Showing papers on "Piezoelectricity published in 1992"

Linear electro-elastic fracture mechanics of piezoelectric materials

Abstract: The concepts of linear elastic fracture mechanics, generalized to treat piezoelectric effects, are employed to study the influence of the electrical fields on the fracture behavior of piezoelectric materials The method of distributed dislocations and electric dipoles, already existing in the literature, is used to calculate the electro-elastic fields and the energy-release rate for a finite crack embedded in an infinite piezoelectric medium which is subjected to both mechanical and electric loads The energy-release rate expressions show that the electric fields generally tend to slow the crack growth It is shown that the stress intensity factor criterion and the energy-release rate criterion differ when the energetics of the electric field is taken into account The study of crack tip singular stress field yields a possible explanation for experimentally observed crack skewing in the presence of a strong electric field

Theory of the electric polarization in crystals

Abstract: Contrary to common textbook statements, the macroscopic electric polarization of a crystal cannot be unambiguously defined as the dipole of a unit cell. The only measurable quantities are either derivatives of the polarization (dielectric susceptibility, Born effective charges, piezoelectricity, pyroelectricity) or finite differences (ferroelectricity). The differential concept is a basic one in theoretical work too. I sketch here the basic theory and the state of the art in its implementation to real materials, both for induced and spontaneous polarization; for the latter case, I also propose a novel approach.

Piezoelectric micromotors for microrobots

Abstract: The authors have begun research into piezoelectric ultrasonic motors using ferroelectric thin films. The authors have fabricated the stator components of these millimeter diameter motors on silicon wafers. Ultrasonic motors consist of two pieces: a stator and a rotor. The stator includes a piezoelectric film in which bending is induced in the form of a traveling wave. A small glass lens placed upon the stator becomes the spinning rotor. Piezoelectric micromotors overcome the problems currently associated with electrostatic micromotors such as low torque, friction, and the need for high voltage excitation. More importantly, they may offer a much simpler mechanism for coupling power out. Using thin films of lead zirconate titanate on silicon nitride membranes, various types of actuator structures can be fabricated. By combined new robot control systems with piezoelectric motors and micromechanics, the authors propose creating micromechanical systems that are small, cheap and completely autonomous. >

Piezothermoelastic behavior of a laminated plate

Abstract: The response of a thin composite plate constructed of piezothermoelastic layers and subject to stationary thermal and electric fields is examined. Solutions based on classical lamination theory, extended here to include piezoelectric effects, are obtained for a “free” plate of arbitrary contour and for a simply supported, rectangular plate. Numerical results illustrate that thermally induced deformation of a structural laminate can be reduced significantly through the addition of a layer of piezoelectric material under an applied electric potential.

Metal–Ceramic Composite Actuators

Abstract: A new type of actuator composed of metal (brass) end caps and piezoelectric ceramics has been developed as a displacement transducer. Shallow cavities positioned between the metal caps and the central ceramic disk convert and amplify the radial displacement of the piezoelectric ceramic into a large axial motion of the metal end caps. Large d33 coefficients exceeding 2500 pC/N are obtained with the composite actuators. The behavior of the electrically induced strain with geometric variables, such as the thickness of the metal end caps, and with pressing force and driving frequency has been evaluated. Sizeable strains are obtained with both PZT (piezoelectric lead zirconate titanate) and PMN (electrostrictive lead magnesium niobate) ceramics.

Piezoelectric ceramic transformer being driven with thickness extensional vibration

Abstract: A piezoelectric ceramic transformer comprises a low impedance portion 11 including a plurality of piezoelectric ceramic layers 111 to 115 having different thicknesses, a high impedance portion 12 and internal electrodes 16. The low and high impedance portions 11 and 12 are subjected to a uniform polarization treatment in a thickness direction and with the same vector of polarization. The low impedance portion 11 includes one or more piezoelectric ceramic layers having a thickness different from those of the other layers therein. No delamination of electrodes or breaking of ceramics occur upon polarization treatment. Therefore, a compact piezoelectric ceramic transformer for power source which has a high mechanical quality coefficient Qm and a high electric power transmission efficiency is provided.

Non-linear constitutive relations for piezoceramic materials

Abstract: Piezoelectric materials produce electric charges when mechanically deformed and an electric potential causes a mechanical deformation. This property makes them suitable for sensor and transducer applications. Understanding of the electroelastic constitutive behavior is critical for predicting the response of a structure with embedded piezoelectric material. A concise formulation of relevant non-linear constitutive relations is presented in this paper.

Uniform fields and universal relations in piezoelectric composites

Abstract: Binary piezoelectric composites with unidirectional fibers are considered. The phase boundaries are cylindrical but otherwise the microgeometry is totally arbitrary. The constituents are transversely isotropic. The existence of uniform fields which can be generated by the application of certain mechanical and electrical boundary conditions in such composites is established. The results are used to derive universal relations for the pointwise fields as well as for the effective piezoelectric constants of such composites.

The determination of the elastic and electric fields in a piezoelectric inhomogeneity

Abstract: The transformed inclusion problem in a piezoelectric solid of general anisotropy is studied. An anisotropic piezoelectric medium contains a subregion Ω of a different piezoelectric solid which undergoes constant eigenstresses and spontaneous electric polarizations. An analytical solution is constructed for ellipsoidal shapes Ω in an unbounded surrounding matrix. A related problem is that in which no eigenstresses and polarizations are prescribed anywhere, but instead the inhomogeneity‐matrix assembly is subjected to an external electromechanical loading. The electric and elastic fields in this case are shown to follow from the solution of the transformed inclusion problem.

Resonant pressure sensor based on piezoelectric properties of ferroelectric thick films

Abstract: The paper describes the design, implementation and performance of a resonant sensor for gas-pressure measurement realized with screen-printed and fired PZT-based layers on an alumina diaphragm. The piezoelectric properties of these layers have been exploited to excite (with low voltage signals) and detect oscillations of the diaphragm. The layer configurations and associated vibrational modes of the diaphragm have been designed and a phase-locked loop (PLL) technique implemented in electronic circuits able to keep the resonant condition, despite the change of resonance frequency due to variation of the applied differential pressure. It is shown that for an adequate choice of operating frequency (i.e. of the vibrational mode) a good sensitivity and thermal stability of the sensor can be obtained; in this device, operating at frequency around 57.8 kHz, corresponding to the third-mode frequency ⨍ 0.3 , a shift Δ⨍ 0.3 = 650 Hz is found by changing the pressure from 0 to 900 mmHg. We found also that ⨍ 0.3 changes less than 6 × 10 −3 by changing the temperature from 23 to 100 °C. Moreover the sensor allows long-term measurements of static pressures without significant hysteresis effects.

Monolithic multipole filters made of thin film stacked crystal filters

Abstract: This invention discloses a monolithic multipole stacked crystal filter comprised of a series of cascaded 2-port semiconductor bulk acoustic resonator stacked crystal filters electrically cascaded and a shunt inductor connected between each of the 2-port filters. Each of the 2-port filters including a first and second piezoelectric layer, typically aluminum nitride. A first input electrode is positioned on a top surface of one of the piezoelectric layers and a second output electrode is positioned on a bottom surface of the other of the piezoelectric layers. A ground electrode is positioned between the piezoelectric layers. In this regard, the piezoelectric layers will resonate at a resonant frequency and provide bandpass filter characteristics. The complete monolithic multipole filter provides control of the passband shape which yields highly desirable filter characteristics.

Four-layer theory for the acoustic shear wave sensor in liquids incorporating interfacial slip and liquid structure

Abstract: A theory is developed which describes the behavior of thickness shear mode acoustic wave sensors in liquids. The linear theory for piezoelectricity is coupled to a treatment which describes interfacial viscosity in terms of an activation energy barrier to interfacial flow.

Simple model for piezoelectric ceramic/polymer 1–3 composites used in ultrasonic transducer applications

Abstract: A theoretical model is presented for combining parameters of 1-3 ultrasonic composite materials in order to predict ultrasonic characteristics such as velocity, acoustic impedance, electromechanical coupling factor, and piezoelectric coefficients. Hence, the model allows the estimation of resonance frequencies of 1-3 composite transducers. This model has been extended to cover more material parameters, and they are compared to experimental results up to PZT volume fraction nu of 0.8. The model covers calculation of piezoelectric charge constants d/sub 33/ and d/sub 31/. Values are found to be in good agreement with experimental results obtained for PZT 7A/Araldite D 1-3 composites. The acoustic velocity, acoustic impedance, and electromechanical coupling factor are predicted and found to be close to the values determined experimentally. >

Bimorph piezoelectric actuator

Abstract: PURPOSE:To constitute a stabilized closed loop position control system in which flexural rigidity of piezoelectric actuator is set higher in the longitudinal direction than in the lateral direction. CONSTITUTION:Lateral slits are made in the intermediate electrode 2 of a bimorph piezoelectric actuator having flexural rigity higher in the longitudinal direction than in the lateral direction. Piezoelectric ceramics 1a, 1b are bonded to the intermediate electrode 2 and when a voltage is applied thereon, voltages are induced between the intermediate electrode 2 and the surface electrodes provided on the opposite surfaces of the actuator thus producing electric fields. The piezoelectric ceramic 1a, 1b elongates or contracts depending on the fact that the direction of the electric field matches with the polarizing direction of the piezoelectric ceramic or not. Vibration characteristics of piezoelectric actuator include single node primary resonance mode in longitudinal direction and double node secondary resonance mode in lateral direction. This constitution realizes a stabilized control system.

Electrode-separated piezoelectric crystal oscillator and method for measurement using the electrode-separated piezoelectric crystal oscillator

Abstract: Herein disclosed is a device for determining the concentration of a substance in a solution by making use of a quartz oscillator In the device, at least one of a plurality of electrodes for applying an electrical voltage to a crystal wafer is separated from the crystal wafer, and the space between the separated electrode and the crystal wafer is filled with a conductive substance The electrode-separated piezoelectric crystal oscillator thus obtained can be made more highly accurate, smaller-sized and more inexpensive

Bonded type piezoelectric apparatus, method for manufacturing the same and bonded type piezoelectric element

Abstract: The features of the present invention are 1) to apply metallization on the bonding surface of a piezoelectric ceramic with a metal likely to react with the piezoelectric ceramic material, 2) when the piezoelectric ceramic material is soldered on the bonding surface, to apply metallization with a metal likely to react with the solder material, 3) to provide between the metallizing layers formed in 1) and 2) a metallizing layer including metal which prevents reaction between the metals and their diffusion, 4) to use a mounting member for the piezoelectric ceramic which has substantially the same thermal expansion coefficient as the piezoelectric ceramic in non-polarization condition and 5) to solder in the non-polarization condition and thereafter to polarize. As the result, a bonded type piezoelectric apparatus with a high reliability or with a broad application temperature range near from the absolute zero temperature to the Curie point of the piezoelectric element, and a method of manufacturing the same are provided.

Theoretical study on the static performance of piezoelectric ceramic- polymer composites with 1-3 connectivity

Abstract: Inhomogeneous displacement profiles have been derived for a single‐rod composite and a single‐tube 1‐3 ceramic‐polymer composite under both uniaxial and hydrostatic stress. The effective piezoelectric constants for the composites have been derived in terms of the ceramic content, the piezoelectric and elastic constants of each component, and the aspect ratio of the ceramic rod. The stress concentration inside both phases is derived from the calculated inhomogeneous displacement profiles. It is found that only a finite portion of the polymer in the vicinity of the ceramic‐polymer interface actually contributes to the stress transfer, and the induced additional stress on the ceramic also has a higher magnitude near the interface. The theoretical results quantitatively predict the performance of a given 1‐3 structure, and can be used to optimize the design parameters, such as ceramic content, aspect ratio of the ceramic rods, rod geometry and rod arrangement, resin hardness, etc., for 1‐3 structures designed for specific purposes.

New opportunities in ultrasonic transducers emerging from innovations in piezoelectric materials (Invited Paper)

Abstract: Piezoelectric materials lie at the heart of ultrasonic transducers. These materials convert electrical energy into mechanical form when generating an interrogating acoustic pulse and convert mechanical energy into an electric signal when detecting its echoes. This paper first surveys the piezoelectric materials in current use: piezoceramics, such as barium titanate, lead zirconate titanate, and modified lead titanate; piezopolymers, such as polyvinylidene difluoride and its copolymer with trifluroethylene; and piezocomposites, consisting of piezoceramic rods in a passive polymer matrix. Each material system has properties which commend them for use in the present single element transducers, annular arrays, sequenced linear arrays, and steered phased arrays. Looking to the future, new transducer possibilities are opening up due to recent piezoelectric material developments, such as, for example, synthesis techniques for fine-grained high-density piezoceramics, electrostrictive relaxor ferroelectric ceramics, novel piezoceramic forming methods, piezoceramic fiber synthesis, piezoceramic/metal multilayer structures, composite acoustoelectric materials, ferroelectric thin film growth and processing, and new piezopolymers. These innovations lead to fabrication of conventional transducers at high frequencies, fine-scale piezocomposites, 11/2-D and 2-D arrays, small intravascular transducers, as well as provide opportunities for new ultrasonic imaging techniques, using pitch-catch and non-resonant traveling wave transducers.

Simultaneous sensing and actuation using piezoelectric materials

Abstract: The possibility of using a single piezoelectric element simultaneously as both a structural actuator and collocated sensor is investigated. The coupled actuator and sensor equations for an arbitrary elastic structure with piezoelectric elements are developed using an assumed modes energy method. Examination of these equations suggests a simple implementation of collocated strain or strain rate sensing using a voltage driven piezoelectric element. The properties of such a collocated strain or strain rate sensor are presented. The general equations are applied to the case of a cantilevered beam with surface mounted piezoceramics. The theoretical derivations are validated experimentally on an actively controlled cantilevered beam test article with a single piezoelectric element used for collocated strain rate feedback.

A Study of the Response of a Simply Supported Beam to Excitation by a Piezoelectric Actuator

Abstract: This article presents a dynamic model of the response of a simply sup ported beam to excitation by actuators made using piezoelectric ceramics glued to the beam surface. The dynamic extensional strain on the beam surface is calculated by includ ing the free stress conditions at the piezoelectric actuator boundaries and by considering the dynamic coupling between the actuator and the structure. The results obtained from this analysis are compared with those from past studies, which were based on the assump tion of static coupling between the structure and the actuator. The analysis shows that the strain field (and so the beam displacement) close to the actuator is significantly different from that obtained by using static stress analysis results, and that to obtain an accurate description of the response, the coupled structural and piezoceramic actuator system must be modelled dynamically.

Characterization of piezoelectric properties of zinc oxide thin films deposited on silicon for sensors applications

Abstract: This paper reports the piezoelectric properties of zinc oxide thin films deposited on silicon wafers by a modified CVD technique based on the pyrolysis of an ultrasonic-generated aerosol. The aerosol was obtained from an organic solvent containing dissolved organometallic precursors. Direct measurement of the piezoelectric effect, as well as electromechanical resonance observations, were achieved on small beams. The coupling factor, k , of the layers reached a value of 0.09, which is comparable with the single crystal value.

Electrical surface perturbation of a piezoelectric acoustic plate mode by a conductive liquid loading

Abstract: Surface loading of a piezoelectric crystal supporting acoustic plate modes (APMs) by a dilute conductive liquid is analyzed using a perturbation theory. The formulation of the problem is such that only the electrical loading is relevant, and the mass loading and viscous entrainment caused by the solute are ignored. The perturbation in the propagation characteristics is then obtained relative to the solvent and is described in terms of the coupling coefficient, the capacitive loading, and the conductivity of the liquid. The results are compared to measurements made on Z-cut X-propagating LiNbO/sub 3/ APM device loaded with various conductive liquids of different concentrations. While an interpretation of the results can be given on the use of the APM device as a detector of the liquid properties, it is shown that a conductive liquid loading of the piezoelectric surface can be used as a means of assessing the electromechanical coupling coefficient of APMs. >

Apparatus for passive damping of a structure

Abstract: An apparatus for controlling the motion of a structural member on a space platform truss structure, launch vehicle, automobile, building, or the like is comprised of a first driving piezoelectric element and a second constraining piezoelectric element. The first piezoelectric element is embedded in or bonded onto the structural member. The second piezoelectric element is bonded onto the structural member, with a viscoelastic material (VEM) layer sandwiched between the structural member and the second piezoelectric element. The first and second piezoelectric elements are electrically connected in opposite phase. When the structural member is deformed by an applied force, the first driving piezoelectric element is correspondingly deformed, generating an electrical field. The electrical field is then applied in an opposite sense to the second piezoelectric element through the electrical connections, thereby oppositely deforming the second piezoelectric element with respect to the first piezoelectric element. This opposite deformation induces a large shear strain in the VEM layer, giving the apparatus a large damping capacity. Because the system is passive, it has great advantages over prior art systems, because of its greater simplicity, lower cost, easier maintainability, and lower weight.

Flexible piezoelectric device

Abstract: A laminated piezoelectric device is formed by sandwiching a relatively rigid central electrode layer with a pair of piezoelectric polymer films and then with a pair of outer electrode layers which are less rigid than the central electrode layer. The laminated piezoelectric device, as a whole, has a good flexibility and shows good piezoelectric characteristics represented by a hydrostatic piezoelectric constant dh and a symmetrical vibration characteristic. The outer electrode layers may preferably be constituted as a sprayed coating electrode which shows good solderability and peel strength.

PmP118. Piezoelectric ceramics for high-temperature transducers

Abstract: The ferroelectrics of the Aurivillius family having TC >700°C are investigated from the point of view of their application as high-temperature transducers. The value of piezoelectric modulus d33 and its stability are the basic parameters determining the range of application.