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BaTiO3 is a well-known piezoelectric material with commercial uses. The ferroelectric state of BaTiO3 generally comprises electrically polarized domains separated by domain walls (DWs). The DW alters local polarization vectors by an angle of 90° for 90° DW or 180° for 180° DW. The DW is crucial to piezoelectric properties such as response time and fatigue. Furthermore, the DW structure and its dynamics in BaTiO3 are not well understood. Hence, for the first time, we theoretically obtained the atomistic structure of the 90° DW via molecular dynamics simulations at 300 K with the core–shell interatomic potential, using a large-scale system with a side length of 2.8 × 10 3 Å. The width of the 90° DW thereby obtained was approximately 30 Å, which was 20 Å wider than that of the 180° DW. Under the external electric field E → ext parallel to the DW, we observed an extension of a domain having a polarization vector with a positive component along the E → ext-direction. The migration velocity of the 90° DW was approximately two times that of the 180° DW at the same E ext in the range 7 – 20 MV / m. For E ext ≥ 15 MV / m, the migration velocity of the 90° DW in the direction with a positive component along the polarization vector of the extending domain was substantially higher than that in the opposite direction. The physical causes of the difference in the migration velocities of the 90° DW in the two directions were analyzed.

Zusammenfassung Die kontinuierliche Weiterentwicklung induktiver Näherungsschalter erweitert zunehmend deren Anwendungsbereiche. Gleichzeitig erlauben der stetige Fortschritt der Mikroelektronik und die höhere Integration von Rechen- und Speicherelementen in Mikrokontrollern komplexere Datenverarbeitung in kompakten Sensorsystemen. In diesem Beitrag wird ein neues Messverfahren vorgeschlagen, das zusätzlich zur eigentlichen Funktion der Präsenzerkennung bzw. Abstandsmessung die Unterscheidung verschiedener Target-Materialien ermöglicht. Das Prinzip dieses Verfahrens wird zunächst vorgestellt und mithilfe eines automatisierten Messaufbaus demonstriert. Im Anschluss werden der Einfluss des Materials, der Einbauumgebung und unterschiedlicher Targets dargestellt und diskutiert. Hierfür werden verschieden geformte Targets und verschiedene Targetgrößen der bereits vorgestellten Materialien eingesetzt. Es werden Potentiale dieses Verfahrens in Bezug auf die Unterscheidbarkeit der Targetmaterialien, der Einbauumgebung und Targetform diskutiert und die weitere Übertragbarkeit des Verfahrens bewertet. Abschließend wird die industrielle Verwertbarkeit beurteilt.

In hot forming and machining process chains heat treatment of steels is controlled by temperature and time. The process parameters significantly influence the material microstructure, which is important for the final component properties. The dependence between the predominant microstructure and the magnetic properties can be determined by means of Magnetic Induction Spectroscopy (MIS). In this paper, we propose to use the induction coil as an in-process sensor element to implement MIS in induction heating processes with subsequent cooling of steel sheets. This novel approach enables contactless, continuous in-process measurement of complex inductance and allows a non-destructive determination of steel microstructure. The novel measurement method can differentiate discrete microstructural states and determine phase transformation points during continuous heating and cooling, by analysing the inductance curve. The realized combination of sensor and actuator features enables both process monitoring and closed-loop control of production processes with integrated heat treatment.

Climate change policy is an important test case for how political agents use narratives to address complex policy issues and define its scope and impacts in a multi-level context. Harnessing a theo...

The reliable classification of coin sets from different countries and counterfeit coins is an essential means of securing cash circulation. Especially bimetallic coins, such as 2-Euro coins, are often subjected to counterfeit by mixing them with coins of other countries or by imitations. In this article, a real-time embedded sensor system is proposed, based on inductance spectroscopy to characterize and identify bimetallic coins having similar geometric properties and looking similar at a first view. The system is based on inductance spectroscopy varying the penetration depth of the magnetic field in the bimetallic structure of the coin, which generally contains buried layers of other metals. The experimental evaluation shows that the bimetallic coins from different countries can be identified and classified by the use of the support vector machine, a machine learning algorithm. Experimental results showed that the system reached a classification accuracy up to 100% within a response rate of 36.62 ms per five bimetallic coins.

Embedded impedance spectroscopy is gaining importance in the Internet of Things (IoT) era, where a new class of impedance spectroscopy devices is needed to fulfill a suitable frequency range, size, power consumption, and costs. In this paper, we investigate the feasibility of embedded impedance spectroscopy measurement systems with a focus on power-aware systems. We propose a novel embedded architecture based on a low-cost microcontroller and using a reduced number of electronic components. In order to enable the system for measuring higher frequencies up to 10 MHz, we use the undersampling technique on a relatively simple microcontroller with 12-bit in-built analog-to-digital converters and a sampling rate of 1 mega samples per seconds (MSPs). For the impedance calculation in the range of $100~\Omega -1 \text{M}\Omega $ , the Discrete Fourier Transform (DFT) is implemented directly on the same microcontroller. The experimental validation shows a maximal standard deviation of 0.5% in amplitude measurement and a standard deviation of 0.55° in phase measurement, which are sufficient for various applications of wearable solutions. The system design provides an outstanding performance considering low-cost, small foot print, and low-power consumption.

The alternating current zero potential circuit (AC-ZPC) has been recently proposed for two-dimensional resistive sensor matrices, where each matrix row is driven by an AC signal at an individual frequency and every column is read separately. The AC-ZPC method enables the simultaneous measurement of all sensors in the matrix and is insensitive to DC offset voltages of amplifiers. This work aims to investigate the feasibility of the AC-ZPC method for matrices of impedimetric sensors and to propose a calibration approach for suppressing the measurement deviations caused by row interface impedances. The feasibility of the AC-ZPC measurement method for the impedimetric sensor matrices and the proposed calibration approach have been proved by both simulation and implementation results. Based on the commercial impedance measurement circuit AD5933, a prototype has been realized. It achieves a measurement deviation below 1% in the range from 1.9 $\text{k}\Omega \vert \vert 361.7$ pF to 15.9 k $\Omega \vert \vert 102.0$ pF.

Due to their high-energy density, shape memory alloys (SMAs) are investigated as material for bending microactuators in applications of self-folding structures, realizing the concept of programmable matter. Here, for the numerical prediction of the electro-thermo-mechanical performance, the quantification of the time-dependent coupling effects in SMA materials during phase transformation is of crucial interest. Isothermal SMA material models cannot treat the time-dependent interaction between deformation, temperature and electric potential in thermally controlled actuation. In this paper, we extend an isothermal SMA model using standard thermodynamics (Coleman–Noll procedure) to treat the time-dependent behavior of polycrystalline SMAs. The model is implemented as a user material subroutine (UMAT) in a standard finite element (FE) code (Abaqus standard). The time-dependent loading of a tensile sample and a bending microactuator made from 20 $$\mu \hbox {m}$$ μ m thick SMA foil are simulated. A comparative study between experimental and simulation results on the thermoelastic and caloric effects during stress-induced phase transformation is presented. Joule heating simulations for shape recovery during both tensile and bending loading are conducted. Time-resolved temperature variations accompanying the loading and Joule heating processes are reported. The coupled SMA material model is found to be capable of approximating the time-dependent field quantities of a polycrystalline SMA microactuator subjected to electro-thermo-mechanical loading.

Numerous attachment systems exist for implant-supported overdentures, with each having specific limitations in terms of retention, cost, wear, maintenance and cleanability. A retrospective analysis of patients restored with implant-supported overdentures using bars, telescopic crowns and Locator-type attachments was performed and the patients were interviewed. An in vitro strain gauge study compared telescopic crowns, Locator-type attachments and a novel flexible attachment system employing a shape memory alloy (NiTi) with respect to peri-implant strain development during insertion, loading and removal of an overdenture. A significantly lower number of attachment-related complications was observed in bars as compared to telescopic crowns (p = 0.00007) and Locator-type attachments (p = 0.00000), respectively. Greater overall patient satisfaction was noted in bar-retained restorations while Locator-type attachments led to lower levels of satisfaction regarding prosthesis retention. In vitro, telescopic crowns caused maximum strain development during prosthesis insertion and loading, while during removal this was observed in Locators with white retentive inserts. NiTi attachments caused significantly lower strain development during insertion as compared to telescopic crowns (p = 0.027). During loading, NiTi attachments caused significantly lower strain development than Locators with blue retentive inserts (p = 0.039). During removal, NiTi attachments caused significantly less strain development as compared to Locators with white retentive inserts (p = 0.027). Positional discrepancies between male and female attachment parts affected the retention and reaction force between both components, which may be minimized by using the novel NiTi attachment system. This may be beneficial in terms of component wear and implant loading.

Modern production equipment is based on the results of quality control as well as process parameters. The magnetic anisotropy of materials is closely connected to internal mechanical stress by the Villari effect, and also to hardening effects due to plastic deformations, and could therefore provide an interesting basis for process control. Nevertheless, the analysis of anisotropic properties is extremely sensitive to sensor and workpiece misalignments, such as tilting. In this work, a novel eddy current sensor system is introduced, performing a non-contact measurement of the magnetic anisotropy of a workpiece and realizing a separation and correction of tilting effects. The measurement principle is demonstrated with the example of two samples with different magnetic anisotropy values induced by cold forming. Both samples are analyzed under different tilt angles between the sensor axis and the surface of the workpiece. In this work, digital signal processing is demonstrated on the acquired raw data in order to differentiate the effects of tilt and of anisotropy, with the use of preliminary results as an example of two prepared samples.

BaTiO3 is a well-known piezoelectric material, which is widely used in various devices. In general, the ferroelectric state of BaTiO3 is composed of polarized domains. The growth of these domains due to an applied electric field or stress is related to the piezoelectric performance. We investigated the effects of various point defects, monovacancies {VBa, VTi, VO}, and first- and second-neighbor divacancies {VBa–VO, VTi–VO} on polarized domain growth in BaTiO3 under an applied electric field by molecular dynamics simulations using the core–shell inter-atomic potential. We found that (i) the first-neighbor divacancy VBa–VO is the most effective in assisting the domain growth under an applied electric field (i.e., a smaller coercive electric field) in an asymmetrical manner with respect to the electric field direction. This is mainly due to the creation of an electric field around VBa–VO by significant Ti shifts toward VBa with the assistance of VO. (ii) Domain growth proceeds in a [Formula: see text] dimensional manner. The domain growth velocity in the direction of the applied electric field is approximately two orders of magnitude higher than that in the perpendicular direction. (iii) Increasing the density of the divacancy VBa–VO further lowers the coercive electric field when the applied electric field is parallel to the divacancy dipoles. The present results will be essential for designing the type, orientation, and density of defects to modify the coercive electric field of BaTiO3 in defect engineering.

This paper presents the design, fabrication and performance of origami-based folding microactuators based on a cold-rolled NiTi foil of 20 µm thickness showing the one-way shape memory effect. Origami refers to a variety of techniques of transforming planar sheets into three-dimensional (3D) structures by folding, which has been introduced in science and engineering for, e.g., assembly and robotics. Here, NiTi microactuators are interconnected to rigid sections (tiles) forming an initial planar system that self-folds into a set of predetermined 3D shapes upon heating. While this concept has been demonstrated at the macro scale, we intend to transfer this concept into microtechnology by combining state-of-the art methods of micromachining. NiTi foils are micromachined by laser cutting or photolithography to achieve double-beam structures allowing for direct Joule heating with an electrical current. A thermo-mechanical treatment is used for shape setting of as-received specimens to reach a maximum folding angle of 180°. The bending moments, bending radii and load-dependent folding angles upon Joule heating are evaluated. The shape setting process is particularly effective for small bending radii, which, however generates residual plastic strain. After shape setting, unloaded beam structures show recoverable bending deflection between 0° and 140° for a maximum heating power of 900 mW. By introducing additional loads to account for the effect of the tiles, the smooth folding characteristic evolves into a sharp transition, whereby full deflection up to 180° is reached. The achieved results are an important step towards the development of cooperative multistable microactuator systems for 3D self-assembly.

This paper presents a simulation model for the coupled dynamic properties of thermomagnetic generators based on magnetic shape memory alloy (MSMA) films. MSMA thermomagnetic generators exploit the large abrupt temperature-induced change of magnetization at the first- or second-order magnetic transition as well as the short heat transfer times due to the large surface-to-volume ratio of films. These properties allow for resonant self-actuation of freely movable MSMA cantilever devices showing thermomagnetic duty cycles in the order of 10 ms duration, which matches with the period of oscillatory motion. We present a numerical analysis of the energy conversion processes to understand the effect of design parameters on efficiency and power output. A lumped element model is chosen to describe the time dependence of MSMA cantilever deflection and of temperature profiles as well as the magnitude and phase dependency of magnetization change. The simulation model quantitatively describes experimentally observed oscillatory motion and resulting power output in the order of 100 mW cm−3. Furthermore, it predicts a power output of 490 mW cm−3 for advanced film materials with temperature-dependent change of magnetization ∆M/∆T of 4 A m2 (kg K)−1, which challenges state-of-the-art thermoelectric devices.

Fundamental social, political and economic changes that have taken hold in the Federal Republic since 1990 have undermined the idea of a single master narrative setting the course for unification. This special issue links processes of national transformation to a wide array of domestic, supranational and global developments, highlighting the long-term impact of unification on policy domains often neglected during earlier stages of analysis. At issue are the dynamics reshaping the political party system, migration and asylum reforms, the reconfiguration of gender roles, along with new responsibilities and constraints affecting German foreign and security policy. We outline the four key questions addressed by each contributor regarding: 1) the causes, effects and the direction of change in each sector; 2) the balance between internal and external, as well as between direct and indirect forces for change; 3) questions of timing and sequence; and 4) the somewhat surprising impact of eastern practices in recon...

Unification has had a catalytic effect on discursive justifications for Germany’s involvement in the European Union at two levels: first, through the Federal Republic’s more exposed leadership role...

A model for the evolution of the mechanical and thermal properties of shape memory alloy (SMA) films during elastocaloric cycling is developed and compared with experiments. The focus is on Ti-Ni-Cu-Co films of 20 μm thickness showing ultra-low fatigue properties. The films undergo a highly localized pseudoelastic transformation under tensile load cycling featuring strain and temperature band patterns that depend on the loading conditions. The corresponding temperature change is of special interest for film-based elastocaloric cooling applications. Starting from a thermodynamics-based Gibbs free energy model comprising mechanical and chemical contributions, we include a martensite-austenite interface free energy term, for which formulations from a phase-field model are adapted. A 3D continuum mechanics description is modified to treat plane stress conditions appropriate for polycrystalline thin films. The nucleation mechanism of strain bands under dynamic loading is described by introducing a spatial random distribution of the transformation stress barriers reflecting the degree of material inhomogeneity. Heat transfer due to conduction and convection is taken into account. The simulations predict the correlated mechanical and thermal local response of the films including band formation and evolution, tilt angle as well as strain-rate dependence. Macroscopic stress-strain characteristics and thermal evolution curves well represent the experimental results.

Mineral precipitations are a common feature and limitation of initially open, permeable rock fractures by forming sealing structures or secondary roughness in open voids. Hence, the objective of this numerical study is the evaluation of hydraulic properties of fractures sealed by hydrothermally induced needle and compact quartz growth. Phase-field models of progressive syntaxial and idiomorphic quartz growth are implemented into a fluid flow simulation solving the Navier–Stokes equation. Flow simulations for both quartz types indicate an obvious correlation between changes in permeability, fracture properties (e.g. aperture, relative roughness and porosity) and crystal growth behavior, which also forms distinct flow paths. Thus, at lower sealing stages initial fracture permeability significantly drops down for the ‘needle fracture’ forming highly tortuous flow paths, while the ‘compact fracture’ records a considerably smaller loss. Fluid flow in both sealing fractures most widely is governed by a “parallel plate”-like cubic law behavior. However, the ‘needle fracture’ also reveals flow characteristics of a porous media. A semi-theoretical equation is introduced that links geometrical ( a m ) with hydraulically effective apertures ( a h ) and the relative fracture roughness. For this purpose, a geometry factor α is introduced being α = 2.5 for needle quartz and α = 1.0 for compact quartz growth. In contrast to most common a h - a m -relationships this novel formulation not only reveals more precise predictions for the needle (RMSE = 1.5) and the compact fractures (RMSE = 3.2), but also exhibit a larger range of validity concerning the roughness of the ‘needle’ (σ/ a m = 0–2.4) and the ‘compact fractures’ (σ/ a m = 0–1.8).

Novel damping devices are presented and characterized that make use of energy dissipation due to the one-way shape memory effect in micromachined shape memory alloy (SMA) foil actuators of 30 µm thickness and lateral dimensions a few mm. The design of SMA foil actuators consists of free-standing planar suspensions with bridge, spiral and folded beam design for load control in-plane and out-of-plane. In contrast to SMA wire-based solutions, this new approach is compatible to MEMS batch fabrication technology. Under pulsed loading, a damping capacity of up to 0.92 is achieved, which compares favorably with the best viscoelastic damping concepts.