Showing papers on "Piezoelectricity published in 1970"

Linear and Nonlinear Attenuation of Acoustic Surface Waves in a Piezoelectric Coated with a Semiconducting Film

Abstract: The interaction of acoustic surface waves in a piezoelectric with carrier waves in a semiconducting film on the surface is considered. Particular attention is paid to the limitation of the small signal theory due to nonlinear effects. It is found that large signal effects, which occur at moderate acoustic power levels, are important when the maximum rf charge density exceeds the available background charge density. Measurements of acoustic attenuation and acoustoelectric current in a CdS film on the surface of Y‐cut quartz are reported. A fair agreement between theory and experiment is found.

Electrical, optical, and mechanical behavior of ferroelectric Gd2(MoO4)3

Abstract: Results of a number of electrical, optical and mechanical measurements on ferroelectric Gd2(MoO4)3, are presented Based on these results it is concluded that the symmetry in the paraelectric phase above 159°C is tetragonal 42m, and the symmetry below the transition is orthorhombic mm2. Twin walls are shown to be ferroelectric domain walls with the relationship between the polarity of the spontaneous polarization P, and the relative positions of the orthorhombic a and b axes being dictated by the piezoelectric effect in the paraelectric phase. A large mechanical dimension change and large optical effects accompanying ferroelectric switching are discussed and possible applications of these effects are considered briefly.

Diffusion potentials in BaTiO3 and the theory of ptc materials

Abstract: We present two methods for calculating the potential profiles of depletion layers in ferroelectric materials. The simplified method is valid for materials possessing a high permittivity and with the electric field parallel to the polarization. The second method is valid for low permittivity materials as well and can be adapted to any orientation. We applied these methods to a study of the 001-001 interfacial barrier on semiconducting BaTiO3. Below the Curie point the calculations are in agreement with the resistivity-temperature behavior of doped, air-sintered ceramics. The theory does not predict a large resistance discontinuity at the Curie point. We discuss several refinements which may account for this discrepancy. The most plausible seems to be the piezoelectric charge compensation resulting from lattice distortion and grain boundary clamping.

Oscillatory circuit for ultrasonic cleaning apparatus

Abstract: A high-efficient oscillatory circuit drives a piezoelectric crystal (transducer) which is coupled to an ultrasonic cleaning tank The circuit includes a transistor switching means in the driver side of the oscillator The primary winding of the transformer is coupled in parallel with a capacitor and forms a circuit having a resonant frequency which is a multiple even integer of the resonant frequency of the crystal which is coupled to the transformer secondary winding

Electrical and Mechanical Loading of a Piezoelectric Surface Supporting Surface Waves

Abstract: The influence of surface loading on the propagation of surface waves on a piezoelectric substrate is analyzed. Both mechanical and electrical loading are described by means of a simple first‐order perturbation theory. General formulas for the perturbation of the surface‐wave phase velocity caused by deposition of a uniform thin film or by electrical interaction with an adjacent conducting or semiconducting medium are developed. The scattering of surface waves from discrete strips is also analyzed. Results from scattering and wave‐propagation analysis are utilized to describe the interdigital surface‐wave transducer. An equivalent circuit for a basic transducer element is developed, and the total transducer is analyzed by means of transmission‐line theory applied to a network of cascade‐coupled elements. The effect of electrode mass loading is specially treated, and the results are compared with measurements made on a Y‐cut Z‐propagation LiNbO3 crystal.

Propagation of Piezoelectric Surface Waves on Cubic and Hexagonal Crystals

Abstract: The propagation of surface waves on free and metallized surfaces of cubic and hexagonal crystals is investigated numerically. Surface wave velocity curves and relative differential velocity curves are presented for propagation on typical surfaces of four selected crystals (gallium arsenide, bismuth germanium oxide, zinc oxide, and cadmium sulfide). Special attention is paid to degenerate modes wherein decoupling among the various components of mechanical displacement and the electric field occurs.

Study of Piezoelectric Oscillations in Wideband Pyroelectric LiTaO3 Detectors

Abstract: The use of freely suspended LiTaO3 pyroelectric detectors for wide‐band application is severely hampered by mechanical resonances of the detector (typically several hundred kHz) which are excited by the incident radiation. These resonances give rise to slowly decaying oscillatory piezoelectric signals superimposed on the pyroelectric signal. It is shown that by suitable mounting of the detector films these resonances can be entirely eliminated, thereby increasing the useful bandwidth of the devices to at least several hundred MHz. In addition, it is shown that when the incident radiation is modulated at a mechanical resonance frequency of a freely suspended LiTaO3 detector, considerable enhancement of the current and voltage response is obtained. The experimental results are found to be in reasonable agreement with results calculated for LiTaO3 by including thermal expansion in the equations of motion of a pyroelectric crystal.

Propagation and Amplification of Ultrasonic Waves in a Layered Structure of Quartz‐Liquid‐CdS

Abstract: Amplification of surface wave has been experimentally observed in a composite structure consisting of a quartz plate, a thin liquid layer, and a piezoelectric semiconductor. An additional time delay is also observed in such a composite structure.

Piezoelectric surface waves in cubic and orthorhombic crystals

Abstract: The existence of a piezoelectric surface wave, which does not arise in nonpiezoelectric materials has been reported in hexagonal crystals by Bleustein and Gulyaev. In this letter, similar waves are reported to exist in cubic crystals of 23 and 43m classes and orthorhombic crystals of mm2 class. Velocity equations for the piezoelectric surface waves in these symmetry classes are presented. It has been demonstrated that the velocities are always smaller than the piezoelectrically stiffened but always larger than the unstiffened bulk shear waves in the corresponding direction of propagation. Numerical results for the particular examples of Bi12GeO20(23) and Ba2NaNb5O15(mm2) are also presented.

Piezoelectric and Photoelastic Properties of Lithium Iodate

Abstract: Considerable interest has recently been drawn to the iodates owing to the large nonlinear optical interactions (second harmonic and photoelastic) reported in α‐HIO3. In the present work, many of the photoelastic and piezoelectric constants and related properties of single‐crystal lithium iodate LiIO3 have been determined. The acousto‐optic figure of merit for LiIO3 has been found to be only about 15% of that for α‐HIO3, making the material unattractive as an acousto‐optic medium. However, LiIO3 has been found to have a rare combination of a large piezoelectric effect (kt=0.51, k15=0.60) and low dielectric constant (e33S/e0≅6, e11Se0≅8), which makes it particularly attractive for broad‐band high‐frequency transducer applications.

Electroacoustic transducers of the bilaminar flexural vibrating type

Abstract: A transducer includes a piezoelectric driven, vibratile diaphragm which acts as the closure for a circular opening in a rigid housing which encloses electronic components. The flexure mode of the diaphragm is controlled to give a sound pattern which is more uniform over a large area. The housing and diaphragm assembly is combined with a set of electrical terminals which serve as a plug for inserting the transducer assembly into a mating socket. The resulting structure provides an economical transducer design with improved sound radiation characteristics and controlled uniformity in large production quantities.

Formulation of Admittance for Parallel Field Excitation of Piezoelectric Plates

Abstract: Parallel field excitation of piezoelectric plates has been analyzed with a matrix method, and the admittance of the plate is derived. This formulation affords the definition of coupling factor to each of three vibrational modes, which is shown to be modified by the antifield effect due to the induced charges on major surfaces of the plate in case of anisotropic crystals. In contrast to the perpendicular field excitation case, the resonant frequencies in this case are odd multiples of the fundamentals and the antiresonant frequencies are determined as solutions of a transcendental equation. The validity of the derived equations is confirmed by comparing measured and calculated frequency constants of lithium tantalate single crystal.

Piezoelectric Surface Waves in Cubic Crystals

Abstract: The existence of a piezoelectric surface wave, which does not arise in nonpiezoelectric materials has recently been reported in hexagonal crystals by Bleustein and Gulyaev. It is shown that similar waves can exist in cubic crystals of 43m and 23 classes, along [110] direction on the (110) plane and their equivalent orientations. Velocity equations for the piezoelectric surface wave and the elastic surface wave are derived and their characteristics discussed.

Efficient low voltage piezoelectric power supply

Abstract: An electric device for efficient transfer of power from a piezoelectric crystal source to a capacitor. The piezoelectric crystal is coupled to a transformer, the secondary of which is shunted by a series combination of a rectifying device and a storage capacitor, all in such manner that energy is transferred from the piezoelectric crystal, essentially a first capacitance device, to the storage capacitor, a second capacitance device, with a new order of efficiency. In a specific embodiment of the invention the piezoelectric crystal and two capacitances are associated with biasing networks and a transistorized switching circuit and a firing circuit in such manner that the energy transferred into the storage capacitor is utilized to fire a squib.

Temperature variation of piezoelectric moduli in oriented poly(γ‐methyl L‐glutamate)

Abstract: The real and imaginary components of the complex piezoelectric strain constant, which relates the polarization to the applied stress, have been determined for elongated films of poly(γ-methyl L-glutamate) over the temperature range −170°C to +170°C at a frequency of 20 Hz. The variation of the piezoelectric constant with temperature is similar for both α-helical and β-form molecular conformations. The sign of piezoelectric polarization is opposite for L and D polymers. A simple model, representing the piezoelectric crystallites as embedded in nonpiezoelectric amorphous regions, is proposed to account for the piezoelectric temperature dispersion curves.

Measurement of Piezoelectric Phase Angles in a Ferroelectric Ceramic

Abstract: A method is described for measuring the phase angle of the piezoelectric coefficient d31 in a ferroelectric ceramic. This method requires only data on the complex electrical admittance of a length-extensional bar resonator. Measurements based on this procedure gave a phase angle on the order of 3° for the piezoelectric constant d31 of the ferroelectric ceramic [Pb0.99 Nb0.02 (Zr0.65 T0.35) 0.98 O3].

Focused piezoelectric transducer and method of making

Abstract: An apparatus and method for fabricating focused high frequency electromechanical transducers especially useful in ultrasonic inspection apparatus is disclosed. An initially flat or planar piezoelectric crystal is placed between a pair of members having mating surfaces contoured to correspond to the desired shape of the crystal. When the members are forced together the crystal is bent or otherwise formed into the desired shape.

Broadband, high frequency, thin film piezoelectric transducers

Abstract: Piezoelectric thin film transducers are provided in a form to match the impedance of a transmission line. The transducer structure includes a plurality of serially connected transducer elements on a single substrate provided by a first pattern of electrodes on the substrate, a single layer of piezoelectric material overlying the first electrode pattern and a second electrode pattern overlying the piezoelectric layer with selective connections between electrodes of the first and second patterns, such structure being directly amenable to fabrication by thin film technology. Such an arrangement provides greatly increased bandwidth characteristics and improved conversion efficiency.

Hybrid surface-wave transducer

Abstract: A transducer for generating and detecting surface elastic waves in a non-piezoelectric material may include an interdigital electrode array coupled to a piezoelectric crystal. The crystal is mechanically coupled to the non-piezoelectric material through an acoustical transmissive medium.

Scattering of Waves by a Cylindrical Piezoelectric Inclusion

Abstract: The general problem of the scattering of waves from a transversely isotropic piezoelectric cylinder is examined. The solution for the interaction of an electromagnetic wave with a circular piezoelectric cylinder or antenna is presented. Solutions for the scattering of axial shear and compressional elastic waves by a piezo‐electric circular cylinder embedded in an elastic medium are also presented. A few numerical results are presented for barium titanate.

Two-dimensional acousto-optic deflection system

Abstract: A system for deflecting a light beam in two dimensions is described. The system includes a piezoelectric crystal having an acoustic surface wave transducer on its surface for propagating acoustic surface waves on the crystal. Means are provided for applying a nonuniform electric field to the crystal to vary the effective stiffness constant of the crystal in a nonuniform manner. When a beam of laser light is directed onto the crystal it is deflected in one dimension as a function of the frequency of the acoustic wave produced by the transducer and in a second dimension as a function of the nonuniform electric field.

Stress Dynamics in High Speed Piezoelectric Pressure Probes

Abstract: In the design of high speed piezoelectric pressure probes the criterion of matching the acoustic impedance of elements in the stress transmission system composed of piezoelement and backing rod is found to be inconsequential. Analysis and empirical evaluation of a typical probe configuration indicate that optimum probe performance can be achieved by utilizing backing rod material with minimum lateral strain (ν/E) characteristics so as to serve effectively to damp induced radial stress oscillations in the piezoelement.

Electrooptic effects in ferroelectric ceramics

Abstract: Ferroelectric ceramics are piezoelectric and optically birefringent. Moreover, their coefficients of piezoelectricity and birefringence are electrically variable. Consequently, these ceramics are applicable to a variety of devices: electrically tuned oscillators and transformers; miniaturized high-Q, high-frequency filters; FM discriminators; optical memories; electrically Controlled light shutters and valves; and electrically activated multicolor displays. This article deals with some possibilities for devices that exploit the electrically controllable optical effects. A later article will consider piezoelectric applications.

Improved Piezoelectric Effect in Polymers

Abstract: Improved poling techniques have led to improvement in the piezoelectric activity of bulk polymers. Results now achieved approach the activity of conventional piezoelectric materials such as quartz, and further improvement is anticipated. The measured value of the piezoelectric strain modulus d31 of a length expander bar of polyvinylchloride was 0.6×10−12 m V−1 and the electromechanical coupling factor k31 was 0.6%. The response of a sample as an underwater sound receiver was −112 dB re 1 V/μbar.

Acoustoelectric Amplification in a Many-Carrier System

Abstract: Acoustoelectric amplification, in the linear approximation, is considered for a system containing several types of carriers in the two limiting cases of fast and slow carrier equilibration. The pertinent expressions are first derived for a piezoelectric semiconductor and then expanded to the more practical case of a layered system containing one or more semiconducting layers coupled to a piezoelectric element. An experimental example is given in the form of a guided elastic plate wave in lead zirconate titanate coupled to a plate of near‐intrinsic Ge.