Ultrasensitive Strain Research Articles

Ultrasensitive and Stretchable Strain Sensors Based on Laser-Induced Graphene With ZnO Nanoparticles.

Laser-induced graphene (LIG) has attracted considerable attention for its use in flexible and stretchable sensors, owing to its electrical/mechanical properties and scalable fabrication processes. Although laser scanning facilitates the formation of LIG and its strain sensor, the strain-sensing sensitivity enhancement of LIG remains limited by the material's properties and structural design. In this study, we demonstrate a substantial improvement in sensitivity that was achieved by fabricating a LIG using ZnO nanoparticle (NP)-assisted photothermal enhancement. The results show that ZnO NPs selectively reduce the threshold fluence needed to convert polyimide (PI) into LIG. By transferring the LIG formed on PI to poly(dimethylsiloxane), we fabricate a stretchable strain sensor with ultrahigh sensitivity and a gauge factor of 1214 at 10% strain, which is approximately 60 times higher than the gauge factor without ZnO NPs. Using the selective graphenization properties of LIG, a flexible, dual-sided integrated sensor sheet that is equipped with flexible strain and ultraviolet (UV) sensors is demonstrated. This sheet enables simultaneous monitoring of UV intensity and joint bending angles of sports wearable devices. We validated the developed sensors by attaching them to a runner's body to monitor and simulate forefoot and heel strikes, demonstrating the sensor's ultrahigh sensitivity and long-term stability without the need for a camera. These findings highlight the potential of the proposed method for developing multifunctional sensor applications with ultrahigh sensitivity and stability.

Ultrasensitive strain sensor of dual parallel FPIs utilizing femtosecond laser processing and Vernier effect

This study proposes and develops a highly sensitive fiber optic strain sensor utilizing femtosecond laser processing and the Vernier effect. The sensor features two parallel Fabry-Pérot interferometers (FPI), with each FPI consisting of an air bubble and a tapered fiber optic cascade. FPI 2 serves as the sensing cavity, while FPI 1 acts as the reference cavity. The strain sensing capability of a single FPI 2 is measured at 6.67 p.m./με, while the parallel configuration of FPI 2 with FPI 1 achieves a sensitivity of 68.3 p.m./με, resulting in an amplification of 10.24. Furthermore, the proposed sensor demonstrates excellent repeatability, low-temperature cross-sensitivity, simple fabrication, and cost-effectiveness, making it a promising tool for strain measurement applications.

Ultrasensitive Flexible Strain Sensor Made with Carboxymethyl-Cellulose-Anchored Carbon Nanotubes/MXene for Machine-Learning-Assisted Handwriting Recognition.

The combination of wearable sensors with machine learning enables intelligent perception in human-machine interaction and healthcare, but achieving high sensitivity and a wide working range in flexible strain sensors for signal acquisition and accurate recognition remains challenging. Herein, we introduced carboxymethyl cellulose (CMC) into a carbon nanotubes (CNTs)/MXene hybrid network, forming tight anchoring among the conductive materials and, thus, bringing enhanced interaction. The silicone-rubber-encapsulated CMC-anchored CNTs/MXene (CCM) strain sensor exhibits an excellent sensitivity (maximum gauge factor up to 71 294), wide working range (200%), ultralow detection limit (0.05%), and outstanding durability (over 10 000 cycles), which is superior to most of the recently reported counterparts also based on a conductive composite film. Moreover, the sensor achieves seamless integration with human skin with the help of a poly(acrylic acid) adhesive layer, successfully obtaining stable and clear waveforms with meaningful profiles from the human body. On this basis, we proposed and realized a novel in-air handwriting recognition method via extracting multiple features of high-quality strain signals assisted by deep neural networks, achieving a high classification accuracy of 98.00 and 94.85% for Arabic numerals and letters, respectively. Our work provides an effective approach for significantly improving strain sensing performance, thereby facilitating innovative applications of flexible sensors.

Femtosecond laser-induced graphene for temperature and ultrasensitive flexible strain sensing

Femtosecond laser-induced graphene for temperature and ultrasensitive flexible strain sensing

Quasi-1D Conductive Network Composites for Ultra-Sensitive Strain Sensing.

Highly performance flexible strain sensor is a crucial component for wearable devices, human-machine interfaces, and e-skins. However, the sensitivity of the strain sensor is highly limited by the strain range for large destruction of the conductive network. Here the quasi-1D conductive network (QCN) is proposed for the design of an ultra-sensitive strain sensor. The orientation of the conductive particles can effectively reduce the number of redundant percolative pathways in the conductive composites. The maximum sensitivity will reach the upper limit when the whole composite remains only "one" percolation pathway. Besides, the QCN structure can also confine the tunnel electron spread through the rigid inclusions which significantly enlarges the strain-resistance effect along the tensile direction. The strain sensor exhibits state-of-art performance including large gauge factor (862227), fast response time (24ms), good durability (cycled 1000 times), and multi-mechanical sensing ability (compression, bending, shearing, air flow vibration, etc.). Finally, the QCN sensor can be exploited to realize the human-machine interface (HMI) application of acoustic signal recognition (instrument calibration) and spectrum restoration (voice parsing).

Strong adhesive, high conductive and environmentally stable eutectogel based on “Water in deep eutectic Solvent”: Ultrasensitive flexible temperature and strain sensors

Eutectogel is a promising candidate of conductive materials for flexible electronic sensors. However, the existing eutectogel sensors still have some problems such as poor mechanical properties and antifatigue ability, limited ionic conductivity, and strong hygroscopicity. Herein, an eutectogel is fabricated via one-stop photoinitiated copolymerization of acrylic acid, hydroxyethyl acrylate, and highly branched modified polyethyleneimine in “water in deep eutectic solvent”. The optimized eutectogel exhibits strong adhesive strength (132 ± 9 kPa, with porcine skin), ultra elongation (3500 %), high conductivity (2.7 ± 0.1 mS cm−1), long term antidrying and antifreezing (∼30 d) in a wide range of working temperatures (−40 − 60 °C), flame resistance, biocompatability, and excellent resistance ability to tear and crack propagation. The superb flame resistance and sensitive response to temperature offer a potential application in fire alarm. Besides, this gel-based wearable strain sensors can sensitively monitor and differentiate large body joint movements and subtle muscle motions. The highly distinguishable and reproducible signals can be recorded while further utilizes as sensors for detecting human healthcare accurately and continuously in medical mobile electrocardiogram machine for a long time. This work provides a new strategy for constructing eutectogel based wearable devices and electronic devices with excellent performance.

Ultrasensitive, highly stretchable and multifunctional strain sensors based on scorpion-leg-inspired gradient crack arrays

Wearable flexible strain sensors based on conductive films have shown great application potential in many high-tech fields. They have high requirements for synergistic performances of sensitivity, flexibility, stability and durability. However, overcoming the trade-off between high sensitivity and high stretchability is still a great challenge in this research. Here we develop a facile strategy to prepare high-performance flexible strain sensors based on gradient crack arrays inspired by the gradient slits on scorpion legs. The gradient crack arrays with branched or hierarchical features controllably form in a periodic thickness-gradient metal film prepared by one-step masking technique on a flexible substrate. The cracks are progressively open from the thickest film region to the thinnest one under mechanical strain, behaving a unique sensing mechanism. As a result, the gradient crack-based strain sensors possess excellent comprehensive performances including high sensitivity (up to 21000), wide sensing range (∼70 %), low detection limit (0.02 %), quick response speed (below to 80 ms), excellent stability and durability (up to 15,000 cycles at 5 % strain). As demonstration of applications, the sensors are used to monitor various human activities and to express and encrypt information by bending bidirectionally. This work provides a novel way to fabricate highly sensitive, stretchable, robust, multifunctional, crack-based flexible strain sensors, which would greatly expand the applications in flexible electronics and wearable devices.

Soybean protein-reinforced highly extensible and self-adhesive hydrogels with ultra-sensitive strain sensing for flexible electronic devices

There is a growing interest in utilizing sustainable and renewable biomass resources to construct high-performance hydrogels for flexible electronics. In this study, soybean protein isolate (SPI) with abundant functional groups was introduced into the hydrogel matrix, while the connection between SPI, MXene and the polymer network was strengthened by hydrogen bonding. The sensible strategy overcame the problems of easy oxidation, agglomeration and weak interactions that existed in the binding of conductive filler MXene nanosheets with polymer chains. The prepared composite hydrogel exhibited integrated properties of high stretchability (>800 %), excellent self-adhesive property, plasticity, injectability, cyclic stability and durability in extreme environments (-20–60°C). Noteworthily, this hydrogel demonstrated high sensitivity and stable electrical resistance response to minor changes in tension, compression, bending, and temperature. In addition, this hydrogel exhibited excellent UV isolation and perspiration properties, making it ideal for practical applications of flexible devices in sports environments. The preparation of green, multipurpose, flexible electronics and human motion monitoring devices is made easier by the practical approach in this study.

A Fabry-Perot interferometer based on probe-embedded bubble for ultrasensitive strain measurement

A high-sensitivity Fabry-Perot interferometer (FPI) strain sensor based on tapered single-mode fiber (SMF) probe embedded in microbubble is proposed and verified. The two reflective surfaces of this FPI are composed of the two tapered SMF ends and assembled within a bubble. The distance between the reflection face can be flexibly adjusted to enhance the strain sensitivity of the sensor. Experimental result shows that the strain sensitivity of proposed FPI sensor reaches to 142.2 pm/με. Meanwhile, the sensor demonstrates low temperature sensitivity of 2.19 pm/°C, which achieves an extremely low temperature-strain crosstalk of less than 16.6 nε/°C. Moreover, the proposed FPI sensor possesses advantages of high sensitivity, low-cost and compact length, which shows potential in areas of micro strain measurement.

Bionic Microstructure‐Inspired Dual‐Mode Flexible Sensor with Photothermal Effect for Ultrasensitive Temperature and Strain Monitoring

Bionic Microstructure‐Inspired Dual‐Mode Flexible Sensor with Photothermal Effect for Ultrasensitive Temperature and Strain Monitoring

Fiber Laser Writing of Highly Sensitive Nickel Nanoparticle-Incorporated Graphene Strain Sensors.

Unlocking new dimensions in wearable sensor technology, this research highlights ultrasensitive stretchable strain sensors fabricated with the customized laser-induced graphene (LIG) decorated with uniformly distributed nickel nanoparticles with a fiber laser writing process. The nickel nanoparticle-incorporated LIG (Ni-NPs@LIG) strain sensors fabricated by a simple all-laser-based method utilize a commercial fiber laser. The Ni-NPs@LIG sensors showcase an impressive gauge factor, reaching up to 248 for strain values below 5%, demonstrating a sensitivity increase of up to 430% compared to the pure LIG sensors. Moreover, these sensors offer adjustable strain sensitivity based on laser fluence. The key advancement of this study lies in the direct laser writing of highly porous nickel-graphene nanostructures with adjustable properties, making them applicable across a broad range of applications. As an application demonstration, the strain sensors were employed to assess the small deformation of a pouch battery or track the large deformation of a balloon surface.

Ultra-sensitive strain sensor based on Sagnac interferometer with different length panda fiber

A high-sensitivity harmonic Vernier effect (HVE) strain sensor is fabricated by cascading Sagnac interferometer (SI) and Fabry-Perot interferometer (FPI). SI is fabricated by the panda fiber (PF). PF is a typical polarization maintaining fiber (PMF) that has two pressure zones, making it particularly sensitive to strain. SI1, SI2, and SI3 are constructed using PF with lengths of 20 cm, 50 cm, and 80 cm, respectively. They have interference spectra similar to sine waves in the wavelength range of 1250 nm to 1650 nm. Research has found that the sensitivity of SI is directly proportional to the effective PF length under strain action. In addition, if the strain acts on the entire length of the PF, the strain sensitivities of SI1, SI2, and SI3 are 30.4 pm/με, 28.4 pm/με, and 30.1 pm/με, respectively, which are relatively close. Then, FPI is fabricated by splicing single mode fiber (SMF) and quartz capillary, and it is an “SMF-Capillary-SMF” sandwich structure, and the free spectral range (FSR) of FPI is approximately half of that of SI2. FPI and SI2 are cascaded to produce a first-order HVE sensor, further amplifying the strain sensitivity of SI2. The intersection point of the internal envelope based on the HVE sensor spectrum can provide accurate spectral wavelength position and drift, and the strain sensitivity of the HVE sensor reaches 293.0 pm/με, improving the strain sensitivity of SI2 by 10.3 times. The detection limit of the HVE sensor is 0.5 µε as the strain varies from 0 to 700 µε. This HVE strain sensor is relatively easy to manufacture, low-cost, linear and reliable, and can achieve high sensitivity strain measurement. It has certain application value in the field of strain measurement.

Ultrasensitive electrospinning fibrous strain sensor with synergistic conductive network for human motion monitoring and human-computer interaction

With the rapid development of wearable electronic skin technology, flexible strain sensors have shown great application prospects in the fields of human motion and physiological signal detection, medical diagnostics, and human-computer interaction owing to their outstanding sensing performance. This paper reports a strain sensor with synergistic conductive network, consisting of stable carbon nanotube dispersion (CNT) layer and brittle MXene layer by dip-coating and electrostatic self-assembly method, and breathable three-dimensional (3D) flexible substrate of thermoplastic polyurethane (TPU) fibrous membrane prepared through electrospinning technology. The MXene/CNT@PDA-TPU (MC@p-TPU) flexible strain sensor had excellent air permeability, wide operating range (0–450 %), high sensitivity (Gauge Factor, GFmax = 8089.7), ultra-low detection limit (0.05 %), rapid response and recovery times (40 ms/60 ms), and excellent cycle stability and durability (10,000 cycles). Given its superior strain sensing capabilities, this sensor can be applied in physiological signals detection, human motion pattern recognition, and driving exoskeleton robots. In addition, MC@p-TPU fibrous membrane also exhibited excellent photothermal conversion performance and can be used as a wearable photo-heater, which has far-reaching application potential in the photothermal therapy of human joint diseases.

Ultrasensitive Temperature and Strain Sensor Based on a Hybrid Fiber Interferometer With the Vernier Effect

Ultrasensitive Temperature and Strain Sensor Based on a Hybrid Fiber Interferometer With the Vernier Effect

Ultra-sensitive axial strain and magnetic field sensor based on three reflection surface interference and harmonic vernier effect

A high-sensitivity fiber optic strain and magnetic field (MF) sensor is designed by two Fabry-Perot interferometers (FPI) cascading and harmonic Vernier effect. Two cascaded FPIs consist of an intrinsic FPI1 and an extrinsic FPI2. FPI1 is fabricated by femtosecond laser pulse ablation on the single-mode fiber core. Then, FPI1 and another single-mode fiber are inserted into a quartz capillary from both sides to form FPI2. By adjusting the cavity length of FPI2, the cascaded FPI1 and FPI2 can form a harmonic Vernier effect sensor. Due to FPI1 being a cantilever beam, it is not subjected to axial strain. The strain of the sensor acts on a longer capillary, resulting in an extension of the effective length of the strain and a many fold increase in the strain sensitivity of the sensor. Due to the compact cascading of FPI1 and FPI2, this strain sensor has a very small structural size. The sensor average strain sensitivity obtained from the experiment reached 260.05 pm/με. Due to the extremely high axial strain sensitivity of this strain sensor, adhering it to the magnetostrictive material results in the average MF sensitivity of 6.82 nm/mT, and the minimum MF intensity detected by the MF sensor is 0.1 mT. The temperature crosstalk of the MF sensor is 0.3 mT/°C.

An Ultrasensitive Perovskite Single‐Model Plasmonic Strain Sensor Based on Piezoelectric Effect

AbstractInterest in flexible photonics has been motivated by the development of artificial smart skins. In particular, coupling of photonics and mechanics can offer opportunities to realize ultrasensitive strain sensor, however, low‐cost fabrication of flexible sensing device with desired photonic functionality remains a challenge. Hereby, the study reports an ultrasensitive strain‐gauge sensor based on the poly(ethylenenaphthalate (PEN))/monocrystal Au/MgF2/CsPbBr3 nanorod/Al2O3/polyacrylonitrile (in short P/mAu/M/CPB@Al2O3@PAN), which are sensitive to nanoscale structure alterations of PEN substrate via the stress response of the single‐mode laser based on the piezoelectric‐effect. Wherein a low‐threshold single‐mode lasing (Pth ≈ 170 nJ cm−2) is achieved through coating Al2O3 on the CsPbBr3 nanorod, producing the higher quality factor (Q ≈ 1637) to guarantee a much higher sensitivity in sensing application. Reversible spectral regulating of ≈3 nm in single‐mode‐lasing wavelength, with a subnanometre scale resolution <0.4 nm and the wavelength sensitivity (Sλ) as high as 160 nm RIU−1, is validated in response to applied strain ranging from −1.31% to 1.31%. This work not only represents essential progress in construction of ultrasensitive and cost‐effective flexible photonic sensor, but also lays the foundation for the potential application in smart photonic skins.

Ag–thiolate interactions to enable an ultrasensitive and stretchable MXene strain sensor with high temporospatial resolution

High-sensitivity strain sensing elements with a wide strain range, fast response, high stability, and small sensing areas are desirable for constructing strain sensor arrays with high temporospatial resolution. However, current strain sensors rely on crack-based conductive materials having an inherent tradeoff between their sensing area and performance. Here, we present a molecular-level crack modulation strategy in which we use layer-by-layer assembly to introduce strong, dynamic, and reversible coordination bonds in an MXene and silver nanowire-matrixed conductive film. We use this approach to fabricate a crack-based stretchable strain sensor with a very small sensing area (0.25 mm2). It also exhibits an ultrawide working strain range (0.001–37%), high sensitivity (gauge factor ~500 at 0.001% and >150,000 at 35%), fast response time, low hysteresis, and excellent long-term stability. Based on this high-performance sensing element and facile assembly process, a stretchable strain sensor array with a device density of 100 sensors per cm2 is realized. We demonstrate the practical use of the high-density strain sensor array as a multichannel pulse sensing system for monitoring pulses in terms of their spatiotemporal resolution.

Ultra-sensitive strain sensor with film-nanowire double layers for health monitoring and smart clothing

Flexible wearable strain sensors are becoming increasingly popular due to their ability to monitor physiological signals and to detect motion in a wide range of applications. However, the development of strain sensors with high sensitivity and wide sensing range remains a challenge. Herein, a film-nanowire double sensoring layer structure (FNDLS) crack strain sensor with high sensitivity, wide strain range and fast response is proposed. The FNDLS with hierarchical synergistic are integrated onto fabrics using a heat pressing process. The FNDLS has a very low initial resistance and a high density of channel cracks to have the high sensitivity of the strain sensor and to extend the strain range of the strain sensor through the synergistic bridging effect of the AgNWs. Due to this structure, the sensitivity of the sensor can reach 70945, the strain range can reach about 40 %, and response time is less than 129 ms. Furthermore, the sensor demonstrates exceptional cycling stability and favourable frequency characteristics. Its superior performance makes it suitable for monitoring pulse waves and detecting motion through smart clothing.

Ultrasensitive, Highly Stable, and Stretchable Strain Sensor Using Gated Liquid Metal Channel

AbstractDeveloping stretchable strain sensors with high sensitivity and stability is crucial for various applications such as prosthetic hands, human health monitoring, and human‐machine interactions. However, achieving these qualities simultaneously remains challenging. Here, an inherently stretchable strain sensor is presented that integrates ultrahigh sensitivity and robust stability, enabling stretch, press, or bend sensing capabilities. This sensor employs a softer elastomeric channel filled with liquid metal (LM) as the conductive path. A stiffer elastomer convex integrated into the channel serves as a strain‐manipulated gate, controlling opening gap of electrical current flow path. During deformation, the softer elastomer undergoes cross sectional reduction due to the Poisson effect, while the stiffer convex gate retains its geometry. This heterogeneous deformation behavior leads to significant contraction or closure of the LM channel, resulting in increased resistance and a remarkable enhancement in sensitivity by more than two orders of magnitude. The all‐soft design maintains exceptional stability even under extended or repetitive substantial deformations. With the ability to monitor subtle and large human body movements, detect grip actions of soft grippers reliably, and monitor the gradual and extended growth process of plants, this sensor holds significant potential for advancements in flexible electronics.

Multifunctional electronic skins for ultra-sensitive strain, temperature, humidity sensing, and energy harvesting

Though gaining increasing attention in various portable and wireless electronic devices and sensors, flexible gels used in strain sensors and triboelectric nanogenerators (TENGs) still suffer from inferior mechanical properties and lack long-term stability. Herein, multifunctional electronic skins (e-skin) from oriented 2D nanosheets enhanced eutectogel were facilely fabricated via a one-step curing strategy with excellent transparency (96%), superb elasticity (1613%), toughness (17.22 MPa). Moreover, the multifunctional e-skin also exhibits temperature and humidity sensibility. Notably, the as-assembled TENG e-skin exhibits high and stable electrical output performances, including an open-circuit voltage of 224 V, short-circuit current of 7.1 μA, and short-circuit charge of 640 nC. Meanwhile, the TENG can easily light up 130 LEDs, charge capacitors to drive a calculator, and sustain a long service life (120 days). Furthermore, it can serve as a self-powered biomechanical sensor to realize the real-time monitoring of various human motions, showing application potentials in wearable electronics, human health management, and energy harvesting systems.