Search

In recent years, hydrogel-based wearable flexible electronic devices have attracted much attention. However, hydrogel-based sensors are affected by structural fatigue, material aging, and water absorption and swelling, making stability and accuracy a major challenge. In this study, we present a DN-SPEZ dual-network hydrogel prepared using polyvinyl alcohol (PVA), sodium alginate (SA), ethylene glycol (EG), and ZnSO4 and propose a self-calibration compensation strategy. The strategy utilizes a metal salt solution to adjust the carrier concentration of the hydrogel to mitigate the resistance drift phenomenon to improve the stability and accuracy of hydrogel sensors in amphibious scenarios, such as land and water. The ExpGrow model was used to characterize the trend of the ∆R/R0 dynamic response curves of the hydrogels in the stress tests, and the average deviation of the fitted curves ϵ ¯ was calculated to quantify the stability differences of different groups. The results showed that the stability of the uncompensated group was much lower than that of the compensated group utilizing LiCl, NaCl, KCl, MgCl2, and AlCl3 solutions ( ϵ ¯ in the uncompensated group in air was 276.158, 1.888, 2.971, 30.586, and 13.561 times higher than that of the compensated group in LiCl, NaCl, KCl, MgCl2, and AlCl3, respectively; ϵ ¯ in the uncompensated group in seawater was 10.287 times, 1.008 times, 1.161 times, 4.986 times, 1.281 times, respectively, higher than that of the compensated group in LiCl, NaCl, KCl, MgCl2 and AlCl3). In addition, for the ranking of the compensation effect of different compensation solutions, the concentration of the compensation solution and the ionic radius and charge of the cation were found to be important factors in determining the compensation effect. Detection of events in amphibious environments such as swallowing, robotic arm grasping, Morse code, and finger–wrist bending was also performed in this study. This work provides a viable method for stability and accuracy enhancement of dual-network hydrogel sensors with strain and pressure sensing capabilities and offers solutions for sensor applications in both airborne and underwater amphibious environments. [ABSTRACT FROM AUTHOR]

With the advancement of intelligent medical robot technology, machine touch utilizing flexible sensors has emerged as a prominent research area. In this study, a flexible resistive pressure sensor was designed incorporating a microcrack structure with air pores and a composite conductive mechanism of silver/carbon. The aim was to achieve enhanced stability and sensitivity with the inclusion of macro through-holes (1–3 mm) to expand the sensitive range. This technology solution was specifically applied to the machine touch system of the B-ultrasound robot. Through meticulous experimentation, it was determined that the optimal approach involved uniformly blending ecoflex and nano carbon powder at a mass ratio of 5:1, and subsequently combining the mixture with an ethanol solution of silver nanowires (AgNWs) at a mass ratio of 6:1. This combination of components resulted in the fabrication of a pressure sensor with optimal performance. Under the pressure testing condition of 5 kPa, a comparison of the resistance change rate was conducted among samples using the optimal formulation from the three processes. It was evident that the sample of ecoflex-C-AgNWs/ethanol solution exhibited the highest sensitivity. Its sensitivity was increased by 19.5% compared to the sample (ecoflex-C) and by 11.3% compared to the sample (ecoflex-C-ethanol). The sample (ecoflex-C-AgNWs/ethanol solution), which only incorporated internal air pore microcracks without through-holes, exhibited sensitive response to pressures below 5 N. However, with the addition of through-holes, the measurement range of its sensitive response increased to 20 N, representing a 400% increase in the measurement range. [ABSTRACT FROM AUTHOR]

A compact flexible fractal ultra‐wideband antenna with band notch characteristic is presented. The antenna is printed on a 12.5 μm flexible polyimide substrate, and an impedance bandwidth of 15.48 GHz (3.6‐19.08 GHz) is achieved along with an overall antenna size of 20.5 × 13.9 mm2. The design of the hexagonal radiator in the fourth iteration effectively enhances the impedance bandwidth of the antenna. By arranging two symmetrical complementary split ring resonators on the ground plane, the band rejection of the X‐band uplink frequency from 7.9 to 8.41 GHz is achieved. The average gain of the antenna can reach 3 dBi in the pass band, while the gain in the notch band is greatly reduced to below 0 dBi. Compared with the existing structure, the antenna has a larger bandwidth and a smaller size. Furthermore, the antenna is tested under bending effects. Test results show that this antenna can be used for integration on flexible electronic devices. [ABSTRACT FROM AUTHOR]

• The ionic flexible pressure sensor with microstructured dielectric layer exhibits high sensitivity and broad sensing range. • The ridge-like microstructure of the dielectric layer plays an important role in capacitance change. • The ionic pressure sensor has great potential in healthcare monitoring and human-machine interaction. Owing to fast response speed and excellent repeatability, flexible capacitive pressure sensors are important for electronic skin and human-machine interaction. However, it is still challenging for the capacitive pressure sensors to meet the requirements of various applications with limited sensitivity in a narrow range. Herein, a flexible capacitive pressure sensor with an ionic dielectric layer is reported. Taking advantages of the interlaced ridge-like microstructure (IRM) of the ionic dielectric layer, this device is able to detect the pressure from 1 Pa to 300 kPa. Meanwhile, the sensitivity of the sensor is 92 kPa−1 in the low pressure range (<0.4 kPa), 45.04 kPa−1 in the middle pressure range (0.4 kPa–20 kPa) and 8.5 kPa−1 in the high pressure range (20 kPa–100 kPa). In addition, the sensor exhibits a short dynamic response time of ∼45 ms and high mechanical stability of over 6000 cycles. Finally, we demonstrated a few practical applications that need broad pressure sensing range, such as liquid evaporation monitoring and human arm bending detecting. The sensor and fabrication method reported here provides a simple and low-cost scheme to fabricate pressure sensors with promising performance. [ABSTRACT FROM AUTHOR]

• The flexible pressure sensor with tunable sensitivity and pressure range was fabricated by 3D printing technique. • The performance of ionic pressure sensor can be highly improved due to the electrical double layers and hierarchical mesh structure. • Human physiological activities in different pressure ranges can be detected by the ionic pressure sensor. Flexible pressure sensors play an indispensable role in numerous future technologies for human beings, especially those with high sensitivity, broad sensing range and tunable fabrication methods. Herein, we demonstrate a tunable ionic pressure sensor based on the dielectric layer with ordered hierarchical mesh structure (OHMS). The OHMS layer was fabricated by a simple and adaptable 3D printing technique, therefore the performance of the sensor can be tuned. Owing to the OHMS and electrical double layers (EDL), the sensor exhibits a high sensitivity of 72.86 kPa−1 in the ultralow pressure range (<0.4 kPa), a fast response time within 43 ms, a high stability for over 7300 cycles, and a broad pressure sensing range from 1 Pa to 400 kPa. The sensor is demonstrated with practical applications, including Morse code, solvent evaporation detection, breathing, swallowing, wrist pulse, and plantar pressure measurement. This work may provide a new approach to tailor and improve the performance of ionic pressure sensors, which have great potential for innovative applications in wearable health-monitoring devices and human-machine interface systems. [ABSTRACT FROM AUTHOR]

• Supercritical ethanol was used for depositing Ni(OH) 2 NSs arrays on carbon cloth. • Hierarchical nanostructured Ni(OH) 2 was obtained due to the supercritical fluids. • Numerous open channels and passages are generated between the Ni(OH) 2 NSs. • Ni(OH) 2 NSs arrays/ECC electrode exhibits superior electrochemical properties. • Flexible solid-state device shows high electrochemical performance. Ni(OH) 2 nanosheets (NSs) were grown onto an electrochemically activated carbon cloth (ECC) with a self-supported microstructure by using efficient ethanol assisted supercritical deposition method. Benefited from the structural features of the well-developed porous architecture with effective channels for electrolyte ions diffusion and accessible redox sites, the nano-heterostructure brings a high utilization of electroactive material and thereby good electrochemical performance. The specific capacity of 918 mC cm−2 at 2 mA cm−2 with good rate performance (68.4 % retention at 20 mA cm−2) was achieved for the obtained Ni(OH) 2 NSs/ECC flexible electrode. The assembled flexible solid-state device with a 1.8 V operating potential displays an energy density of 8.3 mW h cm-3 at 20 mW cm-3. Additionally, the as-fabricated device reveals cyclic stability with 87 % capacity retention (10,000 cycles at 50 mA cm−2). These results show the importance of supercritical fluid deposition as a potential method for supercapacitors electrode. [ABSTRACT FROM AUTHOR]

Flexible pressure sensors are highly desired in a wide variety of areas including artificial intelligence and healthcare monitoring. Amidst them, capacitive pressure sensors are advantaged for simple configuration and fast reponse speed. However, they suffer from some restrictions such as limited and fixed sensitivity as well as unsatisfactory robustness. Herein, a tunable flexible capacitive pressure sensor is realized by bioinspired capillary-driven method. The dielectric layer with double-side microstructure is developed with polycarbonate template molding (PCTEM) driven by capillary force, while the bottom and top electrodes are fabricated by a colorless polyimide (CPI) film coated with silver nanowires. The sensor exhibits a tunable sensitivity from 0.189 k Pa−1 to 5.821 k Pa−1 with an ultralow limit of detection (LOD) of ~1.5 Pa and a fast response time of ~30 ms. The sensor offers a configuration with a thickness of 130 μm and excellent robustness for fatigue test of 200,000 cycles. The pressure sensor fabricated by the PCTEM method allows sensitive and tunable pressure sensing in soft robotics and human-machine interaction. Also, the bioinspired capillary-driven PCTEM strategy may offer a guideline to design other microstructures with improved performance for varied flexible sensors. Unlabelled Image • Tunable sensitivity was achieved by adjusting the density of transverse micropillars. • High sensitive pressure sensor was achieved by bioinspired Capillary-driven Method. • Ultrahigh mechanical robustness of sensor was demonstrated. [ABSTRACT FROM AUTHOR]