Ultrasensitive and ultrastretchable metal crack strain sensor based on helical polydimethylsiloxane.

The majority of crack sensors do not offer simultaneously both a significant stretchability and an ultrahigh sensitivity. In this study, we present a straightforward and cost-effective approach to fabricate metal crack sensors that exhibit exceptional performance in terms of ultrahigh sensitivity and ultrahigh stretchability. This is achieved by incorporating a helical structure into the substrate through a modeling process and, subsequently, depositing a thin film of gold onto the polydimethylsiloxane substrate via sputter deposition. The metal thin film is then pre-stretched to generate microcracks. The sensor demonstrates a remarkable stretchability of 300%, an exceptional sensitivity with a maximum gauge factor reaching 107, a rapid response time of 158 ms, minimal hysteresis, and outstanding durability. These impressive attributes are attributed to the deliberate design of geometric structures and careful selection of connection types for the sensing materials, thereby presenting a novel approach to fabricating stretchable and highly sensitive crack-strain sensors. This work offers a universal platform for constructing strain sensors with both high sensitivity and stretchability, showing a far-reaching significance and influence for developing next-generation practically applicable soft electronics.

Flexible BaTiO3-PDMS Capacitive Pressure Sensor of High Sensitivity with Gradient Micro-Structure by Laser Engraving and Molding.

The significant potential of flexible sensors in various fields such as human health, soft robotics, human-machine interaction, and electronic skin has garnered considerable attention. Capacitive pressure sensor is popular given their mechanical flexibility, high sensitivity, and signal stability. Enhancing the performance of capacitive sensors can be achieved through the utilization of gradient structures and high dielectric constant media. This study introduced a novel dielectric layer, employing the BaTiO3-PDMS material with a gradient micro-cones architecture (GMCA). The capacitive sensor was constructed by incorporating a dielectric layer GMCA, which was fabricated using laser engraved acrylic (PMMA) molds and flexible copper-foil/polyimide-tape electrodes. To examine its functionality, the prepared sensor was subjected to a pressure range of 0-50 KPa. Consequently, this sensor exhibited a remarkable sensitivity of up to 1.69 KPa-1 within the pressure range of 0-50 KPa, while maintaining high pressure-resolution across the entire pressure spectrum. Additionally, the pressure sensor demonstrated a rapid response time of 50 ms, low hysteresis of 0.81%, recovery time of 160 ms, and excellent cycling stability over 1000 cycles. The findings indicated that the GMCA pressure sensor, which utilized a gradient structure and BaTiO3-PDMS material, exhibited notable sensitivity and a broad linear pressure range. These results underscore the adaptability and viability of this technology, thereby facilitating enhanced flexibility in pressure sensors and fostering advancements in laser manufacturing and flexible devices for a wider array of potential applications.

Flexible Microstructured Capacitive Pressure Sensors Using Laser Engraving and Graphitization from Natural Wood.

In recent years, laser engraving has received widespread attention as a convenient, efficient, and programmable method which has enabled high-quality porous graphene to be obtained from various precursors. Laser engraving is often used to fabricate the dielectric layer with a microstructure for capacitive pressure sensors; however, the usual choice of electrodes remains poorly flexible metal electrodes, which greatly limit the overall flexibility of the sensors. In this work, we propose a flexible capacitive pressure sensor made entirely of thermoplastic polyurethane (TPU) and laser-induced graphene (LIG) derived from wood. The capacitive pressure sensor consisted of a flexible LIG/TPU electrode (LTE), an LIG/TPU electrode with a microhole array, and a dielectric layer of TPU with microcone array molded from a laser-engraved hole array on wood, which provided high sensitivity (0.11 kPa-1), an ultrawide pressure detection range (20 Pa to 1.4 MPa), a fast response (~300 ms), and good stability (>4000 cycles, at 0-35 kPa). We believe that our research makes a significant contribution to the literature, because the easy availability of the materials derived from wood and the overall consistent flexibility meet the requirements of flexible electronic devices.

Ramie Fabric Treated with Carboxymethylcellulose and Laser Engraved for Strain and Humidity Sensing.

Wearable fabric sensors have attracted enormous attention due to their huge potential in human health and activity monitoring, human-machine interaction and the Internet of Things (IoT). Among natural fabrics, bast fabric has the advantage of high strength, good resilience and excellent permeability. Laser engraving, as a high throughput, patternable and mask-free method, was demonstrated to fabricate fabric sensors. In this work, we developed a simplified, cost-effective and environmentally friendly method for engraving ramie fabric (a kind of bast fabric) directly by laser under an ambient atmosphere to prepare strain and humidity sensors. We used carboxymethylcellulose (CMC) to pretreat ramie fabric before laser engraving and gained laser-carbonized ramie fabrics (LCRF) with high conductivity (65 Ω sq-1) and good permeability. The strain and humidity sensors had high sensitivity and good flexibility, which can be used for human health and activity monitoring.

Polyimide-Sputtered and Polymerized Films with Ultrahigh Moisture Sensitivity for Respiratory Monitoring and Contactless Sensing.

Respiratory monitoring and contactless sensing using the moisture produced by respiration and perspiration have garnered considerable attention in recent years. In this study, we fabricated polyimide-sputtered and polymerized (PSP) humidity sensors with ultrahigh capacitive sensitivity, fast response, and a wide working range of relative humidity (RH). The sensors produced >40 000 times increment in the sensing signal over the 10-95% RH range at 10 Hz and exhibited good performance at low RH levels (<40%) as well. These sensors displayed excellent sensing properties with small hysteresis, long-time stability, and fast response and recovery times (2.4 and 1.2 s, respectively). In the mechanism study of PSP humidity sensors, we found that the high sensitivity can be attributed to massive hydrophilic functional groups formed on the polymer chains by moist aging with oxidation and the fast response speed is due to the mesoporous structure of PSP films. We also fabricated a 5 × 5 array of PSP humidity sensors to identify the shapes of wet objects and of leaves during transpiration. Thus, we reported a novel and effective method for fabricating high-performance humidity polymer films, channeling new pathways for the development of advanced humidity and gas sensors.

Ultrasensitive and highly stretchable fibers with dual conductive microstructural sheaths for human motion and micro vibration sensing.

Conductive and stretchable fibers are important components of the increasingly popular wearable electronic devices as they meet the design requirements of excellent electrical conductivity, stretchability, and wearability. In this work, we developed a novel dual conductive-sheath fiber (DCSF) with a conductive sheath composed of a porous elastic conductive layer and cracked metal networks, thus achieving ultrahigh sensitivity under a large strain range. The core of the DCSF is made of thermoplastic polyurethane (TPU) elastic fiber wrapped in a porous stretchable conductive layer composed of carbon nanotubes (CNTs) and TPU. Next, a layer of gold film is deposited on the surface of the porous stretchable conductive layer by ion beam sputtering. Due to the fast response time of 184 ms and ultrahigh sensitivity in the 0-100% strain range (a gauge factor of 184.50 for a strain of 0-10%, 4.12 × 105 for 10%-30%, and 2.80 × 105 for 30%-100%) of the DCSF strain sensor, we successfully wove the fiber strain sensor into gloves and could realize the recognition of different hand gestures. Also the DCSF strain sensor can be applied to detect microvibrations efficiently. The demonstrated DCSF has potential applications in the development of smart wearable devices and micro vibration sensors.

A multifunctional hollow TPU fiber filled with liquid metal exhibiting fast electrothermal deformation and recovery.

Conductive fibers have received considerable interest due to their potential applications in the flexible electronics field. Fabricating a conductive fiber that can realize fast deformation with stretchability for multifunctional applications is still highly appealing. Here, we present a deformable conductive fiber (DCF) fabricated by injecting liquid metal (LM) into a hollow thermoplastic polyurethane (TPU) fiber; the DCF can be shaped into a 2D or 3D shape by an electrothermal method at the thermoplastic transition point of TPU. Combined with the solid-liquid phase transition characteristics of the LM at its melting point, the DCF exhibits a variable shape memory feature at two transition points. We have demonstrated that the double-torsional DCF and the helical DCF can act as a capacitive sensor and an inductive sensor, respectively, and they have both been used for human motion monitoring. In addition, the helical DCF can also act as a stretchable electrode with excellent electrical properties (resistance change <2%) under a maximal mechanical strain of 3300%. Overall, the DCF presents great potential for applications in human motion monitoring, soft robotics and smart electronic textiles.