Energy autonomy and conformability are essential elements in the next generation of wearable and flexible electronics for healthcare, robotics and cyber-physical systems. This study presents ferroelectric polymer transducers and organic diodes for imperceptible sensing and energy harvesting systems, which are integrated on ultrathin (1-µm) substrates, thus imparting them with excellent flexibility. Simulations show that the sensitivity of ultraflexible ferroelectric polymer transducers is strongly enhanced by using an ultrathin substrate, which allows the mounting on 3D-shaped objects and the stacking in multiple layers. Indeed, ultraflexible ferroelectric polymer transducers have improved sensitivity to strain and pressure, fast response and excellent mechanical stability, thus forming imperceptible wireless e-health patches for precise pulse and blood pressure monitoring. For harvesting biomechanical energy, the transducers are combined with rectifiers based on ultraflexible organic diodes thus comprising an imperceptible, 2.5-µm thin, energy harvesting device with an excellent peak power density of 3 mW·cm−3.

stimuli and transmits the information to the brain. [1] In the last decade, a substantial understanding of how this complex system behaves has been gained. [2][3][4] Nevertheless, its replication to form artificial skins is still a relatively new field with massive potential. Relying on advancements in functional materials, structural design, and state-of-art production/deposition techniques, a wide variety of single/ multi-stimuli responsive sensory systems, suitable for electronic skin (e-skin) applications, have been reported. [5][6][7][8] An efficient e-skin design requires a combination of functional materials with suitable mechanical and electrical properties, [9] in addition to the micro/nanoscale control of the layer's thickness and dimensions, which is optimized by the choice of suitable fabrication techniques.For pressure and force detection, the most common methods exploit piezoelectric, piezoresistive, or capacitive sensing. [10][11][12][13] Bao's group investigated an e-skin design based on flexible pressure-sensitive organic thinfilm transistors deploying a force-sensitive gate dielectric capacitance. The sensor has a maximum sensitivity of 8.4 kPa −1 and a fast response time of 10 ms. This was realized with a combination of microstructured polydimethylsiloxane (PDMS) gate dielectric and a high-mobility semiconducting polymer in a transistor design. The sensor relies on capacitance change due to mechanical excitations. [14] Another pressure-sensitive e-skin design, investigated by Bao's group, is realized by a composite piezoresistive material consisting of an organic polymer and nickel nanostructured microparticles. [15] Park and Jang investigated hybrid piezoelectric/piezoresistive pressure sensors based on a nanohybrid material from graphene with free-standing nanofibers of PEDOT/P(VDF-HFP). Their e-skin device impresses with a gauge factor as high as 320 under tensile strain thus showing high sensitivity to pressure with a low limit of detection of 0.5 Pa only. [16] Humidity sensors for e-skin applications have also been investigated. [17,18] Guo et al. demonstrated that a tungsten sulfite (WS 2 ) film combined with graphene electrodes and PDMS substrate exhibits a high humidity response (up to 90% relative humidity or RH) due to the change in the WS 2 conductivity. [19] Similarly, e-skin sensitivity to changes in surrounding temperature is desired and has been investigated. [20][21][22] Chen et al.A force, humidity, and temperature-responsive electronic skin is presented by combining piezoelectric zinc oxide (ZnO) and poly-N-vinylcaprolactamco-di(ethylene glycol) divinyl ether hydrogel into core-shell nanostructures using state-of-the-art dry vapor-based techniques. The proposed concept is realized with biocompatible materials in a simplified design that delivers multi-stimuli sensitivity with high spatial resolution, all of which are prerequisites for an efficient electronic skin. While the piezoelectricity of ZnO provides sensitivity to external force, the thermoresponsiveness of the hydrogel...

Zinc oxide (ZnO) thin films are deposited by plasma‐enhanced atomic layer deposition (PE‐ALD). This deposition method allows depositing stoichiometric and highly resistive ZnO films at room temperature. Despite such important requirements for piezoelectricity being met, not much is known in literature about the piezoelectric properties of ZnO thin films (<70 nm) deposited by PE‐ALD. The films are grown at different substrate temperatures to investigate the effect on crystalline and piezoelectric properties. Films deposited on flexible poly(ethylene terephthalate) (PET) generated a higher piezoelectric current (>1.8 nA) and charge (>80 pC) compared with films deposited on glass (>0.3 nA and >30 pC) due to bending effects of the substrate when mechanically excited. Furthermore, increasing the substrate temperature, during deposition, enhances the growth along the (002) crystallographic orientation, which further strengthens the generated piezoelectric current signal for mechanical excitations along the ZnO film's c‐axis.

The ski deflection with the associated temporal and segmental curvature variation can be considered as a performance-relevant factor in alpine skiing. Although some work on recording ski deflection is available, the segmental curvature among the ski and temporal aspects have not yet been made an object of observation. Therefore, the goal of this study was to develop a novel ski demonstrator and to conceptualize and validate an empirical curvature model. Twenty-four PyzoFlex® technology-based sensor foils were attached to the upper surface of an alpine ski. A self-developed instrument simultaneously measuring sixteen sensors was used as a data acquisition device. After calibration with a standardized bending test, using an empirical curvature model, the sensors were applied to analyze the segmental curvature characteristic (m−1) of the ski in a quasi-static bending situation at five different load levels between 100 N and 230 N. The derived curvature data were compared with values obtained from a high-precision laser measurement system. For the reliability assessment, successive pairs of trials were evaluated at different load levels by calculating the change in mean (CIM), the coefficient of variation (CV) and the intraclass correlation coefficient (ICC 3.1) with a 95% confidence interval. A high reliability of CIM −1.41–0.50%, max CV 1.45%, and ICC 3.1 > 0.961 was found for the different load levels. Additionally, the criterion validity based on the Pearson correlation coefficient was R2 = 0.993 and the limits of agreement, expressed by the accuracy (systematic bias) and the precision (SD), was between +9.45 × 10−3 m−1 and −6.78 × 10−3 m−1 for all load levels. The new measuring system offers both good accuracy (1.33 × 10−3 m−1) and high precision (4.14 × 10−3 m−1). However, the results are based on quasi-static ski deformations, which means that a transfer into the field is only allowed to a limited extent since the scope of the curvature model has not yet been definitely determined. The high laboratory-related reliability and validity of our novel ski prototype featuring PyzoFlex® technology make it a potential candidate for on-snow application such as smart skiing equipment.

Most flexible piezoelectric transducers have a vertical setup with top and bottom electrodes, which does not enable the selective, directional detection of mechanical stimuli. Here we present a paradigm shift in the design of such transducers by placing the electrodes in a single layer and fully embedding them in a ferroelectric layer. This approach enables a selective detection of in-plane strains with a linear, orientation-dependent response. Our transducers feature microstructured, densely interdigitated electrodes embedded in the ferroelectric copolymer P(VDF-TrFE) and show an in-plane strain sensitivity of up to 8.3 nC %−1 (21.3 V %−1), while being 23 times less sensitive to transversal loading, compared to vertical setup devices. The embedded electrodes cause a strong anisotropy for in-plane strain coupling and make it possible to distinguish both the bending orientation and the bending intensity on a time-variable curvilinear surface. A high power density of 2.3 mW cm−3 was achieved during a periodic bending movement at 90 Hz. In addition to a photolithography and electroplating-assisted method, we present an alignment-free, elegant microcapillary force-based process for scalable fabrication of embedded electrodes. The presented transducers have a high potential for application as energy-autonomous sensors for condition monitoring, robotics and wearables.