Wearable Electronic Sensors Research Articles

All-Day Mobile Healthcare Monitoring System Based on Heterogeneous Stretchable Sensors for Medical Emergency

Epidermal and wearable electronic sensor technologies have gained extensive interest in recent years owing to deliver real-time healthcare information to the personalized smartphone. Herein, we proposed a fully integrated wearable smart patch-based sensor system with Kirigami-inspired strain-free deformable structures having temperature and humidity sensors along with a commercial acceleration sensor. The presented fully integrated wearable sensor system easily attaches to the skin to accurately determine the body information, and integrated circuit including read-out circuit and wireless communication transfer medical information (temperature, humidity, and motion) to mobile phone to assist with emergencies due to “unpredictable” deviations and to aid in medical checkups for vulnerable patients. This article addresses the challenge of all-day continuous monitoring of human body biological signals by introducing the well-equipped breathable (water permeability ∼ 80 gm−1·h−1), excellent adhesion to the skin (peel strength < 200 gf/12 mm), biocompatible, and conformable smart patch that can absorb the moisture (sweat) generated from the skin without any harshness and allowing the users’ to continuously monitor the early detection of diagnosis. Furthermore, the proposed patch-based medical device enables wireless sensing capabilities in response to rapid variation, equipped with a customized circuit design, low-power Bluetooth module, and a signal processing integrated circuit mounted on a flexible printed circuit board. Thus, a unique platform is established for multifunctional sensors to interface with hard electronics, providing emerging opportunities in the biomedical field as well as Internet-of-Things applications.

Recent Progress in Wireless Sensors for Wearable Electronics

The development of wearable electronics has emphasized user-comfort, convenience, security, and improved medical functionality. Several previous research studies transformed various types of sensors into a wearable form to more closely monitor body signals and enable real-time, continuous sensing. In order to realize these wearable sensing platforms, it is essential to integrate wireless power supplies and data communication systems with the wearable sensors. This review article discusses recent progress in wireless technologies and various types of wearable sensors. Also, state-of-the-art research related to the application of wearable sensor systems with wireless functionality is discussed, including electronic skin, smart contact lenses, neural interfaces, and retinal prostheses. Current challenges and prospects of wireless sensor systems are discussed.

Surface-Treated Nanofibers as High Current Yielding Breath Humidity Sensors for Wearable Electronics

As wearable electronics have gained momentum in the past few years, there is a dire need for smart, responsive, and, most importantly, affordable sensors for biological monitoring. One such noninva...

A transparent, glue-free, skin-attachable graphene pressure sensor with micropillars for skin-elasticity measurement

Strong peeling resistance and water-drainable properties on rough and wet skin surfaces are highly desirable for realizing wearable and skin-attachable electronic sensors. Here, we propose a transparent, sensitive, glue-free pressure sensor for skin electronics. To achieve a thin, light-weight, transparent, and stretchable sensor patch, we laminated a single-layer graphene film as a sensing element on a thin polymeric supporter of polydimethylsiloxane. By assembling the graphene layer with densely populated micropillars, the pressure sensor achieved 10 times the sensitivity of a similar sensor without micropillars in the low-pressure range (<6 kPa). We then employed hexagonal patterns inspired by the toe pads of a tree frog, giving the assembled patch sensor with strong peeling resistance under both dry and wet conditions on surfaces such as silicon (15.5 J cm−2 for dry and 11.6 J cm−2 for wet conditions) and pig skin (2.0 J cm−2 for dry and 1.4 J cm−2 for wet conditions) without contamination after detachment. Our layered sensor patch also demonstrated successful measurement of water-dependent skin elasticity with transparent, conformal, and residual-free attachment, suggesting a variety of cosmetic and medical applications.

Polypyrrole-Doped Conductive Supramolecular Elastomer with Stretchability, Rapid Self-Healing, and Adhesive Property for Flexible Electronic Sensors.

Although recent years have witnessed intense efforts and innovations in the design of flexible conductive materials for the development of next-generation electronic devices, it remains a great challenge to integrate multifunctionalities such as stretchability, self-healing, adhesiveness, and sensing capability into one conductive system for practical applications. In this work, for the first time, we have prepared a new electrically conductive elastomer composite that combines all these functionalities by triggering in situ polymerization of pyrrole in a supramolecular polymer matrix cross-linked by multiple hydrogen-bonding 2-ureido-4[1 H]-pyrimidinone (UPy) groups. The polypyrrole (PPy) particles were uniformly dispersed and imparted to the composite desirable conductive properties, while the reversible nature of the dynamic multiple hydrogen bonds in the polymer matrix allowed excellent stretchability, fast self-healing ability, and adhesiveness under ambient condition. The elastomer composite with the incorporation of 7.5 wt % PPy displayed a mechanical strength of 0.72 MPa with an elongation over 300%, where the rapid self-healing of the mechanical and electrical properties was achieved within 5 min. The elastic material also exhibited strong adhesiveness to a broad range of inorganic and organic substrates, and it was further fabricated as a strain sensor for the detection of both large and subtle human motions (i.e., finger bending, pulse beating). The novel PPy-doped conductive elastomer has demonstrated great potential as functional sensors for wearable electronics, which provides a facile and promising approach to the development of various flexible electronic materials with multifunctionalities by combining conductive components with supramolecular polymers.

(Invited) Nanostructured Materials Based Sensors for Smart and Wearable Electronics

Smart and wearable electronic systems are promising for personal healthcare in near future. For smart health technology, various sensor-integrated portable, mobile and wearable systems have been extensively developed. Recently many sensor devices are being integrated into smartphone, which enables analysis of biomarkers from various body fluids and monitoring of physiological parameters. And many wearable sensor-integrated systems including skin-attachable platform which can monitor physiological signs, detect biomarkers for disease diagnosis and monitor the patients with chronic diseases have been extensively investigated. Here, I will discuss imaging-based fluorescence biosensors for highly sensitive detection of biomolecules and pathogenic bacteria which can be integrated with smartphone or portable IOT systems. In addition, I will present our recent works on stretchable wearable physical sensors (strain, pressure, and temperature), chemical sensors (gas) and biosensors (metabolite, protein) based on low-dimensional nanoscale materials (0D, 1D and 2D), nanocomposites or their hierarchical nanohybrids in FET, resistor or electrochemical device structures. Finally, future prospects in the development of the sensors for smart healthcare will be discussed.

Water-Resistant and Skin-Adhesive Wearable Electronics Using Graphene Fabric Sensor with Octopus-Inspired Microsuckers.

Wearable and skin-attachable electronics with portable/wearable and stretchable smart sensors are essential for health-care monitoring devices or systems. The property of adhesion to the skin in both dry and wet environments is strongly required for efficient monitoring of various human activities. We report here a facile, low-cost, scalable fabrication method for skin-adhesive graphene-coated fabric (GCF) sensors that are sensitive and respond fast to applied pressure and strain. With octopus-like patterns formed on the side of the GCF that touches the skin, the GCF adheres strongly to the skin in both dry and wet environments. Using these characteristics, we demonstrate efficient monitoring of a full range of human activities, including human physiological signals such as wrist pulse and electrocardiography (ECG), as well as body motions and speech vibrations. In particular, both measurements of ECG and wrist-bending motions were demonstrated even in wet conditions. Our approach has opened up a new possibility for wearable and skin-adherent electronic fabric sensors working even in wet environments for health-care monitoring and medical applications in vitro and in vivo.

Tough and conductive nanocomposite hydrogels for human motion monitoring

Conductive hydrogels have received great attention owing to their promising applications in electrodes, supercapacitors, actuators, fuel cells, biosensors and biomedical devices and so on. However, it is still a challenge to achieve conductive hydrogels with integrated high performances, including high strength, large stretchability, high toughness, rapid self-recovery and good self-healing. In the present work, multiple physically cross-linked conductive hydrogels with integrated high performances were fabricated by in situ doping conductive PEDOT:PSS during the formation of dual physically cross-linked poly(N-hydroxyethyl acrylamide)/Laponite hydrogels. At the optimal condition, the conductive gels exhibit high tensile strength, high extensibility, high tearing energy, rapid self-recovery property without any external stimuli, high conductivity, good self-healing property, as well as sensitive strain sensing for monitoring human activities (e.g. the movements of the finger and wrist, and tiny breathing movements). Considering easy preparation and integrated high performances, our conductive gels have potential applications in wearable electronic sensors and bioelectronics.

Highly stable kirigami-structured stretchable strain sensors for perdurable wearable electronics

A kirigami-based graphene–polymer hybrid nanocomposite is realized by a laser direct writing technique for reliable skin-inspired strain sensors, presenting almost no performance degradation even after &gt;60 000 stretching cycle tests.

Tunable terahertz metamaterial by using three-dimensional double split-ring resonators

We present an optically tunable terahertz (THz) metamaterial by using three-dimensional double split-ring resonators (3D-DSRR), which shows superior properties in adjustability. They exhibit tunable single-band and dual-band resonances by changing height between inner and outer SRRs. The maximum tuning range of dual-band resonance is 0.55 THz from the resonance of 0.45 THz shifted to the resonance of 1.00 THz. The corresponding tuning range of free spectrum range (FSR) spanned two resonances can be tuned from 0.20 THz to 0.75 THz. By changing radius of inner SRR from 14.5 μm to 22.5 μm, the tuning range of resonance is 0.40 THz. While changing the height between inner and outer SRRs and kept the radiuses of inner and outer SRRs as constant as 22.5 μm, 3D-DSRR can be tuned to have two resonances and then merge into one resonance. 3D-DSRR shows a tunable and switchable resonance for single-band and dual-band characteristics. These characterizations are very suitable for the use of tunable multi-resonance applications. To further investigate the stability of 3D-DSRR, the rotation angles of inner and outer SRRs are modified from 0° to 180°, respectively. The corresponding resonances are identical. Such results indicate the proposed device with high stability to allow manufacturing tolerance and potentially to be used in wearable electronic devices, pressure sensors, and other fields.

Thin Film FETs on Flexible Substrates: a Case for Biosensing Application

Thin film transistors have been explored for biosensing applications due to their simplicity, fast reaction times and low cost. The fabrication of thin film transistors on flexible substrates open up new avenues for wearable electronic sensors for personal health monitoring. In this study, we investigate the fabrication and characterization of a Zinc Oxide based thin film transistor on a flexible substrate for biosensing application. Oxide based semiconductors have advantages such as deposition at low temperatures, better smoothness and a great potential to be used on a roll to roll fabrication for flexible applications. Zinc oxide (ZnO) serves as an ideal substrate for binding bio-recognition molecules viz., antibodies, Aptamers, enzymes, microorganisms etc. This binding is facilitated by the difference in the isoelectric points of the bio-receptor molecules (~5) and Zinc oxide (~9). Using this peculiarity, we designed back-gated bio-functionalized field effect transistors (FETs) for linker-free and label-free detection of biomarkers. The transistors were fabricated using Atomic layer deposition and sputtering techniques on a polyimide substrate. Polyimide is a stable polymer which has been used in electronic industry as a flexible substrate for various applications. The high temperature stability combined with excellent adhesion to different materials renders it a suitable substrate for this investigation. After fabrication, the transistors were characterized for their electrical parameters and material properties. The channel of the TFT was fictionalized by immobilizing antibodies that were specific to Cortisol on top of it. Cortisol is an important corticosteroid that is produced in humans by the adrenal cortex in the adrenal gland. It has been associated with maintaining healthy bodily functions and is often cited as a biomarker for quantification of stress. It is often released in response to stress and low blood glucose levels. It has been associated with several other important bodily functions and is considered as one the most important biomarkers for detecting stress. Cortisol solution was dispensed on the fictionalized FETs and the source-drain current was measured. The binding of cortisol to the immobilized antibodies causes a change in the charge transfer characteristics of the gate and thus modifies the gate voltage. This change manifests in the form of a change in drain current of the FET. Accordingly, the source-drain current is related to the change in cortisol levels of the samples exposed to the sensor.

3D Printing Technologies for Flexible Tactile Sensors toward Wearable Electronics and Electronic Skin.

3D printing has attracted a lot of attention in recent years. Over the past three decades, various 3D printing technologies have been developed including photopolymerization-based, materials extrusion-based, sheet lamination-based, binder jetting-based, power bed fusion-based and direct energy deposition-based processes. 3D printing offers unparalleled flexibility and simplicity in the fabrication of highly complex 3D objects. Tactile sensors that emulate human tactile perceptions are used to translate mechanical signals such as force, pressure, strain, shear, torsion, bend, vibration, etc. into electrical signals and play a crucial role toward the realization of wearable electronics and electronic skin. To date, many types of 3D printing technologies have been applied in the manufacturing of various types of tactile sensors including piezoresistive, capacitive and piezoelectric sensors. This review attempts to summarize the current state-of-the-art 3D printing technologies and their applications in tactile sensors for wearable electronics and electronic skin. The applications are categorized into five aspects: 3D-printed molds for microstructuring substrate, electrodes and sensing element; 3D-printed flexible sensor substrate and sensor body for tactile sensors; 3D-printed sensing element; 3D-printed flexible and stretchable electrodes for tactile sensors; and fully 3D-printed tactile sensors. Latest advances in the fabrication of tactile sensors by 3D printing are reviewed and the advantages and limitations of various 3D printing technologies and printable materials are discussed. Finally, future development of 3D-printed tactile sensors is discussed.

Using Sociometers to Advance Small Group Research

New technologies transform research specialties and potentiate new fields. Sociometers—wearable electronic sensors collecting quantitative, dynamic data about embodied social interactions at hyperfine scales—represent such a possibility for small group research. This article introduces this new method and its distinctive qualities and affordances. Next, we relate its potential for advancing understanding of three types of small group phenomena: (1) rhythmic entrainment, emotional energy, and solidarity; (2) nonverbal dominance and deference; and (3) groups as complex systems. We then present findings from two pilot studies of small group creativity in science and art collaborations. To do so, we combine sociometric, survey, and ethnographic data to consider how speech participation, body movement, and volume shape group creativity and to illustrate how sociometric data complements traditional qualitative and quantitative methods. We close by relating practical lessons learned to aid future researchers working to harness this powerful new research technology.

Wearable strain sensing textile based on one-dimensional stretchable and weavable yarn sensors

Flexible, wearable, and even stretchable sensors are the key components of smart electronic textiles. However, most reported flexible and wearable sensors for wearable electronics are usually fabricated in two-dimensional (2D) planar strip configurations, which cannot be properly integrated into textile structures and thus greatly degrade intrinsic properties such as the softness, flexibility, and air permeability of textiles and the aesthetic feeling of clothing. In this work, a new one-dimensional weavable strain sensing yarn consisting of an elastic polyurethane (PU) core, a conductive Ag-nanoparticles/graphene-microsheets composite sheath, and a silicone encapsulation layer was designed and fabricated through an easily manipulated protocol. Arising from the reasonable structural design and appropriate material selection, the as-fabricated strain sensor not only exhibited excellent flexibility, stretchability, and highly repeatable electromechanical stability (a repeatability error of 1.56%) but also possessed both high sensitivity (a gauge factor of nearly 500) and a relatively wide working range (0–50% applied strain) with good linearity (a correlation coefficient of 0.98). In addition, the facile, nearly all-solution-based fabrication protocol enabled the scalable production of long conductive yarns. Thus, the proper yarn length and superb mechanical properties endowed the stretchable conductive yarn with good weavability. The excellent wearability of the stretchable conductive yarn was derived from the outermost isolating, hydrophobic, and biocompatible silicone encapsulation layer. A wearable high-sensitivity strain sensing textile, fabricated by directly weaving the as-prepared yarn-based sensor, showed great potential for application to wearable textile sensors for real-time monitoring of human motions from vigorous walking to subtle and complex pronunciations.

Highly Stretchable and Conductive Superhydrophobic Coating for Flexible Electronics.

Superhydrophobic materials integrating stretchability with conductivity have huge potential in the emerging application horizons such as wearable electronic sensors, flexible power storage apparatus, and corrosion-resistant circuits. Herein, a facile spraying method is reported to fabricate a durable superhydrophobic coating with excellent stretchable and electrical performance by combing 1-octadecanethiol-modified silver nanoparticles (M-AgNPs) with polystyrene- b-poly(ethylene- co-butylene)- b-polystyrene (SEBS) on a prestretched natural rubber (NR) substrate. The embedding of M-AgNPs in elastic SEBS matrix and relaxation of prestretched NR substrate construct hierarchical rough architecture and endow the coating with dense charge-transport pathways. The fabricated coating exhibits superhydrophobicity with water contact angle larger than 160° and a high conductivity with resistance of about 10 Ω. The coating not only maintains superhydrophobicity at low/high stretch ratio for the newly generated small/large protuberances but also responds to stretching and bending with good sensitivity, broad sensing range, and stable response cycles. Moreover, the coating exhibits excellent durability to heat and strong acid/alkali and mechanical forces including droplet impact, kneading, torsion, and repetitive stretching-relaxation. The findings conceivably stand out as a new tool to fabricate multifunctional superhydrophobic materials with excellent stretchability and conductivity for flexible electronics under wet or corrosive environments.

Multilayer Distributed Circuit Modeling for Galvanic Coupling Intrabody Communication

Characterization of the human body as a transmission medium for electrical signals is a necessity for using intrabody communication (IBC) technique into connecting wearable electronic sensors and devices. In this paper, we propose a novel multilayer distributed circuit model for galvanic-coupling type IBC, which is emphasized on the propagation characteristics in contrast with other IBC models. Based on the model, a program is written in MATLAB to investigate the propagation characteristics of a human body channel with the frequency of 10 MHz to 20 MHz and the distance of 5 cm to 10 cm. Finally, a galvanic coupling IBC measurement is implemented to verify the proposed model. The outcome proves that the model is valid and correct.

Wearable Electronics: High‐Resolution Patterning and Transferring of Graphene‐Based Nanomaterials onto Tape toward Roll‐to‐Roll Production of Tape‐Based Wearable Sensors (Adv. Mater. Technol. 12/2017)

In article number 1700223, Liang Dong and co-workers present a graphene patterning and transferring method to manufacture low-cost, installation-free, wearable electronic sensors on adhesive tapes. The minimum feature size of the transferred graphene patterns is in the order of a few micrometers. Smart gloves are demonstrated to monitor human body motion. Wearable leaf sensors are realized to monitor plant transpiration process and water status.

Cotton-based wearable PEDOT:PSS electronic sensor for detecting acetone vapor

Developing a wearable sensor to detect acetone vapor has great potential for healthcare applications. PEDOT:PSS has recently attracted great interest as a highly conductive polymeric electronic material that can be easily processed. Cotton thread is one of the basic materials used in producing garments. Here, we show for the first time the development of a wearable PEDOT:PSS sensor based on cotton thread. The sensor provides rapid and highly sensitive detection of acetone vapor. We anticipate that these results could open significant opportunities for fundamental studies of wearable electronic sensors, as well as a variety of real-time and on-site applications in fields including medical diagnosis, environmental monitoring, and defense.

Recent Progress of Self‐Powered Sensing Systems for Wearable Electronics

Wearable/flexible electronic sensing systems are considered to be one of the key technologies in the next generation of smart personal electronics. To realize personal portable devices with mobile electronics application, i.e., wearable electronic sensors that can work sustainably and continuously without an external power supply are highly desired. The recent progress and advantages of wearable self-powered electronic sensing systems for mobile or personal attachable health monitoring applications are presented. An overview of various types of wearable electronic sensors, including flexible tactile sensors, wearable image sensor array, biological and chemical sensor, temperature sensors, and multifunctional integrated sensing systems is provided. Self-powered sensing systems with integrated energy units are then discussed, separated as energy harvesting self-powered sensing systems, energy storage integrated sensing systems, and all-in-on integrated sensing systems. Finally, the future perspectives of self-powered sensing systems for wearable electronics are discussed.

Integration of Graphene Oxide on Nylon/Polyester/Cotton Fabrics for a Wearable Electronic Nose Sensor

This work presents a facile solution method to fabricate graphene oxide (GO) on fabrics for a wearable electronic nose sensor. Three types of fabrics such as nylon, polyester, and cotton were used as wearable substrates. Thin PVC film was laminated on the fabrics to promote deposition of electrodes on the fabrics. To determine types of solution for constructing GO on the fabrics, water and ethanol were compared as typical solvents to disperse GO. Water distributed GO nanoflake was uniformly coated on the fabrics by simple drop coating. Room temperature gas sensing was examined with GO integrated on the fabrics, and it exhibited n-type gas sensing behavior on 100 ppm ammonia and its response showed comparable values in resistance change with flat substrates.