Piezoelectric Transducer Applications Research Articles

Dielectric polarization and strain behavior of Ba(Ti 0.92Zr 0.08)O 3 single crystals

The ferroelectric polarization and strain behavior was studied for Ba(Ti 0.92Zr 0.08)O 3 single crystals with a rhombohedral symmetry at room temperature. The anisotropic dielectric spectra obtained from different orientation cuts showed suppression of permittivity maximum ( ε max) with increasing frequencies. However, no significant T c-shift with increasing frequencies was observed. The polarization data obtained from the hysteresis loops measured in a wide temperature range indicated a relaxation-like behavior as the remnant polarization exists much beyond T c. The unipolar strain level is 0.17% at 55 kV/cm and the piezoelectric strain coefficient d 33 ∼850 pC/N measured for the 〈001〉 oriented Ba(Ti 0.92Zr 0.08)O 3 single crystals are promising values in a lead-free material for the piezoelectric transducer applications.

Growth of Ba(Ti 1− xZr x)O 3 single crystals by the laser heated pedestal growth technique

Single crystals of the ferroelectric Ba(Ti 1− x Zr x )O 3 ( x=0.05 and 0.08) were grown by the laser heated pedestal growth (LHPG) technique. The perovskite structure of the crystals was identified by the X-ray diffraction technique. Crystals were examined by Laue patterns and scanning electron microscopy (SEM), which indicated that the single crystals were of good crystallinity and compositional homogeneity. The anisotropic dielectric and piezoelectric behavior was characterized. The Ba(Ti 1− x Zr x )O 3 single crystals possessed a high-level hysteresis-free electromechanical strain and are promising lead-free ferroelectric crystals for the piezoelectric transducer applications.

Dielectric relaxation in Ba-based layered perovskites

Ferroelectric materials with Bi-layered structure such as SrBi2Ta2O9 and SrBi2Nb2O9 are now intensively investigated in view of their applications in nonvolatile computer memories and high-temperature piezoelectric transducers. When Sr2+ is substituted with Ba2+, a significant disorder is induced and the material exhibits broadening of the phase transition. Such broadening is essential for applications since it allows achieving smooth temperature characteristics while maintaining high dielectric and piezoelectric properties. In this work, stoichiometric dense BaBi2Nb2O9 (BBN) ceramics are sintered using a mixed oxide route. Dielectric and ferroelectric properties are investigated in a broad range of temperatures and frequencies. Strong dispersion of the complex relative dielectric permittivity is observed including typical relaxor features such as shift of the permittivity maximum with frequency and broadening of the relaxation time spectrum with decreasing temperature. The dielectric relaxation obeys the Vögel–Fulcher relationship with anomalously low freezing temperature (Tf≈100 K), which is much lower than the permittivity maximum in the radio-frequency range. Polarization hysteresis loops testify linear properties of BBN at all temperatures above Tf. The properties of BBN ceramics are compared to conventional relaxor systems such as Pb(Mg, Nb)O3 and (Pb, La)(Zr, Ti)O3.

Quartz Crystal Microbalance for Bioanalytical Applications

The quartz crystal microbalance (QCM) was first introduced as a mass sensor in gas phase and in vacuum. Since oscillator circuits capable of exciting shear vibrations of quartz resonators under liquid load have been developed, the QCM became accepted as a new powerful technique to monitor adsorption processes at solid/liquid interfaces in chemical and biological research rendering the method an attractive low-cost alternative for bioanalytic applications. In the last decade, adsorption of biomolecules on functionalized surfaces turned out to be one of the paramount applications of piezoelectric transducers comprising the interaction of DNA and RNA with complementary strands, specific recognition of protein-ligands by immobilized receptors, the detection of virus capsids, bacteria, mammalian cells and last but not least the development of complete immunosensors. Piezoelectric transducers allow a label-free detection of molecules; they are more than mere mass sensors since the sensor response is also influenced by interfacial phenomena, viscoelastic properties of the adhered biomaterial, surface charges of adsorbed molecules and surface roughness. These new insights have recently been used to investigate the adhesion of cells, liposomes and proteins onto surfaces allowing to determine morphological changes of cells as a response to pharmacological substances and changes in the water content of biopolymers in situ. However, future will show whether the quartz crystal microbalance will assert itself against established label-free sensor devices like surface plasmon resonance spectroscopy and interferometry.

Relaxor properties of Ba-based layered perovskites

Ferroelectric materials with Bi-layered structure such as SrBi2Ta2O9 (SBT) and SrBi2Nb2O9 (SBN) are now intensively investigated in view of their applications in non-volatile computer memories and high-temperature piezoelectric transducers. When Sr is substituted with Ba, significant disorder is induced and material exhibits broadening of the phase transition. In this work, BaBi2Ta2O9 (BBT) and Ba2Bi2Nb2O9 (BBN) ceramics were sintered using mixed oxide route. Dielectric properties were investigated in the temperature range 20–600°C at frequencies 25 Hz to 1 MHz. Strong dispersion of the dielectric permittivity is found indicating relaxor nature of the phase transition. It is shown that the dielectric relaxation in BBN ceramics is different from that of conventional relaxors such as PbMg1/3Nb2/3O3 (PMN). Fitting with Vögel–Fulcher relationship is used to evaluate parameters of the dielectric relaxation such as freezing temperature and attempt frequency.

Piezoelectric Mass-Sensing Devices as Biosensors-An Alternative to Optical Biosensors?

In the early days of electronic communication-as a result of the limited number of quartz resonators available-frequency adjustment was accomplished by a pencil mark depositing a foreign mass layer on the crystal. In 1959, Sauerbrey showed that the shift in resonance frequency of thickness-shear-mode resonators is proportional to the deposited mass. This was the starting point for the development of a new generation of piezoelectric mass-sensitive devices. However, it was the development of new powerful oscillator circuits that were capable of operating thickness shear mode resonators in fluids that enabled this technique to be introduced into bioanalytic applications. In the last decade adsorption of biomolecules on functionalized surfaces turned in to one of the paramount applications of piezoelectric transducers. These applications include the study of the interaction of DNA and RNA with complementary strands, specific recognition of protein ligands by immobilized receptors, the detection of virus capsids, bacteria, mammalian cells, and last but not least the development of complete immunosensors. Piezoelectric transducers allow a label-free detection of molecules; they are more than mere mass sensors since the sensor response is also influenced by interfacial phenomena, viscoelastic properties of the adhered biomaterial, surface charges of adsorbed molecules, and surface roughness. These new insights have recently been used to investigate the adhesion of cells, liposomes, and proteins onto surfaces, thus allowing the determination of the morphological changes of cells as a response to pharmacological substances and changes in the water content of biopolymers without employing labor-intense techniques. However, the future will show whether the quartz-crystal microbalance will assert itself against established label-free sensor devices such as surface plasmon resonance spectroscopy and interferometry.

Effect of poling procedure on the properties of lead zirconate titanate/vinylidene fluoride-trifluoroethylene composites

Lead zirconate titanate/vinylidene fluoride-trifluoroethylene [PZT/P(VDF-TrFE)] 0–3 composites for pyroelectric sensor and piezoelectric transducer applications have been fabricated by incorporating PZT powder into a P(VDF-TrFE) copolymer matrix. The properties of these composites can be tailored to suit designated applications by varying the ceramic volume fraction and by using different poling procedures. As both phases in the composite are ferroelectric, and the piezoelectric coefficients of the ceramic and copolymer phases have opposite signs while the pyroelectric coefficients have like signs, special ways can be used to produce three groups of samples with (1) only the ceramic phase poled, (2) two phases poled in the same direction to achieve reinforced pyroelectric activity and reduced piezoelectric activity, and (3) two phases poled in opposite directions to obtain reinforced piezoelectric activity and reduced pyroelectric activity. In this work, original experimental results on the properties of PZT/P(VDF-TrFE) composites poled under different conditions are presented and possible reasons behind the reinforcement and cancellation of piezoelectric and pyroelectric properties are discussed.

Development of Ferroelectric Aerogels

For ultrasonic applications in gases porous piezoelectric transducers with low acoustic impedances are required. Highly porous piezoceramics can be prepared by sol-gel processing, supercritical drying and subsequent firing. These PT and PZT aerogels are obtainable as crystalline monoliths with porosities up to 70 vol%. In this paper the influence of sol-gel-synthesis, stoichiometry, drying conditions and heat treatment on the material properties are reviewed. Lowering the coercive field strength by dopants is necessary in order to facilitate the polarization of highly porous PZT-ceramics. New results show that the introduction of 2 mol% neodymium is possible in the sol-gel synthesis of the aerogel precursor. Most structural properties of the resulting PbNd0.02Zr0.53Ti0.47O3 aerogels are similar to those of the undoped material.

Maximum length sequences in non-destructive material testing: application of piezoelectric transducers and effects of time variances

In this paper it is shown that even in the field of non-destructive material testing MLS has great advantages. The application of a correlation measuring technique promises a higher dynamic resolution in many acoustical measurements, especially when using maximum length sequences (MLS) as excitation signals. After a short introduction to the measuring principle, problems are described arising when relatively narrow banded piezoelectric transducers are applied. Piezoelectric transducers are common in non-destructive material testing. By means of a phase shift in sampling, effects of frequency aliasing can be used in a constructive way to improve the dynamic range of the system. After that the paper reports on experimental investigations of the effects of time variances on the measuring results, as may appear due to a sudden or continuous motion of the sample in testing practice.

Inorganic ceramic/polymer ferroelectric composite electrets

Ferroelectric composites are now an established alternative to conventional ferroelectric ceramic materials and to the more recently discovered ferroelectric polymers. These materials due to their unique blending of polymetric properties of mechanical flexibility, formability and low cost with high electro-active properties have been been suggested to be a viable alternative both in piezoelectric and pyroelectric transducer applications. This review is devoted to the piezoelectric and pyroelectric properties exhibited by these type of composites with a special reference to those made of ceramic particles embedded in a polymer matrix (i.e. 0-3 connectivity type composite). A review of models predicting the electro-active properties of 0-3 composites is presented together with a proposal for a new mixed connectivity cubes model to be applicable to the case of high ceramic loading and/or when the ceramic grain size incorporated in the polymer matrix is comparable to the thickness of the sample. A review of the experimental results of the piezo- and pyroelectric properties of various ferroelectric composite materials, reported by several workers, is also presented in this paper. Special reference is made to composites made from calcium modified lead titanate and poly(vinyldene fluoride-trifluorethylene) emphasizing their advantages in the poling process which is a critical phase in the process of obtaining successful electro-active 0-3 composite electrets.

Effect of surface acoustic waves on activity in heterogeneous catalysis

A synopsis of the recent developments in acoustically influencing and controlling gas-surface interactions is presented. The cleaning effect of ultrasound and its surface activation play an important role for the sonochemical enhancement of reactivity in chemical processes involving solid and liquid phases. So far, there have only been a few studies on the effects of surface acoustic waves on surface chemical reactions under high-vacuum conditions by the application of piezoelectric surface acoustic wave transducers. Very recently, metal films deposited between InterDigital Transducer (IDT) electrodes on a LiNbO3 substrate have shown a significant inerease in catalytic activity during surface acoustic excitation and Edge-Bonded Transducers (EBT) with a metal single crystal as a substrate have been used to acoustically influence the rate in the oscillatory reaction for CO oxidation. Tunable narrowband surface acoustic excitation is anticipated to be an efficient route to control catalytic processes, and in our work this approach is being used to investigate the physical basis of this process.

Powderless processing of ceramics: Thin-layer electroceramics

A review is made of progress on the sol-gel processing of dense insulating electroceramics by polymeric condensation routes. Up until the past ten years, powders and porous coatings were principally made for optical and conductive applications. Much effort was expended on silica (SiO2) and silicate-based systems. Recently, these approaches have been extended to non-silicate systems [1]. In this paper information is presented for the powderless processing of selected electroceramics in thin-layer form. Materials include PbTiO3, BaTiO3, Ba1−x Pb x TiO3, PbZrO3, Pb(Zr1−y Ti y )O3 and (Pb1−x La x )(Zr1−y Ti y )O3 which find applications in ceramic capacitors, piezoelectric transducers and electrooptic modulators. The approach is to avoid powders, and the attendent problems of powder handling, flow, packing, etc., and make use of polymerization condensation reactions to form extended networks with chemical linkage. Data are reported for the synthesis and low temperature processing routes for amorphous and polycrystalline ceramics.

Application of Golay codes and piezoelectric ultrasound transducer to biomedical noninvasive measurement

Golay codes posses the property that combining the products of the two individual codes of the pair causes the self-induced noise to cancel out. This gives significant improvements in the signal to noise ratio obtained with short codes in signal to noise ratio enhancement systems, making the codes useful in biomedical Doppler applications. The present work combines these codes with an experimental piezoelectric ultrasound transducer in a water bath. It is shown that the resulting signal-to-noise-ratio improvements are greatest when the input-signal-to-noise ratio is greater than unity and the target is obscured by clutter. This system can be used to send multiple codes, with code identification after detection, to extend the range-velocity limit in medical Doppler systems. It is also shown that pulse shape integrity is important in these systems, and that the required bandwidth is large. Transducers using polyvinylidene fluoride (PVDF) sensor material are shown to give increased pulse integrity and bandwidth in comparison with PZT. >

Numerical simulation for electromechanical transducers : Piezoelectric transducer and actuator applications

Numerical simulation for electromechanical transducers : Piezoelectric transducer and actuator applications

Thermodynamic theory of the lead zirconate-titanate solid solution system, part I: Phenomenology

Abstract Compositions within the lead zirconate-titanate (PZT) solid solution system have been extensively used in polycrystalline ceramic form in a wide range of piezoelectric transducer applications. However, the growth of good quality PZT single crystals for compositions across the entire phase diagram has not been accomplished. Due to the lack of single-crystal data, an understanding of the properties of polycrystalline PZT has been limited. If the single domain (intrinsic) properties of PZT could be determined, then the extrinsic contributions (e.g. domain wall and defect motions) to the polycrystalline properties could be separated from the intrinsic contributions. The purpose of this research has been to develop a thermodynamic phenomenological theory to model the phase transitions and single-domain properties of the PZT system. This paper is the first of a series of five papers describing the thermodynamic theory of PZT that has been developed for the entire solid solution system. In this paper th...

Thermodynamic theory of the lead zirconate-titanate solid solution system

Abstract Compositions within the lead zirconate-titanate (PZT) solid solution system have been extensively used in polycrystalline ceramic form in a wide range of piezoelectric transducer application. However, the growth of good quality PZT single crystals for compositions across the entire phase diagram has not been accomplished. Due to the lack of single crystal data, an understanding of the properties of ceramic PZT has been limited. If the single domain (intrinsic) properties of PZT could be determined, then the extrinsic contributions (e.g., domain wall and defect motions) to the ceramic properties could be separated from the intrinsic contributions. The purpose of this research has been to develop a thermodynamic phenomenological theory to model the phase transitions and single domain properties of the PZT system. A two-sublattice theory, where each sublattice has a separate polarization, was used to account for the ferroelectric and antiferroelectric phases. An additional order parameter was also included to account for the tilting of the oxygen octahedra in the low temperature rhombohedral phase. The resulting energy function can be used to calcuate the phase diagram; spontaneous polarization, strain, tilt angle, and entropy change; and dielectric, piezoelectric, and elastic properties of the PZT system. Without single crystal data, the development of this theory was complicated and involved indirect methods of determining the coefficients of the energy function. To provide additional experimental data, a sol-gel method was used to prepare pure homogeneous powders of PZT compositions across the phase diagram. High temperature x-ray diffraction of these powders was used to determine the spontaneous strain which was related to the spontaneous polarization through the electrostrictive coefficients. These data were then used to determine some of the coefficients of the energy function, and to locate a second tricritical point between the cubic and tetragonal phases, where the transition changes from first to second order. The calculations from this theory are in good agreement with the available experimental data, and provide a method of predicting the intrinsic single domain properties of the PZT system. The extrinsic contributions of the properties of ceramic PZT can not be separated from these intrinsic contributions. This theory can also be used to study the effect of mechanical and electrical boundary conditions on the properties and phase stability, which will be useful in understanding ceramic materials. A future direction of this research is to extend the present theory into the lanthanum modified PZT system (PLZT) to further the understanding of relaxor type materials.

Perforated pzt-polymer composites for piezoelectric transducer applications

Abstract Composites of PZT and polymer with 3-1 and 3-2 connectivity patterns have been fabricated by drilling holes in sintered PZT blocks and filling the holes with epoxy. The influence of hole size and volume fraction PZT on the hydrostatic properties of the composite was evaluated. By decoupling the piezoelectric [dbar]33 and [dbar]31 coefficients in the composite, the hydrostatic coefficients are greatly enhanced. On samples optimized for hydrophone performance, the dielectric constants of 3-1 and 3-2 composites are 600 and 300 respectively. The piezoelectric coefficients [dbar]h, [gbar]h, and [dbar]hdh for 3-1 composites are 230 (pCN−1), 34 (x10−3 VmN−1), and 7800 (10−15 m2N−1) respectively, and the corresponding values for 3-2 composites are 372 (pCN−1), 123 (10−3 VmN−1), and 45000 (10−15 m2N−1).

The piezoelectric effect, transducers and their applications

The piezoelectric effect is described and the crystal classes showing the effect are presented. The behaviour of microcrystallites under artificial poling procedures, to macroscopically produce the piezoelectric effect in ceramics, is explained.The application of single crystals and man-made piezoelectric ceramics in transducers to measure acceleration, pressure and force is presented. Some commonly used designs for such transducers are shown and the various “trade-offs” of device parameters is described.Two applications of piezoelectric transducers to measure physical phenomena in industry, aviation and fast breeder nuclear reactors, i.e. difficult physical environments, are presented.

Overlapping advance control systems for microelectrode positioning

This report discusses overlapping advance control systems in relation to the problems of resolution, compactness, and speed of response which are now present in varying degrees in commercially available rolling diaphragm hydraulic microdrives and which are considerations in certain applications. A mechanical microdrive was first described which achieves resolution (to 0.1 μm) and compactness by mounting a differential-screw translator concentrically within a micrometer screw. A prototype of this microdrive is approximately 6.5 × 6.5 cm, but the design of the unit allows a reduction of diameter to approximately 2 cm with no appreciable loss in resolution. Since the cost of construction is reasonable, this microdrive is a feasible and worthwhile alternative for the advance control of hydraulic systems. The application of piezoelectric transducer (PTZ) devices to impact rapid motion was then discussed: First, it was illustrated how a high load bearing PZT could be placed in series between a mechanical microdrive and a hydraulic system. This allows the wide range positioning capabilities of the mechanical microdrive to effect initial electrode control, while the high speed (“pulsed”) motion of the PZT is reserved to aid in the penetration of small cells or for exceedingly fine position adjustments. In this configuration, the PZT is located so as to avoid the drawbacks produced were such a device to be mounted on the final stage of a hydraulic system where its size would be likely to interfere. Finally, a newly designed PZT device—the inchworm—was described and its application to electrode positioning problems discussed as an additional and new alternative. Under boundary constraints defined by the cost of presently available stepping hydraulic microdrives, the alternatives discussed in this paper are certainly reasonable and the gains in resolution, compactness, and speed may therefore be viewed as attractive bonuses to be had in the event that they are demanded by experimental considerations.

Crystallographic Orientation of Zinc Oxide Films Deposited by Triode Sputtering

Zinc oxide films for thin film piezoelectric transducer applications have been deposited by triode sputtering onto gold film surfaces. Films sputtered under relatively hydrocarbon-free conditions showed the “normal” orientation with the c axis perpendicular to the substrate surface. The addition of hydrocarbon vapors to the sputtering gas at the beginning of the deposition resulted in films at least partly oriented with the c-axis parallel to the substrate surface, and the simultaneous application of a reverse bias to the substrate holder produced films essentially completely oriented with this parallel orientation. Under oblique deposition conditions the average c axis direction in the film plane was directed towards the target, yielding good piezoelectric shear mode transducers with a uniform polarization. It is suggested that the hydrocarbon vapors polymerize in the discharge, covering the substrate with an organic film on which zinc oxide grows with the parallel orientation, and that alignment of the c-axis in the oblique deposition arises from preferential growth of crystallites oriented with their c axis towards the target.