High-sensitivity Strain Sensor Research Articles

Flexible and self-healing tannic acid-Fe3O4@MXene-composited dual network hydrogel multifunctional strain sensor

In light of the exponential growth of flexible human-computer interactions and telecommunications, it is becoming increasingly important to develop a high-sensitivity strain sensor to monitor human movement. Herein, the biocompatible, adhesive, and flexible Tannic acid-Fe3O4@MXene-poly(methacryloxyethyl sulfobetaine/acrylamide) (TFM) hydrogel has been prepared to realize the dual-functional applications in strain sensitive sensor and electromagnetic interference (EMI) shielding. The polymer network and 2D conductive filler MXene together construct the conductive network inside the hydrogel. The interpenetrating network and hydrogen bond between poly(acrylamide) and poly(methacryloxyethyl sulfobetaine) chain enhance the mechanical property of hydrogel, which is also improved by the complexation between Fe3O4 and the catechol groups of tannic acid. Benefiting from the excellent electrical conductivity (∼1.33 S/m) and mechanical property of the TFM hydrogels, the strain sensor displays compressive strain (∼77.6 %) and elongation (∼308.5 %), adhesion (∼16 kPa), compression sensitivity (∼42.6 Pa−1), gauge factor (GF = 2.38), and cyclic stability (∼50 cycles). TFM hydrogels can monitor strain distribution sensing, pulse beating and human movement detection. Moreover, the TFM hydrogel exhibits an absorption-predominant EMI shielding performance with an effective value of ∼25.2 dB. This work provides a new inspiration for the development of multifunctional hydrogels in the fields of artificial intelligence, human-computer interaction, and EMI shielding technology.

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.

High-sensitivity strain sensor based on an asymmetric tapered air microbubble Fabry-Pérot interferometer with an ultrathin wall

A Fabry-Pérot interferometer (FPI) with an asymmetric tapered structure and air microbubble with an ultrathin wall is designed for high-sensitivity strain measurement. The sensor contains an air microbubble formed by two single-mode fibers (SMF) prepared by fusion splicer arc discharge, and a taper is applied to one side of the air microbubble with a wall thickness of 3.6 µm. In this unique asymmetric structure, the microbubble is more easily deformed under stress, and the strain sensitivity of the sensor is up to 15.89 pm/µɛ as evidenced by experiments.The temperature sensitivity and cross-sensitivity of the sensor are 1.09 pm/°C and 0.069 µɛ/°C in the temperature range of 25-200°C, respectively, thus reducing the measurement error arising from temperature variations. The sensor has notable virtues such as high strain sensitivity, low-temperature sensitivity, low-temperature cross-sensitivity, simple and safe process preparation, and low cost. Experiments confirm that the sensor has good stability and repeatability, and it has high commercial potential, especially strain measurements in complex environments.

In-situ forming ultra-mechanically sensitive materials for high-sensitivity stretchable fiber strain sensors.

Fiber electronics with flexible and weavable features can be easily integrated into textiles for wearable applications. However, due to small sizes and curved surfaces of fiber materials, it remains challenging to load robust active layers, thus hindering production of high-sensitivity fiber strain sensors. Herein, functional sensing materials are firmly anchored on the fiber surface in-situ through a hydrolytic condensation process. The anchoring sensing layer with robust interfacial adhesion is ultra-mechanically sensitive, which significantly improves the sensitivity of strain sensors due to the easy generation of microcracks during stretching. The resulting stretchable fiber sensors simultaneously possess an ultra-low strain detection limit of 0.05%, a high stretchability of 100%, and a high gauge factor of 433.6, giving 254-folds enhancement in sensitivity. Additionally, these fiber sensors are soft and lightweight, enabling them to be attached onto skin or woven into clothes for recording physiological signals, e.g. pulse wave velocity has been effectively obtained by them. As a demonstration, a fiber sensor-based wearable smart healthcare system is designed to monitor and transmit health status for timely intervention. This work presents an effective strategy for developing high-performance fiber strain sensors as well as other stretchable electronic devices.

Collaborative Deformation Modified Hinge-Linkage Unit Model for Optimal Design of High-Sensitivity Optical Fiber Strain Sensor

Collaborative Deformation Modified Hinge-Linkage Unit Model for Optimal Design of High-Sensitivity Optical Fiber Strain Sensor

High-Sensitivity Strain Sensor With Antiresonance Suppression Based on the Vernier Effect

High-Sensitivity Strain Sensor With Antiresonance Suppression Based on the Vernier Effect

Comparative analysis for strain response and life monitoring of composite using carbon-based nanosensors

Sensing technology based on carbon nanomaterials has become a very promising technology in the field of composite health monitoring, which requires high-sensitivity piezoresistive strain sensors to serve. In this study, two different carbon nano-sensors were used. Based on the traditional carbon nano-paper sensor, a flexible printed circuit and a polysulfone membrane were added to ensure the stability and sensitivity of the sensor. The conductive mechanism of adjacent carbon nanotubes (CNT) was analyzed. The electrical network model inside the carbon nanosensor was established, and its working mechanism during loading and unloading was described. The research mainly adopts three-point bending experiment. The deformation and failure of composite laminates containing two kinds of sensors under load experience low strain and high strain cyclic loading. Both sensors have the same response and stability as the load growth trend. Experiments show that the CNT-Paper sensor is suitable for long-term health monitoring of composite materials. The carbon nanotube-ultrafiltration membrane (CNT-UM) sensor is more sensitive to the cyclic monitoring of small strain.

A high-sensitivity strain sensor based on the core-offset fiber with a micro air bubble

A highly sensitive optic-fiber strain sensor based on the air-microbubble Fabry–Perot interferometer (FPI) formed in a core-offset tapered fiber is proposed. By drawing tapers on the staggered spliced single-mode fibers, micro air bubbles with an average wall thickness of 2.6 μm are formed. The experimental results show that the sensor has a high strain sensitivity of 17.24 pm/με and good linear response in the range of 0–1500 με. A numerical simulation model is developed to study the axial strain response, and the results show that the core-offset structure increases the strain sensitivity by 46 %. In addition, the sensor has a temperature sensitivity of 3.43 pm/°C and a cross-sensitivity with strain as low as 0.199 με/°C over the range of 50–350 °C.

Development of a High-Sensitivity and Adjustable FBG Strain Sensor for Structural Monitoring

In this paper, a new fiber Bragg grating (FBG) strain sensor with adjustable sensitivity is invented. The sensitivity adjustment, strain sensing, and temperature compensation principles of the sensor and the corresponding formulae are developed. The prototype sensor specimen is developed, and a series of tests are performed to investigate its strain sensitivity and temperature compensation characteristics. The results show that the strain sensitivity of the sensor can be adjusted effectively by the correspondent L/LFBG parameter, with an acceptable discrepancy within ±5% of the theoretical value. The linearity, repeatability, and hysteresis were analyzed, and the errors were 0.98%, 1.15%, and 0.09%, respectively, with excellent performance. When the temperature difference was 20°C, through temperature compensation calibration, the error between the monitored strain and the actual strain was within 5% after temperature compensation correction, showing that this new type of FBG strain sensor can meet the strain monitoring needs of various engineering structures and provide reliable data acquisition.

High-Saline-Enabled Hydrophobic Homogeneous Cross-Linking for Extremely Soft, Tough, and Stretchable Conductive Hydrogels as High-Sensitive Strain Sensors.

Design of admirable conductive hydrogels combining robust toughness, soft flexibility, desirable conductivity, and freezing resistance remains daunting challenges for meeting the customized and critical demands of flexible and wearable electronics. Herein, a promising and facile strategy to prepare hydrogels tailored to these anticipated demands is proposed, which is prepared in one step by homogeneous cross-linking of acrylamide using hydrophobic divinylbenzene stabilized by micelles under saturated high-saline solutions. The influence of high-saline environments on the hydrogel topology and mechanical performance is investigated. The high-saline environments suppress the size of hydrophobic cross-linkers in micelles during hydrogel polymerization, which weaken the dynamic hydrophobic associations to soften the hydrogels. Nevertheless, the homogeneous cross-linked networks ensure antifracture during ultralarge deformations. The obtained hydrogels show special mechanical performance combining extremely soft deformability and antifracture features (Young's modulus, 5 kPa; stretchability, 10200%; toughness, 134 kJ m-2; and excellent anticrack propagation). The saturated-saline environments also endow the hydrogels with desirable ion conductivity (106 mS cm-1) and freezing resistance (<20 °C). These comprehensive properties of the obtained hydrogels are quite suitable for flexible electronic applications, which is demonstrated by the high sensitivity and durability of the derived strain sensors.

High-sensitivity fiber SPR strain sensor based on n-type structure.

At present, fiber strain sensors are mainly of the grating type and interference type, while there is relatively little research on fiber surface plasmon resonance (SPR) strain sensors. In this Letter, we propose a highly sensitive fiber SPR strain sensor based on an n-type structure. The strain changes the shape of the fiber n-type structure, causing the transmission mode of light in the fiber to change, thereby changing the SPR incidence angle and causing the SPR resonance valley wavelength to shift, achieving highly sensitive SPR strain sensing. The test results indicate that the strain sensing sensitivity of the proposed sensor reaches 21.33 pm/µε, and two n-type structures are connected in series to obtain a double n-type structure, further enhancing the strain sensing sensitivity to 33.44 pm/µε. This fiber strain sensor has advantages of high sensitivity, low temperature cross talk, strong structural stability, and low production cost, and is expected to become a new solution for wearable intelligent monitoring equipment and strain sensors in the aerospace field.

A high-sensitivity wearable flexible strain sensor based on three-dimensional twist-like network structure

With the rapid development of the flexible electronics field, flexible pressure sensors are widely used inwearable devices, medical monitoring and other fields. However, it is still a huge challenge to design a sensor with highsensitivity, low cost and a simple manufacturing process. In this work, we report a flexible strain sensor based on discarded mask straps (MS) with a unique three-dimensional (3D) twist-like network structure. Multi-walled carbon nanotubes (MWCNTs)/carbon nanoparticles (CN)/MS composites were prepared by a simple dip-drying method and encapsulated using a medical Polyurethane (PU) film. It is founded that the fabricated MWCNTs/CN/MS/PU flexible strain sensor (MCMP-FSS) exhibits a high gauge factor (GF) of 13,928 and advanced performance with a large sensing range of 0%–72%. Moreover, good water-repellent harmony and various types of stimuli over 1000 cycles were obtained for the MCMP-FSS. Benefiting from the unique 3D twist-like network structure and the MWCNTs/CN synergistic conductive network, MCMP-FSS also has broad application prospects in the fields of human motion detection, encrypted communication, and natural human-robot interaction.

Self-strengthening and conductive cellulose composite hydrogel for high sensitivity strain sensor and flexible triboelectric nanogenerator

Triboelectric nanogenerators (TENGs) as promising energy harvesting devices have gained increasing attention. However, the fabrication of TENG simultaneously meets the requirements of green start feedstock, flexible, stretchable, and environmentally friendly remains challenging. Herein, the hydroxyethyl cellulose macromonomer (HECM) simultaneously bearing acrylate and hydroxyl groups was first synthesized and used as a crosslinker to prepare the chemically and physically dual-crosslinked cellulose composite hydrogel for an electrode material of stretchable TENG. Meanwhile, the in-situ polymerization of pyrrole endowed the hydrogel with satisfactory conductivity of 0.40 S/m. More impressively, the synergies of the cellulose rigid skeleton and the construction of the dual-crosslinking network significantly improved the mechanical toughness, and the hydrogel exhibited excellent self-strengthening through cyclic compression mechanical training, the self-strengthening efficiency reached 124.7 % after 10 compression cycles. Given these features, the hydrogel was used as wearable strain sensors with extremely high sensitivity (GF = 3.95) for real-time monitoring human motions. Additionally, the hydrogel showed practical applications in stretchable H-TENG for converting mechanical energy into electric energy to light LEDs and power a digital watch, and in self-powered wearable sensors to distinguish human motions and English letters. This work provided a promising strategy for fabricating sustainable, eco-friendly energy harvesting and self-powered electronic devices.

Highly sensitive strain sensor based on tapered few-mode fiber.

A high sensitivity strain sensor using a sandwich structure of "single mode fiber (SMF)-few mode fiber (FMF)-single mode fiber (SMF)" was proposed and experimentally validated. The designed sensor is achieved by splicing a segment of FMF between two segments of SMFs, and then using a fiber optic fusion tapering machine to double the length of FMF. Introducing tapered optical fibers into the structure to excite more evanescent waves improves the sensitivity of the sensor to the surrounding environment. In addition, due to the fact that the FMF is tapered into a very fine shape, the tensile stress applied to the FMF will increase. Therefore, conical FMF has excellent stress concentration ability, which is easily deformed under stress, thus achieving a high strain sensitivity of -23.9 pm/με. Finally, a cascaded FBG was used to compensate for the temperature cross-sensitivity of the sensor. This strain sensor with an extremely simple structure and high sensitivity has wide application value in the industry.

High-sensitivity strain sensor with micron-scale imitation dumbbell structure based on differential temperature self-compensation

A micron-sized dumbbell-like -MZI structure has been developed using hydroxide flame melt taper and arc fusion discharge, with the dumbbell rod region prepared by melt taper drawing and the dumbbell sheet region prepared by arc fusion discharge. This structure has a sensitive light intensity response in the sensing field due to a double-order mode-field coupled excitation region. The geometrical parameters of the dumbbell-like system are optimized theoretically, and the feasibility of the microstructure to achieve high strain sensing sensitivity is analyzed. Experimental results show that the microstructure has a high strain sensing sensitivity of ∼ 0.074 dB/µε and a consistent temperature sensing sensitivity over the entire monitoring wavelength range. Therefore, a light intensity-dependent temperature self-compensation calculation is proposed to achieve a uniform light intensity-strain response for each characteristic peak in the monitored wavelength domain. Since the device has a significant advantage in light intensity modulation and is not affected by polarization light perturbations, it can be used as an alternative light intensity modulation device in optical communication networks and laser research. It can also be used as a probe for medical diagnostic testing based on its enhanced evanescent field properties.

High-sensitivity interferometric high-temperature strain sensor based on optical harmonic vernier effect

We present a fiber optic vernier harmonic sensor for simultaneous detection of temperature and strain in high temperature conditions based on a parallel dual fiber Fabry-Perot interferometers (FPI). Two air-cavity FPIs were assembled from SMF, MMF and a hollow silica tube (HST). A fiber Bragg grating (FBG) is inscribed in one of the arms of the Fabry-Perot interferometers (FPIs) for temperature compensation. Based on the fiber optic vernier harmonic effect, the strain sensitivity of the sensor is further increased to 178.75 pm/µε, with a good linear response to strain and temperature in the range of 24 ℃-900 ℃. And the fabrication is straightforward and economy. It is a potential tool for micro strain measurements under extreme high temperature conditions.

Highly stretchable strain sensors based on Marangoni self-assemblies of graphene and its hybrids with other 2D materials

Graphene and other two-dimensional materials (2DMs) have been shown to be promising candidates for the development of flexible and highly-sensitive strain sensors. However, the successful implementation of 2DMs in practical applications is slowed down by complex processing and still low sensitivity. Here, we report on a novel development of strain sensors based on Marangoni self-assemblies of graphene and of its hybrids with other 2DMs that can both withstand very large deformation and exhibit highly sensitive piezoresistive behaviour. By exploiting the Marangoni effect, reference films of self-assembled reduced graphene oxide (RGO) are first optimized, and the electromechanical behaviour has been assessed after deposition onto different elastomers demonstrating the potential of producing strain sensors suitable for different fields of application. Hybrid networks have been then prepared by adding hexagonal boron nitride (hBN) and fluorinated graphene (FGr) to the RGO dispersion. The hybrid integration of 2D materials is demonstrated to become a potential solution to increase substantially the sensitivity of the produced resistive strain sensors without compromising the mechanical integrity of the film. In fact, for large quasi-static deformations, a range of gauge factor values up to 2000 were demonstrated, while retaining a stable performance under cyclic deformations.

Experimental demonstration of offset-induced sensitivity enhancement in SMS-based temperature and strain sensing

A simple, inexpensive, and high-sensitivity temperature and strain sensor based on a single-mode–multimode–single-mode (SMS) structure with core offset is developed and experimentally characterized. This sensor does not require specialty fibers and can be fabricated using a standard fiber fusion splicer. The dependencies of the temperature and strain sensitivities on the core-offset amplitudes at the input and output single-mode/multimode fiber boundaries are investigated. The results indicate that the maximum temperature and strain sensitivities are two times and eight times higher than those of the standard SMS structure, respectively. The limit of the sensitivity enhancement by core offset is also revealed.

Multifunctional two-way shape memory RGO/ethylene-vinyl acetate composite yarns for electro-driven actuators and high sensitivity strain sensors

Shape memory polymer fibers (SMPFs) coated with conductive layers are attracting increasing attention in soft robots and wearable electronics. However, the thickness and poor stretchability of the conductive layer hinder its applications. Here, the multifunctional two-way shape memory reduced graphene oxide (RGO)/ethylene–vinyl acetate copolymer (EVA) composite yarn is designed following the “swelling-ultrasonicating” and one-step twisting procedures. These RGO/EVA composite fiber conductive paths connected with each other by constructing the helical conductive network. The RGO/EVA composite yarn presents excellent electro-thermal conversion performance and outstanding load-bearing capability, enabling controlled electro-driven reversible strain (more than 10% reversible strain) and high energy density (72.5 J/kg). Additionally, the composite yarn has great stretchability (130% strain), high strain sensing sensitivity (gauge factor of 7.3), large linear working range (up to 70% strain). This work provides an innovative manufacturing strategy for the RGO/EVA composite yarn with two-way shape memory, electro-driven actuation, and strain sensing performance.

High-Sensitivity Composite Dual-Network Hydrogel Strain Sensor and Its Application in Intelligent Recognition and Motion Monitoring

Flexible electronic sensors are attracting more and more attention because of their outstanding flexibility and foldability. Based on this background, a composite hydrogel with excellent flexibility, good stability, and high sensitivity is prepared in this work. This high-performance hydrogel is composed of polyacrylamide, sodium alginate, MXene, and PEDOT:PSS through dynamic supramolecular cross-linking. The electrical conductivity is significantly enhanced by the addition of the conductive polymer PEDOT:PSS and MXene. Hydrogel conductivity increased by 150% with the addition of conductive materials at the same tensile strain. It exhibits high sensitivity (GF = 1.99) and excellent linearity over a wide operating range of 1000% of strain, which ensures the detection performance of the hydrogel sensor under large strain conditions. In addition, it has excellent repeatability (600 cycles) and fast response/recovery times (0.624 s/0.912 s). Due to this excellent performance, it was made into a smart sensor to explore its application in smart electronic skin. The hydrogel sensor and data acquisition module were integrated for real-time monitoring of pressure. We combine it with deep learning algorithms to provide a new solution for human motion recognition, such as joint flexion, facial expression change, health monitoring, and handwriting recognition.