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The piezoelectric dij coefficient is often regarded in materials science as the most important figure of merit of piezoelectric performance. For many applications, the piezoelectric gij coefficient which correlates to voltage output and sensitivity of a piezoelectric material can be considered of equal or increased importance, however is often an overlooked parameter in materials science literature. The aim of this review is to highlight the importance of this parameter and to provide insight into the mechanisms that drive a high piezoelectric voltage coefficient in single crystal, polycrystalline, and composite form. For bulk ceramics, special attention is given to tetragonal systems due to the availability of electrical and crystallographic data allowing for a clear structure-property relation. Orthorhombic and rhombohedral systems are mentioned and specific cases highlighted, however investigating structure-property relations is difficult due to the lack of crystallographic datasets. Composite materials have been the forefront of high gij piezoelectric materials over the decades and are therefore also considered in both ceramic-matrix and polymer-matrix form. An overview of applications in medical, energy, fishing and defence industries where a high gij is desirable are considered and the scientific and commercial considerations that must be made for the transition from laboratory to industry are discussed from the perspective of integrating new piezoelectric materials into sonar devices.

Die Ultraschall-Computertomographie (USCT) ist ein vielversprechendes medizinisches Bildgebungsverfahren zur Früherkennung von Brustkrebs. Am Karlsruher Institut für Technologie wird derzeit ein Gerät der dritten Generation (3D-USCT-III) für 3D-Aufnahmen entwickelt. Unter den kritischsten und technologisch anspruchsvollsten Komponenten dieses Geräts sind die Schallwandlerarrays. Diese müssen eine pseudozufällige Positionierung einzelner Wandler ermöglichen, hohe Bandbreiten, große Öffnungswinkel und eine isotrope Schallabstrahlung aufweisen sowie den Vorschriften für Medizinprodukte genügen. In dieser Arbeit wird die Realisierung neuer Schallwandlerarrays (TAS-III) für die 3D-USCT-Bildgebung umfassend vorgestellt. Dies beinhaltet die Definition von Anforderungen, Systemdesign, automatisierte Fertigung, Charakterisierung und Entwurfsoptimierung. Kernelement des TAS-III-Designs sind Scheiben aus piezoelektrischen Verbundwerkstoffen, die 18 in Polymer eingebettete, räumlich verteilte piezokeramische Fasern enthalten. Zusätzliche Scheiben zur akustischenAnpassung und Dämpfung werden auf beiden Seiten angebracht, um die Arrays zu finalisieren. Für die Herstellung der benötigten 256 TAS-III wurde ein teilautomatisierter Fertigungsprozess entwickelt. Quantitative Qualitätsprüfungen ergaben, dass mehr als 96% der produzierten Wandler voll funktionsfähig waren. Die Amplitude und der Phasenwinkel des akustischen Feldes von 54 Wandlern wurden gemessen und ausgewertet. Die meisten der definierten Anforderungen wurden erfüllt. Es wurde eine mittlere Mittenfrequenz von 2,6 MHz, mit einer fraktionellen Bandbreite von 134% bei -10 dB ermittelt. Die Bandbreite resultiert dabei aus zwei unterschiedlichen Schwingungsmoden. Messungen in 3D zeigten isotrope Abstrahlcharakteristiken mit einem mittleren Öffnungswinkel von 42,8°. Für die Analyse und Optimierung des Designs wurden verschiedene Modellierungsansätze entwickelt. Geringfügige Änderungen der Länge und des Durchmessers der piezoelektrischen Fasern sowie eine höhere laterale Dämpfung konnten die Leistung in gewissem Maße verbessern. Der Umfang weiterer möglicher Verbesserungen zeigte jedoch, dass das TAS-III Design nahe am erreichbaren Optimum liegt. Alternative Wandlertechnologien wurden untersucht, umdie grundsätzlichen Grenzen von Verbundwerkstoffen bestehend aus piezoelektrischen Fasern in Bezug auf Öffnungswinkel und Bandbreite zu überwinden. Der Ersatz der Fasern durch einkristalline piezoelektrische Materialien verspricht eine Erhöhung der Bandbreite um 35%, erfordert jedoch umfangreiche Anpassungen in den Herstellungsprozessen. Die Charakterisierung von mikromechanischen Ultraschallwandlern ergab eine signifikante Vergrößerung des Öffnungswinkels, aber geringere erzeugte Schalldrücke. Dennoch machen die Eigenschaften und die verfügbare Designfreiheit diese Schallwandlertechnologie sehr vielversprechend für zukünftige 3D-USCT- Generationen. Die entworfenen und realisierten TAS-III erwiesen sich als rundum geeignet für den vorgesehenen Einsatz und wurden in zwei 3D-USCT-III-Geräten integriert. Ausführliche klinische Tests werden in naher Zukunft durchgeführt, um die Sensitivität und Spezifität dieser neuartigen 3D-Ultraschallbildgebungsmethode zu bewerten.

Despite many years of clinical use of ultrasound, the results of different reviews of controlled trials on the efficacy of ultrasound physical therapy for different musculoskeletal injuries continue to question its efficacy. However, “in vitro” experiments with well-controlled cell cultures and experiments with animal models show positive results. The question is whether the commercial systems used by physiotherapists can deliver the required ultrasonic dose to the exact location on the body. The object of this work is the design, realization and testing of a new concept of ultrasound system for Physiotherapy capable of focusing the ultrasound beam to apply the required ultrasonic energy dose at the point targeted by the physiotherapist. The system is designed for non-thermal effects Physiotherapy. The system consists of conceptually new piezocomposite arrays with a metallic delay line, multi-pulser electronics for emission focusing, parallel robots for mechanical steering and positioning of the array transducers, and linear and angular encoders to allow the physiotherapist to direct the focus to the target. The multi-pulser and parallel robot angulation are controlled by the computer, using a graphical interface software., The authors acknowledge support from the Spanish Research Agency- Ministry of Sciencie and Innovation-, grant number DPI2016-80254-R.

Piezoelectric composites are a class of functional materials consisting of piezoelectric active materials and non-piezoelectric passive polymers, mechanically attached together to form different connectivities. These composites have several advantages compared to conventional piezoelectric ceramics and polymers, including improved electromechanical properties, mechanical flexibility and the ability to tailor properties by using several different connectivity patterns. These advantages have led to the improvement of overall transducer performance, such as transducer sensitivity and bandwidth, resulting in rapid implementation of piezoelectric composites in medical imaging ultrasounds and other acoustic transducers. Recently, new piezoelectric composite transducers have been developed with optimized composite components that have improved thermal stability and mechanical quality factors, making them promising candidates for high temperature, high power transducer applications, such as therapeutic ultrasound, high power ultrasonic wirebonding, high temperature non-destructive testing, and downhole energy harvesting. This paper will present recent developments of piezoelectric composite technology for high temperature and high power applications. The concerns and limitations of using piezoelectric composites will also be discussed, and the expected future research directions will be outlined.

A micromechanics-based analytical model is developed to evaluate the performance of 1-3-2 piezoelectric composite where both matrix and fiber materials are piezoelectrically active. A parametric study is conducted to investigate the effects of variations in the poling characteristics of the fiber phase on the overall thermo-electro-mechanical behavior of a 1-3-2 piezocomposite. The performance of the 1-3-2 composite as a transducer for underwater and biomedical imaging applications is analyzed. The proposed model is capable of predicting the effective properties of the composite subjected to thermo-electro-mechanical loading conditions. The predicted variations in the effective elastic, piezoelectric and dielectric material constants with fiber volume fraction are nonlinear in nature. It is observed that the influence of thermal effects on effective properties of the composite also induces polarization in the composite. The analytical results show that an appropriate selection of the poling characteristics of the individual fiber and matrix phases could lead to the development of a piezocomposite with significant effective properties. � Springer-Verlag 2012.

An analytical model is developed to evaluate the performance of 1-3-2 piezoelectric composite where both matrix and fiber materials are piezoelectrically active. A parametric study is conducted to investigate the effects of variations in the poling characteristics of the matrix phase on the overall thermo-electro-mechanical behavior of a 1-3-2 piezocomposite. The figures of merit (FOM) of the 1-3-2 composite as a transducer for underwater acoustics and biomedical imaging applications have been analyzed. It is demonstrated that the effective electromechanical coupling coefficient (K t) can be enhanced by poling the polymer matrix at 180� poling direction for low ceramic rod volume fraction. The predicted variations in the effective elastic, piezoelectric, and dielectric material constants are nonlinear in nature with fiber volume fraction. It is observed that the influence of thermal effects on effective properties of the composite also induces the polarization in the composite. Also, it is observed from the results that an appropriate selection of the poling characteristics of the individual fiber and matrix phases could lead to the development of a piezocomposite with significant effective properties. � 2011 Elsevier B.V. All rights reserved.

In this paper a Euler–Bernoulli-like model of layered piezoelectric beams is presented. It describes more accurately than the others already presented in the literature both transverse (Poisson and piezoelectrically induced) cross-sectional deformations and through-the-thickness variations of the electric field and electric displacement. A deductive approach based on a mixed variational formulation is adopted and distributions of deformation, stress, electric field and electric displacement are simultaneously prescribed. The attention is focused on the choice of the most fitting assumptions to recover complex 3D cross-sectional field distributions. In particular, transverse interactions between different layers are taken into account by enforcing specific conditions on transverse stress through the Lagrange multipliers method. The estimate of electromechanical beam constitutive coefficients is discussed and comparison with standard modelling approaches, which assume either vanishing transverse stresses or vanishing transverse strains, is emphasized. For a sandwich piezoelectric beam and for a two-layer beam, expressions of the beam constitutive coefficients are provided and the main features of the proposed model are highlighted by presenting the through-the-thickness distribution of the 3D state fields associated to beam-axis deformations and applied voltage. As a main peculiarity, the proposed beam model is able to coherently estimate the equivalent piezoelectric capacitance also when the thickness of elastic and piezoelectric layers is comparable.

Experiments are conducted to measure the effective properties and also the time dependent behaviour of 1-3 piezocomposites and bulk piezoceramics subjected to cyclic electric field at room temperature under quasi static loading condition in the non-linear regime. Experimental dielectric and butterfly hysteresis show that 1-3 piezocomposite exhibits the time dependent behaviour. Hence a viscoelastic based numerical model has been proposed to predict the time dependent effective properties of 1-3 piezocomposites and bulk piezoceramics. The predicted effective properties are incorporated in the proposed 3D finite element based micromechanical model to predict the time dependent non-linear electromechanical behaviour of 1-3 piezocomposites and compared with experimental observations. The experimental and simulated results show that the presence of epoxy polymer constituent in 1-3 piezocomposite has an influence on the non-linear time dependent electromechanical response of 1-3 piezocomposite. � 2014 Elsevier Ltd and Techna Group S.r.l.

Under high mechanical loading, 1-3 piezocomposites experience ferroelastic switching that causes depolarization. The combination of thermal and mechanical loads may affect the performance of 1-3 piezocomposites. A theoretical and experimental analysis has been carried out to study the ferroelastic behaviour of 1-3 piezocomposites under thermal load. Temperature dependent effective properties are determined analytically using equivalent layered approach and compared with the experimental values measured based on resonance technique. Experiments are conducted on poled piezocomposite samples subjected to large compressive stress, parallel to the fiber (poling) direction at elevated temperatures. A thermodynamically consistent uni-axial model is proposed to simulate the macroscopic behaviour of ferroelastic switching on piezocomposites. Volume fractions of three distinct uni-axial variants (instead of six variants) are used as internal variables, which describes the distribution of crystallographic orientation and polarization state of the crystal. Non-linear hardening parameter, based on gaussian function, is introduced to incorporate the grain boundary effects. The predicted effective properties are used in the uni-axial model and the classical stress versus strain and stress versus electrical displacement curves are simulated. Comparison between the experiments and simulations show that the proposed model can reproduce the characteristics of non-linear response. It is observed that the fiber volume fraction and temperature has a strong influence on the ferroelastic response of 1-3 piezocomposites. � 2013 Elsevier Ltd. All rights reserved.

A systematic investigation of the stress-dependent non-linear electromechanical properties of 1-3 piezocomposites for different fiber volume fractions and bulk piezoceramics is carried out. Experiments are conducted to measure the electrical displacement and longitudinal strain on piezocomposites and bulk ceramics under uni-axial compressive stress loading conditions. A simplified uni-axial micro-macromechanical model based on thermodynamic framework is developed to predict the behaviour. Volume fractions of three distinct uni-axial variants (instead of six variants) are used as internal variables to describe the microscopic state of the material. In order to calculate the effective properties (elastic, piezoelectric and dielectric constants) of piezocomposites for different fiber volume fractions, an analytical model based on equivalent layered approach is proposed. The predicted effective properties are incorporated into uni-axial model and the classical stress versus strain and stress versus electrical displacement curves are simulated. Comparison between the experiments and simulations show that the proposed model can reproduce the characteristics of non-linear coupled response. It is observed that, the variation in the fiber volume fraction has a significant influence in the response of 1-3 piezocomposites. � 2012 Elsevier Masson SAS. All rights reserved.

A study is carried out to compare the non-linear behaviour of 1-3 piezocomposites with different volume fractions and bulk piezoceramics. Experiments are conducted to measure the electrical displacement and strain on piezocomposites and ceramics under high cyclic electrical loading. A thermodynamically consistent framework, combining the phenomenological and micromechanical models, is developed to predict the coupled behavior. Volume fractions of three distinct uni-axial variants (instead of six variants) are used as internal variables to describe the microscopic state of the material. In this model, the grain boundary effects are taken into account by introducing the back fields (electric field and stress) as non-linear kinematic hardening functions. In order to calculate the effective properties (elastic, piezoelectric, and dielectric constants) of piezocomposites for different volume fractions, an analytical model based on equivalent layered approach is proposed. The predicted effective properties are incorporated in the proposed model, and the classical hysteresis (electrical displacement versus electric field) as well as butterfly curves (strain versus electric field) is simulated. Comparison between the experiments and the simulations shows that this model can reproduce the characteristics of non-linear coupled response. It is observed that the variation in fiber volume fraction has a significant influence on the response of the 1-3 piezocomposites. � 2012 American Institute of Physics.

An analytical method based on parallel and series models is developed to evaluate the performance of 1-3 piezoelectric composite where both matrix and fiber phases are piezoelectrically active. A parametric study is conducted to investigate the influence of the volume fraction of ceramic on the smart composite and the performance of the 1-3 composite for underwater acoustics and biomedical imaging has been addressed. The present model is capable of predicting the effective properties of the composite subjected to thermo-electro-mechanical loading conditions. Simulated results are compared with experimentally measured data reported in literature (Taunaumang et al., 1994 [1]) and are found to be in reasonable agreement. The outcome of the present study demonstrates the influence of thermal effect on effective properties of the composite induces the polarization in the composite. Along the loading direction, there is a significant reduction in the effective pyroelectric coefficient of the piezocomposites, except near the monolithic ceramic fiber material. � 2010 Elsevier B.V. All rights reserved.

This work focuses on evaluating the time-dependent non-linear ferroelastic behaviour of 1-3 piezocomposites under pure uni-axial compressive stress loading condition. An experimental setup is developed to study the influence of high-stress levels on the stress-strain and stress-polarization behaviour of 1-3 piezocomposites. The electro-elastic effective properties of 1-3 piezocomposites are measured experimentally based on IEEE standard and compared with the proposed numerical model using finite-element software ABAQUS. The time-dependent effective properties are evaluated using viscoelastic model and it is incorporated into a 3D micromechanical model to predict the viscoelastic behaviour of 1-3 piezocomposites under mechanical loading. The simulated results are compared with the viscoelastic behaviour of 1-3 piezocomposites obtained from experiments. � 2015 Author(s).

A micromechanics-based analytical model is developed to evaluate the performance of 1-3-2 piezoelectric composite where both matrix and fiber materials are piezoelectrically active. A parametric study is conducted to investigate the influence of the ceramic base and the fiber volume fraction on the modified 1-3 composite. The performance of the 1-3-2 composite as a transducer for underwater acoustics and biomedical imaging applications has been analyzed. The proposed model is capable of predicting the effective properties of the composite subjected to thermoelectromechanical loading conditions. Simulated results of 1-3 type piezocomposite compare well with experimentally measured data reported in the literature (Taunaumang et al 1994 J. Appl. Phys. 76 484-9). The present study demonstrates that the low end ceramic base volume fraction of 1-3-2 composite yields comparative performance with 1-3 type composite. It is observed that the influence of thermal effects on the effective properties of the composite also induces the polarization in the composite. � 2010 IOP Publishing Ltd.

0-3 and 1-3 composites have been fabricated using piezoelectric single crystals (PSCs). These two connectivities were specifically chosen for large area fabrication. In particular, a lamination technique was used for 1-3 piezocomposites instead of the standard dice and fill method. For 0-3 connectivity, the thickness coupling factor of fabricated materials using PSC phase is twice the value obtained using standard PZT powder for the same volume fraction (60%). But the efficiency of the poling stays low. For the 1-3 piezocomposites, the properties (such as the thickness coupling factor) of the samples fabricated by the lamination technique are comparable to those obtained with standard methods. Finally, three ultrasonic transducers with center frequency between 600 and 850 kHz were fabricated to evaluate the performance of these new piezoelectric composites.

Summarization: A mathematical model of smart composite beams and plates with piezoelectric layers that take into account the adhesive between the layers has been created. The finite element method has been used for the numerical solution of related static and dynamic problems. Furthermore, delamination between various layers has been modelled, in order to estimate one of the most commonly appearing damage in composites. Finally, active control is applied by means of optimally tuned fuzzy inference rules. Tuning has been achieved using genetic optimization. The results demonstrate a viable way of modelling and optimal design of active smart piezocomposites. Παρουσιάστηκε στο: 3rd Polish Congress of Mechanics, PCM 2015 and 21st International Conference on Computer Methods in Mechanics