Showing papers on "Gauge factor published in 2018"

Stretchable Ti3C2Tx MXene/Carbon Nanotube Composite Based Strain Sensor with Ultrahigh Sensitivity and Tunable Sensing Range

Abstract: It remains challenging to fabricate strain-sensing materials and exquisite geometric constructions for integrating extraordinary sensitivity, low strain detectability, high stretchability, tunable sensing range, and thin device dimensions into a single type of strain sensor. A percolation network based on Ti3C2Tx MXene/carbon nanotube (CNT) composites was rationally designed and fabricated into versatile strain sensors. This weaving architecture with excellent electric properties combined the sensitive two-dimensional (2D) Ti3C2Tx MXene nanostacks with conductive and stretchable one-dimensional (1D) CNT crossing. The resulting strain sensor can be used to detect both tiny and large deformations with an ultralow detection limit of 0.1% strain, high stretchability (up to 130%), high sensitivity (gauge factor up to 772.6), tunable sensing range (30% to 130% strain), thin device dimensions ( 5000 cycles). The versatile and scalable Ti3C2Tx MXene/CNT strain sens...

MXenes stretch hydrogel sensor performance to new limits

Abstract: The development of wearable electronics, point-of-care testing, and soft robotics requires strain sensors that are highly sensitive, stretchable, capable of adhering conformably to arbitrary and complex surfaces, and preferably self-healable. Conductive hydrogels hold great promise as sensing materials for these applications. However, their sensitivities are generally low, and they suffer from signal hysteresis and fluctuation due to their viscoelastic property, which can compromise their sensing performance. We demonstrate that hydrogel composites incorporating MXene (Ti3C2T x ) outperform all reported hydrogels for strain sensors. The obtained composite hydrogel [MXene-based hydrogel (M-hydrogel)] exhibits outstanding tensile strain sensitivity with a gauge factor (GF) of 25, which is 10 times higher than that of pristine hydrogel. Furthermore, the M-hydrogel exhibits remarkable stretchability of more than 3400%, an instantaneous self-healing ability, excellent conformability, and adhesiveness to various surfaces, including human skin. The M-hydrogel composite exhibits much higher sensitivity under compressive strains (GF of 80) than under tensile strains. We exploit this asymmetrical strain sensitivity coupled with viscous deformation (self-recoverable residual deformation) to add new dimensions to the sensing capability of hydrogels. Consequently, both the direction and speed of motions on the hydrogel surface can be detected conveniently. Based on this effect, M-hydrogel demonstrates superior sensing performance in advanced sensing applications. Thus, the traditionally disadvantageous viscoelastic property of hydrogels can be transformed into an advantage for sensing, which reveals prospects for hydrogel sensors.

A Highly Sensitive Capacitive-type Strain Sensor Using Wrinkled Ultrathin Gold Films

Abstract: Soft strain sensors are needed for a variety of applications including human motion and health monitoring, soft robotics, and human/machine interactions. Capacitive-type strain sensors are excellent candidates for practical applications due to their great linearity and low hysteresis; however, a big limitation of this sensor is its inherent property of low sensitivity when it comes to detecting various levels of applied strain. This limitation is due to the structural properties of the parallel plate capacitor structure during applied stretching operations. According to this model, at best the maximum gauge factor (sensitivity) that can be achieved is 1. Here, we report the highest gauge factor ever achieved in capacitive-type strain sensors utilizing an ultrathin wrinkled gold film electrode. Our strain sensor achieved a gauge factor slightly above 3 and exhibited high linearity with negligible hysteresis over a maximum applied strain of 140%. We further demonstrated this highly sensitive strain sensor i...

Highly Stretchable and Wearable Strain Sensor Based on Printable Carbon Nanotube Layers/Polydimethylsiloxane Composites with Adjustable Sensitivity

Abstract: Strain sensors that are capable of monitoring complex human motions with high accuracy are highly desirable for developing wearable electronics. This paper reports the fabrication of highly stretchable and sensitive multidirectional strain sensors with tunable strain gauge factors by employing a digitally controlled printer to incorporate carbon nanotube (CNT) layers into polydimethylsiloxane (PDMS) substrates. The fabricated sensors exhibit a high stretchability (up to 45%) and sensitivity with a gauge factor of 35.75. The gauge factors could be easily modulated by tuning the number of CNT printing cycles to accommodate diverse requirements. The cyclic loading–unloading test results revealed that the composite strain sensors exhibited excellent long-term durability. Particularly, in this work, for the first time, human-motion-induced strain was measured by a motion capture system and compared with the strain data obtained from the fabricated strain sensors. The deviation of strains measured by composite ...

Network cracks-based wearable strain sensors for subtle and large strain detection of human motions

Abstract: As an imitation of human skin's tactile sensing ability, flexible and stretchable strain sensors are highly desirable because of their various applications in health monitoring, robotics, and human–machine interfaces. However, it is still a big challenge to fabricate strain sensors with both high sensitivity and broad sensing range. Herein, we report a simple, low cost and scalable fabrication strategy to construct high performance strain sensors based on network cracks formed in multilayer carbon nanotubes (CNTs) films/polydimethylsiloxane (PDMS) composites. The microscopic thickness of multilayer CNTs can be precisely controlled to tune the formation of network cracks in CNTs films/PDMS composite, which is critical for simultaneously amplifying the sensitivity signal and sensing range of strain sensors. The optimized CNTs films/PDMS composite under appropriate stretching would fracture into gaps, islands, and bridges connecting separated islands. The formed network cracks easily, resulting in both high gauge factor (maximum value of 87) and a wide sensing range (up to 100%) of the strain sensor, which allows the detection of strain as low as 0.007% with excellent stability (1500 cycles), making it suitable for both subtle and large strain detection, including subtle signals of artery pulses, music vibration and large scale motions of joint bending.

Highly sensitive and stretchable piezoresistive strain sensor based on conductive poly(styrene-butadiene-styrene)/few layer graphene composite fiber

Abstract: High stretchability and sensitivity are the major desired requirements of strain sensors for wearable electronics applications, especially in health and medical monitoring. Herein, a highly sensitive and stretchable strain sensor based on conductive poly(styrene-butadienestyrene)/few layer graphene (SBS/FLG) composite fiber is fabricated through an easy and scalable wet-spinning process. Owing to the super flexibility of SBS matrix and the excellent electrical and mechanical properties of FLG, the SBS/FLG fiber based strain sensor revealed superior performance, including wide workable strain range (>110%), superior sensitivity (gauge factor of 160 at a strain of 50% and of 2546 at a strain of 100%), and durability. Furthermore, the mechanism behind the excellent performances of SBS/FLG fiber based sensors is discussed in detail.

Polydimethylsiloxane (PDMS)-Based Flexible Resistive Strain Sensors for Wearable Applications

Abstract: There is growing attention and rapid development on flexible electronic devices with electronic materials and sensing technology innovations. In particular, strain sensors with high elasticity and stretchability are needed for several potential applications including human entertainment technology, human–machine interface, personal healthcare, and sports performance monitoring, etc. This article presents recent advancements in the development of polydimethylsiloxane (PDMS)-based flexible resistive strain sensors for wearable applications. First of all, the article shows that PDMS-based stretchable resistive strain sensors are successfully fabricated by different methods, such as the filtration method, printing technology, micromolding method, coating techniques, and liquid phase mixing. Next, strain sensing performances including stretchability, gauge factor, linearity, and durability are comprehensively demonstrated and compared. Finally, potential applications of PDMS-based flexible resistive strain sensors are also discussed. This review indicates that the era of wearable intelligent electronic systems has arrived.

Highly Sensitive and Stretchable Resistive Strain Sensors Based on Microstructured Metal Nanowire/Elastomer Composite Films

Abstract: High sensitivity and high stretchability are two conflicting characteristics that are difficult to achieve simultaneously in elastic strain sensors. A highly sensitive and stretchable strain sensor comprising a microstructured metal nanowire (mNW)/elastomer composite film is presented. The surface structure is easily prepared by combining an mNW coating and soft-lithographic replication processes in a simple and reproducible manner. The densely packed microprism-array architecture of the composite film leads to a large morphological change in the mNW percolation network by efficiently concentrating the strain in the valley regions upon stretching. Meanwhile, the percolation network comprising mNWs with a high aspect ratio is stable enough to prevent electrical failure, even under high strains. This enables the sensor to simultaneously satisfy high sensitivity (gauge factor ≈81 at >130% strain) and high stretchability (150%) while ensuring long-term reliability (10 000 cycles at 150% strain). The sensor can also detect strain induced by bending and pressure, thus demonstrating its potential as a versatile sensing tool. The sensor is successfully utilized to monitor a wide range of human motions in real time. Furthermore, the unique sensing mechanism is easily extended to detect more complex multiaxial strains by optimizing the surface morphology of the device.

Pressure Insensitive Strain Sensor with Facile Solution-Based Process for Tactile Sensing Applications

Abstract: Tactile sensors that can mechanically decouple, and therefore differentiate, various tactile inputs are highly important to properly mimic the sensing capabilities of human skin. Herein, we present an all-solution processable pressure insensitive strain sensor that utilizes the difference in structural change upon the application of pressure and tensile strain. Under the application of strain, microcracks occur within the multiwalled carbon nanotube (MWCNT) network, inducing a large change in resistance with gauge factor of ∼56 at 70% strain. On the other hand, under the application of pressure to as high as 140 kPa, negligible change in resistance is observed, which can be attributed to the pressure working primarily to close the pores, and hence minimally changing the MWCNT network conformation. Our sensor can easily be coated onto irregularly shaped three-dimensional objects (e.g., robotic hand) via spray coating, or be attached to human joints, to detect bending motion. Furthermore, our sensor can dif...

Dually Synergetic Network Hydrogels with Integrated Mechanical Stretchability, Thermal Responsiveness, and Electrical Conductivity for Strain Sensors and Temperature Alertors.

Abstract: The first example of dually synergetic network hydrogel, which has integrated mechanical stretchability, thermal responsiveness, and electrical conductivity, has been constructed by a versatile and topological co-cross-linking approach. Poly(N-isopropylacrylamide) (PNIPAAm) is introduced as the thermally responsive ingredient, and polyaniline (PANI) is selected as the electrically conductive ingredient. PNIPAAm network is cross-linked by double-bond end-capped Pluronic F127 (F127DA). PANI network is doped and cross-linked by phytic acid. These two ingredients are further mechanically interlocked. Due to the integrated multiple functionalities, the topologically co-cross-linked hydrogels, as will be mentioned as F-PNIPAAm/PANI hydrogels, can be fabricated into resistive-type strain sensors. The strain sensors can achieve a gauge factor of 3.92, a response time of 0.4 s, and a sensing stability for at least 350 cycles and can be further applied for monitoring human motions, including motion of two hands, be...

Highly stretchable strain sensors with reduced graphene oxide sensing liquids for wearable electronics

Abstract: Strain sensors with high sensitivity, broad sensing ranges and excellent durable stability are highly desirable due to their promising potential in electronic skins and human-friendly wearable interactive systems Herein, we report a high-performance strain sensor based on rGO (reduced graphene oxide)/DI (deionized water) sensing elements The strain sensors were fabricated by using Ecoflex rubber filled with rGO/DI conductive liquids via template methods, making the process simple, low-cost and scalable The as-assembled strain sensors can be used to reflect both stretching and compressing with high sensitivity (a maximum gauge factor of 316 and a pressure sensitivity of 0122 kPa−1), an ultralow limit of detection (01% strain), and excellent reliability and stability (>15 000 cycles for pressuring and >10 000 cycles for stretching) In particular, the maximum sensing range is up to 400%, much wider than that of the sensor recently reported More significantly, the strain sensors are able to distinguish between touch/compressive (resistance decrease) and tensile (resistance increase) deformation, which has not been explored before This interesting property of strain sensors is due to the micro-contact of nanomaterials in a liquid environment The sensing liquid of the device can be refilled when it fails, and this enables the recycling of the materials and reduces the waste rate Therefore, it is attractive and promising for practical applications in multifunctional wearable electronics such as the detection of acoustic vibration, human vocalization and other human motions

Highly Sensitive Electromechanical Piezoresistive Pressure Sensors Based on Large-Area Layered PtSe2 Films

Abstract: Two-dimensional (2D) layered materials are ideal for micro- and nanoelectromechanical systems (MEMS/NEMS) due to their ultimate thinness. Platinum diselenide (PtSe2), an exciting and unexplored 2D transition metal dichalcogenide material, is particularly interesting because its low temperature growth process is scalable and compatible with silicon technology. Here, we report the potential of thin PtSe2 films as electromechanical piezoresistive sensors. All experiments have been conducted with semimetallic PtSe2 films grown by thermally assisted conversion of platinum at a complementary metal-oxide-semiconductor (CMOS)-compatible temperature of 400 °C. We report high negative gauge factors of up to -85 obtained experimentally from PtSe2 strain gauges in a bending cantilever beam setup. Integrated NEMS piezoresistive pressure sensors with freestanding PMMA/PtSe2 membranes confirm the negative gauge factor and exhibit very high sensitivity, outperforming previously reported values by orders of magnitude. We employ density functional theory calculations to understand the origin of the measured negative gauge factor. Our results suggest PtSe2 as a very promising candidate for future NEMS applications, including integration into CMOS production lines.

Ultra-stretchable, sensitive and durable strain sensors based on polydopamine encapsulated carbon nanotubes/elastic bands

Abstract: High-performance flexible and wearable strain sensors for human motion detection have been widely investigated recently. Here, we report a flexible strain sensor with ultra-high stretchability, large sensitivity and excellent durability based on common elastic bands from every day life. The strain sensor was fabricated by embedding carbon nanotubes (CNTs) into elastic bands (EB) through swelling-ultrasonication treatment. It is found that the CNTs with a large aspect ratio migrated into the inner regions of the EB successfully, generating a conductive CNT/EB shell with a thickness of about 30 μm. The CNT/EB bands were then coated with a polydopamine (PDA) layer by self-polymerization of dopamine to stabilize the sensitive regions. Interestingly, the specific strength and specific elongation of PDA/CNT/EB are enhanced by about 55% and 23% respectively after the coating of PDA, compared to the pure EB. Strain sensing tests indicated that our strain sensors had desirable integration of an ultra-high sensing range (920% strain), large sensitivity (a gauge factor (GF) of 129 under a strain of 780–920%), superior stability (10 000 cycles at 100% strain) and a fast response speed. Additionally, there was a direct correlation between the mechanical hysteresis HM value and the weak shoulder peak. The sensing mechanism of the strain sensors were investigated. Monitoring of human body motions (such as finger bending, muscle movements and knee-joint movements) indicates that our stretchable PDA/CNT/EB sensor has broad application prospects for human-machine interfaces in the artificial intelligence (AI) field.

Simultaneously Detecting Subtle and Intensive Human Motions Based on a Silver Nanoparticles Bridged Graphene Strain Sensor.

Abstract: There is a growing demand for flexible electronic devices. In particular, strain sensors with high performance have attracted more and more attention, because they can be attached on clothing or human skin for applications in the real-time monitoring of human activities. However, monitoring human-body motions that include both subtle and intensive motions, and many strain sensors cannot meet the diverse demands simultaneously. In this work, a silver nanoparticles (Ag NPs) bridged graphene strain sensor is developed for simultaneously detecting subtle and intensive human motions. Ag NPs serve as many bridges to connect the self-overlapping graphene sheets, which endows the strain sensor with many excellent performances. Because of the high sensitivity, with a large gauge factor (GF) of 475 and a strain range of >14.5%, high durability of the sensor has been achieved. Besides, the excellent consistency and repeatability of the fabrication process is verified. Furthermore, the model for explaining the working mechanism of the strain sensor is proposed. Most importantly, the designed wearable strain sensor can be applied in human motion detection, including large-scale motions and small-scale motions.

High-performance flexible strain sensor with bio-inspired crack arrays.

Abstract: Biomimetic sensor technology is always superior to existing human technologies. The scorpion, especially the forest scorpion, has a unique ability to detect subtle vibrations, which is attributed to the microcrack-shaped slit sensillum on its legs. Here, the biological sensing mechanism of the typical scorpion (Heterometrus petersii) was intensively studied in order to newly design and significantly improve the flexible strain sensors. Benefiting from the easy-crack property of polystyrene (PS) and using the solvent-induced swelling as well as double template transferring method, regular and controllable microcrack arrays were successfully fabricated on top of polydimethylsiloxane (PDMS). Using this method, any physical damage to PDMS could be effectively avoided. More fortunately, this bio-inspired crack arrays fabricated in this work also had a radial-like pattern similar to the slit sensillum of the scorpion, which was another unexpected imitation. The gauge factor (GF) of the sensor was conservatively evaluated at 5888.89 upon 2% strain and the response time was 297 ms. Afterward, it was demonstrated that the bio-inspired regular microcrack arrays could also significantly enhance the performance of traditional strain sensors, especially in terms of the sensitivity and response time. The practical applications, such as the detection of human motions and surface folding, were also tested in this work, with the results showing significant potential applications in numerous fields. This work changes the traditional waste cracks on some damaged products into valuable things for ultrasensitive mechanical sensors. Moreover, with this manufacturing technique, we could easily realize the simple, low cost and large-scale fabrication of advanced bioinpired sensors.

Ultrasensitive and Stretchable Strain Sensors Based on Mazelike Vertical Graphene Network

Abstract: Here, we report a new type of strain sensors consisting of vertical graphene nanosheets (VGNs) with mazelike network, sandwiched between poly(dimethylsiloxane) (PDMS) substrates. The new sensors outperform most graphene thin-film-based sensors reported previously and show an outstanding combination of high stretchability of ∼120%, excellent linearity over the entire detection range, and high sensitivity with a gauge factor of ∼32.6. The sensitivity can be tuned by controlling the thickness of VGNs, with sensors consisting of thicker VGNs showing higher sensitivity but slightly lower stretchability (the maximum gauge factor is ∼88.4 with a maximum detection strain of ∼55%). Detailed microscopic examinations reveal that the ultrahigh sensitivity stems from the formation of microcracks initiated in the buffer layer. These microcracks are bridged by strings of graphene/PDMS, enabling the conductive network to continue to function up to a strain level significantly higher than that of previously reported graphene thin-film-based sensors. Furthermore, the present sensors have been found to be insensitive to temperatures and various liquids, including water and 0.1 mol L-1 sodium chloride solution (similar to the sweat on human skin). Demonstrations are presented to highlight the new sensors' potential as wearable devices for human motion detection and pressure distribution measurement.

A photonic sintering derived Ag flake/nanoparticle-based highly sensitive stretchable strain sensor for human motion monitoring

Abstract: Recently, the demand for stretchable strain sensors used for detecting human motion is rapidly increasing. This paper proposes high-performance strain sensors based on Ag flake/Ag nanocrystal (NC) hybrid materials incorporated into a polydimethylsiloxane (PDMS) elastomer. The addition of Ag NCs into an Ag flake network enhances the electrical conductivity and sensitivity of the strain sensors. The intense localized heating of Ag flakes/NCs is induced by intense pulsed light (IPL) irradiation, to achieve efficient sintering of the Ag NCs within a second, without damaging the PDMS matrix. This leads to significant improvement in the sensor sensitivity. Our strain sensors are highly stretchable (maximum strain = 80%) and sensitive (gauge factor = 7.1) with high mechanical stability over 10 000 stretching cycles under 50% strain. For practical demonstration, the fabrication of a smart glove for detecting the motions of fingers and a sports band for measuring the applied arm strength is also presented. This study provides an effective method for fabricating elastomer-based high-performance stretchable electronics.

Stretchable and Washable Strain Sensor Based on Cracking Structure for Human Motion Monitoring

Abstract: Stretchable and wearable strain sensors have been intensively studied in recent years for applications in human motion monitoring. However, achieving a high-performance strain sensor with high stretchability, ultra-sensitivity, and functionality, such as tunable sensing ranges and sensitivity to various stimuli, has not yet been reported, even though such sensors have great importance for the future applications of wearable electronics. Herein, a novel and versatile strain sensor based on a cracking (silver ink patterned silicone elastomer)-(silver plated nylon structure) (Ag-DS/CF) has been designed and fabricated. The unique structure combined precisely shaped stretchable conductive fabrics and wrinkled Ag-ink pattern to achieve an excellent electrical performance. The Ag-DS/CF could be used to detect both large and subtle human motions and activities, pressure changes, and physical vibrations by achieving high stretchability up to 75%, ultrahigh sensitivity (gauge factor >104–106), tunable sensing ranges (from 7 to 75%). Excellent durability was demonstrated for human motion monitoring with machine washability. The extremely versatile Ag-DS/CF showed outstanding potential for the future of wearable electronics in real-time monitoring of human health, sports performance, etc.

Highly Sensitive and Very Stretchable Strain Sensor Based on a Rubbery Semiconductor.

Abstract: There is a growing interest in developing stretchable strain sensors to quantify the large mechanical deformation and strain associated with the activities for a wide range of species, such as humans, machines, and robots. Here, we report a novel stretchable strain sensor entirely in a rubber format by using a solution-processed rubbery semiconductor as the sensing material to achieve high sensitivity, large mechanical strain tolerance, and hysteresis-less and highly linear responses. Specifically, the rubbery semiconductor exploits π–π stacked poly(3-hexylthiophene-2,5-diyl) nanofibrils (P3HT-NFs) percolated in silicone elastomer of poly(dimethylsiloxane) to yield semiconducting nanocomposite with a large mechanical stretchability, although P3HT is a well-known nonstretchable semiconductor. The fabricated strain sensors exhibit reliable and reversible sensing capability, high gauge factor (gauge factor = 32), high linearity (R2 > 0.996), and low hysteresis (degree of hysteresis <12%) responses at the mec...

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

Abstract: 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.

A low-cost, printable, and stretchable strain sensor based on highly conductive elastic composites with tunable sensitivity for human motion monitoring

Abstract: Strain sensors with high stretchability, broad strain range, high sensitivity, and good reliability are desirable, owing to their promising applications in electronic skins and human motion monitoring systems. In this paper, we report a high-performance strain sensor based on printable and stretchable electrically conductive elastic composites. This strain sensor is fabricated by mixing silver-coated polystyrene spheres (PS@Ag) and liquid polydimethylsiloxane (PDMS) and screen-printed to a desirable geometry. The strain sensor exhibits fascinating comprehensive performances, including high electrical conductivity (1.65 × 104 S/m), large workable strain range (> 80%), high sensitivity (gauge factor of 17.5 in strain of 0%–10%, 6.0 in strain of 10%–60% and 78.6 in strain of 60%–80%), inconspicuous resistance overshoot (< 15%), good reproducibility and excellent long-term stability (1,750 h at 85 °C/85% relative humidity) for PS@Ag/PDMS-60, which only contains ∼ 36.7 wt.% of silver. Simultaneously, this strain sensor provides the advantages of low-cost, simple, and large-area scalable fabrication, as well as robust mechanical properties and versatility in applications. Based on these performance characteristics, its applications in flexible printed electrodes and monitoring vigorous human motions are demonstrated, revealing its tremendous potential for applications in flexible and wearable electronics.

Piezoresistive stretchable strain sensors with human machine interface demonstrations

Abstract: Stretchable strain sensors are important elements in flexible and skin-mountable electronics typically fabricated using semiconductor materials in cleanroom-based manufacturing processes. This work demonstrates piezoresistive strain sensors with both strain and pressure sensing capabilities by a cost-effective and versatile process utilizing a laser patterning, graphite conversion, and polymeric transfer process. The resulting sensing systems exhibit high gauge factor of 37 and pressure sensitivity of 0.088kPa-1 with high sustainable strain up to 70%. These exceptional performances are explained and observed by deforming the sensor under an in-situ SEM to show self-healing characteristics of films under large deformations. The highly sensitive strain sensors have been shown in human interface demonstrations, such as measuring the physiological signal of the human pulses, finger pressure and bending of fingers as well as assisting a robotic arm for gripping and releasing operations.

Multifunctional Highly Sensitive Multiscale Stretchable Strain Sensor Based on a Graphene/Glycerol-KCl Synergistic Conductive Network.

Abstract: Stretchable strain sensors have promising applications in health monitoring and human motion detection. However, only a few of the strain sensors reported to date have exhibited a multiscale strain range and a high gauge factor simultaneously. As such, most strain sensors cannot be used in applications that require both high sensitivity and a multiscale strain range. In this work, we develop a wearable multifunctional strain sensor using graphene and a new ionic conductor as the sensing material and Ecoflex as the encapsulant. In the ionic conductor, KCl and glycerol are used as the electrolyte and solvent, respectively. This deformable ionic conductor connects cracked graphene sheets electronically, enabling the strain sensor to be stretched to 300% of its original length with a moderate gauge factor of 25.2. The sensor can respond to various mechanical deformations including stretching, bending, and pressing. When attached to human body, the sensor can monitor large-scale strains (>50%) for joint movement and small-scale strains (<10%) for facial expressions and pulses. When stretched, the sensor also shows good sensitivity in static temperature sensing. Therefore, this multifunctional stretchable sensor has good prospect of applications in human motion detection and health monitoring.

Transparent Polymeric Strain Sensors for Monitoring Vital Signs and Beyond

Abstract: Wearable sensors that can precisely detect vital signs are highly desirable for monitoring personal health conditions and medical diagnosis. In this paper, we report an ultrasensitive strain sensor consisting of a 150 nm thick highly conductive dimethylsulfoxide-doped poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) sensing layer and an elastic fluorosilicone rubber substrate. This sensor exhibits a high sensitivity at small strains (e.g., gauge factor at 0.6% strain = 280), low limit of detection (<0.2% strain), and excellent repeatability and cycling stability. Therefore, it is promising for practically detecting vital signs, tiny human motions, and sounds. Furthermore, the semitransparent shallow blue color and the soft rubbery substrate make the strain sensor beautiful and comfortable to the human body.

2D end-to-end carbon nanotube conductive networks in polymer nanocomposites: a conceptual design to dramatically enhance the sensitivities of strain sensors

Abstract: New generation wearable devices require mechanically compliant strain sensors with a high sensitivity in a full detecting range. Herein, novel 2D end-to-end contact conductive networks of multi-walled carbon nanotubes (MWCNTs) were designed and realized in an ethylene-α-octene block copolymer (OBC) matrix. The prepared strain sensor showed a high gauge factor (GF) of 248 even at a small strain (5%) and a linear resistance response throughout the whole strain range. The sensors also exhibited very good stretchability up to 300% and high cycling durability. This novel design solved the intrinsic problem of sensors based on carbon nanotube bundles, i.e., a long sliding phase before the disconnection of CNTs in a cost-effective and scalable way. This study rationalizes the 2D end-to-end contact concept to improve the sensitivity of the existing sensors and has great potential to be used in a wide variety of polymer based sensors.