Showing papers on "Piezoelectricity published in 1968"

A method for estimating optimal crystal cuts and propagation directions for excitation of piezoelectric surface waves

Abstract: A criterion for judging the relative effeciency of excitation of piezoelectric surface waves as a function of crystal plate orientation and propagation direction is developed. This criterion is based on a velocity change upon application of a thin conducting sheet to the surface. Plots of surface wave velocity for various orientations of the crystal surface are presented as a function of propagation direction for the conducting sheet in contact with and infinitely far removed from the crystal surface. A plot of a typical velocity variation as a function of height of the conducting sheet is also presented. Evidence in support of the criterion of using velocity changes as an indicator of efficiency is presented in the form of mechanical displacement and electric potential plots for several orientations and propagation directions. All velocity displacements and potential calculations were carried out under the assumption that the crystal medium was lithium niobate.

A new surface wave in piezoelectric materials

Abstract: A type of surface wave with no counterpart in a purely elastic homogeneous material is shown to exist in a piezoelectric material Expressions for the velocity of propagation of this wave are obtained for various electrical boundary conditions on the free surface of a piezoelectric half‐space

Electro-optic and Piezoelectric Coefficients and Refractive Index of Gallium Phosphide

Abstract: Measurements of the constant‐strain electro‐optic coefficient of GaP between 0.56 and 3.39 μ wavelength were made using both pulsed electric field and optical heterodyne techniques. At 0.6328 μ wavelength its value is −0.97×10−12 m/V. A dispersion of only 10% is present between 0.56 and 3.39 μ. Approximate values of the piezoelectric coefficient and the constant‐stress electro‐optic coefficient are also obtained from the analysis of the experiments. For GaP the magnitude of the constant‐stress coefficient is less than the constant‐strain coefficient. The analysis also points out an often ignored effect: electro‐optic measurements made with electric field frequencies in the range of resonant acoustic frequencies may not exhibit the expected symmetry of the crystal plus field but may also evidence effects from the crystal shape. Accurate refractive index measurements made on many GaP crystals between 0.545 and 0.70 μ wavelength are also reported.

Piezoelectric thin multilayer composite resonators

Abstract: Alternate thin layers of piezoelectric material having differently orientated piezoelectric axes with respect to each other are placed on a substrater and electroded to form a high frequency resonator. The thickness mode resonant frequency of the composite structure corresponds a proper fraction of the resonator operating frequency, layer thickness varying between 0.2 and 100 microns corresponding to approximately 10 percent of the substrate thickness.

Piezoelectricity as a fundamental property of wood

Abstract: The piezoelectric effect in wood, i.e. the occurrence of electric polarization under mechanical stress and also of mechanical strain in an electric field, was accounted for by considering the uniaxial orientation of cellulose crystallites in fibers and their monoclinic symmetry. A shear stress in one plane, including the grain direction, produced electrical polarization perpendicular to it. The value of the piezoelectric modulus for wood was approximately one twentieth of that of a quartz crystal. The chemical treatments which transform the lattice structure from cellulose I to II or III, increased the piezoelectric modulus. However, gamma-ray irradiation up to a dose sufficiently high to decrease the molecular weight had only little influence on the piezoelectric modulus. The variation with temperature of the phase angle between sinusoidal stress and polarization showed a maximum of advanced phase around room temperature and a maximum of delayed phase at about-100°C. Dielectric and viscoelastic measurements indicated that the former was caused by the dielectric loss due to water at a temperature above freezing and the latter by the viscoelastic loss due to local vibrations of cellulose molecules. The piezoelectric polarization in wood can be utilized in technical problems such as the measurement of shock velocity in timber. The physiological meaning of the piezoelectrical effect in plants has not been investigated.

Piezoelectric Properties of Modified PbTiO 3 Ceramics

Abstract: PbTiO3 ceramics with high density and high resistivity have been prepared by adding less than 5 mol % of Bi2/3TiO3, PbZn1/3Nb2/3O3 or their derivatives. These ceramics have dielectric constants of about 200, and can be poled at 200°C under a d. c. field of 40 to 70 kV/cm. The piezoelectric coupling factors k15, k33 and k31 amount to 0.43, 0.35 and 0.068, respectively. The value of k33 is nearly constant up to the Curie temperature of about 500°C. The aging rate of frequency constant does not exceed 0.1%/time decade. The present ceramics can be used as stable piezoelectric elements in high temperature and high frequency.

Vibrational Waves in a Thick Infinite Plate of Piezoelectric Crystal

Abstract: Vibrational waves in an infinite piezoelectric plate bounded by two planes of symmetry are investigated. The surfaces of the plate are kept traction free and are completely coated with electrodes, which are shorted. The lowest symmetric and antisymmetric wave modes are discussed. Both types of mode change to surface modes whenever surface modes are possible along the direction of propagation. The waves propagating in the (1,0,0) direction of a cadmium selenide crystal have been analyzed numerically.

Stimulated Brillouin Scattering in Piezoelectric Semiconductors

Abstract: A classical theory of Stimulated Brillouin Scattering (SBS) in piezoelectric semiconductors is presented. It is shown that, to a first approximation, acoustoelectric interactions act to change the inverse absorption length of sound from a value α = αs, where αs is the absorption coefficient in the absence of acoustoelectric phenomena, to α = αs+αw+ikβ, where αw is the ultrasonic attenuation and β is the relative change in sound velocity due to piezoelectric stiffening, both as derived by White. Calculations based on a solution obtained with simple boundary conditions indicate that the threshold for SBS can be significantly reduced when the scattering process takes place in the presence of ultrasonic amplification. Results indicate that the threshold may be reduced to a flux in the neighborhood of 106 W/m2, a value attainable with currently available cw lasers.

Electrical Properties of the Hot-pressed SbSI Polycrystals

Abstract: SbSI is a ferroelectric material with the c-axis as ferroelectric axis and the most strongly piezoelectric material known. The permittivity of SbSI single crystal of the c-direction is about 25000 whereas that of the a-direction is 25. Till now, due to the difficulties in obtaining large crystal, it is very hard to use this material for practical applications. Specimens used in piezoelectric measurement reported by RCA group consisted of thin discs cut from bundles of SbSI needles embedded in Araldite.SbSI single crystal tends to grow in form of thin needles along the c-axis. In this report, the hot-pressing technique was applied to the powder of SbSI crystals in order to obtain the hard polycrystalline ingot having the oriented c-axis and systematic experiments were carried out on the effects of the hot-pressing temperature (Tm), the pressure (Ph) and the time (tp) influencing upon the orientation of the c-axis in the hot-pressed specimens.The results obtained are summarized as follows.(1) When Ph was applied to the z-direction of the press mould, the c-axis of SbSI microcrystals were oriented in the x-y plane of the press mould. In this case, the permittivity of the x-direction (ex) is 1400 at the Curie point whereas that of the z-direction (ez) is 160.(2) When the pre-forming pressure to the y-direction and the hot-pressing pressure to the z-direction were applied, the c-axis were oriented to the x-direction of the pressed specimens. In this case, the permittivity of x, y, and z-directions at the Curie point are 3000, 1000, and 240 respectively.(3) The orientation of the c-axis in the hot-pressed specimens was also ascertained by the observation of the etched surface by mean of a microscope.(4) The piezoelectric constants such as k33, s33E, s33D, d33, fR⋅t were measured for the hot-pressed specimens prepared under a condition of Tm=370°C, Ph=250kg/cm2, and tp=1hr. This specimens showed an electromechanical coupling coefficient k33 of 35%.(5) The Curie temperature of the hot-pressed SbSI of 30°C is higher by 10°C than that of the SbSI single crystal If the phase transition of SbSI is order-disorder type, it may be considered that the rise of the Curie point by the hot-pressing is the effect of the residual strain generated while hot-pressing.

Mechanical and Piezoelectric Properties of Shock‐Loaded X‐Cut Quartz at 573°K

Abstract: The mechanical and piezoelectric properties of uniaxially strained X‐cut quartz were studied at 573°K over a stress range of 6 to 21 kilobars by monitoring the current output from a shock‐loaded quartz disk. In addition to providing fundamental knowledge of the behavior of quartz under these conditions, the results yield data necessary for the application of quartz as a submicrosecond stress gauge at this temperature. The elastic wave velocity was found to be 5.70 mm/μsec at 573°K, a 0.35% decrease from the room temperature value. The piezoelectric factor relating the piezoelectric charge to stress was determined as k = (1.895×10−8+1.470×10−10σx) C/(kilobar‐cm2). This value is based on room temperature values of the electrode area and the gauge thickness. In the zero stress limit, the piezoelectric factor determined by shock loading compares favorably with the e11/c11 piezoelectric coefficient of quartz. Above 14 kilobars, relaxation in the current output of the quartz was observed. Therefore, when using ...

ERRATA: Ultrasonic Holography by Electronic Scanning of a Piezoelectric Crystal

Abstract: Images have been optically reconstructed from acoustical holograms displayed by electronic scanning of a piezoelectric crystal, irradiated by the sonic beams.

Neutron Diffraction on Piezoelectric Vibrating Resonators

Abstract: THIS communication explains some experimental results published by Parkinson and Moyer1,2* by proving that the wave amplitude associated with neutrons reflected from a lattice of vibrating piezoelectric resonators corresponds to the amplitude of a frequency modulated wave3,4.

Direct reading pyrometer employing pyroelectric crystal detector

Abstract: A lead zirconium titanate crystal possessing pyroelectric characteristics is employed in a direct reading pyrometer for measuring directly the temperature of an object, principally by the infrared radiation emitted therefrom. The pyroelectric crystal is provided on two opposing surfaces with an electrically conductive material and absorbing coating is placed on the surface exposed to the incident radiation to convert that radiation into heat thereby polarizing the pyroelectric crystal and developing an electrical voltage related to the temperature of the object. A low inertia oscillating vane interrupts the incident radiation to provide a continuous voltage output from the crystal, and filtering and gating circuits are included in the electronic readout circuit to minimize piezoelectric voltages which may be generated by mechanical forces transmitted to the crystal.

Performance of bonded, single-crystal LiNbO 3 and LiGaO 2 as ultrasonic transducers operating above 100 Mhz

Abstract: Fabrication of bonded, single-crystal transducers to operate in fundamental thickness-shear and thickness-longitudinal modes at frequencies around 300 MHz is reported. The experimental results show that these transducers have performance that is superior in a number of ways to competitive thin-film piezoelectric transducers.

Calculation of the Piezoelectric Constants of α Quartz on Born's Theory

Abstract: The phenomenon of piezoelectricity in α quartz is related to the phenomena of infrared absorption and Raman scattering, using a model due to Kleinman and Spitzer. For right quartz the values computed for e11 and e14 are −0.052 C/m2 and 0.076 C/m2, respectively. (The values measured by Bechmann are −0.171 C/m2 and 0.0406 C/m2.) The calculation seems to be the first of its type to obtain the correct signs.

Temperature Variation of Complex Piezoelectric Modulus in Cellulose Acetate

Abstract: Piezoelectric properties of elongated films of cellulose diacetate and cellulose triacetate were investigated in a temperature range from -160°C to +160°C. The sinusoidal stress was given to a film specimen cut at 45 degrees obliquely to the orientation axis at frequency 20c/s, and measurement was taken of the electrical polarization that appeared on the faces of the film. Not only the absolute value of piezoelectric constant but also the phase difference between the stress and the polarizatian was detected. Defining the complex piezoelectric modulus as d*=d'-id", d' and d" were quantitatively determined as a function of temperature.In cellulose diacetate, d' increased with the rise of temperature accompanied by a peak of d" with a positive sign, indicating that the polarization lagged behind the stress. On the contrary, in cellulose triacetate, d' decreased with the rise of temperature, accompanied by a trough of d" with a negative sign, indicating that the polarization overreached the stress. Such results may be called as piezoelectric dispersion and absorption with temperature.Dynamic viscoelastic and dielectric measurements were also carried out for the same specimens. Comparison of the results indicated that piezoelectric, elastic, and dielectric absorptions took place over the same range of temperature, and that the piezoelectric absorption was the sharpest among them.The oriented polar molecules or oriented crystallites are supposed to be the units responsible for the piezoelectric polarization in the elongated polymer films. Distribution of mechanical stress and dielectric shielding around these units and even piezoelectric moduli of units themselves can be altered by the thermal variation of the molecular motion in polymers.

Frequency response of a distributed piezoelectric source of sound

Abstract: It is shown that the frequency dependence of the ultrasonic signal produced by a piezoelectric source may be simply calculated using the Fourier transform of the spatial distribution of piezoelectric stress.

Acceleration dependent phase control seismic exploration

Abstract: SEISMIC WAVES ARE DETECTED AND RECORDED BY GENERATING ACCELERATION SIGNALS THROUGH PRESTRESSED PIEZOELECTRIC CRYSTALS OF WIDE BAND FREQUENCY CAPABILITY AND PASSING THE WIDE BAND SIGNAL TO A MULTI-STAGE AMPLIFIER HAVING WIDE BAND INPUT AND PROGRESSIVELY NARROWED FREQUENCY BAND THROUGH SUCCESSIVE STAGES OF THE AMPLIFIER WHILE RETAINING SIGNALS OF FREQUENCY IN THE RANGE OF ABOUT 100 CYCLES PER SECOND AND ABOVE.

Ultrasonic piezoelectric transducer cartridge

Abstract: A transducer cartridge assembly providing means to readily interchange transducer crystals and to match crystal impedance with that of the backing member.

Temperature stabilized piezoelectric crystal transducer and oscillator

Abstract: A CRYSTAL TRANSDUCER AND AN OSCILLATOR CIRCUIT IS DISCLOSED IN WHICH A TEMPERATURE GRADIENT IS APPLIED BETWEEN THE CRYSTAL FACES. ONE FACE IS HELD AT A PREDETERMINED REFERENCE TEMPERATURE WHILE THE TEMPERATURE OF THE OTHER FACE VARIES WITH THE ENVIRONMENT TO WHICH IT IS EXPOSED. FOR THIS ARRANGEMENT A LINEAR RELATIONSHIP EXISTS BETWEEN THE TEMPERATURE GRADIENT AND THE NATURAL RESONANCE OF THE CRYSTAL. APPLICATIONS AS TEMPERATURE SNSOR, MICROBALANCES AND PARTICULAR MODES OF OPERATING THE TRANSDUCER ARE DISCLOSED.

Heterojunction semiconductor transducer having a region which is piezoelectric

Abstract: A stress sensitive semiconductor device having two adjacent semiconductor regions at least one of which is piezoelectric, with a PN-heterojunction between the regions. Upon application of stress to the heterojunction, the polarization of the piezoelectric semiconductor is altered to modulate current flow across the PN junction.