Piezoceramic Components Research Articles

Applicability of Piezoceramic Components in the Automotive Industry

Applicability of Piezoceramic Components in the Automotive Industry

A gravity-driven sintering method to fabricate geometrically complex compact piezoceramics

Highly compact and geometrically complex piezoceramics are required by a variety of electromechanical devices owing to their outstanding piezoelectricity, mechanical stability and extended application scenarios. 3D printing is currently the mainstream technology for fabricating geometrically complex piezoceramic components. However, it is hard to print piezoceramics in a curve shape while also keeping its compactness due to restrictions on the ceramic loading and the viscosity of feedstocks. Here, we report a gravity-driven sintering (GDS) process to directly fabricate curved and compact piezoceramics by exploiting gravitational force and high-temperature viscous behavior of sintering ceramic specimens. The sintered lead zirconate titanate (PZT) ceramics possess curve geometries that can be facilely tuned via the initial mechanical boundary design, and exhibit high piezoelectric properties comparable to those of conventional-sintered compact PZT (d33 = 595 pC/N). In contrast to 3D printing technology, our GDS process is suitable for scale-up production and low-cost production of piezoceramics with diverse curved surfaces. Our GDS strategy is an universal and facile route to fabricate curved piezoceramics and other functional ceramics with no compromise of their functionalities.

Monolithic piezoceramic actuators with a twist

Designing artificial structures with heterogeneous elements and manipulating their interface coupling ways usually bring in synthetic neo-nature to functional devices. For piezoceramic devices, the deformation response refers to a variety of extensional, contractional, or shear modes of crystals, and also relies on boundary conditions from morphology design. However, to pursue fundamental torsion actuation in an integrated piezoceramic component is still a long-term tough task due to nil twist mode limited by microscopic crystal mirror symmetry. Herein, we demonstrate a design of cofired monolithic actuators to originally overcome this obstacle. The prototype device is composed of two sets of stacked actuation subunits that work on artificially reverse face shear modes, and their chiral stiffness couplings will synergistically contribute to synthetic twist outputs at a broad bandwidth. Finite element simulation reveals twist displacements are highly tunable by manipulating the geometrical dimensions. Transverse deflection measurements manifest the stable and sizeable linear actuation response to applied electric fields (around 3.7 µm under 40 V at 1 Hz). Importantly, the design actually introduces a more general route to enable arbitrary modes and actuation states in integrated piezoceramic components.

Micro-stereolithography of KNN-based lead-free piezoceramics

The additive manufacturing technique of micro-stereolithography (µSL) is applied to fabricate alkaline niobate (K0.48Na0.52NbO3, KNN) based lead-free piezoceramics. Complex KNN-based piezoceramic green parts with fine dimensional characteristics, such as a piezoceramic transducer array and a hollow hemisphere, have been printed. The two-step debinding and sintering processes are employed to obtain crack-free dense KNN ceramics with complex shapes. These printed KNN ceramics exhibit superior piezoelectric and ferroelectric performance (εr = 2150, d33 = 170 pC/N, Pr = 12.1 μC/cm2, EC = 6.1 kV/cm, and TC = 230 °C), which are comparable to those of KNN piezoceramics made by traditional methods. These results suggest that the µSL technique may serve as an alternative method to manufacture KNN lead-free piezoceramic components, especially for the application with complex architectures.

Manufacturing Technologies of Piezoelectric Components for Integration into Lightweight Structures

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. The authors 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.

Influence of ferroelectric domain texture on the performance of multilayer piezoelectric actuators

Lead zirconate titanate (PZT)-based multilayer piezoelectric actuators (MAs) present a maximum in their piezoelectric properties when pre-stressed with a low mechanical load (ca. 50MPa) along the longitudinal axis of the actuator. In this work, we investigate this phenomenon by combining polarised Raman spectroscopy with a Reverse Monte Carlo (RMC) method in order to quantify the domain orientation distribution of PZT-based MAs, both in-situ and at the remanent state, under combined applied electric field and mechanical load. Our study shows that the performance maximum of MAs is the result of two competing effects: (i) an increasing reservoir for non-180° domain switching for increasing applied compressive pre-stress and (ii) a large activation energy for domain switching at high pre-stresses. Hence, our study uncovers structure-property relationships in piezoceramic components that could be used to finely tune the electromechanical response of actuators.

Exact solution of thermoelectroelastic behavior of a fluid-filled FGPM cylindrical thin-shell

This study deals with the thermoelectroelastic behaviors of a fluid-filled functionally graded piezoelectric material (FGPM) cylindrical thin-shell under the combination of mechanical, thermal and electrical loads. The FGPM is composed of piezo ceramic and metal components and the holistic material properties are assumed to vary continuously through the thickness of the shell with power law. Based on the classical cylindrical shell theory, the governing differential equations are derived. Applying the analytical method, exact solution of the problem is obtained. Finally, through numerical examples, the influences of various factors on the thermoelectroelastic behaviors of the fluid-filled FGPM cylindrical thin-shell have been analyzed and discussed.

Studies on the Characterization of Novel Piezoelectric Sensor Elements, Integrated in Glass Fibre-reinforced Polyurethane Composites

Within this contribution, studies on the characterization of piezoelectric sensor elements embedded in composite structures are presented. Using piezoceramic components like fibres and pearls as well as appropriate electrode structures, novel piezoelectric transducers are created and locally embedded into the composite structure, mainly to realize sensory functions. After embedding, the piezoelectric functional layer is polarized to activate the sensor. Various specifications of these sensors with different piezoceramic components and electrodes have been characterized using cyclic three-point bending and compression tests. Hereby, bending respectively compression of the composite structure leads to deformation of the embedded piezoceramic components and generation of electric charges due to the piezoelectric effect. Even if the values of the determined electric charges are relatively small, the functional capability of the novel sensors could be proven.

Studies on the polarisation behaviour of novel piezoelectric sensor modules

A novel approach to the manufacture of adaptive composite structures with integrated piezoelectric modules focusses on combining the previously separate production steps – production of the piezoceramic transducer, composite fabrication and integration of the transducers – into an efficient single-stage process. Based on the long fibre injection (LFI) technology, a novel multi fibre injection (MFI) method is developed. By integrating piezoceramic components like short fibres or pearls and suitable electrode structures into the composite, novel piezoelectric functional elements are created and embedded during the structure's manufacturing process. For the functionalisation of these elements, mainly to provide sensory properties, poling of the piezoceramic components during or after the production process is required. Based on initial simulations of electric field strength, poling process and resulting small signal properties, conclusions for an adapted poling strategy of these novel sensor modules are elaborated.

Integration of Piezoceramic Tube under Prestress into a Load Carrying Structure

Smart structures consisting of a load carrying structure and smart materials with actuatory and sensory capabilities feature high potential in numerous applications. However, to master the assembly conditions of smart structures, there is a need to integrate additional design parameters such as prestress of the smart material, critical loads and electric contacting as well as insulation into the process development. This paper focusses on the design of an incremental bulk forming process to integrate piezoceramic components into an aluminum tube simultaneously to the manufacturing process. Axial forces imposed on the piezoceramic are investigated numerically and experimentally to verify the design of critical components and the process control. Within this investigation, in situ measurement of the direct piezoelectric effect provides a method to validate the numerical design with regard to failure of the piezo tube and the functional properties of the overall structure.

Influences of Nozzle Material on Laser Droplet Brazing Joints with Cu89Sn11 Preforms

Abstract This paper presents latest results on the influences of nozzle material and geometry on the electromechanical contacting of sensitive piezoceramic actuator modules. Two nozzle types have been investigated,a standard WC/Co nozzle which is used for soldering applications and a novelceramic nozzle. Applications for active piezoceramic components integrated in structural parts are e.g. active damping, energy harvesting, or monitoring of vibrations and material failure. Anup to now unsolved problem is the electrical contacting of such components without damaging the conductor or the metallization of the ceramic substrate. Since piezoelectric components are to be integrated into structures made of casted aluminum, requirements are high mechanical strength and temperature resistance. Within this paper a method forcontacting piezoceramic modules is presented. A spherical braze preform of tin bronze Cu89Sn11 with a diameter of 600 μm is located in a ceramic nozzle and is subsequently melted by a laser pulse. The liquid solder is ejected from the nozzlevia nitrogen overpressure and wets the surface of the metallization pad and the Cu-wire, resulting in a brazing joint after solidification. The process is called laser droplet brazing (LDB). To asses the thermal evolution during one cycle WC/Co and ZTA have been simulated numerically for two different geometries enabling a proposition weather the geometry or the material properties have a significant influence on the thermal load during one cycle. To evaluate the influence of the nozzle on the joint the positioning accuracy, joint height and detachment times have been evaluated. Results obtained with the ZTA nozzle show comparable positioning accuracies to a WC/Co nozzle with a lower standard deviation of solder detachment time.

Laser Droplet Brazing for Electrical Contacting of Composite Materials with Integrated Active Elements

To be used as actuators or sensors, piezoceramic components have to be electronically contacted. A temperature stable connection can be achieved with brazing techniques. Since piezoceramics are susceptible to damage by high temperatures and temperature gradients, it is important to control the energy input in the brazing process. Therefore, we use a laser droplet brazing method which allows for precise contacting of piezoceramics and avoids thermal damage. The influence of the laser parameters on the brazing process and the contacting accuracy is presented in this paper.

Processing Studies for the Development of a Manufacture Process for Intelligent Lightweight Structures with Integrated Sensor Systems and Adapted Electronics

The cross-industry trend towards efficient lightweight solutions continues unabatedly and leads to an increasing use of structural components made of fibre composites. At the same time, there is an increasing demand for the realization and integration of additional functions such as sensory properties. For the widespread application of intelligent lightweight components, manufacturing technologies suitable for series production are required. Fibre-reinforced polyurethane composites offer a great potential for the production of smart lightweight structures. A novel method based on the Long Fibre Injection (LFI) technology enables the integration of piezoceramic components and by their direct connection to suitable electrode structures the process immanent fabrication of sensory elements.

New Semi-active Multi-modal Vibration Control Using Piezoceramic Components

Active vibration control using piezoelectric elements has been extensively studied due to the requirement for increasingly high performances. Semi-active control, such as Synchronized Switch Damping, is an alternative technique. It consists in switching a piezoelectric element to a specific circuit synchronously with the motion of the structure, unlike active control. This method requires very low power supply, but performances remain poor in the case of broad bandwidth excitation. This article proposes a new method which is a combination of the SSDI semi-active control and technique developed for active control and has low power supply requirements. It extends semi-active control to any type of excitation, while optimizing modal damping on several targeted modes. Experimental measurements carried out on a clamped free beam are presented and a significant damping on targeted modes is demonstrated.

Design and fabrication of PZT-actuated tools for micromanipulation

In this paper novel tools for micromanipulation are presented. The devices have been purposely designed for integration in small mobile micro-robots, aimed at performing co-operative precision manipulation and assembly tasks. Concerning the actuation, multilayer piezoceramic components were developed and employed. The selected fabrication techniques for the grippers are shape deposition manufacturing of polymer and electro-discharge machining of stainless steel, and different alternatives have been investigated in order to select the optimal design. Several prototypes have been fabricated and preliminary experimental tests have been performed, both regarding the characterization and the grasping capabilities.

Properties of Lead-Free Piezoceramics Based on Alkali Niobates

The market for piezoceramic components is dominated by lead zirconate titanate (PZT) materials containing more than 60 wt% lead. Since lead is a toxic heavy metal, it has become a great concern how to eliminate the use of PZT by replacing it by non-harmful materials while maintaining comparable piezoelectric properties. This was the objective of the European LEAF project within the GROWTH programme, ending in February 2004. In this project, alkali niobates were proposed as alternative piezoceramic materials, and special emphasis was given to potassium sodium niobate, (K,Na)NbO 3 . Among the interesting properties of this system is a low theoretical density, leading to a relatively low acoustic impedance of 24 MRa. The partners of the project have developed lead-free ceramics based on potassium sodium niobate that can be a competitive alternative to PZT for certain applications. A selection of obtained properties, examples of industrial applications and an overview of end-user considerations will be presented. Furthermore, some considerations on the origin of even harmonics in the impedance spectrum, as seen in certain KNN ceramics will be given.

Lead-free piezoceramics based on alkali niobates

The market for piezoceramic components is dominated by lead-based PZT materials containing more than 60 wt.% lead. Since lead is a toxic heavy metal, it has become a great concern how to eliminate the use of PZT by replacing it with non-harmful materials while maintaining comparable piezoelectric properties. This was the objective of the European LEAF project within the GROWTH programme, ending in February 2004. In this project, alkali niobates were proposed as alternative piezoceramic materials, and special emphasis was given to potassium sodium niobate, (K, Na)NbO 3. The partners of the project have developed lead-free ceramics that can be a competitive alternative to PZT for certain applications. Considerations on powder synthesis and ceramic processing, obtained properties and examples of industrial applications will be presented.

Fabrication of multilayer 2D ultrasonic transducer microarrays by green machining

This paper presents a fabrication technique for multilayer 2D ultrasonic transducer arrays based on wet building and mechanical machining of piezoelectric PZT ceramics. The arrays are intended for microparticle trapping and manipulation using ultrasonic standing waves in microfluidic devices. The developed fabrication technique is relevant also for the miniaturization of other multilayer piezoceramic components. Array elements were fabricated monolithically on a common carrier with voids integrated behind each element, to work as acoustic reflectors. Their function was later proved by identification of thickness resonances of the supported multilayer transducers. The voids were integrated by using sacrificial material that was removed during firing of the component. Electrodes, vias, sacrificial material and finally the array itself were structured in the green state using a high precision dicing saw. The fabrication technique with integrated multilayer electrodes and electrical vias was shown to allow for miniaturized array elements working above 10 MHz with lateral dimensions down to 350 × 350 µm2. The resolution of electrode patterning was below 10 µm with insulating spaces down to 30 µm. The smallest dimension of via interconnects was 20 µm and integrated voids were fabricated with lateral dimensions reaching from 10 µm to 600 µm.

Miniaturized flowthrough microdispenser with piezoceramic tripod actuation

In this paper, the further development of a silicon flowthrough microdispenser is described. Previously reported designs of the dispenser used bimorph, and later multilayered, piezoelectric actuator elements for the generation of droplets. The introduction of a multilayered actuator significantly reduced the voltage amplitude needed to dispense droplets. Dispenser properties relevant for chemical analysis systems, e.g., reduced sample volume, internal surface area, and dispersion, were improved by miniaturization of the device. A new actuator design, the tripod, is presented to enable further dispenser miniaturization and to facilitate device assembly. Tripod actuators were manufactured using a prototyping process, based on micromilling, for multilayer piezoceramic components. A building technique for miniaturized electrical interconnects, based on microstructured flexible printed circuits, is also suggested in line with the prospect of future miniaturization. The microfluidic properties of the tripod-actuated dispenser were evaluated. Stable droplet generation in the frequency range from 0 to 3 kHz was demonstrated, providing a maximum dispensed flow rate of 7.8 /spl mu/L/min.

Tensile fracture of soft and hard PZT

Power applications generate high stresses which can damage piezoceramic components. In this study tensile fracture of several types of PZT (hard/soft) is investigated. After validation of the specimen geometry by means of numerical simulation, samples are led to failure using a specific device. Weibull law parameters enable the characterisation of the tensile strength distribution and highlight clear differences between soft and hard ceramics. A fractographic approach emphasises the specificities of the fracture mode and the fracture origin for each type of samples.