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This paper presents compositional modifications on lead-free material system based on barium titanate to optimize its electrocaloric (EC) properties. By addition of strontium and tin we prepared solid solutions of Ba1-xSrxSnyTi1-yO3 (BSSnT-100∙x-100∙y) which allow for shifting of maximum EC effect to room temperature as well as broadening the temperature range of high EC temperature changes Δ T E C . Bulk ceramic samples of BSSnT were prepared by solid-state reaction route and the influence of Sn:Sr ratio on dielectric and ferroelectric properties was investigated. The EC temperature change was measured directly using resistance welded thermocouple wires. Most promising results could be achieved for BSSnT-18−6.5, which showed a maximum Δ T E C of 0.49 K around 30 °C with Δ T E C > 0.3 K in the temperature range from 10 °C to 50 °C under a comparatively low electric field change of 2 V μm−1.

The present contribution reports on a novel approach for enhanced piezoelectric patch transducers based on round piezoceramic fibres. Starting from a critical review of the well-known Active Fibre Composite (AFC) concerning electrical coupling between electrodes and ceramic fibres, a new electrode design is proposed. By introducing notches into the fibres perpendicular to their axis and filling these notches witch a conductor, a much better coupling is created. This leads to a significantly better alignment of the intrinsic dipoles over a wide volume of the fibres during poling and thus to much higher piezoelectric performance of the transducers. With the aid of a finite element analyses, design rules for optimization of notched electrodes as well as prediction of transducer behaviour have been derived. For verification of the approach, transducers with varying notch depths have been built and glued onto polystyrene beams attaining active cantilevers. The setup was used to measure free displacement and blocking force generated by the transducers in comparison to other existing patch transducers. An improvement of the piezoelectric actuation up to a factor of four is observed for free deflection and blocking force, significantly exceeding results from state-of-the-art patch transducers such as Macro Fiber Composites (MFC).

The paper reports on our latest developments on fabrication of fine scale 1–3 piezocomposites for application as high frequency ultrasonic transducers using soft mold process. In previous work we showed that operating frequencies can be increased to frequencies of at least 40 MHz by modifying piezoceramic pillar size and layout within 1–3 piezocomposites. Especially circular pillars with hexagonal arrangement turned out to be beneficial to reduce influence of spurious modes. The current investigation focuses on the improvement of piezoelectric properties of 20 MHz ultrasonic transducers to enhance ultrasonic performance. During experimental verification process parameters like PZT powder as well as sintering and poling conditions were systematically varied to optimize dielectric and electromechanical properties, in particular thickness mode coupling factor k t . The results show that sintering temperature and polarization field strength are the most crucial parameters to influence coupling factor. By modifying fabrication process coupling factor could be increased to values of up to k t = 0.6. Best results were achieved by using calcined and pre-sintered PZT powder in combination with relatively low sintering temperatures ϑ s = 1060–1110 °C and high electric fields during poling $E$ pol ≥ 9 V /µm.

Substantial efforts are dedicated worldwide to use lead-free materials for environmentally friendly processes in electrocaloric cooling. Whereas investigations on bulk materials showed that Na0.5Bi0.5TiO3 (NBT)-based compounds might be suitable for such applications, our aim is to clarify the feasibility of epitaxial NBT-based thin films for more detailed investigations on the correlation between the composition, microstructure, and functional properties. Therefore, NBT-based thin films were grown by pulsed laser deposition on different single crystalline substrates using a thin epitaxial La0.5Sr0.5CoO3 layer as the bottom electrode for subsequent electric measurements. Structural characterization revealed an undisturbed epitaxial growth of NBT on lattice-matching substrates with a columnar microstructure, but high roughness and increasing grain size with larger film thickness. Dielectric measurements indicate a shift of the phase transition to lower temperatures compared to bulk samples as well as a reduced permittivity and increased losses at higher temperatures. Whereas polarization loops taken at −100 °C revealed a distinct ferroelectric behavior, room temperature data showed a significant resistive contribution in these measurements. Leakage current studies confirmed a non-negligible conductivity between the electrodes, thus preventing an indirect characterization of the electrocaloric properties of these films.

Zusammenfassung Ultraschallwandler werden zum Senden und Empfangen akustischer Wellen eingesetzt und bilden damit das Herzstück eines jeden Ultraschallprüfgeräts. Je nach Anwendung arbeiten sie in unterschiedlichen Frequenzbereichen. Ultraschallwandler mit niedrigen Arbeitsfrequenzen von 1 kHz bis 1 MHz werden insbesondere für Sonaranwendungen benötigt, wohingegen Hochfrequenz-Ultraschallwandler mit Arbeitsfrequenzen von mehr als 15 MHz für die hochauflösende Bildgebung im Rahmen biomedizinischer Untersuchungen und zerstörungsfreier Prüfverfahren interessant sind. Herkömmliche zerstörungsfreie Diagnose- und klinische Ultraschallbildgebungssysteme werden typischerweise mit Ultraschallwandlern, die bei Frequenzen zwischen 1 MHz und 10 MHz arbeiten, betrieben. Im Hinblick auf eine leistungsfähige Auslegung und kosteneffektive Fertigung müssen sowohl die verwendeten piezoelektrischen Komponenten als auch die Größe und innere Struktur solcher Wandler auf den Anwendungsfall zugeschnitten sein. Neben dem Ultraschallwandler, als aktives Element zur Umwandlung von elektrischer Energie in Schallenergie und umgekehrt, werden in einem Ultraschallprüfkopf weitere Komponenten wie Dämpfungskörper und Anpassschichten integriert um die Funktion an die jeweilige Messaufgabe anzupassen. Der Aufbau funktionsfähiger Ultraschallgeräte umfasst darüber hinaus die Ansteuer- und Auswerteelektronik sowie die Bildverarbeitung. Im vorliegenden Artikel werden verschiedene Fertigungstechnologien für Ultraschallwandler unterschiedlicher Frequenzbereiche vorgestellt, die von den Autoren in den vergangenen Jahren entwickelt wurden. 1-3-Piezokomposite auf der Basis von piezokeramischen Fasern können in nahezu jeder Dicke hergestellt werden, was Arbeitsfrequenzen entsprechender Ultraschallwandler zwischen 40 kHz und 8 MHz erlaubt. Das Soft-Mold-Verfahren ermöglicht die Herstellung von Hochfrequenz-Ultraschallwandlern mit Arbeitsfrequenzen von 5 MHz bis 40 MHz. Hochintegrierte Wandler können durch Siebdruck von Elektroden-, Piezokeramik- und Isolationsschichten auf mikroelektronischen Substraten hergestellt werden. Damit sind strukturierte Ultraschallwandler mit Arbeitsfrequenzen zwischen 5 MHz und 30 MHz möglich.

Piezoceramic thick films offer the possibility of integrated functional components in planar design. They can be applied as sensors, actuators, ultrasonic transducers, transformers and generators. Typically, piezoceramic thick films are excited through the film thickness. In contrast, in-plane mode of excitation will be beneficial especially for actuator applications. The use of interdigitated electrodes (IDEs) enables in-plane excitation of piezoceramic thick films. Actuator performance of cantilever structures with through thickness and in-plane polarised piezoceramic thick films are investigated. The performance of in-plane polarised cantilevers depends on the particular IDE spacing. Using finite element simulations of the E-field distribution, geometrical and design efficiencies are considered and compared to experimentally derived data.

A method for direct measurement of the adiabatic temperature change inside the active region of multilayer ceramic (MLC) components without detailed knowledge on geometry and properties of inactive regions in the MLC is reported. Thin thermocouple wires serve as the temperature sensor with sufficiently small response time with regard to the relaxation time into the inactive regions. They are mounted on top of the MLC by resistance welding. The accuracy of the method is estimated using finite element analyses of the measuring setup. Experiments are used to validate the numerical analyses as well as the proposed measuring method. In its current implementation the method reaches an accuracy of almost 90 %, which can be improved to approximately 97 %. Therefore, neither fitting nor correction is required.

The electrocaloric effect of 0.92 Pb(Mg1/3Nb2/3)O3-0.08 PbTiO3 (PMN-8 PT) bulk ceramics and multilayer ceramic (MLC) structures is reported. The results are compared to lead-free, barium-titanate-based materials. Phase transition temperature and electrocaloric temperature change could be altered by targeted doping and this is discussed with the help of dielectric and electrocaloric measurements. By reduction of single layer thickness in MLCs, electrical loads and thus electrocaloric temperature changes of PMN-8 PT based multilayers could be increased. Simulations that outline the intrinsic cooling performance of electrocaloric MLC components in dependence of the multilayer design and operation frequency for two different modes of heat transfer are presented. The performance of the fabricated MLC layout for a driving frequency of 1 Hz is discussed in detail and an optimum layout by varying of design parameters derived. Additionally, the effect of driving frequency on the electrocaloric cooling power is investigated.

The present paper deals with the development of lead zirconate titanate (PZT) fibres, pearls and fibre fragments, for their use as active phase in piezocomposites. As new a approach, the green ceramic components are shaped by polysulphone spinning, allowing for effective and flexible forming over a wide range of different geometries and sizes. The correlation between processing parameters, e.g. the slurry composition, nozzle size and operation velocity, and the resultant shape of ceramic components is analysed. Sintered piezoceramic parts show a dense microstructure. Performance data are evaluated on PZT/epoxy composites. Measurement results of strain, polarisation and piezoelectric coupling are given and discussed. The developed PZT components are seen as key for the creation of smart and lightweight structural components. Further, free formed PZT components open new design approaches for sensing and actuating devices and ultrasound transducers.

Ultrasound Computer Tomography (USCT) medical imaging is a promising approach for early detection of breast cancer. At Karlsruhe Institute of Technology (KIT) a 3D USCT system is developed. The system operates 2041 ultrasound transducers in a semi-ellipsoidal aperture surrounding a region of interest (ROI) of 10 cm x 10 cm x 10 cm. Results from a first patient study reveal the requirement of a significantly increased ROI to cover bodily variations. Design considerations and simulations show a demand for circular transducers of approximately 500 mm diameter, increasing the opening angle of the transducers to approximately 60°. Piezofiber composite technology is predestinated to simply provide circular transducers of the required dimensions. Moreover, piezocomposites based on single PZT (lead zirconate titanate Pb[ZrxTi1-x]O3) fibers enable a cost-effective and series-production alternative to currently used dice-and-fill composites. A transducer design is presented which utilizes individually arranged single piezoceramic fibers with 460 µm in diameter within piezocomposite discs. As result fibers are independently addressable as single transducer elements allowing for the desired transducer arrangement. The electrical performance of each piezoceramic fiber is determined proofing a strong dependence of coupling coefficient and resonance frequency from transducer thickness. In further processing, the piezocomposite discs are connected to printed circuits, integrated into a cylindrical housing and backfilled with polyurethane. Ultrasound characteristics such as sound pressure and opening angle are evaluated quantitatively. The transducer opening angles are in the expected range, desired center frequency is achieved and bandwidth preserved compared to former dice-and-fill transducers.

Piezoelectric sensors and actuators have gained increasing interest in lightweight engineering for shape control, vibration damping, condition, and structural health monitoring. In combination with complementary control units, these adaptive structures become more relevant as cost-effective technologies and mass production of suitable piezoelectric components are available. We investigate serial and cost-effective fabrication of piezoceramic components and composites, which allow for direct integration into lightweight structures. To succeed functional integration, layout, structure and composition of the piezoelectric components need to be adjusted to the lightweight material and to the constraints of the entire manufacturing process. Examples of robust piezoelectric components for integration into fiber-reinforced plastics and light metal parts are given. Manufacturing, properties and influence of structure integration on physical characteristics are described and discussed in detail.

This paper presents an extract of modifications of lead magnesium niobate–lead titanate in order to optimize its electrocaloric properties. Electrocaloric entropy (Δ S EC ) and temperature changes (Δ T EC ) are measured in a temperature range from −5 °C up to 100 °C using differential scanning calorimetry. The influence of dopants (Li + , Mn 2+ , Sr 2+ , Ta 5+ ) on the electrocaloric effect as well as on microstructure, dielectric and ferroelectric behavior is investigated. The maximum of relative permittivity can be shifted to lower or higher temperatures depending on the added dopant and decreased ferroelectric hysteresis losses were observed for all altered compositions. For the undoped PMN–8PT ceramics maximum Δ T EC of 0.58 K and Δ S EC of 0.51 J kg −1 K −1 were measured, when applying an electric field of 2 kV mm −1 at 30 °C. The electrocaloric temperature change showed lower values for all doped PMN–8PT. Remarkably, this is accompanied with an increase of the entropy change for the Li-doped sample.

In the present work we investigate the influence of acceptor (K+, Cu+, Li+), donor (La3+, Bi3+, Eu3+, Nd3+, Y3+, Cr3+) and charge equivalent dopants (Sr2+, Co2+, Mn2+, Ta5+) on the dielectric and ferroelectric behavior of 0.92 Pb(Mg 1/3 Nb 2/3 )O 3 -0.08 PbTiO 3 (0.92PMN-0.08PT). As a criterion for the basic suitability for electrocaloric cooling application, we directly measure the temperature change (ΔT) upon the application and withdrawal of an electric field as a function of the ambient temperature. For the undoped 0.92PMN-0.08PT bulk ceramics fabricated by the columbite route, we observed the maximum ΔT of 0.24 K when applying an electric field of 2 kv-rnm−1 at 28°C (ΔT up ). Withdrawing the electric field at same conditions showed a temperature decrease of 0.20 K (ΔT down ). The resulting ΔT down :ΔT up ratio is also considered.

In this work, the polarization state of piezofiber composites consisting of lead zirconate titanate (PZT) fibers embedded in epoxy resin was evaluated by means of thermal wave methods. The average pyroelectric coefficient was found to be one order of magnitude less than that of PZT ceramic plates. The pyroelectric current spectrum was recorded during irradiating the composites with an intensity-modulated laser beam. We obtained a homogeneous polarization of the samples and were able to detect differences in the polarization magnitude. Additionally, the thermal conductance at the interface between PZT and epoxy resin was estimated. The thermal diffusivity of the material was determined by three different methods: (i) by means of the frequency dependence of the pyroelectric coefficient, (ii) by the laser flash analysis, and (iii) by calculation based on a parallel connection model. Its value yielded approximately 0.4 mm2/s.

This paper reports on a novel construction of a deformable mirror for laser beam shaping. The deformable mirror is actuated by screen-printed thick film piezoceramic unimorphs based on lead zirconate titanate (PZT). Different actuator layouts are realized and will be presented. We use Low Temperature Cofired Ceramics (LTCC) as a substrate material with a metallization as reflective surface. LTCC offers easy integration of holding structures. The reflective mirror surface is electroplated copper. After deposition, the copper layer is diamond machined to achieve excellent optical surface quality

A PZT thick-film is printed on an Al2O3-Substrate, generating a cantilever monomorph. A task of positioning with two degrees of freedom is successfully fulfilled. It is realized by two parallel arranged cantilevers that are mechanically combined with a bar with solid hinges. The solid hinges allow flexibility for different amounts of bending of the two cantilevers, while the bar permits a stiff support for a lens. As the bar underlies very small torsion there is no stress induced change in the index of refraction of the lens. Different combinations of hinges are simulated and practically tested. In the presented work, a lens is successfully positioned in front of a laser diode. The loss of the coupling efficiency due to the shrinking of the adhesive joint can be scaled down. The paper presents the theoretical work including the report on analytic and FEM simulation of both deflection and stress. The practical validation is also presented. A simple sensor system is used to find an optimized position of the lens in front of the diode. This position is automatically held over a long period of time. With the fabrication of the actuator using thick-film printing and laser cutting a low cost device is built.

This paper reports on the thermomechanical modeling and characterization of a micro-opto-electro-mechanical systems deformable mirror (DM). This unimorph DM offers a low-temperature cofired ceramic substrate with screen-printed piezoceramic actuators on its rear surface and a machined copper layer on its front surface. We present the DM setup, thermomechanical modeling, and hybrid fabrication. The setup of the DM is transferred into a thermomechanical model in ANSYS Multiphysics. The thermomechanical modeling of the DM evaluates and optimizes the mount material and the copper-layer thickness for the loading cases: homogeneous thermal loading and laser-loading of the mirror. Subsequently, the developed and theoretically optimized DM setup is experimentally validated. The homogeneous loading of the optimized design results in a membrane deformation with a rate of −0.2 μm K −1 , whereas the laser loading causes an opposed change with a rate of −0.2 μm W −1 . Therefore, the proposed mirror design is suitable to precompensate laser-generated mirror deformations by homogeneous thermal loading (heating). We experimentally show that a 35-K preheating of the mirror assembly compensates for an absorbed laser power of 1.25 W. Therefore, the novel compensation regime “compound loading” for the suppression of laser-induced deformations is developed and proven.