A Multitasking Flexible Sensor via Reservoir Computing.

Natural disasters are reported globally, and one source of severe damage to cities is flooding caused by locally heavy rain. Sharing of local weather information can save lives. However, it is difficult to collect local weather information in real-time because such data collection requires bulky, expensive sensors.

A wearable, flexible sensor for real-time, home monitoring of sleep apnea.

A flexible sensor that can be attached to the body to collect vital data wirelessly enables real-time human healthcare management. One potential application for home-use healthcare devices is monitoring of sleep conditions to diagnose sleep apnea syndrome. Such data are not readily gathered using conventional tools, owing to the bulk and cost of instrumentation.

Controlling the thermal conductivity of multilayer graphene by strain.

Straintronics is a new concept to enhance electronic device performances by strain for next-generation information sensors and energy-saving technologies. The lattice deformation in graphene can modulate the thermal conductivity because phonons are the main heat carriers. However, the device fabrication process affects graphene's heat transport properties due to its high stretchability.

Wireless and Flexible Skin Moisture and Temperature Sensor Sheets toward the Study of Thermoregulator Center.

A disorder in the thermoregulator center in a human body leads to some potential diseases such as fever and hyperthyroidism. To predict these diseases early, monitoring the health condition of the human body due to the influence of thermoregulation disorders is important. Although extensive works are performed on sweat-rate detection by constructing microfluidic channels, skin-moisture evaporation before sweating remains unknown.

Multimodal Wearable Sensor Sheet for Health-Related Chemical and Physical Monitoring.

Continuous multiple data health monitoring has high potential to detect abnormal conditions or early stages of diseases in the future. To monitor a continuous small vital signal, one of the promising architectures is an attachable flexible multimodal sensor system, which can detect multiple health conditions from the skin surface. Recent breakthroughs have realized continuous sweat chemicals or physical conditions using flexible sensors.

A Wearable Body Condition Sensor System with Wireless Feedback Alarm Functions.

Emerging feedback systems based on tracking body conditions can save human lives. In particular, vulnerable populations such as disabled people, elderly, and infants often require special care. For example, the high global mortality of infants primarily owing to sudden infant death syndrome while sleeping makes request for extraordinary attentions in neonatal intensive care units or daily lives.

Highly stable Pd/HNbO-based flexible humidity sensor for perdurable wireless wearable applications.

Real-time, daily health monitoring can provide large amounts of patient data, which may greatly improve the likelihood of diagnosing health conditions at an early stage. One potential sensor is a flexible humidity sensor to monitor moisture and humidity information such as dehydration. However, achieving a durable functional nanomaterial-based flexible humidity sensor remains a challenge due to partial desorption of water molecules during the recovery process, especially at high humidities.

Multimodal Plant Healthcare Flexible Sensor System.

The rising global human population and increased environmental stresses require a higher plant productivity while balancing the ecosystem using advanced nanoelectronic technologies. Although multifunctional wearable devices have played distinct roles in human healthcare monitoring and disease diagnosis, probing potential physiological health issues in plants poses a formidable challenge due to their biological complexity. Herein an integrated multimodal flexible sensor system is proposed for plant growth management using stacked ZnInS(ZIS) nanosheets as the kernel sensing media.

Very Thin, Macroscale, Flexible, Tactile Pressure Sensor Sheet.

In artificial intelligence and deep learning applications, data collection from a variety of objects is of great interest. One way to support such data collection is to use very thin, mechanically flexible sensor sheets, which can cover an object without altering the original shape. This study proposes a thin, macroscale, flexible, tactile pressure sensor array fabricated by a simple process for economical device applications.

Wrist flexible heart pulse sensor integrated with a soft pump and a pneumatic balloon membrane.

To monitor health and diagnose disease in the early stage, future healthcare standards will likely include the continuous monitoring of various vital data. One approach to collect such information is a wearable and flexible device, which detects information from the skin surface. An important dataset is heart pulse information.

Highly Precise Multifunctional Thermal Management-Based Flexible Sensing Sheets.

Elaborate manipulation of heat transfer renders proper operation of diverse thermal-related technologies. However, accurate implementation of thermal-based or transduction sensing on a thin flexible film over unusual surfaces remains challenging. Herein, efficient thermal management realizes highly accurate flexible multifunctional sensor sheets using a low thermal conductive medium as a thermal barrier.

Graphene and Carbon Nanotube Heterojunction Transistors with Individual Gate Control.

Heterogeneously integrated nanomaterial devices show interesting characteristics for transistors and sensors due to their band diagram or steep material junctions. If these junctions and band alignments can be tuned by an electrical input bias, the device platform not only could be expanded but also could be used to explore fundamental characteristics. However, most reports on hetero-nanomaterial junctions use a global back-gate voltage, which makes it difficult to control band alignment at an interface.

All-Solution-Based Heterogeneous Material Formation for p-n Junction Diodes.

All-solution-based devices have potential as the next class of macroscale and multifunctional electronics on versatile amorphous substrates. Different methods and materials have been studied to control the formation of p-type and n-type semiconducting materials because forming active materials for transistors and sensors remains a challenge. This study proposes an approach for solution-based devices in which a p-n junction diode is fabricated using a solution-based InZnO thin film for the n-type semiconductor and a carbon nanotube network film for the p-type semiconductor.

Photoresponse of graphene field-effect-transistor with n-type Si depletion layer gate.

Graphene/semiconductor Schottky junctions are an emerging field for high-performance optoelectronic devices. This study investigates not only the steady state but also the transient photoresponse of graphene field-effect transistor (G-FET) of which gate bias is applied through the Schottky barrier formed at an n-type Si/graphene interface with a thin oxide layer, where the oxide thickness is sufficiently thin for tunneling of the charge carrier. To analyze the photoresponse, we formulate the charge accumulation process at the n-Si/graphene interface, where the tunneling process through the SiO layer to graphene occurs along with recombination of the accumulated holes and the electrons in the graphene at the surface states on the SiO layer.

Resonance Control of a Graphene Drum Resonator in a Nonlinear Regime by a Standing Wave of Light.

We demonstrate the control of resonance characteristics of a drum-type graphene mechanical resonator in a nonlinear oscillation regime using the photothermal effect, which is induced by a standing wave of light between graphene and a substrate. Unlike the resonance characteristics of a conventional Duffing-type nonlinearity, those of the nonlinear oscillation regime are modulated by the standing wave of light with a contribution of the scattered light of an actuation laser, despite a slight variation of amplitude. Numerical calculations conducted with a combination of equations of heat and motion with the Duffing-type nonlinearity explain this modulation: the photothermal effect delays the modulation of graphene stress or tension.

Wearable, Flexible, and Multifunctional Healthcare Device with an ISFET Chemical Sensor for Simultaneous Sweat pH and Skin Temperature Monitoring.

Real-time daily healthcare monitoring may increase the chances of predicting and diagnosing diseases in their early stages which, currently, occurs most frequently during medical check-ups. Next-generation noninvasive healthcare devices, such as flexible multifunctional sensor sheets designed to be worn on skin, are considered to be highly suitable candidates for continuous real-time health monitoring. For healthcare applications, acquiring data on the chemical state of the body, alongside physical characteristics such as body temperature and activity, are extremely important for predicting and identifying potential health conditions.

Efficient Skin Temperature Sensor and Stable Gel-Less Sticky ECG Sensor for a Wearable Flexible Healthcare Patch.

Wearable, flexible healthcare devices, which can monitor health data to predict and diagnose disease in advance, benefit society. Toward this future, various flexible and stretchable sensors as well as other components are demonstrated by arranging materials, structures, and processes. Although there are many sensor demonstrations, the fundamental characteristics such as the dependence of a temperature sensor on film thickness and the impact of adhesive for an electrocardiogram (ECG) sensor are yet to be explored in detail.

Direct measurement of optical trapping force gradient on polystyrene microspheres using a carbon nanotube mechanical resonator.

Optical tweezers based on optical radiation pressure are widely used to manipulate nanoscale to microscale particles. This study demonstrates direct measurement of the optical force gradient distribution acting on a polystyrene (PS) microsphere using a carbon nanotube (CNT) mechanical resonator, where a PS microsphere with 3 μm diameter is welded at the CNT tip using laser heating. With the CNT mechanical resonator with PS microsphere, we measured the distribution of optical force gradient with resolution near the thermal noise limit of 0.

Printed multifunctional flexible device with an integrated motion sensor for health care monitoring.

Real-time health care monitoring may enable prediction and prevention of disease or improve treatment by diagnosing illnesses in the early stages. Wearable, comfortable, sensing devices are required to allow continuous monitoring of a person's health; other important considerations for this technology are device flexibility, low-cost components and processing, and multifunctionality. To address these criteria, we present a flexible, multifunctional printed health care sensor equipped with a three-axis acceleration sensor to monitor physical movement and motion.

Oscillation control of carbon nanotube mechanical resonator by electrostatic interaction induced retardation.

Despite the superb intrinsic properties of carbon nanotube mechanical resonators, the quality factors at room temperature are 1,000 or less, even in vacuum, which is much lower than that of mechanical resonators fabricated using a top-down approach. This study demonstrates the improvement of the quality factor and the control of nonlinearity of the mechanical resonance of the cantilevered nanotube by electrostatic interaction. The apparent quality factor of the nanotube supported by insulator is improved drastically from approximately 630 to 3200 at room temperature.

Highly photosensitive graphene field-effect transistor with optical memory function.

Graphene is a promising material for use in photodetectors for the ultrawide wavelength region: from ultraviolet to terahertz. Nevertheless, only the 2.3% light absorption of monolayer graphene and fast recombination time of photo-excited charge restrict its sensitivity.

Mechanically Flexible and High-Performance CMOS Logic Circuits.

Low-power flexible logic circuits are key components required by the next generation of flexible electronic devices. For stable device operation, such components require a high degree of mechanical flexibility and reliability. Here, the mechanical properties of low-power flexible complementary metal-oxide-semiconductor (CMOS) logic circuits including inverter, NAND, and NOR are investigated.

High-performance, mechanically flexible, and vertically integrated 3D carbon nanotube and InGaZnO complementary circuits with a temperature sensor.

A vertically integrated inorganic-based flexible complementary metal-oxide-semiconductor (CMOS) inverter with a temperature sensor with a high inverter gain of ≈50 and a low power consumption of <7 nW mm(-1) is demonstrated using a layer-by-layer assembly process. In addition, the negligible influence of the mechanical flexibility on the performance of the CMOS inverter and the temperature dependence of the CMOS inverter characteristics are discussed.

Air Ambient-Operated pNIPAM-Based Flexible Actuators Stimulated by Human Body Temperature and Sunlight.

Harnessing a natural power source such as the human body temperature or sunlight should realize ultimate low-power devices. In particular, macroscale and flexible actuators that do not require an artificial power source have tremendous potential. Here we propose and demonstrate electrically powerless polymer-based actuators operated at ambient conditions using a packaging technique in which the stimulating power source is produced by heat from the human body or sunlight.

Fully printed flexible fingerprint-like three-axis tactile and slip force and temperature sensors for artificial skin.

A three-axis tactile force sensor that determines the touch and slip/friction force may advance artificial skin and robotic applications by fully imitating human skin. The ability to detect slip/friction and tactile forces simultaneously allows unknown objects to be held in robotic applications. However, the functionalities of flexible devices have been limited to a tactile force in one direction due to difficulties fabricating devices on flexible substrates.