Showing papers on "Piezoelectricity published in 1987"

Use of piezoelectric actuators as elements of intelligent structures

Abstract: This work presents the analytic and experimental development of piezoelectric actuators as elements of intelligent structures, i.e., structures with highly distributed actuators, sensors, and processing networks. Static and dynamic analytic models are derived for segmented piezoelectric actuators that are either bonded to an elastic substructure or embedded in a laminated composite. These models lead to the ability to predict, a priori, the response of the structural member to a command voltage applied to the piezoelectric and give guidance as to the optimal location for actuator placement. A scaling analysis is performed to demonstrate that the effectiveness of piezoelectric actuators is independent of the size of the structure and to evaluate various piezoelectric materials based on their effectiveness in transmitting strain to the substructure. Three test specimens of cantilevered beams were constructed: an aluminum beam with surface-bonded actuators, a glass/epoxy beam with embedded actuators, and a graphite/epoxy beam with embedded actuators. The actuators were used to excite steady-state resonant vibrations in the cantilevered beams. The response of the specimens compared well with those predicted by the analytic models. Static tensile tests performed on glass/epoxy laminates indicated that the embedded actuator reduced the ultimate strength of the laminate by 20%, while not significantly affecting the global elastic modulus of the specimen.

A two‐dimensional theory for high‐frequency vibrations of piezoelectric crystal plates with or without electrodes

Abstract: Two‐dimensional equations of motion of successively higher‐order approximations for piezoelectric crystal plates with triclinic symmetry are deduced from the three‐dimensional equations of linear piezoelectricity by expansion in series of trigonometric functions of the thickness coordinate of the plate. These equations, complemented by two additional relations: one, the usual relation of face tractions to the mass of electrodes, and the other relating face charges to face potentials and face displacements, can accommodate either the traction and charge boundary conditions at the faces of the plate without electrodes or the traction and potential boundary conditions at the faces of the plate with electrodes. Dispersion curves are obtained from the first‐ to fourth‐order approximate plate equations for a rotated 45° Y‐cut lithium tantalate plate without electrodes, and these curves are compared with those from the frequency equation of the three‐dimensional equations with close agreement. Solutions of force...

Ferroelectric domain inversion caused in LiNbO3 plates by heat treatment

Abstract: It is demonstrated that heat treatment of a LiNbO3 plate at temperatures somewhat lower than the Curie point causes a ferroelectric domain inversion, thereby yielding an inversion layer useful for various piezoelectric devices. The dependences of the inversion layer thickness on the heat treatment conditions, such as temperature, time, and atmosphere, are experimentally examined. The results show that the domain boundary appears to stop at the median plane of the plate finally. The possible mechanism of the domain inversion is also discussed.

Nonlinear, elastic, piezoelectric, electrostrictive, and dielectric constants of lithium niobate

Abstract: All eight electrostrictive, all three third‐order dielectric, all thirteen third‐order piezoelectric, and all fourteen third‐order elastic constants of lithium niobate have been determined. Measurements for the electrostrictive constants have been made by measuring the electric capacity in selected directions when the directed static stresses were applied to the crystal. The third‐order dielectric constants have been calculated from these measured electrostrictive constants and the measured capacitance as functions of the applied static electric field. The third‐order piezoelectric and elastic constants have both been determined from the above‐mentioned two kinds of measured constants and the measured velocities for small‐amplitude ultrasonic waves as functions of several applied stresses and static electric fields.

The role of domain walls on the dielectric, elastic and piezoelectric properties of ferroelectric ceramics

Abstract: Domain splitting in the grains of ferroelectric ceramics reduces the internal elastic stresses which are caused by spontaneous deformation. Hysteresis switching reflects the increase or absence of internal stress. Small signal elastic and electric ac fields applied to the ceramic cause reversible domain wall motion thus giving contributions to the dielectric, piezoelectric and elastic constants of these materials.

Piezoelectricity of c‐axis oriented PbTiO3 thin films

Abstract: Through seeded lateral overgrowth, c‐axis oriented PbTiO3 films are formed on patterned Pt electrode films that are on a SrTiO3 single crystal The impedance characteristics are then measured for this sample as if it were a composite bulk wave resonator A series of resonance and antiresonance characteristics is observed Using a conventional circuit model, the electrical impedance is analyzed to evaluate the electromechanical coupling constant kt of the PbTiO3 films It is found that kt is as large as 08

Electron-beam poling of piezoelectric polymer electrets

Abstract: Irradiation with a monoenergetic electron beam is demonstrated as a poling technique for piezoelectric polymer electrets. Poling‐current measurements during electron irradiation indicate a ferroelectric polarization of typically about 0.1 C/m2. The generated nonuniform polarization profiles are probed by means of laser‐induced pressure pulses. It is found that the thickness of the unpoled sample volume is proportional to the 1.5th power of the electron energy used. The proposed method thus allows the fabrication of polymer electrets with a polarization zone of predetermined thickness for, e.g., application in flexure‐mode devices.

Piezoelectric bending actuator

Abstract: A piezoelectric actuator comprising a longitudinal effect-type laminated piezoelectric element composed of piezoelectric ceramic sheets laminated in their thickness direction, and a supporting member fixed to one side in the longitudinal direction of the element and being bending and capable of constraining expansion of the element.

Analysis of a single-mode optical fibre piezoceramic phase modulator

Abstract: The behaviour of a cylindrical single-mode optical fibre piezoceramic phase modulator was investigated in the frequency range below resonance. The integral and differential phase modulation efficiencies are reported for different geometrical dimensions of the modulator and for various piezoelectric ceramic materials. p ]The results obtained show that a phase-modulation depth in excess of ≪ can be easily achieved using commercially available piezoelectric cylinders, with driving voltage amplitude as low as 5 V.

System for sustaining and monitoring the oscillation of piezoelectric elements exposed to energy-absorptive media

Abstract: The disclosed system includes a piezoelectric crystal exposed to an energy-absorptive medium of interest. A crystal oscillation circuit is included for sustaining oscillation of the crystal in contact with the fluid. To accomplish this, the circuit includes feedback elements for providing automatic gain control of the amplifier portion of the oscillator. In this manner, the conditions required for crystal oscillation are maintained independent of variations in the medium the crystal is exposed to. Information regarding the gain adjustment and oscillation frequency of the crystal are applied to a microprocessor-based system for determining fluid characteristics such as viscosity, density, and dielectric constant. Alternatively, this information is used to correct for the influence of such parameters on the resonant behavior of piezoelectric crystals undergoing mass change, in the analysis of, for example, corrosion, adsorption and electroplating. The relationship between the particular characteristics determined and the output information received from the oscillation circuit is dependent upon the hydrodynamic and electrokinetic coupling experienced between the medium and crystal.

Monomorph actuators using semiconductive ferroelectrics

Abstract: A new type of bending actuator, "monomorph", is proposed by using a single plate of semiconductive piezoelectric ceramics. The principle of bending originates from the nonuniform distribution of the electric field in a single plate caused by the semiconductor–metal electrode contact. Monomorph characteristics are exemplified in lead zirconate based and barium titanate ceramics. A bend curvature comparable to that of conventional piezoelectric "bimorphs" can be obtained.

Piezoelectric element drive circuit

Abstract: Disclosed is a piezoelectric element drive circuit which comprises a charge circuit for charging the piezolectric element in response to an external signal, and a switching circuit connected between the terminals of the piezoelectric element via reactor means to allow a current flow in one direction selected in response to an external signal for transferring the charges supplied from the charge circuit and stored in the piezoelectric element from its high-potential side to its low-potential side whereby the piezoelectric element is charged to be in the opposite polarity. Optionally, the power stored in the piezoelectric element is regenerated at the power source instead of charging the piezoelectric element in the opposite polarity. With the above drive circuit, the power once supplied to the piezoelectric element from the power source is cyclically used for improved power efficiency.

Dielectric and piezoelectric properties of pb1-xbaxnb2o6 ferroelectric tungsten bronze crystals

Abstract: Tungsten bronze single crystals in the Pb1-xBaxNb2O6 system were grown from a melt using the Czochralski technique. The dielectric, piezoelectric and pyroelectric properties were determined. The dielectric constant Ka and piezoelectric coefficient d15 showed a strong enhancement upon approaching the tetragonal: orthorhombic morphotropic phase boundary as predicted by thermodynamic phenomenology. It is clear that crystals with a composition in the tetragonal phase field near this boundary will be of major interest for various piezoelectric device applications.

Dual mode transducer

Abstract: An electroacoustic transducer such as a piezoelectric element transducer includes an output mode for generating an alert signal and an input mode for generating a switching signal. The transducer comprises an actuating means, such as a pushbutton, a resilient member, such as a snap action dome, a housing and a piezoelectric element. In the output mode, voltage is supplied to the piezoelectric element to generate mechanical vibrations which are converted to acoustical energy by a resonant cavity and port in the housing. In the input mode, manual pressure on the pushbutton forces the dome, being interposed between the pushbutton and piezoelectric element to collapse and deform the piezoelectric element. In response, the piezoelectric element generates an electrical signal. A voltage sensing circuit senses the electrical signal and generates an input signal. The circuit distinguishes between the voltage supplied to the piezoelectric element to generate mechanical vibrations and the electrical signal generated by the collapsed dome.

Piezoelectric deformable mirrors and gratings

Abstract: An apparatus and method for rapidly and accurately positioning an optical surface comprises at least one piezoelectric element 10 with an optical surface 16 located thereon and means 12,30 for applying an electric field to the piezoelectric element 10. The piezoelectric element 10 is piezoelectrically polarized along a first axis and the electric field is supplied along a second axis perpendicular to the first axis. Thus, piezoelectric shear deformation of the piezoelectric element occurs and there is rotation of the optical surface 16 about a third axis which is perpendicular to both the first and second axes. The deformation is sufficient to alter the direction of incident radiation and to alter the direction and distribution of diffracted incident radiation after interaction with the optical surface 16. Varying the magnitude of the electric field alters the magnitude of the deformation thereby accurately positioning the optical surface 16.

Thermal expansion and piezoelectric response of PZT Channel 5800 for use in low‐temperature scanning tunneling microscope designs

Abstract: The thermal expansion of the ceramic piezoelectric material PZT Channel 5800 between 2 and 300 K is found to be anisotropic, being negative parallel to the poling direction and positive normal to this direction. The piezoelectric response is temperature dependent, decreasing significantly as the temperature is reduced.

Acoustoelectric effects in superlattices using a separate‐medium structure

Abstract: The interaction of the surface acoustic wave (SAW) with the GaAs/AlAs superlattice is investigated using a separate‐medium convolver structure. The magnitude and polarity of the acoustoelectric voltages exhibit strong temperature and SAW frequency dependences, a phenomenon that is not observed in homogeneous semiconductors. Possible SAW‐superlattice interaction models that tentatively explain the observed data are discussed.

Piezoelectric and Acoustic Properties of Piezoelectric Flexible Composites

Abstract: Piezoelectric and acoustic properties of piezoelectric flexible composites or Piezo-Rubbers which have been developed at NTK-NGK are reported. The frequency dependences and hydrostatic pressure dependences of underwater receiving sensitivities of hydrophone using the Piezo-Rubber are discussed in terms of the properties of Piezo-Rubber materials. Also single pulse acoustic transmitting/receiving responses of the Piezo-Rubber are compared with those of PZT ceramics, PVDF polymer and PZT/polymer 1-3 type composites.

LIPP investigation of piezoelectricity distributions in PVDF poled with various methods

Abstract: Laser-induced pressure pulses (LIPP's) were used to investigate the distribution of polarization and piezoelectric e-constant in the thickness direction of 22 μm thick films of polyvinylidenefluoride (PVDF) with a resolution of 1 to 2 μm. The samples were poled with four different methods, namely a newly developed electron beam technique and the older field, thermal, and corona methods. Results obtained on such samples indicate the existence of different distributions of the piezoelectricity or polarization, ranging from highly uniform profiles for the field-poled samples to step-shaped (monomorph-type) or bidrectional (bimorph-type) distributions for the electron-beam poled samples. The results demonstrate the influence of the fields set up by space charge on the poling process.

Temperature compensated piezoelectric transducer assembly

Abstract: An apparatus for monitoring the curing of a fiber reinforced composite plastic which is cured at temperatures of the order of 350° C. and an ultrasonic transducer assembly useful in the apparatus. The transducer assembly comprises a lithium niobate piezoelectric element having anisotropic coefficients of thermal expansion which is mounted on a metal base of the transducer assembly by means of a layer of structured copper. The structured copper is thermo-compression diffusion bonded to the lithium niobate element and to the metal base, and is compliant in a transverse direction to compensate for differential thermal expansions while affording good electrical and thermal conductivity and good acoustic coupling between the lithium niobate element and metal base.

Piezoelectric activity in films of poly(1-bicyclobutanecarbonitrile)

Abstract: We observed significant piezoelectric activity in cast films of poly(1-bicyclobutanecarbonitrile).

Method of manufacturing an ultrasonic transducer

Abstract: An ultrasonic transducer includes a piezoelectric member consisting of either a unpolarized piezoelectric polymer material or the like, or an in-advance polarized piezoelectric polymer material or the like, a first flexible substrate on which a first electrode set and their connecting leads are formed, these being bonded to one surface of the piezoelectric member, and a second flexible substrate on which a second electrode and its connecting lead are formed, these being bonded to the other surface of the piezoelectric member, wherein the piezoelectric member is sandwiched between the first electrode set and second electrode. The electrodes can apply a voltage to polarize the unpolarized piezoelectric polymer material in a manufacturing process of the piezoelectric member, or apply a drive voltage to the finished ultrasonic transducer.

Piezoelectric polymer transducers.

Abstract: Poly(vinylidene fluoride) (CH2-CF2)n is a tough, flexible polymer readily available in the form of thin film which can be made piezoelectric by the temporary application of a high electric field. The areas of the film which become piezoelectric can be controlled to be the areas where metal electrodes are evaporated onto the film. The same electrodes and associated leads are subsequently used to detect the electric charge generated by the application of pressure to the active area. Such films may have applications in the measurement of occlusal forces.Many of the problems that might be encountered in an occlusal gauge have been addressed separately in other applications. For example, polymer transducers less than 100 μm thick have been developed and tested for measuring the nip pressure on an intaglio printing press. Piezoelectric polymer gauges have been successfully encased in a protective layer of another polymer to prevent the sharp edges of sand particles from breaking through the piezoelectric film. ...

Ultrasonic probe using piezoelectric composite material

Abstract: In an ultrasonic probe produced by forming stripe electrodes on a piezoelectric composite material consisting of a plurality of piezoelectric ceramic rods buried in an organic material, the gaps between the stripe electrodes in the direction of disposition are expanded as much as possible while the gaps of the piezoelectric ceramic rods or their width in the direction of disposition is reduced as much as possible. When the width of the piezoelectric ceramic rod is reduced in the manner described above, the width of the piezoelectric ceramic rod is expanded in a direction orthogonal to the direction of disposition or the gaps of the piezoelectric ceramic rods in that direction is reduced in order to reduce crosstalk and to improve flexibility and sensitivity.

Bending piezoelectricity in monomorph polymer films

Abstract: Studies with laser‐induced pressure pulses show the existence of a piezoelectric monomorph polarization in 22–25‐μm‐thick PVDF films after irradiation with a 30‐kV electron beam. The bending piezoelectric stress constant β31 and the tensile piezoelectric strain constant d31 were determined for such monomorph samples. Both β31 and d31 increase with increasing irradiation time and a linear relation between them is found. The highest values of β31 and d31 achieved are 90 nC/m and 3 pC/N, respectively. A theory is presented for a film with a step‐shaped distribution of polarization along the thickness. A bending piezoelectric strain constant f31 is defined which relates the electric displacement to the stress gradient along the thickness. It is concluded that β31 is determined by the distribution of d31 and f31.

Quantum-well acoustic charge transport device

Abstract: An improved acoustic charge transport device having an acoustic wave passing through a piezoelectric semiconductor is improved by utilizing heterostructure Quantum-wells for confining charge packets.

Pyroelectric and isotropic piezoelectric polymer blends

Abstract: A pyroelectric and isotropic piezoelectric polymeric film, the film being formed from a blend of polyvinylidene fluoride and at least one polymer miscible therewith, and prepared by forming the film, heating it to a temperature sufficient to render the film substantially amorphous, cooling at a rate and to a temperature sufficient to prevent crystallization, and polarizing the film to render same β-crystalline and pyroelectric and isotropically piezoelectric.