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This study developed a triboelectric nanogenerator capable of harvesting energy from omnidirectional wind at a wide range of speeds. This harvester consists of a flexible cylindrical shell surrounding a rigid column. Each surface of the two components is composed of aluminum and polytetrafluoroethylene (PTFE), a pair of triboelectric materials. The thin shell forms a self-suspended structure due to the Coulombic attraction between the two triboelectric materials. Therefore, the electrical connection between the aluminum and electrodes is maintained, and it can be easily deformed even by the low-velocity wind. The change in the relative distance between these two charged layers enables energy harvesting via a triboelectric energy conversion mechanism. In addition, due to its cylindrical structure, the harvester exhibited homogeneous energy generation performance for all wind directions. It was experimentally confirmed that the generated voltage and current increased as the wind speed increased, from a very low speed of 0.3 m/s to a high speed of 10 m/s. The measured RMS power density harvested from a wind speed of 10 m/s was 8.43 mW/m2. Measured individually at the electrodes for the PTFE layer divided into eight sections, the voltages were asymmetric along any given direction. By utilizing the dependence of the generated voltage on wind speed and direction, we demonstrated that the harvester could be used as a self-powered wind-monitoring sensor with high durability. [Display omitted] • A self-suspended shell-based wind-driven triboelectric nanogenerator was demonstrated. • The device could operate at wind speeds as low as 0.3 m/s to strong winds of 10 m/s. • The device can harvest wind energy evenly from the wind in any direction. • The device can be used as a self-powered wind-speed and direction sensor. [ABSTRACT FROM AUTHOR]

We propose a gas sensor operable over a wide temperature range and using suspended GaN nanowires functionalized with Pt–Pd. The sensor is batch-fabricated by directly integrating the GaN nanowires onto batch-processed silicon microelectrodes in parallel. The high thermal stability of the sensor originates from a large band gap of GaN nanowires that enables the detection of NO2 gas at an elevated temperature of up to 350 °C without a decrease in responsiveness. Exposed to NO2 at 100–1000 ppm at 350 °C, the sensor shows a linear increment in relative response with respect to the change in gas concentration. The sensor results in a two- to four-fold increase in responsiveness to NO2 at 100 ppm compared to NH3 at 100 ppm and CO2 at 1000 ppm. The nanowires suspended over a substrate provide increased surface area that could interact with gas molecules for enhanced responsiveness, and prevent any unnecessary interactions between the nanowires and the substrate. [ABSTRACT FROM AUTHOR]

Abstract: A highly sensitive hydrogen sensor based on suspended and functionalized single tungsten nanowire is presented. The sensing tungsten nanowire is synthesized by focused ion beam-chemical vapor deposition (FIB-CVD) using W(CO)6 precursor gas on batch-fabricated microelectrodes. The nanowire measures 10μm in length and 150nm in diameter, and is suspended 50μm above the wafer substrate connecting two microelectrodes to enhance the exposure of nanowire surface to target gas molecules for improved chemisorptions. The nanowire is then functionalized by palladium–platinum (Pd–Pt) sputtering process to be sensitive to the hydrogen molecules. The significant increase of nanowire resistance is observed whenever it is exposed to hydrogen molecules, and the resistance is recovered to the original value after hydrogen molecules are purged out. The experimentally characterized hydrogen sensor shows 11.52% increase of resistance to the exposure to 1% (10,000ppm) hydrogen and 99% nitrogen gas mixture at room temperature and atmospheric pressure. The lowest hydrogen concentration measured is 0.001% (10ppm) with 0.58% corresponding resistance increase. [Copyright &y& Elsevier]

Abstract: Selective stiction has been successfully applied to the batch fabrication of angular vertical comb actuators made of single-crystal silicon with self-aligned comb sets. The possible failure modes of the devices during the manufacturing process are studied, and a novel design of stiction plate and mechanical spring is also presented to suppress the failure modes. The fabrication process with unique designs of mechanical springs enables the stiction of microstructures in a controlled manner and significantly reduces unwanted compliances on the actuators, preventing unwarranted motion and providing stable operations. The prototype microactuators operate at a resonant frequency of 0.92kHz with 85° optical scanning angle and quality factor of 162 in air under driving voltages of 19Vdc plus 15Vpp. A reliability test on an unpackaged actuator with more than 800 million cycles of operation showed extremely small variation in the resonant frequency and scanning angle, showing no sign of degradation in the induced stiction interface or the microstructures. Applications include scanning micromirrors, optical switches, and variable capacitors and we present results obtained with MEMS scanning mirrors. [Copyright &y& Elsevier]

Characterization of pitch and roll motions of the slider in the hard disk gimbal system is important to achieve higher aerial recording densities. This paper describes a novel piezoresistive-type microsensor that could be directly mounted on the existing slider/gimbal system of a hard disk drive to simultaneously measure the pitch and roll angles of the slider. The size of the fabricated microsensor is designed as 1 mm×1 mm×0.1 mm for picoslider applications and the sensor is fabricated by a silicon micromachining process for mass production. The dynamic behavior of the system is slightly altered as expected in a simulation after the sensor is mounted on the slider and the fundamental frequency shift of pitch and roll motion is calculated to be less than 5% of the original system but it is believed that this sensor could provide the best in situ measurement than other currently existing methods. Experimentally, the prototype sensor is capable of detecting pitch and roll angles within ± 3° and the performance is compared with interferometric measurement data and the mismatch is nominally within 14% in average. [Copyright &y& Elsevier]

Resistive Tactile Sensor In article number 2100428, Jongbaeg Kim and co‐workers develop a resistive tactile sensor using carbon nanotube‐ and silver nanoparticle inkjet‐printed mulberry paper as a pressure‐sensing element and electrodes, respectively. Compared with previously reported paper‐based tactile sensors, the presented sensor exhibits high sensitivity over a wide pressure range due to the distinctive characteristics and stacked structure of mulberry paper. [ABSTRACT FROM AUTHOR]

Wearable wireless gas sensors have attracted enormous interest due to precise, real‐time healthcare and environmental monitoring without temporal and spatial limitations. Among various toxic gases, detecting ammonia is crucial because of its highly hazardous nature and applicability as a noninvasive biomarker for diagnosing health conditions. In this study, silver nanowires‐decorated silicon nanomembrane (AgNW‐SiNM) chemiresistive gas sensor with high selectivity to ammonia is fully integrated with an ultrathin flexible Joule heater and wireless communication system to fabricate wearable wireless real‐time toxic gas monitoring system. The sensor exhibits improved performance to ammonia gas, attributed to heating‐induced changes in adsorption/desorption rates, along with electronic and chemical sensitization facilitated by AgNW decoration. The gas sensing system exhibits stable and high responses of ≈1.83, 1.47, and 1.19 on the ammonia exposure at concentrations of 10, 5, and 1 ppm even under mechanical deformations. The real‐time dynamic response of the sensor is wirelessly transmitted to portable electronics and displayed on the screen. Moreover, the system alerts the users in advance through the integrated haptic interface when exposed to dangerous gas environments for early evacuation. The system paves the way for timely warnings from hazardous gas and more accurate noninvasive medical diagnosis related to respiratory disorders. [ABSTRACT FROM AUTHOR]

A widely tunable variable capacitor using mechanical switching and a reversible latching mechanism was developed. This variable capacitor can increase the total capacitance by utilizing three discrete switches to sequentially connect four sets of fixed capacitors arranged in parallel. Continuous fine tuning is achieved by closing gaps with these interdigitated capacitors, and connected states are maintained through the use of a mechanical latching mechanism. By combining switching and gap-closing modes, a maximum tuning ratio of 9.42 was obtained. [ABSTRACT FROM PUBLISHER]

The rise of flexible electronics has sparked a demand for components, such as loudspeakers, that seamlessly integrate into various applications while maintaining their performance. However, current loudspeakers typically rely on electromechanical systems, necessitating significant space for components such as coils and magnets. This limits their flexibility and usage in thin, conformable devices. To address this, a paper‐based thermoacoustic (TA) loudspeaker utilizing carbon nanotubes (CNTs) via inkjet printing is introduced. This TA loudspeaker demonstrates exceptional flexibility and durability, maintaining high acoustic performance across human‐audible frequencies up to 20 kHz, even when subjected to extensive mechanical deformation. Additionally, employing inkjet printing technology streamlines their manufacturing processes, offering a cost‐effective solution with scalability for mass production. Furthermore, an origami‐inspired 3D folding architecture enhances the loudspeaker's portability and enables versatile shape configurations, thus broadening its utility across electronic devices. These demonstrations offer a potential solution for next‐generation audio systems in flexible electronics. [ABSTRACT FROM AUTHOR]

Resistive tactile sensors based on changes in contact area have been extensively explored for a variety of applications due to their outstanding pressure sensitivity compared to conventional tactile sensors. However, the development of tactile sensors with high sensitivity in a wide pressure range still remains a major challenge due to the trade‐off between sensitivity and linear detection range. Here, a tactile sensor comprising stacked carbon nanotubes and Ni‐fabrics is presented. The hierarchical structure of the fabrics facilitates a significant increase in contact area between them under pressure. Additionally, a multi‐layered structure that can provide more contact area and distribute stress to each layer further improves the sensitivity and linearity. Given these advantages, the sensor presents high sensitivity (26.13 kPa−1) over a wide pressure range (0.2–982 kPa), which is a significant enhancement compared with the results obtained in previous studies. The sensor also exhibits outstanding performances in terms of response time, repeatability, reproducibility, and flexibility. Furthermore, meaningful applications of the sensor, including wrist‐pulse‐signal analysis, flexible keyboards, and tactile interface, are successfully demonstrated. Based on the facile and scalable fabrication technique, the conceptually simple but powerful approach provides a promising strategy to realize next‐generation electronics. [ABSTRACT FROM AUTHOR]

A polymer-based tactile sensor with flexibility and multi-directional sensing capability is presented. The proposed sensor consists of a polydimethylsiloxane (PDMS) bump, a polyimide (PI) substrate, Cr/Au electrode lines for electrical connection, NiCr piezoresistors, and an SU-8 support structure. The sensing mechanism is based on piezoresistive effect, in which the resistance of NiCr changes under mechanical load. The PMDS bump positioned at the center of the sensor transfers an applied force to the PI film, and the piezoresistors are differently deformed depending on the magnitude and direction of the force. A diaphragm structure formed by the SU-8 support with a trench allows the piezoresistor to be effectively deformed. Simulation and experimental results confirm that magnitude and direction can be obtained from an arbitrarily applied force by comparing the change in resistance of each sensing element. Based on its compatibility with conventional microfabrication, the proposed sensor may be a promising candidate for a low-cost tactile sensing solution for human‒machine interfaces. [ABSTRACT FROM AUTHOR]

Transparent and flexible UV sensors have attracted considerable attention for use in portable/wearable optoelectronic systems. Although UV sensors based on photoactive nanomaterials have been reported for such applications, achieving full transparency and flexibility remains a challenge because they still rely on opaque or brittle electrodes. Here, a fully transparent, flexible, and highly sensitive UV sensor based on 1D carbon nanotubes (CNTs)–2D graphene hybrid is demonstrated. Under UV illumination, oxygen molecules on the CNT surfaces are desorbed by photoinduced plasmon energy, leading to a significant decrease in hole concentration, and correspondingly an increase in the electrical resistance of CNT. The combination of CNT and graphene minimizes the effect of contact resistance and facilitates effective charge transfer between them without potential barrier, resulting in a high photoresponse, which is 30 times as high as that of Au‐electrode‐based CNT sensor. Simultaneously, CNT–graphene UV sensor shows remarkable transparency (over 80% at 550 nm) and outstanding mechanical flexibility without any significant change in electrical resistance for 500 cycles at a bending radius of 5.5 mm. The integration of CNT–graphene hybrid onto flexible substrates through scalable microfabrication is expected to provide exciting opportunities for the development of high performance, optically and mechanically invisible optoelectronic devices. Transparent, flexible, and visible‐blind UV sensor based on carbon nanotube (CNT)–graphene hybrids is presented. Based on the excellent properties of carbon nanomaterials, the combination of photoactive CNT channels and a graphene electrode provides high photoresponse and outstanding flexibility while preserving remarkable transparency. The proposed UV sensor can be used for low‐cost, high‐performance optoelectronic applications that require optical invisibility and mechanical flexibility. [ABSTRACT FROM AUTHOR]

A volatile organic compound (VOC) sensor array based on metal oxide nanoparticles (MOX NPs) functionalized by metalloporphyrins (MPPs) was demonstrated. The VOC sensor array was composed of four single sensors based on SnO2 NPs/cobalt-porphyrin, SnO2 NPs/zinc-porphyrin, SnO2 NPs/nickel-porphyrin and ZnO NPs/cobalt-porphyrin. The MOX NP/MPP-based sensors were fabricated by drop-casting the MOX NPs dispersion and MPPs solution onto a MEMS platform. The fabricated sensor successfully detected toluene at a concentration as low as 20 ppb, which is below the limit detection concentration of previously reported porphyrin-based VOC sensor arrays. We also confirmed the selectivity between benzene, toluene, ethylbenzene, and xylene (BTEX) by using principal component analysis in contrast to previous studies on MOX/MPP-based sensor. BTEX was classified from 1 to 9 ppm at a resolution of 2 ppm, and the sensor array showed stable performance even after considerable impact. [ABSTRACT FROM AUTHOR]