Ultrasensitive Strain Research Articles

A wirelessly multi stimuli-responsive ultra-sensitive and self-healable wearable strain sensor based on silver quantum dots of 3D organo-hydrogel nanocomposites

Novel multifunctional flexible strain sensors with enhanced properties have become an urgent requirement to comprehensively study the challenges of monitoring the full-range of human activities.

Photolithography-assisted precise patterning of nanocracks for ultrasensitive strain sensors

A photolithography-assisted nanocrack patterning method is reported to precisely define the nanocrack pattern in metal films. This method is used to fabricate an ultrasensitive strain sensor with a gauge factor of ∼20 000 in 0–1.2% strain range.

Fundamental Insights into Graphene Strain Sensing.

Graphene has been studied extensively for use in flexible electronics as ultrasensitive and wide-area strain sensors. Many sensors demonstrated so far rely on graphene networks, such that the spatial resolution is compromised, and they are unable to measure strain variations on a fine scale such as those resulting from substrate/interface failure. In this study, mono-/few-layer graphene are demonstrated to be good candidates for strain sensing with high spatial resolution to evaluate features <100 nm. The fundamentals of strain sensing-interaction with the target-have been discussed to shed light on the sensitivity and durability for future sensor fabrication. The proof-of-concept strain sensors have been shown to be able to monitor different states, e.g., the initiation and evolution, of crazes. The analysis also leads to the evaluation of interfacial energy and realization of high local strain in graphene that is applicable for other 2D materials for ultrasensitive strain sensing and bandgap opening applications.

Bi2S3/PVDF/Ppy-Based Freestanding, Wearable, Transient Nanomembrane for Ultrasensitive Pressure, Strain, and Temperature Sensing.

Flexible nanofiber-based composites have been widely explored because of their light weight, high surface area, scalability, and tunable physical and mechanical properties. In this work, we report electrospun 2D-Bi2S3 incorporated PVDF/PPy nanofibers as a versatile platform for ultrasensitive pressure, strain, and temperature sensing. Detailed characterization studies revealed the formation of ultrathin nanofibers and characteristic Raman and IR vibration modes of PPy, 2D-Bi2S3, β-phased PVDF. The fabricated pressure sensor exhibited a sensitivity of 1.51 kPa-1 in the wide linear range of 1-50 kPa and a response time of 0.04 s. The practical ability of pressure sensor was tested by successfully detecting pulse rate of human radial arteries. Further, the BS- PVDF/PPy composite was employed as a strain sensor in the range of 3.1-61.5%, displayed a gauge factor (GF) of 45.45 and a response time of 0.1 s. The wearable sensor was capable of detecting minute changes in hand gestures by recognizing the microstrains applied to the device. The sensing mechanism can be attributed to the excellent piezoelectric property of β- phase PVDF, electron transport property of PPy nanoparticles and tensile strength of the BS nanoparticles embedded in the polymer matrix. When used as a wearable temperature sensor, the versatile device demonstrated a linear range of detection 24- 48 °C with a response time of 0.33 s and Temperature coefficient of resistance (TCR) of -0.1117 °C-1 that can be attributed to the phonon-assisted hoping mechanism. The nanofiber composite dissolved in volatile organic solvent acetone in 5 days with the least impact on the surrounding environment thus making this a promising strategy to develop transient technologies aimed at zero-waste, green electronics.

Controllable configuration of conductive pathway by tailoring the fiber alignment for ultrasensitive strain monitoring

Fiber-based architectures exhibit remarkable advantages in wearable electronics. Despite the various techniques to achieve strain sensitive fibers, important factors concerning the sensing performance, e.g. fiber arrangement, have been rarely explored. Herein, various fiber sensing patterns with anisotropic and isotropic microstructures were fabricated, and their localized strain distribution and conductive pathway configuration were tailored through fiber alignment. The sensing performance and mechanisms were investigated based on experimental characterization and theoretical modeling. We find out that the fibers arrangement strongly determines their strain sensitive behavior including sensitivity and sensing range. Additionally, by introducing a mechanical-guided step to realize a constant microcrack density in the fiber patterns, strain sensitivity and stability can be further improved. As a proof of concept, we integrated two fiber array sensors into a strain sensing system to simultaneously achieve an ultrahigh sensitivity (gauge factor up to 9540) and a wide sensing range (0.01–110%) as well as fast response.

Ultrasensitive Strain Sensing by Using Two Parallel Structured Fabry--Perot Interferometers in Cascaded Connection

An optical fiber in-line Fabry-Perot interferometric device is presented for ultrasensitive strain sensing by use of vernier effect. The device consists of two parallel structured Fabry-Perot cavities in cascaded connection, formed by two pairs of femtosecond laser inscribed in-fiber reflection mirrors. The cavity lengths and their difference can be accurately controlled, which enables an extremely large amplification factor when vernier effect is used and the strain sensitivity achieved is ~236.32 pm/με. Moreover, the temperature cross sensitivity realized is as low as ~29.2 nε/°C. The device is featured with ultra-compact size, robust structure, easy fabrication, convenient operation and good reproducibility, which makes it highly attractive in many sensing applications where extremely large strain sensitivity is critically required.

Ultra-sensitive and resilient compliant strain gauges for soft machines.

Soft machines are a promising design paradigm for human-centric devices1,2 and systems required to interact gently with their environment3,4. To enable soft machines to respond intelligently to their surroundings, compliant sensory feedback mechanisms are needed. Specifically, soft alternatives to strain gauges-with high resolution at low strain (less than 5 per cent)-could unlock promising new capabilities in soft systems. However, currently available sensing mechanisms typically possess either high strain sensitivity or high mechanical resilience, but not both. The scarcity of resilient andcompliant ultra-sensitive sensing mechanisms has confined their operation to laboratory settings, inhibiting their widespread deployment. Here we present a versatile and compliant transduction mechanism for high-sensitivity strain detection with high mechanical resilience, based on strain-mediated contact in anisotropically resistive structures (SCARS). The mechanism relies upon changes in Ohmic contact between stiff, micro-structured, anisotropically conductive meanders encapsulated by stretchable films. The mechanism achieves high sensitivity, with gauge factors greater than 85,000, while being adaptable for use with high-strength conductors, thus producing sensors resilient to adverse loading conditions. The sensing mechanism also exhibits high linearity, as well as insensitivity to bending and twisting deformations-features that are important for soft device applications. To demonstrate the potential impact of our technology, we construct a sensor-integrated, lightweight, textile-based arm sleeve that can recognize gestures without encumbering the hand. We demonstrate predictive tracking and classification of discrete gestures and continuous hand motions via detection of small muscle movements in the arm. The sleeve demonstration shows the potential of the SCARS technology for the development of unobtrusive, wearable biomechanical feedback systems and human-computer interfaces.

Integrated Sensing and Warning Multifunctional Devices Based on the Combined Mechanical and Thermal Effect of Porous Graphene.

Wearable devices with integrated alarm functions play a vital role in daily life and can help people prevent potential hazards. Although many wearable sensors have been extensively studied and proposed to monitor various physiological signals, most of them are needed to integrate with the external alarm elements to realize warning, such as light-emitting diodes and buzzers, resulting in the system complexity and poor flexibility. In this paper, an integrated sensing and warning multifunctional device based on the mechanical and thermal effect of porous graphene is proposed on a bilayer asymmetrical pattern of laser-induced graphene (LIG). Compared with the strain sensor with nonpatterned LIG, the mechanical performance is greatly improved with the highest gauge factor value of up to 950 for the strain sensor with mesh-patterned LIG. On the contrary, the heating performance of the heater with nonpatterned LIG is better than that with mesh-patterned LIG. Combining the performance differences of different LIG patterns, the integrated wearable device with a bilayer asymmetrical LIG pattern is demonstrated. It can generate enough heating energy to warn the person when the detected signal meets the threshold condition measured in real time by the ultrasensitive strain sensor. This work will provide a new way to construct an integrated wearable device for realizing multifunctional applications. This integrated multifunctional device shows great potential toward the applications in healthcare monitoring and timely warning.

Fabrication of a Sensitive Strain and Pressure Sensor from Gold Nanoparticle-Assembled 3D-Interconnected Graphene Microchannel-Embedded PDMS.

Manufacture of uniform, sensitive, and durable microtextured sensing materials is one of the greatest challenges for pressure sensors and electronic skins. Reported in this article is a gold nanoparticle-assembled, 3D-interconnected, graphene microchannel-embedded PDMS (3D GMC-PDMS) film for strain and pressure sensors. The film consists of porous nickel foam with its inner walls coated by multilayer graphene. Embedding in PDMS with etching removal of the Ni yields a 3D GMC-PDMS. Coating the inner walls with Au nanoparticles yields an Au nanoparticle-assembled 3D GMC-PDMS (AuNPs-GMC-PDMS) film, which is useful as an ultrasensitive pressure and strain sensor. This sensor exhibits a wide detection range (∼50 kPa) and ultrahigh sensitivity of 5.37, 1.56, and 0.5 kPa-1 in the ranges of <1, 1-10, and 10-50 kPa, respectively. Its lower detection limit is 4.4 Pa, its response time is 20 ms, and its strain factor is up to 15. Comparison of a AuNPs-GMC-PDMS film with a 3D GMC-PDMS film reveals a sensitivity improvement of 40 times in the 0-1 kPa pressure range and a gauge factor of more than 4 times in the 0-30% tensile strain range. The device has broad applications as a traditional or wearable medical sensor.

Highly Stretchable, Self-Healable, Ultrasensitive Strain and Proximity Sensors Based on Skin-Inspired Conductive Film for Human Motion Monitoring.

Recently, flexible electronics have been paid great attention due to their unique characteristics, such as high stretchability, arbitrary bending, and recoverable deformation. As a core component, flexible conductive materials with skin-like properties are desirable and valuable for the development of flexible electronics. However, the integration of skin-like mechanical properties, inherent self-healing ability, ultrahigh sensitivity, and electrical conductivity into one material is difficult to be realized. Here, this study reports a kind of conductive film (PAM-dc-fGO) fabricated by cross-linking intrinsic self-repair polyazomethine (PAM) and ethylenediamine-functionalized graphene oxide (fGO) through dynamic covalent bonds (imine bonds, -CH═N-). The as-prepared conductive films exhibit skin-like mechanical properties with a stretchability of 212-275% and elastic moduli of 0.76-4.23 MPa. In addition, the healing efficiency in mechanical properties of the 24 h healed specimen can restore up to 99%, and the healing efficiency in terms of electrical conductivity still maintains above 95% after five breaking/healing cycles, indicating an excellent capability of self-repair. Due to the ultrahigh sensing sensitivity with the gauge factor (GF) of 641, the PAM-dc-fGO film-based strain sensor can precisely detect the weak signals from the human body. Moreover, the remote monitoring of human motions with a long distance of about 100 cm has been successfully conducted by a PAM-dc-fGO proximity sensor. This work provides a new path for the development of multifunctional soft materials, and the sensors show great potential in health diagnoses and security protection applications.

Recent Progress in Hybridized Nanogenerators for Energy Scavenging.

SummaryAs the world's demand for alternative energy increases, the development of green energy harvesters becomes ever more important. As a result, the creation of triboelectric (TENG), piezoelectric (PENG), and pyroelectric nanogenerators, electromagnetic generators (EMG), solar cells, and electrochemical cells is attracting interest in an effort to convert mechanical, thermal, magnetic, solar, and chemical energy into electricity. In order to take advantage of the ambient energies from our surrounding environment, the design of hybridized generator units that can simultaneously scavenge energy in a variety of forms continues to develop. These systems are being considered to satisfy the energy needs of a range of electronic devices and adapt to a variety of working environments. This review demonstrates the latest progress in hybridized nanogenerators in accordance with their structure, operating principle, and applications. These studies demonstrate new approaches to developing hybrid techniques and novel assemblies for efficiently harvesting environmental energy from a number of sources.

An Ultrasensitive, Durable and Stretchable Strain Sensor with Crack-wrinkle Structure for Human Motion Monitoring

Flexible strain sensor has promising features in successful application of health monitoring, electronic skins and smart robotics, etc. Here, we report an ultrasensitive strain sensor with a novel crack-wrinkle structure (CWS) based on graphite nanoplates (GNPs)/thermoplastic urethane (TPU)/polydimethylsiloxane (PDMS) nanocomposite. The CWS is constructed by pressing and dragging GNP layer on TPU substrate, followed by encapsulating with PDMS as a protective layer. On the basis of the area statistics, the ratio of the crack and wrinkle structures accounts for 31.8% and 9.5%, respectively. When the sensor is stretched, the cracks fracture, the wrinkles could reduce the unrecoverable destruction of cracks, resulting in an excellent recoverability and stability. Based on introduction of the designed CWS in the sensor, the hysteresis effect is limited effectively. The CWS sensor possesses a satisfactory sensitivity (GF = 750 under 24% strain), an ultralow detectable limit (strain = 0.1%) and a short respond time of 90 ms. For the sensing service behaviors, the CWS sensor exhibits an ultrahigh durability (high stability > 2×104 stretching-releasing cycles). The excellent practicality of CWS sensor is demonstrated through various human motion tests, including vigorous exercises of various joint bending, and subtle motions of phonation, facial movements and wrist pulse. The present CWS sensor shows great developing potential in the field of cost-effective, portable and high-performance electronic skins.

Ultrasensitive Fabry–Perot Strain Sensor Based on Vernier Effect and Tapered FBG-in-Hollow Silica Tube

A dual Fabry-Perot interferometers (FPIs) sensor is demonstrated theoretically and experimentally for ultrasensitive strain sensing by using the Vernier effect and the tapered FBG-in-hollow silica tube (HST) structure. The proposed sensor consists of two parallel structured FPIs connected by a 3dB coupler to generate the Vernier effect, and the tapered FBG-in-HST structure has long active length to achieve strain sensitivity enhancement and plays the role as the sensing interferometer. Moreover, utilizing the characteristic of FBG not affected by strain, the temperature compensation has been achieved by means of a demodulating matrix. The fabricated strain sensor achieves an ultra-high strain sensitivity of 1.307 nm/με, which is the highest strain sensitivity of the FPI-based sensors reported so far. It is low-cost, robust, easy-fabrication, and expected to have great application prospects in several fields where large strain sensitivity is really required.

Ultra-sensitive and durable strain sensor with sandwich structure and excellent anti-interference ability for wearable electronic skins

Smart and wearable strain sensors have sparked enormous research interests in various applications of flexible electronic devices. For this topic, it remains a huge challenge to acquire wide sensing range, high sensitivity, superior durability and fast response synergistically. Herein, we present an ultra-sensitive and durable strain sensor with sandwich structure to address the issues, which is mainly composed of the composite of carbon black (CB)/aligned thermoplastic polyurethane (TPU) fibrous mat and the Ecoflex. The CB/TPU/Ecoflex strain sensor (CTESS) is prepared via decorating CB nanoparticles onto the aligned electrospun TPU fibrous mats by ultrasonication, then encapsulated with Ecoflex to develop a sandwich structure. This structure provides effective protection for the conductive CB/TPU fibrous network, endowing the strain sensor with excellent sensing performances, including low detection limit (0.5% strain), wide response range (up to 225% strain), ultrahigh sensitivity (maximum gauge factor of 3186.4 at strain of 225%), fast response time (70 ms) and favorable repeatability even after 5000 stretching/releasing cycles. CTESS also shows an excellent anti-interference capability to external humidity and temperature. The CTESS is then assembled as artificial electronic skins to monitor various human motions, exhibiting great application prospects in next-generation wearable electronics.

Development of ultrasensitive mechanical strain sensor made of 2D-assembled graphene monolayers aligned parallel into polysilicon nanocomposites

A monolayer graphene sheets have been prepared via sonochemical approach. Nanocomposites made of graphene doped polysilicon were prepared via mill-roll approach to develop 2D-assembled graphene monolayers aligned parallel in the polysilicon matrices, specifically for ultrasensitive mechanical sensor devices. The developed nanocomposites were characterized via SEM, XRD, FTIR and Raman spectroscopy. It was found that the graphene tended to align parallel in the polysilicon matrices, where Si-H and Si-C bonds between the graphene and polysilicon was formed. Moreover, the increase of graphene contents into the polysilicon matrices instigated a decrease of the amorphous silicon bands and increasing the crystalline Si-C bands. The distance between the aligned graphene layers was strongly dependent on the amount of graphene incorporated in the polysilicon. The mechanical measurements were analyzed based on Ogden and Halpin–Tsai models. These two models indicated that the graphene aligned parallel in the polysilicon matrices and their modulus of elasticity is increased by 10 times at concentration of 0.15 wt%, only. The dissipation energy and linear damage factor were determined under the cyclic stress-strain fatigue. The prepared nanocomposites were examined as mechanical strain sensor. Among all samples, the doping of polysilicon with 0.09 wt% of graphene resulted in a highly sensitive mechanical strain sensor with linear regression up to 22 %. This sample exhibited fast response time of 4−5 s and very fast recovery time around 2−3 s. Therefore, this developed sensor will pave the way to manufacture ultrasensitive mechanical sensor for real daily life use.

Ultrasensitive and robust two-dimensional indium selenide flexible electronics and sensors for human motion detection

Abstract To accurately detect human motion, a sensing material/device must be flexible, ultrasensitive to strain, and electrically and mechanically robust. However, existing electronics and sensors, which are either not flexible enough, or not ultrasensitive to strain, or suffering from poor on/off ratio and low charge mobility, do not meet these stringent requirements. Here, we demonstrate a flexible and ultrasensitive three-terminal strain sensor based on two-dimensional (2D) InSe for detecting human-motion activities. The 2D InSe exhibits a tunable bandgap and a large piezoresistive effect via strain engineering. Through electrostatic gating effect, the gauge factor of the sensor can be enhanced by 8-fold and 7-fold for a low tensile and compressive strain of only ±0.25%, respectively. Remarkably, the fabricated 2D InSe-based transistor achieves both a record high on/off ratio of ~108 and an electron mobility of ~383 cm2/V s, superior to all existing ones. Furthermore, flexible InSe logic inverters with a high voltage gain of ~10 and a large noise margin of ~0.7 × VDD (supply voltage) are realized under various strain conditions. This work paves the way to enable simultaneous integration of high-performance flexible sensors and electronics based on a common 2D InSe material platform towards achieving a fully integrated sensing system.

Ultrasensitive Strain Gauges Enabled by Graphene‐Stabilized Silicone Emulsions

AbstractHere, an approach is presented to incorporate graphene nanosheets into a silicone rubber matrix via solid stabilization of oil‐in‐water emulsions. These emulsions can be cured into discrete, graphene‐coated silicone balls or continuous, elastomeric films by controlling the degree of coalescence. The electromechanical properties of the resulting composites as a function of interdiffusion time and graphene loading level are characterized. With conductivities approaching 1 S m−1, elongation to break up to 160%, and a gauge factor of ≈20 in the low‐strain linear regime, small strains such as pulse can be accurately measured. At higher strains, the electromechanical response exhibits a robust exponential dependence, allowing accurate readout for higher strain movements such as chest motion and joint bending. The exponential gauge factor is found to be ≈20, independent of loading level and valid up to 80% strain; this consistent performance is due to the emulsion‐templated microstructure of the composites. The robust behavior may facilitate high‐strain sensing in the nonlinear regime using nanocomposites, where relative resistance change values in excess of 107 enable highly accurate bodily motion monitoring.

Stretching-enhanced triboelectric nanogenerator for efficient wind energy scavenging and ultrasensitive strain sensing

ABSTRCT The development of intelligent electronic devices increasingly facilitates the configuration of smart city. However, the heavy using of Li-ion batteries can cause high cost and a series of environmental pollution owing to frequent charging induced by their limited electric capacity. Here, we report a stretching-enhanced triboelectric nanogenerator for efficient wind energy scavenging and ultrasensitive strain sensing based on stretchable composites. The output voltage and current signals can be dramatically increased by 220% and 380% by applying a 70% stretched strain as compared with that under the condition of 0% strain, which is associated with the stretched strain-induced increase of contact area. Moreover, the corresponding output power can be increased by 680% due to the stretched strain of 70%, while the impedance can be decreased by 58.3%. A high strain sensitivity of 1.75 ln(V) or 0.97 ln(Hz) under the stretched strains ranged from 0% to 45% can be obtained as a self-powered strain sensor.

Ultrasensitive piezoresistive strain sensors based on CNTs/Ag-NPs coated highly stretchable textile

Highly sensitive and extremely stretchable piezoresistive strain sensors have shown intense applications in wearable electronics. In this context, a comparative study of stretchable strain sensors based on hybrid layers of silver nanoparticles and carbon nanotubes spray coated on stretchable textile is presented in this manuscript. For this persistence, three stretchable and highly flexible electrodes are fabricated: first devoid of pre-strain, second with 25 × 25% multiaxial pre-strain, and third with 50 × 50% multiaxial pre-strain. Pre-strain technique was employed to improve the stretchability and resistance stability of the electrodes. Surface morphology and elemental composition of the as-prepared electrodes were analyzed via scanning electron microscope associated with energy-dispersive detector. The fabricated electrodes were used for the assembly of strain sensors. The sensing measurements revealed high sensitivity, significant stretchability, and fast response of the fabricated strain sensors. Cost-effective and extremely facile fabrication strategy as well as direct fabrication on textile substrates can be significant advancements in fabrication of strain sensors for practical applications in human motion detection and wearable electronics.

Monolayer MoSe₂-Based Tunneling Field Effect Transistor for Ultrasensitive Strain Sensing

This article presents a detailed investigation of the impact of mechanical strain on transition metal dichalcogenide (TMD) material-based tunneling field-effect transistor (TFET). First, the impact of mechanical strain on material parameters of MoSe2 is calculated using the first principle of density functional theory (DFT) under meta-generalized gradient approximation (MGGA). The device performance of the TMD TFET has been studied by solving the self-consistent 3-D Poisson and Schrodinger equations in nonequilibrium Green’s function (NEGF) framework. The results demonstrate that both ${I}_{\scriptscriptstyle {\rm {ON}}}$ and ${I}_{\scriptscriptstyle {\rm {OFF}}}$ increase with uniaxial tensile strain, however the change in ${I}_{\scriptscriptstyle {\rm {ON}}}/{I}_{\scriptscriptstyle {\rm {OFF}}}$ ratio remains small. This strain-dependent performance change in TMD TFET has been utilized to design an ultrasensitive strain sensor. The device shows a sensitivity ( $\Delta {I}_{\text {DS}}/{I}_{\text {DS}}$ ) of 3.61 for a strain of 2%. Due to the high sensitivity to the strain, these results show the potential of using MoSe2 TFET as a flexible strain sensor. Furthermore, the strained TFET is analyzed for backend circuit performance. It is observed that the speed and energy efficiency of ten-stage inverter chain based on controlled strain improve substantially in comparison to unstrained TFETs.