Karl Lubitz

Dielectric, elastic and piezoelectric properties of porous pzt ceramics

Abstract Porous ceramics with type 3–3 connectivity were prepared and investigated with a view to their application for ultrasound transducers. Ceramics with a porosity in the order of 0.4 to 0.5 exhibit sufficiently high permittivity (≈ 500), a thickness coupling factor equalling that of dense material (≈ 0.5), a low transverse coupling factor, a low vibrational Q (≈ 20) and low acoustic impedance (≈ 9·106kg/m2·s), all of which indicates their eminent suitability as a material for the fabrication of transducers as used in medical diagnostics. The experimentally determined influence of the porosity on the dielectric constants of these materials was used for the critical testing of various theories for calculating the constants of multiphase materials. It was found that the dielectric and elastic constants of porous piezoelectric ceramics can be very satisfactorily described on the basis of Bruggemans theory, which has fallen somewhat into obscurity. Their piezoelectric properties are discussed with refer...

Anisotropic piezoelectric effect in modified PbTiO/sub 3/ ceramics

Experimental and theoretical investigations of the electromechanical anisotropy of ceramics modified with Ca, Ni-Nb, and Mn are presented. It is demonstrated that the large anisotropy of these ceramics is neither a bulk property of the PbTiO/sub 3/-crystallites nor a domain wall effect. The anisotropy is caused by the statistical orientation of the crystallites in the ceramics and by the material properties due to this orientation. The ratio of electrostrictive coefficients and the ratio of single-crystal permittivities in these ceramics also play a decisive role. The result enables one to comprehend easily the dependence of the ceramics electromechanical anisotropy on the material composition, the degree of poling, and the temperature.<<ETX>>

Effect of temperature on grain size, phase composition, and electrical properties in the relaxor-ferroelectric-system Pb(Ni1∕3Nb2∕3)O3-Pb(Zr,Ti)O3

Relaxor ferroelectrics near the morphotropic phase boundary were prepared by pressureless sintering at various temperatures in order to study the influence of grain size on phase composition and electrical properties. Investigations of the microstructure indicate an increase in grain size from 0.5 to 3.7 μ m when the sintering temperature is increased from 1050 to 1290 ° C . The corresponding phase composition is changed from predominantly rhombohedral for small grain sizes to more than 80% tetragonal for larger grain sizes. Low-voltage measurements of poled and unpoled samples correlate well with the x-ray diffraction results. An increase of the permittivity after poling is found for samples with a high tetragonal phase content, while samples with a predominantly rhombohedral composition show a slight decrease. The remanent polarization as well as uni- and bipolar strain increase with increasing sintering temperature by a factor larger than 2, whereas the coercive field E C remains nearly constant for all sintering conditions.

Piezoceramic multilayer actuators for fuel injection systems in automotive area

Cofired multilayer piezoceramic actuators as extremely fast valve driving elements will lead to a significant progress in the field of fuel injection systems. A careful adaptation of the component performance to the system demands, an extraordinary high reliability, and competitive low production costs are prerequisites for this large-scale industrial application. With proper material selection as basis, conventional multilayer technology has to be substantially extended in order to achieve large stack volumes, to avoid degradation effects during cofiring and nevertheless to meet the target costs. Under large-signal driving conditions, the static and dynamic behavior of the component is essentially influenced by driving pulse shape, clamping force, and stiffness of the load. Linear FE methods are employed to calculate the performance criteria of different actuator designs. Moreover, a FE-implementation using a micromechanical domain switching model was developed in order to describe the strongly nonlinear material behavior. Together with a quantitative estimation of crack initiation and propagation by means of fracture mechanics, these methods can give valuable hits for controlling the effects of fatigue and deterioration which may limit the operating life time. In order to optimize the interaction of the electrical and mechanical parts in the injection system, dynamic models of piezoelectric components must be provided. A nonlinear model of the stack actuator has been developed for the analysis software MATLAB/SIMULINK. Special attention has been paid to the hysteresis properties.

PcI2: New piezoelectric composites for ultrasonic transducers

Abstract The combination of photolithographic processes and green ceramic body structuring methods allow the fabrication of 1–3 or 2–2 composites with very fine structures and a free geometric design. Two suitable methods – named lost mould resp. jet machining – are presented with their potential to make new transducer geometries in the frequency range ≥ 5 MHz.

Optical two channel elongation measurement of PZT piezoelectric multilayer stack actuators

A fast optical deflection measurement of multilayer actuators is described. This two beam method eliminates the measuring problems arising from fixing one side of clamped actuators by detecting the movements of both sides of the actuator. The frequency range of this interferometric measurement reaches from static up to 200 kHz. In this way fast mechanical response can be detected even in the case of rectangular pulses. The accuracy of the deflection measurement is better than 1%. The small and large signal effective d/sub 33/ data of PZT multilayer actuators, consisting of up to 500 single layers, are determined using this method. The dependence of these data on clamping force and pulse duration is investigated. For characterization of reliability of multilayer actuators the maximum number of cycles under hard driving conditions of rectangular pulses with rise times of 10 /spl mu/s leading to maximum loading currents of 20 A is determined.

Method for the manufacture of an ultrasonics antenna array

A method for the manufacture of a linear or annular ultrasonics antenna array for the megahertz range, which consists in providing a laminate of alternating layers of unsintered ceramic and spacing layers, the spacing layers being composed of a filler material which is heat fugitive at the sintering temperature of the ceramic, the spacing material also including refractory grains distributed therein of a size which corresponds to the spacing desired between the ceramic layers, sintering the laminate to thereby liberate the filler material and leave voids between the refractory grains, impregnating the resulting laminate with a polymerizable resin to bond the sintered ceramic layers together, and separating the resulting laminate into individual transducer elements.

Energy considerations of PZT multilayer actuators under dynamic driving conditions

By means of fast optical two channel elongation measurement, with a resolution of 0.05 /spl mu/m, the dynamic behavior of PZT multilayer stack actuators, consisting of some layers and with typical dimensions of 10/spl times/10/spl times/20 mm/sup 3/, driven under different clamping conditions is investigated. In addition to the deflection measurement, the electrical power consumption and the dynamic and static forces are measured simultaneously. Starting from the measurement of the working characteristics, including the determination of dynamic stiffness and blocking force, the mechanical output for different mechanical preloads and for different mechanical stiffnesses of load is evaluated. Choosing the optimum preload and stiffness of load, maximum mechanical output can be achieved. It can be shown that the mechanical load also influences the electrical power consumption of the clamped actuator. Depending on the composition of the PZT ceramic, the clamping conditions may cause depolarization. Under driving conditions additional repolarization effects induce increased deflection. This can be used to find optimum material compositions for given mechanical preloads of clamped actuators.

Limitation of the degradation effect in piezoelectric multilayer actuators with ceramic layer thickness below 50 /spl mu/m

During the cofiring of PZT actuators, interactions between electrodes and ceramics occur that induce a degradation in the large signal piezoelectric properties for ceramic layer thicknesses below 50 /spl mu/m. It has been shown that the clamping forces applied to the ceramics due to thermal mismatch between the electrode and the ceramics are responsible for the reduction in the large signal piezocoefficient d/sub 33/ A shift in the ratio of electrode/ceramic layer thickness proved to be the best method to reduce the clamping forces applied to the ceramics. Consequently, an increase in d/sub 33/ of 50% could be achieved for samples with a 17 /spl mu/m ceramic layer thickness.