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Piezoelectric sensors and energy harvesters have received considerable interest due to their self‐powered capability and potential applications in various electronic devices. However, it is still a challenge to fabricate stretchable piezoelectric devices because piezoelectrics mainly consists of stiff crystalline structures. Here, extremely stretchable and tough piezoelectric gels are reported, which are prepared simply by swelling poly(ethylene glycol) (PEG)‐based poly(urethane‐urea) (PUU) gels with aqueous solution of molecular ferroelectrics. The hydrogen interactions between the PEG segments in the gels and the molecular ferroelectrics (dabcoHReO4, DH) enable well dispersion and crystallization of DH in the PEG segments. The resulted PUU/DH composite piezoelectric gels exhibit unique tensile mechanical properties, including superior strain (>1000%), high breaking strength (>10 MPa), modulus (>2 MPa), and toughness (>57 MJ cm−3). The extremely stretchable and tough piezoelectric gels show excellent piezoelectric properties (d33 ≈ 62 pC N−1 for films with a 10 wt% of DH and light transparency (>90%), and can quantitatively detect different mechanical deformations. Additionally, the energy generators can harvest mechanical energy with a power density of 1.7 µW cm−2. This work is expected to motivate new design principles for fabricating piezoelectric materials with excellent mechanical and piezoelectric properties for various applications. [ABSTRACT FROM AUTHOR]

Artificial electronic skin (e‐skin), a network of mechanically flexible sensors which can wrap irregular surfaces conformally and quantify various stimuli sensitively, is potentially useful in healthcare monitoring and human‐machine interaction (HMI). Although various approaches have mimicked the structures and functions of the human skin, challenges remain with high‐density integration, super sensitivity, and multi‐functionality. A multimodal and comfortable skin‐inspired active‐matrix circuitry is reported here with high pixel density (>100 cm–2) based on all 2D materials, which exhibits excellent performance to detect both mechanical interactions and humidity variations. The ultra‐high sensitivity (>400 and ≈ 104 for strain and humidity sensing, respectively), long‐term stability (>1000 cycles), and rapid response time for every pixel can fulfill simultaneous multi‐stimulus sensing. Accordingly, a respiratory monitor is constructed to realize healthcare monitoring through observing the human breath frequency, intensity, and humidity in real‐time. Moreover, the multimodal e‐skin breaks through shackles of the contact sensor medium for HMI. 3D strain and humidity spatial mapping can reflect object location information even without contact, avoiding cross‐infection of viruses effectively between users during the COVID‐19 pandemic. The reported e‐skin will broaden applications for future healthcare and human–machine interactive devices. [ABSTRACT FROM AUTHOR]

We present an electronic skin with proximity sensing capabilities. Through a simple and cheap fabrication process, we integrate carbon nanotube forests, which serve as the sensing element, into soft, flexible, and transparent artificial skin. Numerical simulations demonstrate the operational principle of the electronic skin proximity sensors. Experimental characterization reveals excellent repeatability and performance of the electronic skin proximity sensors, which are unaffected by the applied strain. Mounting the electronic skin on experimenter’s finger further demonstrates its high performance, variability, and potential to interface with humans. Thus, the cheap and simple fabrication process of this electronic skin, together with its straightforward operation, high reliability, and excellent performance under large deformations and different working conditions, set the stage for the development of a new generation of high-end flexible sensory electronic skin, which is attractive in a wide range of engineering fields, such as autonomous soft robotics, biomedicine, and the Internet of Things. [ABSTRACT FROM AUTHOR]

This report demonstrates the fabrication of SnS/paper based low-cost and flexible pressure sensor, employing a facile solvothermal synthesis followed by vacuum filtration, for artificial electronic skin and touchpad applications. The fabricated pressure sensor displayed a high sensitivity of 3.18 kPa $^{- {\sf 1}}$ and a response time $\sim 300$ msec. Inspired by the high value of sensitivity and an appreciable flexibility, a large-area pressure sensor array (${\sf 3} \times {\sf 3}$) was fabricated and integrated onto a human arm for demonstrating real-time applications. The fabricated sensor array was able to consistently detect and track random localized points of contact, the shape of an unknown object placed on top of it, and an index finger trajectory along the surface with high accuracy and precision. The fabricated device showed a negligible change in the performance over 500 bending cycles which indicates the highly robust nature of the device. Successful fabrication of such a cost-effective large-area pressure sensor array is a major step in flexible electronics, and holds immense potential in artificial electronic skin, security, personal healthcare applications. [ABSTRACT FROM AUTHOR]

This report demonstrates of the direct growth of ternary compound ZnSnO 3 nanocubes on silica cloth for the fabrication of scalable tactile sensors for monitoring physiological signals which even the highly sensitive tactile sensors fail to measure and artificial electronic skin (E-skin) without the use of sophisticated silicon wafer based technologies. The fabricated sensor exhibited a sensitivity and response time of 0.12 KPa−1 and 350 ms respectively. Inspired by the inherent alignment of the ZnSnO 3 nanocubes on silica microfibers, the fabricated sensor was further demonstrated to be able to recognize wrist pulse pressure, finger movement, wrist movement and finger pressing. Furthermore, large area sensors array (4 × 4) were fabricated and integrated onto human hand which can "feel" the touch and spatially map the response paving way for the development of E-skin. Also, the sensor array was able to detect and map the shape and location of unknown objects placed on it and could trace the index finger trajectory made on the sensor array. The fabricated pressure sensor was tested for its reliability by performing bending test studies under harsh deformations and 500 bending cycles which resulted in negligible change in the performance of the sensor. [ABSTRACT FROM AUTHOR]

Abstract: Stretchable capacitive devices are instrumental for new‐generation multifunctional haptic technologies particularly suited for soft robotics and electronic skin applications. A majority of elongating soft electronics still rely on silicone for building devices or sensors by multiple‐step replication. In this study, fabrication of a reliable elongating parallel‐plate capacitive touch sensor, using nitrile rubber gloves as templates, is demonstrated. Spray coating both sides of a rubber piece cut out of a glove with a conductive polymer suspension carrying dispersed carbon nanofibers (CnFs) or graphene nanoplatelets (GnPs) is sufficient for making electrodes with low sheet resistance values (≈10 Ω sq−1). The electrodes based on CnFs maintain their conductivity up to 100% elongation whereas the GnPs‐based ones form cracks before 60% elongation. However, both electrodes are reliable under elongation levels associated with human joints motility (≈20%). Strikingly, structural damages due to repeated elongation/recovery cycles could be healed through annealing. Haptic sensing characteristics of a stretchable capacitive device by wrapping it around the fingertip of a robotic hand (ICub) are demonstrated. Tactile forces as low as 0.03 N and as high as 5 N can be easily sensed by the device under elongation or over curvilinear surfaces. [ABSTRACT FROM AUTHOR]

In the development of artificial electronic skin (e-skin), a flexible tactile sensor is a critical component that imitates human skin response to dynamic and static stimuli. In this study, we developed a novel multifunctional tactile sensor to mimic human skin with high force sensitivity, high flexibility, and temperature measurable performance. The unique geometry of the interlocked structures enabled differentiation between different mechanical stimuli, including pressure, bending and torsion forces. The substrate was flexible because of the material properties of the polydimethylsiloxane (PDMS) layer. The top electrode and bottom electrode layers were interlocked by high-aspect-ratio zinc oxide nanorods (NRs), which were grown vertically on the PDMS surface, providing high sensitivity for the measurement of contact force and environmental temperature. Moreover, the sensor was applied for measuring and monitoring arterial pulse pressure. Thus, we successfully fabricated a 3 × 3 sensor array with multiple functions, which were verified through experiments. In the future, the proposed tactile sensor can be used in wearable health care devices, flexible interfaces, and bionic robotic skins in the industry. [ABSTRACT FROM AUTHOR]

It remains challenging to fabricate strain-sensing materials and exquisite geometric constructions for integrating extraordinary sensitivity, low strain detectability, high stretchability, tunable sensing range, and thin device dimensions into a single type of strain sensor. A percolation network based on Ti 3 C 2 T x MXene/carbon nanotube (CNT) composites was rationally designed and fabricated into versatile strain sensors. This weaving architecture with excellent electric properties combined the sensitive two-dimensional (2D) Ti 3 C 2 T x MXene nanostacks with conductive and stretchable one-dimensional (1D) CNT crossing. The resulting strain sensor can be used to detect both tiny and large deformations with an ultralow detection limit of 0.1% strain, high stretchability (up to 130%), high sensitivity (gauge factor up to 772.6), tunable sensing range (30% to 130% strain), thin device dimensions (<2 μm), and excellent reliability and stability (>5000 cycles). The versatile and scalable Ti 3 C 2 T x MXene/CNT strain sensors provide a promising route to future wearable artificial intelligence with comprehensive tracking ability of real-time and in situ physiological signals for health and sporting applications.

Stretchable capacitive devices are instrumental for new-generation multifunctional haptic technologies particularly suited for soft robotics and electronic skin applications. A majority of elongating soft electronics still rely on silicone for building devices or sensors by multiple-step replication. In this study, fabrication of a reliable elongating parallel-plate capacitive touch sensor, using nitrile rubber gloves as templates, is demonstrated. Spray coating both sides of a rubber piece cut out of a glove with a conductive polymer suspension carrying dispersed carbon nanofibers (CnFs) or graphene nanoplatelets (GnPs) is sufficient for making electrodes with low sheet resistance values (≈10 Ω sq -1 ). The electrodes based on CnFs maintain their conductivity up to 100% elongation whereas the GnPs-based ones form cracks before 60% elongation. However, both electrodes are reliable under elongation levels associated with human joints motility (≈20%). Strikingly, structural damages due to repeated elongation/recovery cycles could be healed through annealing. Haptic sensing characteristics of a stretchable capacitive device by wrapping it around the fingertip of a robotic hand (ICub) are demonstrated. Tactile forces as low as 0.03 N and as high as 5 N can be easily sensed by the device under elongation or over curvilinear surfaces.

We report on the facile fabrication of a stretchable array of highly sensitive pressure sensors. The proposed pressure sensor consists of the top layer of Au-deposited polydimethylsiloxane (PDMS) micropillars and the bottom layer of conductive polyaniline nanofibers on a polyethylene terephthalate substrate. The sensors are operated by the changes in contact resistance between Au-coated micropillars and polyaniline according to the varying pressure. The fabricated pressure sensor exhibits a sensitivity of 2.0 kPa(-1) in the pressure range below 0.22 kPa, a low detection limit of 15 Pa, a fast response time of 50 ms, and high stability over 10000 cycles of pressure loading/unloading with a low operating voltage of 1.0 V. The sensor is also capable of noninvasively detecting human-pulse waveforms from carotid and radial artery. A 5 × 5 array of the pressure sensors on the deformable substrate, which consists of PDMS islands for sensors and the mixed thin film of PDMS and Ecoflex with embedded liquid metal interconnections, shows stable sensing of pressure under biaxial stretching by 15%. The strain distribution obtained by the finite element method confirms that the maximum strain applied to the pressure sensor in the strain-suppressed region is less than 0.04% under a 15% biaxial strain of the unit module. This work demonstrates the potential application of our proposed stretchable pressure sensor array for wearable and artificial electronic skin devices.

Graphene-based strain sensors have attracted much attention recently. Usually, there is a trade-off between the sensitivity and resistance of such devices, while larger resistance devices have higher energy consumption. In this paper, we report a tuning of both sensitivity and resistance of graphene strain sensing devices by tailoring graphene nanostructures. For a typical piezoresistive nanographene film with a sheet resistance of ∼100 KΩ/□, a gauge factor of more than 600 can be achieved, which is 50× larger than those in previous studies. These films with high sensitivity and low resistivity were also transferred on flexible substrates for device integration for force mapping. Each device shows a high gauge factor of more than 500, a long lifetime of more than 10(4) cycles, and a fast response time of less than 4 ms, suggesting a great potential in electronic skin applications.