface electrodes is calculated subject to the assumption that the piezoelectric coupling of the material can be neglected. This electric field acts as the forcing term for the inhomogeneous elastic equation, which is then solved to obtain the amplitude of the surface wave generated by the transducer. A reciprocal relationship between the excitation and detection problems is used to obtain the power extracted from the surface wave by an interdigital arrangement of surface electrodes. Measurements made on single crystals of quartz and cadmium sulfide are found to be in good agreement with theoretical predictions. The maximum value of the product (efficiency×fractional bandwidth) for a surface‐wave transducer is calculated. For an interdigital surface‐wave transducer on the basal plane of CdS, the maximum value of this product is found to be 7.8×10−2. It is shown that one can connect linear pairs of surface electrodes in an appropriate binary code so as to obtain high efficiency and large bandwidth transducers.

Interaction between elastic surface waves in piezoelectric materials

Abstract: Nonlinear interaction between elastic surface waves and an almost uniform time‐dependent electric field is demonstrated in LiNbO3 at 17 MHz.

Characterization of Piezoelectric Transducers Used in Ultrasonic Devices Operating Above 0.1 GHz

Abstract: Piezoelectric transducers for ultrasonic devices operating at frequencies above 100 MHz are presently being made either by thin‐film deposition techniques or by bonding thin plates to the substrate and lapping them to the required thickness. In either case the performance of the transducers cannot be evaluated separated from the device, and the evaluation is complicated by the presence of intermediate layers and spurious circuit elements. This paper uses Mason's equivalent circuit to critically appraise the validity of methods used to evaluate transducer performance from loss and admittance measurements made under these circumstances. Computed families of curves are presented, spanning the practically important range of mechanical impedances and coupling factors. Experimental data from a ZnO film and a LiNbO3 thin‐plate transducer on fused quartz substrates are presented to demonstrate the application of equivalent circuit descriptions to obtain the coupling factors.

Piezoelectric and Elastic Properties of LiTaO3: Temperature Characteristics

Abstract: Piezoelectric and elastic constants of lithium tantalate single crystal were measured from room temperature up to the Curie point (630°C). These constants were obtained by measuring resonant and antiresonant frequencies of bars and plates with various orientations. Temperature dependence of piezoelectric constants was discussed on the basis of the electrostrictive effect in the paraelectric phase biased by spontaneous polarization. Anomalous behavior of d33 and d31 was well explained by the dielectric anomaly of e33T.

Piezoelectric Elastic Surface Waves in Anisotropic Layered Media

Abstract: Solutions for surface elastic waves propagating in a layered media consisting of a CdS film on a fused quartz substrate have been found. Piezoelectric coupling in the CdS has been included. The Rayleigh, Sezawa, and Love modes are discussed. The surface wave velocity, mechanical displacements, and electric fields are found as a function of layer thickness for the Rayleigb and Sezawa modes. Velocity dispersion was experimentally measured and found to be in good agreement with theory.

Stress-strain transducer charge coupled to a piezoelectric material

Abstract: A piezoelectric material is connected to a semiconductor having source and drain electrodes at opposite ends thereof. The piezoelectric material is charge coupled to the semiconductor and spaces and electrically insulated the semiconductor and spaces and electrically insulates the semiconductor from a gate electrode disposed between the source and the drain. Application of a voltage to the source and drain and of a constant voltage to the gate and source causes a current flow which is a function of the stress-strain to which the piezoelectric material is subjected and can thus be employed to indicate the magnitude of such stress-strain.

Elastic and Piezoelectric Constants of Ba2NaNb5O15

Abstract: The elastic, piezoelectric, and dielectric constants of Ba2NaNb5O15 have been measured. The experimental techniques used involve mostly thickness‐mode measurements made on small plate‐shaped samples of various crystallographic orientations. As reported previously, the z‐cut plate has a thickness longitudinal mode coupling factor of 0.57, which makes this material attractive for application as a high‐frequency longitudinal mode transducer. However, from the measured constants and the theory of piezoelectric plate vibrations, it is determined that no crystallographic orientation other than the z‐cut has properties suitable for ultrasonic transducer applications.

Piezoelectric effect in blood vessel walls

Abstract: Piezoelectric effect has been observed in various kinds of tissues such as trachea, intestines, ligament, aorta and vena. The anisotropy of piezoelectric modulus indicates the preferred orientation of piezoelectric protein fibers including collagen and elastin. The value of piezoelectric modulus in completely dried state is from 10 -10 to 10 -9 c.g.s.e.s.u.. Temperature variation of the piezoelectric modulus is influenced by the thermal motion of molecules and the moisture absorbed in the specimen. It is estimated that 1 precent oblique cyclic deformation of blood vessel walls at a frequency of about 1 c/s could produce the alternating electric current of approximately 3 pico ampere between the surfaces of the vessel wall.

High pressure piezoelectric transducer

Abstract: An alternating voltage is applied to the electrodes of a piezoelectric crystal at the frequency of natural vibration of the crystal in the thickness mode which causes the crystal to vibrate in the thickness mode. This vibration is at one-half wavelength resonance. Vibrations from the front surface are transmitted through an epoxy window as an ultrasonic wave. Vibrations off the back surface are reflected from a reflector which is spaced one-quarter wavelength from the crystal. A filler material with negligible reflective qualities, such as neoprene, synthetic or natural rubbers, or the like, is sandwiched between the crystal and the reflective material. The filler also has the properties of compressions so that the crystal will not break or cave in when the transducer is subject to high pressures when submerged in very deep water.

PIEZOELECTRIC PROPERTIES OF Ba2 NaNb5 O15

Abstract: Single‐crystal Ba2NaNb5O15 (z plate) has been found to have a piezoelectric coupling factor in the thickness longitudinal mode kt equal to 0.57. As a value of kt determined by direct measurement, this result is the highest value yet reported for a single‐crystal ferroelectric material usable at and above room temperature. Since this material has good mechanical handling characteristics, a relatively low dielectric constant (e33S/e0 = 30), and a pure mode of vibration, plates of this material are attractive for applications as high‐frequency longitudinal mode transducers. The approximate values of the thickness shear mode coupling factors for x and y plates are k15 = 0.20 and k24 = 0.20.

Piezoelectric applications of ferroelectrics

Abstract: The utility of ferroelectrics for piezoelectric devices rests on two characteristics, asymmetry and high dielectric constant. In one type of ferroelectric crystal, including Rochelle salt, asymmetry is intrinsic in the structure. Substances which owe their piezoelectric effect to ferroelectric polarity are of particular utility because domain orientation by electric field imparts piezoelectric response to polycrystalline bodies. Once this orientation has been achieved one usually desires to have a minimum of the nonlinearity, hysteresis losses, and high temperature coefficients connected with ferroelectricity. This has been achieved with modified barium titanate and especially lead titanate zirconate ceramics. Use of piezoelectric transducers in electroacoustics and ultrasonics has kept pace with the general growth in these fields, especially in phonograph pickups, industrial ultrasonics, and underwater acoustics. Piezoelectric spark sources for gas lighting are becoming a substantial consumer item. Piezoelectric ceramic IF filters both for 455 kHz and 10.7 MHz are of increasing interest due to their ruggedness and small size compatible with transistor and integrated circuitry.

Piezoelectric generation and detection of ultrasonic surface waves by interdigital electrodes: an electrical equivalent circuit

Abstract: Experiments with voltage pulses applied to an interdigital array of electrodes on the surface of a piezoelectric material suggest a 1-dimensional electrical equivalent circuit valid for generation and detection of ultrasonic surface waves, both transient and sinusoidal. The study also indicates a new method of assessing the piezoelectric coupling coefficient.

Growth and Some Electrical Properties of Orientated Fibriform Crystal of SbSI

Abstract: The dielectric and piezoelectric properties of the orientated fibriform crystal of SbSI grown by the Bridgeman method under high pressure, have been investigated. As-grown fibriform crystal of SbSI is an aggregate of many densely packed single crystalline needles orientated nearly parrallel to ingot axis which is ferroelectric axis (c-axis). The dielectric constant (e33T is about 6400 at the Curie point (10°C). The electro-mechanical coupling factor (k33) shows a high value of about 70–74% constantly in range of temperature from -50 to -10°C and rapidly decreases near the Curie point. The piezoelectric modulus (d33) shows the highest value of 8×10-10 (C/N) near the Curie point. The temperature dependence of the frequency constant (f×l), elastic compliance co-efficnents (S33D, S33E), spontaneous polarization (Ps3) and chemical analysis are discussed.

Piezoelectricity in helical polymer chains

Abstract: Piezoelectric effect has been observed by a number of investigators in the uniaxially orientated helical polymers, in which the piezoelectric polarization appears perpendicular to the shearing plane. To explain this, the piezoelectric polarization is theoretically treated for a distorted helical polymer chain with effective charges or dipole moments on the main chain. The piezoelectric effect occur only in an optical shear mode of lattice vibration along the helical axis. As examples, the piezoelectric polarization is calculated in polyoxymethylene-type helical chain and quasi-polypeptide-type one.

Method and apparatus for removing material by means of spark erosion

Abstract: An electric discharge machining apparatus utilizing a piezoelectric element having two metal coatings which form a capacitor. A voltage is applied to the coatings which causes the piezoelectric element to oscillate, and by controlling the current to the piezoelectric element, the gap distance can be varied. The oscillation frequency is determined by the current supplied and the gap discharge rate.

Self-scanned optical sensor using elastic surface waves

Abstract: A self-scanning optical sensor array that is based on the use of elastic surface waves is described. In the device, a photoconducting material is adjacent to an array of surface wave transducers on a piezoelectric slab. Initial tests have successfully demonstrated the principle of operation.