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High-performance stretchable strain sensors are highly desirable for various scenarios, such as health monitoring and human-robot interfaces. Here, we propose a universal strain engineering strategy that introduces an inhomogeneous spatial distribution of stress and promotes crack propagation behavior leading to a critical state between network and channel morphologies, achieving stretchable strain sensors with high sensitivity, a wide working range and good linearity. Approaches for introducing soft-rigid interfaces, enlarging elastic modulus mismatches and matching dimensions have been employed to execute the strategy for network-crack strain sensors with collapsed nanocone cluster structures as representatives. The strain sensors can be tuned to realize a gauge factor of 690.95 in a linear working range of 0–40% (R 2 = 0.993) or a gauge factor of 113.70 in a larger linear working range of 0–120% (R 2 = 0.999). Intraocular pressure monitoring and dynamic facial asymmetry assessment have been demonstrated based on these sensors to show their great application potential. [Display omitted] • A critical state between network and channel morphologies was achieved for crack-based sensors via strain engineering. • Sensitivity, stretchability, and linearity are co-optimized in strain sensors. • A GF of 690.95 in a linear working range of 0–40% can be realized with adjustability. • The highest sensitivity for intraocular pressure monitoring was achieved. • Dynamic facial asymmetry assessment was demonstrated for the first time. [ABSTRACT FROM AUTHOR]

Sign language recognition is of great significance to connect the hearing/speech impaired and non-sign language communities. Compared to isolated word recognition, sentence recognition is more practical in real-world scenarios, but is also more complicated because continuous, high-quality sign data with distinct features must be collected and isolated signs must be identified with high accuracy. Here, we propose a wearable sign language recognition system enabled by a convolutional neural network (CNN) that integrates stretchable strain sensors and inertial measurement units attached to the body to perceive hand postures and movement trajectories. Forty-eight Chinese sign language words commonly used in daily life were collected and used to train the CNN model, and an isolated sign language word recognition accuracy of 95.85% was achieved. For sentence-level sign language recognition, we proposed a method that combines multiple sliding windows and uses correlation analysis to improve the CNN recognition performance, achieving a correct rate of 84% for 50 sign language sentence samples, showing good extendibility. [Display omitted] • A wearable system that attached to the body to perceive hand postures and movement trajectories was demonstrated. • A high accuracy of 95.85% was achieved in isolated sign language word recognition for Chinese sign language. • Combining multiple sliding windows and correlation analysis, a correct rate of 84% for sign language sentence was achieved. [ABSTRACT FROM AUTHOR]

Abstract Physiological monitoring sensors have attracted increasing research interest due to their broad application potential in daily activities, sports performance and health status monitoring for next generation athletic/clinical technologies. Having high sensitivity and low power consumption are essential to realize these applications in advanced portable/remote forms. In this work, triboelectric nanogenerators (TENGs), which are based on expandable microspheres in a polydimethylsiloxane (PDMS) mixture, were constructed as self-powered pressure sensors with ultrahigh sensitivity for biological signal monitoring through a low-cost and simple processing technique. Different sensitivities can be obtained by adjusting the weight percentage of microspheres in the PDMS, and the output voltage of the sensor was analyzed by a theoretical model, which was consistent with the simulation results. The maximum sensitivity of the sensor can reach 150 mV/Pa so respiratory and pulse monitoring can be implemented by attaching the ultrasensitive pressure sensor to the chest and wrist of a human body, respectively. Graphical abstract Ultrasensitive pressure sensors based on triboelectric nanogenerator (TENG) is constructed with the mixture of expandable microspheres and polydimethylsiloxane (PDMS). The microspheres expanded after heating and microstructure forms on the triboelectrification layer's surface. The sensitivity of the sensor can be tuned by adjusting the weight percentage of microspheres in PDMS. Subtle biological signals monitoring, including respiration and pulse, are demonstrated by attaching the flexible pressure sensor onto the chest and wrist of the human body, respectively. fx1 Highlights • Self-powered pressure sensors with tunable sensitivity are fabricated through a very simple and low-cost processing. • A sensitivity of 150 mV/Pa is achieved in the pressure sensor, which is the highest sensitivity realized by TENG-based pressure sensors. • Respiration and pulse monitoring are demonstrated by attaching the flexible pressure sensor onto the human body. [ABSTRACT FROM AUTHOR]

Abstract Textile-based triboelectric nanogenerators (t-TENGs) are excellent choices of mechanical energy harvesting and self-powered sensing for wearable technology, especially for constructing smart fabrics. They combine advantages of textile for its flexibility, breathability, lightweight and TENG for its ease of fabrication and promising output performance. Many progresses have been made due to the surging interests. In this review, we will introduce the construction of t-TENGs briefly at first, including three dominant types of device structure and the new emerging design based on three-dimensionally textile. Investigation about the effect of textile processing method (weaving, knitting, sewing, etc.) and structure pattern on the t-TENG's performance is reviewed for further understanding and optimizing the device. Several great demonstrations about the washability and tailorability of t-TENGs are presented based on elevated material properties and rational device design, which is long-cherished for wearable electronics. Finally, the article ends with reviewing progresses in integrations of t-TENGs with other energy harvesting/storing technology for a more powerful textile energy source and construction of smart fabrics with diverse functions for emerging applications in wearable technologies. Graphical abstract fx1 Highlights • Device structures of t-TENGs are divided into three categories for comparison. • Processing technology and pattern design's effect on the output performance and washability and tailorability of t-TENGs are reviewed. • Applications of t-TENGs in acting as smart fabrics to provide self-powered sensing capability are summarized. [ABSTRACT FROM AUTHOR]

Higher requirements have been put forward for self-powered systems operated with weak energy in the environment. Sensitivity, efficiency and power management design of the energy harvesting module play key roles on the sustainability of the system. In this work, we present an ultrasensitive triboelectric nanogenerator (TENG) with Cu coated fluorinated ethylene propylene films stacked in a unipolar manner and suspended by springs. Triboelectrification and electrostatic induction take place between every adjacent film surfaces, during which transferred charges are increased by at least 50%, leading to an increased efficiency. Also, the reduced framework weight makes soft spring can be adopted for greatly improved sensitivity. Depending on the investigation of mechanical motion in the system, TENG's energy harvesting efficiency is boosted by bringing down the moment of inertia. The linear region characteristic of an n-type junction field-effect transistor is utilized for a low-loss power management design with greatly reduced power consumption and start-up time for superior weak energy harvesting applications. Ultrasensitive and high efficient energy harvester with low-loss power management demonstrated in this work promises an outlook for an effective approach to achieve more powerful and more sustainable self-powered systems working with comprehensive ambient weak mechanical energy fitted in diverse application circumstances. [ABSTRACT FROM AUTHOR]

Mechanical energy sources are abundant in our living environment, such as body motion, vehicle transportation, engine vibrations and breezy wind, which have been underestimated in many cases. They could be converted into electrical energy and utilized for many purposes, including driving small electronic devices or even constructing an integrated system operated without bulky batteries and power cables. Many progresses have been made recently in the mechanical energy harvesting technology based on piezoelectric nanogenerators (PENGs). By introducing a new sandwich structure design, high performance PENGs can be achieved through very simple fabrication process with good mechanical stability by utilizing ZnO nanowires (NWs). By further optimizing the nanomaterials׳ properties and device structure, the PENG׳s open circuit (OC) voltage can be elevated to over 37 V. Two important applications of this technology are that the nanogenerator can be used as a sustainable power source for self-powered system and can worked as active sensors. Several demonstrations are reviewed here. Finally, perspectives of this mechanical energy harvesting technology are discussed. Co-operation with power management circuit, capability of integrating with a system, and low cost large-scale manufacturing processing are suggested to be the key points toward commercialization of PENGs. [ABSTRACT FROM AUTHOR]

The coupling of piezoelectric and semiconducting properties gives rise to the effect of piezotronics, which regulates charge carrier transport through the modulation of energy barriers at contact interfaces. With piezoelectric semiconductors as the building blocks, extensive progress has been made, covering the fundamental physics level, the individual device level as well as the integrated system level, effectively establishing a new field of study. By manipulating interfacial processes incorporating ionic charges, free electrons/holes, photons and chemicals, novel interdisciplinary effects have been studied and reported. This article aims at reviewing the milestone progress and offering perspectives of this new field of study in applications for multi-functional sensing systems, human-electronics interfacing, MEMS, energy harvesting and so on. [ABSTRACT FROM AUTHOR]

Spatiotemporal recognition of multiple mechanical stimuli is essential for electronic skin (e-skin), which can provide more complete and accurate interaction information to enable elaborated functions, such as gesture recognition, object manipulation, and fine tactile discrimination. However, nonspecific sensor response and performance sacrifice for integration limit the perceptual capability of the current systems. Here, we report a bioinspired e-skin that can measure strain, shear and pressure independently with direction information using three-dimensional integrated, mechanically isolated multiple sensors. Novel microstructures of collapsed nanocone clusters, hemi-ellipsoids, and wrinkles are introduced in different sensors to achieve a gauge factor of 6 with a linear working range of 80% (linearity > 0.99) for strain, a sensitivity of 0.1 N−1 for shear force, and a sensitivity of 3.78 kPa−1 for pressure, and all of these sensors possess short response times on the order of 100 ms. The independent, highly sensitive, and fast response of these sensors makes real-time recording and mapping of multiple mechanical stimuli to be achieved. Multi-touch gesture recognition and perception of a red bean (0.065 g) in the hand are demonstrated to illustrate the potential applications in wearables, robotics and bionic prostheses. A bioinspired e-skin that discriminates strain, shear and pressure is developed through a three-dimensional mechanical design cooperated with sophisticated microstructures. Isolated responses of different sensors that possessing excellent performance enabled spatiotemporal recognition of multiple mechanical stimuli toward advanced wearable clinical/biological technologies. [Display omitted] • Collapsed nanocone clusters are newly developed to maintain high electrical conductivity of the coated metal film even stretched up to 95% strain. • Simultaneously -identifying strain, shear and pressure with direction information was realized for the first time. • Spatiotemporal recognition of multiple mechanical stimuli was demonstrated. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we fabricated transparent flexible nanogenerators (NGs) by employing flexible polydimethylsiloxane (PDMS) substrate for the growth of ZnO nanowires. The fully packaged NG showed good transparency with a transmittance of 50–60% in the visible range. The output voltage and current was 8V and 0.6μA, respectively, corresponding to an output power density of ∼5.3mW/cm3. The NG also showed excellent robustness and could stably scavenge energy from the motion of a vehicle. Based on this characteristic, we demonstrated its application as a self-powered sensor for monitoring vehicle speed and detecting vehicle weight. [Copyright &y& Elsevier]

Utilization of textile's triboelectric effect to realize the perception of pressure is of great interest for self-powered wearable electronics that integrate seamlessly with smart fabrics. However, the challenges associated with rational material/device designs based on conventional textile structures and the lack of understanding of the mechanical circumstances experienced by textile devices hamper the further advancement of this technology. Here, textile pressure sensors based on triboelectric nanogenerators (TENGs) with machine washability and excellent breathability are manufactured by using machines to interlace robust Cu-coated polyacrylonitrile (Cu-PAN) yarns and parylene coated Cu-PAN (parylene-Cu-PAN) yarns via multiple textile industry compatible technologies for the first time, simultaneously achieving devices with stitched, woven, and knitted structures. TENG-based pressure sensors with different textile structures are investigated under as-fabricated conditions and after machine washing, and a relation is proposed between textile structure and the key characteristics of the sensors. The material/device designs, mechanical circumstances, manufacturing methods, etc., will affect the sensitivity, linearity, saturation trend and washability of the obtained sensors. Finally, a smart textile glove with stitched pressure sensors is made to demonstrate grip posture detection in various circumstances. Triboelectric nanogenerator-based, machine-washable textile pressure sensors are manufactured using machines via multiple textile industry compatible technologies for the first time, simultaneously achieving devices with stitched, woven, and knitted structures, and the relation between textile structure and the key characteristics of the sensors is revealed. Image 1 • TENG-based textile pressure sensors are manufactured by adopting multiple textile manufacturing technologies via machine. • Understanding of the effects of design, mechanical circumstances and manufacturing methods on the textile sensors' behaviors. • Pressure sensors with different textile structures are investigated under as-fabricated conditions and after machine washing. [ABSTRACT FROM AUTHOR]

Electronic devices with configurability to providing multiple functions are of great interests for their superior adaptability to the ever-changing and multifarious application scenarios. Here, we report flexible integrated circuits (ICs) possessing configurable functions constructed with dual-material gate (DMG) devices based on carbon nanotube thin films, which can serve as either transistors or diodes, on a 2-μm-thick parylene substrate. When configured as a transistor, the DMG device has great advantages over the normal-gated (NG) devices regarding the current on/off ratio (I on / I off), the subthreshold swing (SS) and the drain-induced barrier lowering (DIBL) due to the regulated energy band distribution in channel area. When operating as a diode, a typical DMG device demonstrates a sufficient rectification ratio of 8 × 10 4 and a diode-on-current of over 26 μA. Scalable manufacturing of DMG devices was also demonstrated with great uniformity both in diode and transistor configurations. Finally, multifunctional integrated circuits, which can dynamically switch their function from rectifier to follower or from OR gate to voltage adder by changing controlling signals, were constructed. The functional-configurability, together with scalable manufacturing and the realization on ultrathin flexible substrates, will open up great opportunity for the future environmentally-adaptive system in the field of flexible electronics. Image 1 [ABSTRACT FROM AUTHOR]