Wrist Pulse Research Articles

Crack Control in Biotemplated Gold Films for Wide‐Range, Highly Sensitive Strain Sensing

AbstractStrain sensors with high sensitivity and large sensing range have great potential in a wide range of applications. However, in the design of strain sensors, there is usually a trade‐off between sensitivity and sensing range. Herein, a crack‐based strain sensor with engineered microstructure is facilely prepared through a biotemplating method. Under large tensile strains, randomly distributed microcavities on the strain sensor surface can effectively trap and terminate propagating cracks to prevent catastrophic fracture failure. As a result, the strain sensor shows both wide sensing range (up to 80%) and high sensitivity (gauge factor = 20 at 20% strain, 350 at 80% strain). The strain sensor enables sensitive and reliable detection of both subtle human motions, including wrist pulse and throat vibration, and large motions, such as finger bending. Moreover, a multipixel strain sensor array has been fabricated and applied for both static and dynamic strain mapping. The good sensing performance, together with its easy‐fabrication process, make the biotemplated strain sensor a promising candidate for applications in e‐skins and wearable electronics.

Highly sensitive and stable printed pressure sensor with microstructured grid arrays

Flexible pressure sensors with high sensitivity, broad pressure range and a large array are highly desired for wearable applications. In this work, a flexible pressure sensor with a polyvinyl chloride/carbon black microgrid films was obtained by screen printing. Compared to other recent pressure sensors, these printed pressure sensors with microstructured grids have a broad pressure range up to 666.7 kPa, an excellent sensitivity of typically 4.71 kPa−1 in the dynamic range between 0 and 15 kPa, a fast response of typically 25 ms, a high stability, a good durability in a broad pressure range for more than 5300 cycles and long effectiveness. We showed that the printed pressure sensors can be customized to fit in a smart insole. Moreover, a wrist pulse could be detected accurately by a single sensor. The proposed printed pressure sensors will have a great potential a smart devices in health monitoring, for preventive health care, and in rehabilitation care.

Stretchable and Highly Sensitive Optical Strain Sensors for Human-Activity Monitoring and Healthcare.

Flexible and stretchable strain sensors are essential to developing smart wearable devices for monitoring human activities. Such sensors have been extensively exploited with various conductive materials and structures, which, however, are normally in need of complex manufacturing processes and confronted with the challenge to achieve both large stretchability and high sensitivity. Here, we report a simple and low-cost optical strategy for the design of stretchable strain sensors which are capable of measuring large strains of 100% with a low detection limit (±0.09%), a fast responsivity (<12 ms), and high reproducibility (over 6000 cycles). The optical strain sensor (OS2) is fabricated by assembling plasmonic gold nanoparticles (GNPs) in stretchable elastomer-based optical fibers, where a core/cladding structure with step-index configuration is adopted for light confinement. The stretchable, GNP-incorporated optical fiber shows strong localized surface plasmon resonance effects that enable sensitive and reversible detection of strain deformations with high linearity and negligible hysteresis. The unique mechanical and sensing properties of the OS2 enable its assembling into clothing or mounting on skin surfaces for monitoring various human activities from physiological signals as subtle as wrist pulses to large motions of joint bending and hand gestures. We further apply the OS2 for quantitative analysis of motor disorders such as Parkinson's disease and demonstrate its compatibility in strong electromagnetic interference environments during functional magnetic resonance imaging, showing great promises for diagnostics and assessments of motor neuron diseases in clinics.

Dynamically Stretchable Supercapacitor for Powering an Integrated Biosensor in an All-in-One Textile System

Textile-based electronics have attracted much attention as they can perfectly combine the functionality of wearable devices with the soft and comfortable properties of flexible textile fibers. In this work, we report a dynamically stretchable high-performance supercapacitor for powering an integrated sensor in an all-in-one textile system to detect various biosignals. The supercapacitor fabricated with MWCNT/MoO3 nanocomposite electrodes and nonaqueous gel electrolyte, along the course direction of the fabric, exhibits stable and high electrochemical performance under dynamic and static deformation, including stretching in real time, regardless of the strain rate. The strain sensor created along the wale direction of the fabric shows a high sensitivity of 46.3 under an applied strain up to 60%, a fast response time of 50 ms, and high stability over 10 000 cycles of stretching/releasing. Finally, the supercapacitor and strain sensor are integrated into an all-in-one textile system via liquid-metal interconnections, and the sensor is powered by the stored energy in the supercapacitor. This system sewed into cloth successfully detects strain due to joint movement and the wrist pulse. This work demonstrates the high feasibility of utilizing the fabricated stretchable all-in-one textile system for real-time health monitoring in everyday wearable devices.

An Emotion Recognition Based on Physiological Signals

Emotion recognition is alluring considerable interest among the researchers. Emotions are discovered by facial, speech, gesture, posture and physiological signals. Physiological signals are a plausible mechanism to recognize emotion using human-computer interaction. The objective of this paper is to put forth the recognition of emotions using physiological signals. Various emotion elicitation protocols, feature extraction techniques, classification methods that aim at recognizing emotions from physiological signals are discussed here. Wrist Pulse Signal is also discussed to fill the lacunae of the other physiological signal for emotion detection. Working on basic as well as non-basic human emotion and human-computer interface will make the system robust.

Ultralow-Cost, Highly Sensitive, and Flexible Pressure Sensors Based on Carbon Black and Airlaid Paper for Wearable Electronics.

Flexible pressure sensors have attracted considerable attention because of their potential applications in healthcare monitoring and human-machine interactions. However, the complicated fabrication process and the cos of sensing materials limit their widespread applications in practice. Herein, a flexible pressure sensor with outstanding performances is presented through an extremely simple and cost-efficient fabrication process. The sensing materials of the sensor are based on low-cost carbon black (CB)@airlaid paper (AP) composites, which are just prepared by drop-casting CB solutions onto APs. Through simply stacking multiple CB@APs with an irregular surface and a fiber-network structure, the obtained pressure sensor demonstrates an ultrahigh sensitivity of 51.23 kPa-1 and an ultralow detection limit of 1 Pa. Additionally, the sensor exhibits fast response time, wide working range, good stability, as well as excellent flexibility and biocompatibility. All the comprehensive and superior performances endow the sensor with abilities to precisely detect weak air flow, wrist pulse, phonation, and wrist bending in real time. In addition, an array electronic skin integrated with multiple CB@AP sensors has been designed to identify spatial pressure distribution and pressure magnitude. Through a biomimetic structure inspired by blooming flowers, a sensor with the open-petal structure has been designed to recognize the wind direction. Therefore, our study, which demonstrates a flexible pressure sensor with low cost, simple preparation, and superior performances, will open up for the exploration of cost-efficient pressure sensors in wearable devices.

Wearable Piezoresistive Sensors with Ultrawide Pressure Range and Circuit Compatibility Based on Conductive-Island-Bridging Nanonetworks.

Wearable pressure sensors with wide operating pressure ranges and enhanced wearability via seamless integration with circuits can greatly improve the fields of digital healthcare, prosthetic limbs, and human-machine interfaces. Herein, we report an approach based on a conductive-island-bridging nanonetwork to realize wearable resistive pressure sensors that are operative over ultrawide pressure ranges >400 kPa and are circuit-compatible. The sensor has a simple two-layered structure, where nanonetworks of single-walled carbon nanotubes selectively patterned on a surface-modified elastomeric film interface and bridge conductive Au island patterns on printed circuit boards (PCBs). We show that varying the design of the Au islands and the conductivity of the nanonetworks systematically tunes the sensitivity, linearity, and the operation range of the pressure sensor. In addition, introducing microstructured lead contacts into the sensor based on a Au-island-bridging nanonetwork produces a record-high sensitivity of 0.06 kPa-1 at 400 kPa. Furthermore, the PCB that serves as the bottom layer of the pressure sensor and contains embedded interconnects enables facile integration of the sensor with measurement circuits and wireless communication modules. The developed sensor enables the monitoring of wrist pulse waves. Moreover, an insole-shaped PCB-based pressure-sensing system wirelessly monitors pressure distributions and gait kinetics during walking. Our scheme can be extended to other nanomaterials and flexible PCBs and thus provides a simple yet powerful platform for emerging wearable applications.

Low-Cost and Highly Sensitive Wearable Sensor Based on Napkin for Health Monitoring.

The development of sensors with high sensitivity, good flexibility, low cost, and capability of detecting multiple inputs is of great significance for wearable electronics. Herein, we report a napkin-based wearable capacitive sensor fabricated by a novel, low-cost, and facile strategy. The capacitive sensor is composed of two pieces of electrode plates manufactured by spontaneous assembly of silver nanowires (NWs) on a polydimethylsiloxane (PDMS)-patterned napkin. The sensor possesses high sensitivity (>7.492 kPa−1), low cost, and capability for simultaneous detection of multiple signals. We demonstrate that the capacitive sensor can be applied to identify a variety of human physiological signals, including finger motions, eye blinking, and minute wrist pulse. More interestingly, the capacitive sensor comfortably attached to the temple can simultaneously monitor eye blinking and blood pulse. The demonstrated sensor shows great prospects in the applications of human–machine interface, prosthetics, home-based healthcare, and flexible touch panels.

Facile Preparation of Hybrid Structure Based on Mesodome and Micropillar Arrays as Flexible Electronic Skin with Tunable Sensitivity and Detection Range.

The development of flexible pressure sensors has attracted increasing research interest for potential applications such as wearable electronic skins and human healthcare monitoring. Herein, we demonstrated a piezoresistive pressure sensor based on AgNWs-coated hybrid architecture consisting of mesoscaled dome and microscaled pillar arrays. We experimentally showed that the key three-dimensional component for a pressure sensor can be conveniently acquired using a vacuum application during the spin-coating process instead of a sophisticated and expensive approach. The demonstrated hybrid structure exhibits dramatically improved sensing capability when compared with the conventional one-fold dome-based counterpart in terms of the sensitivity and detectable pressure range. The optimized sensing performance, by integrating D1000 dome and D50P100 MPA, reaches a superior sensitivity of 128.29 kPa-1 (0-200 Pa), 1.28 kPa-1 (0.2-10 kPa), and 0.26 kPa-1 (10-80 kPa) and a detection limit of 2.5 Pa with excellent durability. As a proof-of-concept, the pressure sensor based on the hybrid configuration was demonstrated as a versatile platform to accurately monitor different kinds of physical signals or pressure sources, e.g., wrist pulse, voice vibration, finger bending/touching, gas flow, as well as address spatial loading. We believe that the proposed architecture and developed methodology can be promising for future applications including flexible electronic devices, artificial skins, and interactive robotics.

High Sensitivity and Broad Range Flexible Pressure Sensor Using Multilayered Porous PDMS/AgNP Sponge

AbstractFlexible pressure sensors attract wide attentions in recent years for their significant applications in wearable electronics and health monitoring. It is strongly desired that a pressure sensor possesses both low detection limit and wide measuring capability, covering a broad pressure range from Pa to hundred kPa, to meet diverse demands in different applications. This paper proposes a novel flexible pressure sensor based on thermosensation, using a multilayered and graded‐porosity polydimethylsiloxane/silver nanoparticle sponge as piezo‐thermic transduction. The sensor exhibits a high sensitivity, a low detection limit of 4.1 Pa, and a wide measuring range up to 200 kPa, which leads to a high range‐to‐limit ratio of about 50 000. The pressure sensor is monolithically integrated with a temperature sensor and dissolves temperature‐compensation. The unique combination of properties makes it feasible to monitor various human signals from subtle wrist pulse to finger tapping pressure and foot stepping pressure by a single device, which shows competent capabilities for multifarious applications in wearable electronics and health monitoring.

Highly Sensitive Flexible Piezoresistive Pressure Sensor Developed Using Biomimetically Textured Porous Materials.

In recent times, high-performance flexible pressure sensors that can be fabricated in an environmentally friendly and low-cost manner have received considerable attention owing to their potential applications in wearable health monitors and intelligent soft robotics. This paper proposes a highly sensitive flexible piezoresistive pressure sensor based on hybrid porous microstructures that can be designed and fabricated using a bio-inspired and low-cost approach employing the Epipremnum aureum leaf and sugar as the template. The sensitivity and detection limit of the obtained pressure sensor can be as high and low as 83.9 kPa-1 (<140 Pa) and 0.5 Pa, respectively. According to the mechanism and simulation analyses, the hybrid porous microstructures lower the effective elastic modulus of the sensor and introduce an additional pore resistance, which increases the contact area and conductive path with loads, thereby contributing to the high sensitivity that exceeds that of traditional microstructured pressure sensors. Real-time monitoring of human physiological signals such as finger pressing, voice vibration, swallowing activity, and wrist pulse is demonstrated for the proposed device. The high performance and easy fabrication of the hybrid porous microstructured sensor can encourage the development of a novel approach for the design and fabrication of future pressure sensors.

MoS2-Decorated Laser-Induced Graphene for a Highly Sensitive, Hysteresis-free, and Reliable Piezoresistive Strain Sensor.

Advancement of sensing systems, soft robotics, and point-of-care testing requires the development of highly efficient, scalable, and cost-effective physical sensors with competitive and attractive features such as high sensitivity, reliability, and preferably reversible sensing behaviors. This study reports a highly sensitive and reliable piezoresistive strain sensor fabricated by one-step carbonization of the MoS2-coated polyimide film to obtain MoS2-decorated laser-induced graphene. The resulting three-dimensional porous graphene nanoflakes decorated with MoS2 exhibit stable electrical properties yielding a reliable output for longer strain/release cycles. The sensor demonstrates high sensitivity (i.e., gauge factor, GF ≈1242), is hysteresis-free (∼2.75%), and has a wide working range (up to 37.5%), ultralow detection limit (0.025%), fast relaxation time (∼0.17 s), and a highly stable and reproducible response over multiple test cycles (>12 000) with excellent switching response. Owing to the outstanding performances of the sensor, it is possible to successfully detect various subtle movements ranging from phonation, eye-blinking, and wrist pulse to large human-motion-induced deformations.

A Novel MOGA-SVM Multinomial Classification for Organ Inflammation Detection

Wrist pulse signal (WPS) contains crucial information of humans’ health condition. It can serve as an alternative method for diagnosing of organ inflammation instead of traditional clinical measurement. In this paper, a novel multi-objective genetic algorithm based support vector machine (MOGA-SVM) has been proposed for the multinomial classification of the inflammations of appendix, pancreas, and duodenum. A customized similarity kernel (KCS) has been optimally designed. The performance of multinomial classification using KCS is compared with five types of kernels, linear, radial basis function (RBF), polynomial and sigmoid kernel, as well as mixtures of polynomial and RBF, to verify the effectiveness of KCS. The sensitivity, specificity and accuracy (Acc) of the proposed method are 92%, 91.2%, and 91.6% respectively. The results have demonstrated that KCS improves the accuracy of classification from 8.9% to 59.6%. When compared to related work, the proposed method increases the performance by more than 10%. It is believed that WPS can serve as alternative measures to diagnose organ inflammations.

Ultrasoft, Adhesive and Millimeter Scale Epidermis Electronic Sensor for Real-Time Enduringly Monitoring Skin Strain.

Epidermal electronic sensors (EESs) possess great advantages in the real-time and enduring monitoring of human vital information compared to the traditional medical device for intimately making contact with human skin. Skin strain is a significant and effective routine to monitor motion, heart rate, wrist pulse, and skin growth in wound healing. In this paper, a novel skin sensor combined with a ternary conductive nanocomposite (Carbon black (CB)/Decamethylcyclopentasiloxane (D5)/Silbione) and a two-stage serpentine connector is designed and fabricated to monitor skin strain. The ultrasoft (~2 kPa) and adhesive properties of the ternary conductive nanocomposite ensure the capacity of the EES to intimately couple with human skin in order to improve accuracy with a relative error of 3.39% at strain 50% as well as a large strain range (0~50%) and gauge factor (GF ~2.5). The millimeter scale EES (~5 mm × 1 mm × 100 μm), based on the micro-nano fabrication technique, consisted of a two-stage serpentine connector and screen print of the ternary conductive nanocomposite. EESs with high comprehensive performance (electrical and mechanical properties) are fabricated to confirm the analytical results and monitor the motion of a human hand. The good agreement between experimental and analytical results paves the way for bettering monitoring of skin growth during wound healing in order to avoid necrosis and scarring. This EES in monitoring the motion of a human exhibit presents a promising application for assisting prosthetic movement.

A high-sensitivity and low-hysteresis flexible pressure sensor based on carbonized cotton fabric

Flexible pressure sensors have grown rapidly in the past few years. The great challenge for these sensors is the complex and expensive manufacturing process, as well as the electromechanical performance that is not compatible with sensitivity and hysteresis. In this work, a flexible resistive-type pressure sensor using carbonized cotton fabric (CCF) is manufactured through a facile, low-cost and scalable preparation process, which exhibits excellent flexibility and electromechanical performance. The composite material, obtained by immersing CCF in a thermoplastic urethane (TPU) solution, is combined with interdigitated electrodes to assemble the desired pressure sensor. The natural porous network of CCF with high-conductivity carbon fibers and the flexible substrate with low concentration TPU solution (resulting in reduced viscoelasticity) endow the flexible pressure sensor remarkable electromechanical performance, including ultrahigh sensitivity (up to 74.80 kPa−1) and ultralow hysteresis (3.39%), which are crucial for its practical application as flexible electronics. Moreover, the pressure sensor shows a large pressure range (0˜16 kPa), low detection limit (˜0.70 Pa) and excellent durability (>4000 cycles). Moreover, the influence of carbonization temperature on the electromechanical performance is also discussed. Based on the superior property of CCF/TPU pressure sensor, its applications in monitoring light items, wrist pulse, movements of fingers and wrists are demonstrated. Resultantly, low-cost raw materials, simple preparation processes and excellent electromechanical performance make the CCF/TPU pressure sensor a great potential in wearable flexible electronics.

Anatomy of the Cun Position at Wrist and Its Application in Pulse Diagnosis.

Information on anatomy of the Cun position at wrist is lacking; whether the blood vessel taking pulse in Cun is the radial artery or the superficial palmar branch is also clinically controversial. The objective was to investigate the boundaries and contents, and the vascular distribution and their pulse points in Cun. Thirty-two upper extremities of 16 human cadavers were investigated for dissection and observation. The boundaries, contents, and blood vessel distribution in Cun were observed; the location of pulse points in Cun was identified; the length of the superficial palmar branch in wrist pulse (L1), the pulp width of the index finger (L2), and the angle between the radial artery and the superficial palmar branch were measured. The results showed that the Cun was located in the region formed by the bulge of the prominent bone proximal to the palm, the radial flexor tendon, the tubercle of scaphoid, and the abductor longus muscle tendon. In this area, the radial artery could be pulsed part in the medial side of the abductor longus muscle tendon, while the superficial palmar branch lied near the surface and was easy to pulse in the lateral side of the radial flexor tendon and the medial side of the tubercle of scaphoid. The ratio of L1 to L2 was 1.2±0.8, and the angle was 23.3±9.9°. The results suggested that it could not be generalized that the blood vessel taking pulse in Cun was the radial artery or the superficial palmar branch; it might depend on the vascular distribution in Cun, the region of finger positioning, and the patient's pulse condition.

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.

Monitoring of physiological body signals and human activity based on ultra-sensitive tactile sensor and artificial electronic skin by direct growth of ZnSnO3 on silica cloth

This report demonstrates of the direct growth of ternary compound ZnSnO3 nanocubes on silica cloth for the fabrication of scalable tactile sensors for monitoring physiological signals which even the highly sensitive tactile sensors fail to measure and artificial electronic skin (E-skin) without the use of sophisticated silicon wafer based technologies. The fabricated sensor exhibited a sensitivity and response time of 0.12 KPa−1 and 350 ms respectively. Inspired by the inherent alignment of the ZnSnO3 nanocubes on silica microfibers, the fabricated sensor was further demonstrated to be able to recognize wrist pulse pressure, finger movement, wrist movement and finger pressing. Furthermore, large area sensors array (4 × 4) were fabricated and integrated onto human hand which can “feel” the touch and spatially map the response paving way for the development of E-skin. Also, the sensor array was able to detect and map the shape and location of unknown objects placed on it and could trace the index finger trajectory made on the sensor array. The fabricated pressure sensor was tested for its reliability by performing bending test studies under harsh deformations and 500 bending cycles which resulted in negligible change in the performance of the sensor.

Highly Sensitive and Durable Structured Fibre Sensors for Low-Pressure Measurement in Smart Skin.

Precise measurements of low pressure are highly necessary for many applications. This study developed novel structured fibre sensors embedded in silicone, forming smart skin with high sensitivity, high durability, and good immunity to crosstalk for precise measurement of pressure below 10 kPa. The transduction principle is that an applied pressure leads to bending and stretching of silicone and optical fibre over a purposely made groove and induces the axial strain in the gratings. The fabricated sensor showed high pressure sensitivity up to 26.8 pm/kPa and experienced over 1,000,000 cycles compression without obvious variation. A theoretical model of the sensor was presented and verified to have excellent agreement with experimental results. The prototype of smart leg mannequin and wrist pulse measurements indicated that such optical sensors can precisely measure low-pressure and can easily be integrated for smart skins for mapping low pressure on three-dimensional surfaces.

Highly sensitive and multifunctional piezoresistive sensor based on polyaniline foam for wearable Human-Activity monitoring

A highly stretchable and sensitive multifunctional piezoresistive sensor was reported. These sensors contain micro-cracked and hollowed-out polyaniline (PANI) foams which are supported by polydimethylsiloxane (PDMS). The cracked-PANI foam/PDMS (C-PF/PDMS) strain sensor shows high sensitivity with a gauge factor of ∼10 and excellent linearity and high durability over 500 stretching-releasing cycles. The fabricated C-PF/PDMS pressure sensor exhibits a sensitivity of ∼0.055 kPa−1 in the pressure range of 0–5.0 kPa, a low detection limit of 4 Pa, a fast response time (∼60 ms), recovery time (∼90 ms) and the capability of detecting and distinguishing various mechanical stimuli including compression, shear and torsion forces. When the sensor is attached to the human body, it can function as a health-monitoring device by detecting various human motions such as the bending of fingers and wrist, phonation and the wrist pulse.