Three-dimensional printing-based additive manufacturing has emerged as a new frontier in materials science, with applications in the production of functionalized polymeric-based hybrid composites for various applications. In this work, a novel conceptual design was conceived in which an AC electric field was integrated into a commercial 3D printer (-based fused filament fabrication (FFF) working principle) to in situ manufacture hybrid composites having aligned ceramic filler particles. For this work, the thermoplastic poly lactic acid (PLA) was used as a polymer matrix while 10 vol% KNLN (K0.485Na0.485Li0.03NbO3) ceramic particles were chosen as a filler material. The degree of alignment of the ceramic powders depended upon print speed, printing temperature and distance between electrodes. At 210 °C and a 1 kV/mm applied electric field, printed samples showed nearly complete alignment of ceramic particles in the PLA matrix. This research shows that incorporating electric field sources into 3D printing processes would result in in situ ceramic particle alignment while preserving the other benefits of 3D printing.

Current transformational developments in automotive user interface (UI) technology are causing a shift in emphasis from safety and efficiency to emotion and flexibility. The many factors to consider in parallel make this a difficult process, in which technological affordances all too easily push the user to the background. To address this issue, this paper introduces an interaction model linking the different tangible control elements, including smartphone functionality, and shows how non-driving-related activities (e.g. climate control, multimedia access) can be represented physically. Next, a working prototype is presented that supports the design and development of novel tactile UIs. By integrating layers of sensors and actuators, a flexible UI is created that pushes technology to the background, giving proper attention to the user again and enabling effective research on how to make the digital world tangible for users.

Polymer-piezoceramic composites have drawn a lot of attention for sensor and energy harvesting applications. Poling such materials can be difficult due to the electric field getting mostly distributed over the low dielectric constant matrix. During this process, the electrical matrix conductivity plays a vital role. This work shows how two different polymer materials, loaded with various piezoelectric ceramic fillers, have very different poling efficiencies simply due to their intrinsic matrix conductivity. It is shown how temperature increases the matrix conductivity, and hence, increases the piezoelectric charge constant of the composites. By choosing the proper matrix material under the proper conditions, piezoelectric composites can be poled at electric fields as low as 2 kV mm^-1, which is identical to that of bulk ceramic fillers. In addition, the matrix conductivity can be altered by aging the composites in a high humidity atmosphere, which can increase the piezoelectric charge constant in similar fashion. This is a simple method to increase the matrix conductivity, and hence the piezoelectric charge constant, without the need to add any conductive fillers into the composites, which increase complexity, and leads to an increased dielectric losses.

BiFeO₃ is a multiferroic material with the perovskite structure which is promising for use in sensors and transducers. Single phase production of BiFeO₃ remains a challenge, however. In this study, the optimal calcination temperature to obtain close to single phase powder was determined to be 750°C. The sintering temperature of 775°C was also found to obtain high density ceramics (≈ 95 % of theoretical density). It is shown that off-stoichiometry of bismuth oxide in precursors effects the content of secondary phase. Impedance spectroscopy indicates that the content of secondary phases has a large effect on the electrical conductivity BiFeO₃.

A commonly used strategy in the fabrication of organic electronics involves the use of orthogonal solvents, i.e. the alternating use of organic solvents and water for the application of consecutive layers to prevent dissolution of previous layers. This strategy therefore requires the deposition of sequential layers with a large mismatch in surface energy. In case of organic photovoltaics (OPV) a particularly challenging deposition is that of the aqueous Poly(3,4-ethylenedioxythiophene) Polystyrene sulfonate (PEDOT:PSS) on the hydrophobic Poly(3-hexylthiophene-2,5-diyl/Phenyl-C61-butyric acid methyl ester (P3HT/PCBM) layer. The mismatch in surface energy causes dewetting and inhomogeneous layer formation. In inkjet printing individually placed droplets should spread sufficiently far to form a homogeneous closed layer before the solvents in the droplet evaporate. A formulation for the aqueous PEDOT:PSS layer has been developed in which the combination of solvents and surfactants is essential for achieving a homogenous layer on the timescales needed for inkjet printing. Homogenous layers of PEDOT:PSS on P3HT/PCBM were achieved for layer thicknesses from 400 nm to 50 nm. The efficiency of the OPV's fabricated with the new formulation were comparable with reference devices, where evaporated molybdenum oxide (MoO_x) was used as a topelectrode. This shows that by the addition of solvents and surfactants a hydrophilic solution can be inkjet printed successfully to form homogenous layers on hydrophobic surfaces and achieve good efficiencies in an inverted organic solar cell.

The production of electronic devices using solution based (“wet”) deposition technologies has some decisive technical and commercial advantages compared to competing approaches like vacuum based (“dry”) manufacturing. Particularly, the potential to scale up production processes to large areas and high volumes by introducing continuous roll-to-roll (R2R) methods on flexible substrates has been the topic of intense studies from both applied research institutes and industry already for some years. Decisive steps forward have been achieved during that time, resulting in the dawn of commercial applications for a number of processes, while additional development work is still needed in some other fields. This review summarizes the work published during the last few years on the R2R printing and wet coating of electronic devices. An overview is presented of the basic operational principles for the most commonly used R2R printing and coating methods and techniques for proper web handling in R2R lines. Then, the most commonly used types of flexible substrate materials are introduced, followed by a review of the work published in the application areas of transparent conductor materials, printed electric connections, light emitting devices, photovoltaic energy generation, printed logic, and sensing.

Recently reported piezoresponse force microscopy (PFM) measurements have proposed that porcine aortic walls are ferroelectric. This finding may have great implications for understanding biophysical properties of cardiovascular diseases such as arteriosclerosis. However, the complex anatomical structure of the aortic wall with different extracellular matrices appears unlikely to be ferroelectric. The reason is that a prerequisite for ferroelectricity, which is the spontaneous switching of the polarization, is a polar crystal structure of the material. Although the PFM measurements were performed locally, the phase-voltage hysteresis loops could be reproduced at different positions on the tissue, suggesting that the whole aorta is ferroelectric. To corroborate this hypothesis, we analyzed entire pieces of porcine aorta globally, both with electrical and electromechanical measurements. We show that there is no hysteresis in the electric displacement as well as in the longitudinal strain as a function of applied electric field and that the strain depends on the electric field squared. By using the experimentally determined quasi-static permittivity and Young's modulus of the fixated aorta, we show that the strain can quantitatively be explained by Maxwell stress and electrostriction, meaning that the aortic wall is neither piezoelectric nor ferroelectric, but behaves as a regular dielectric material.

Conductive polymer composites have been receiving increased interest both from the scientific community and industry with a special focus on electromagnetic interference (EMI) shielding applications. In this paper, we present the design, EM wave simulation, and validation through S-parameters measurements of an EMI shielding effectiveness (SE) tester based on the ASTM D4935 standard, to be used in the development of such materials. EM wave simulations and computer aided design were used in parallel to improve the SE test setup performance, which resulted in a unique low-loss coaxial-spherical-conical smooth transition design that ensured the best tradeoff between sample size and performance. The proposed SE tester has an insertion loss smaller than 1 dB, with good reproducibility and a setup-independent frequency response in the frequency range from a few kHz up to 3 GHz.

The large volume production of flexible electronics by solution based roll-to-roll (R2R) manufacturing technologies is a promising upscaling strategy for the organic electronics industry. Typical optoelectronic devices like organic light emitting diodes (OLEDs) consist of a complex stack of functional layers. Solution deposition of these structures eliminates the need for expensive vacuum processing. This contribution presents approaches for solution based R2R production methods of functional OLED layers on flexible polymer substrates. The development of a R2R line with two slot-die coating stations is discussed which can deposit two uniform layers consecutively in a single run (“tandem coating”) at web speeds up to 30 m/min. Furthermore, it offers the unique feature that there is no contact between the rollers and the top side of the substrate where the functional coating is deposited. Thereby, an important source of particle contamination and other damage to the device is eliminated. In addition to continuous deposition, stripe and intermittent coating techniques have been developed, allowing the production of patterned layers. Finally, examples will be shown of OLEDs where two functional materials are deposited by R2R processing from solution.

A highly sensitive, lead-free, and flexible piezoelectric touch sensor is reported based on composite films of alkaline niobate K_0.485Na_0.485Li_0.03NbO₃ (KNLN) powders aligned in a polydimethylsiloxane (PDMS) matrix. KNLN powder is fabricated by solid-state sintering and consists of microcubes. The particles are dispersed in uncured PDMS and oriented by application of an oscillating dielectrophoretic alignment field. The dielectric constant of the composite film is almost independent of the microstructure, while upon alignment the piezoelectric charge coefficient increases more than tenfold up to 17 pC N^-1. A quantitative analysis shows that the origin is a reduction of the interparticle distance to under 1.0 μm in the aligned bicontinuous KNLN chains. The temperature stable piezoelectric voltage coefficient exhibits a maximum value of 220 mV m N^-1, at a volume fraction of only 10%. This state-of-the-art value outperforms bulk piezoelectric ceramics and composites with randomly dispersed particles, and is comparable to the values reported for the piezoelectric polymers polyvinylidenefluoride and its random copolymer with trifluoroethylene. Optimized composite films are incorporated in flexible piezoelectric touch sensors. The high sensitivity is analyzed and discussed. As the fabrication technology is straightforward and easy to implement, applications are foreseen in flexible electronics such as wireless sensor networks and biodiagnostics.