High Gauge Factor Research Articles

Superhydrophobic, Multifunctional, and Mechanically Durable Carbon Aerogel Composites for High-Performance Underwater Piezoresistive Sensing.

Carbon aerogel piezoresistive sensors (CAPSs), owing to their good thermal stability, self-constructed conductive network, and fast response to pressure, have attracted extensive attention in the field of flexible and wearable electronics in recent years. However, it is still a great challenge for CAPSs to monitor subtle deformations and achieve high-performance underwater piezoresistive sensing. Herein, a superhydrophobic and electrically conductive carbon aerogel composite (CAC) was fabricated by the combination of fluorination of carbon aerogels and decoration of fluorinated halloysite nanotubes (HNTs). Due to the exceptional light absorption and excellent photothermal conversion performance, CAC has a fast and accurate response to temperature with a high-temperature coefficient of resistance (TCR) of -1.06%/°C. The resistance of CAC exhibits a linear response toward compressive strain up to 80% with a high gauge factor of -1.24. Significantly, the CAC sensor can effectively detect tiny deformations, thanks to its excellent waterproof performance, and it enables stable output of sensing signals in an underwater environment. This work provides new insights into the development of superhydrophobic, multifunctional, and mechanically durable piezoresistive sensors with potential applications in underwater flexible electronics.

E-waste driven eco-friendly highly sensitive wearable capacitive sensors for physical activity monitoring and sign language recognition

Owing to the continual and rapid advancement in technology, there has been a significant surge in electronic waste (e-waste) in recent decades, resulting in a harmful impact on our environment. Due to the growing demand for battery-powered devices, non-rechargeable batteries are a significant source of e-waste. This study describes fabricating a paper-based graphite strain sensor that is eco-friendly, inexpensive, biodegradable, and sensitive to the applied strain. Readily accessible materials are employed to design and fabricate MIDC strain sensors. The Modified Interdigital Capacitor (MIDC) structure is formed on basic printing paper, and the conductive substance made with the ink of a gel pen and graphite from a drained dry cell is painted on the paper and used as electrode material. The suggested sensor has a high gauge factor value of 1998.578 and fast response and recovery time of 112 ms and 100 ms, respectively. The proposed prototype has also been utilized to inspect fitness exercises and physical activities on the human body, inspiring the potential for its integration into wearable systems for various applications. Reliable detection and differentiation of finger positions are achieved, highlighting the sensor's potential for more advanced sign language applications. It’s a good option to integrate the suggested strain sensor in wearable systems, such as telemedicine systems, electromechanical detection, healthcare, and physical activity monitoring of humans.

Robust biomimetic strain sensor based on butterfly wing-derived skeleton structure

A biomimetic strain sensor was designed and constructed based on Ir nanoparticles-modified multi-wall carbon nanotubes (Ir NPs@MWCNTs) and parallel Pt layer/dragon skin with carbonized butterfly wing patterns. This sensor exhibits high gauge factor (∼515.4), extensive tensile range (0%–96%), and swift response (∼300 ms), especially remarkable stability up to 60 000 cycles. The work mechanism has been proposed based on the experimental test and finite-element method. Some important applications such as human motion and micro-expression recognition have been confirmed using 3 × 3 flexible biomimetic sensor array.

Unique framework effect induced by uniform silk fibroin dynamic nanospheres enables multiscale hydrogel with outstanding elastic resilience and strain sensing performance

It is a significant challenge to obtain hydrogels simultaneously with low tensile energy dissipation, high compressive resilience and long durability. Herein, the uniform dynamic nanospheres (Sil-4H0.75) derived from 4-Hydroxybutyl acrylate glycidyl ether grafted silk fibroin is designed to overcome this issue. Due to its uniform and dynamic characteristic, Sil-4H0.75 could endow hydrogel with homogeneous multiscale structure and produce unique framework effect. Thus, transparent Sil-4H0.75 crosslinked acrylamide hydrogel doped with Ag nanowires APS3.75%/AgNW0.1 exhibits a high stretchability (1260 %) and outstanding elastic resilience. The tensile energy dissipation ratio maintains a low value of 9 % across a wide 800 % strain range. A high compression resilience ratio of 92.2 % is kept after ten compression cycles under 90 % compressive strain. The orderly AgNWs motion guided by framework effect also make it be used as both tensile and compressive sensors and exhibits high gauge factor of 7.35, outstanding compression sensitivity of 30.379 kPa−1 and excellent durability (up to 2000 cycles). The detection or other applications based on both two sensing modes are also demonstrated. In a word, this work affords a general strategy to achieve high-performance hydrogel based on uniform dynamic nanospheres which exhibits great potential in the applications of flexible wearable strain sensors.

Printing highly sensitive strain gauges with polymer-derived ceramics and In2O3 composites for high-temperature applications

The development of high-temperature thick film strain gauges (TFSGs) that offer both durability and a high gauge factor (GF) remains a formidable challenge. This study integrates polymer-derived ceramic technology with filler techniques to introduce the SiCNO/In2O3 TFSG. The proposed TFSG demonstrates a stable strain response and exceptional thermal stability, enabling its application at temperatures up to 1100°C. Notably, the SiCNO/In2O3 TFSG exhibits minimal resistance drift of 0.31%/h at 1100°C, and an impressive GF of 10.94 at 1000°C. These advancements underscore its significant potential for applications requiring precise strain monitoring under harsh thermal conditions, such as propulsion systems and industrial processes.

Cathodic arc deposited tetrahedral amorphous carbon as thin film contact pressure sensing material

Tetrahedral amorphous carbon (ta-C) film was deposited using the filtered pulsed cathodic arc deposition method. The ta-C structures deposited on high velocity oxygen fuel thermally sprayed steel beam substrates were investigated for piezoresistive properties under direct contact pressing. A load of up to 1.4 GPa was applied with point contact, with no detrimental influence on the material. The linear response for the strain applied homogeneously on the whole film surface and on the local portion of the film surface under a cylindrical contact was observed. A high gauge factor of the measured system of 305 was measured, showing the potential of the material as a good candidate for sensing applications on direct contact measurement devices.

Strain detection based on magnetic domain wall motion in amorphous FeSiBNb thin film

The strain dependence of the pulse voltage induced in a pickup coil originating from the domain wall motion in an amorphous FeSiBNb thin film was investigated. No significant change in the peak pulse voltage was observed when tensile strain was applied to the thin film, whereas the peak pulse voltage changed steeply when compressive strain was applied. In addition, strain susceptibility could be controlled via appropriate annealing. Evaluation of the strain gauge comprising the amorphous FeSiBNb thin film, a pickup coil, an electrical circuit (which converts the pulse voltage into direct current voltage), and a Helmholtz coil revealed that strain gauge has a notably high gauge factor of approximately 37,500.

Machine Learning-Assisted Gesture Sensor Made with Graphene/Carbon Nanotubes for Sign Language Recognition.

Gesture sensors are essential to collect human movements for human-computer interfaces, but their application is normally hampered by the difficulties in achieving high sensitivity and an ultrawide response range simultaneously. In this article, inspired by the spider silk structure in nature, a novel gesture sensor with a core-shell structure is proposed. The sensor offers a high gauge factor of up to 340 and a wide response range of 60%. Moreover, the sensor combining with a deep learning technique creates a system for precise gesture recognition. The system demonstrated an impressive 99% accuracy in single gesture recognition tests. Meanwhile, by using the sliding window technology and large language model, a high performance of 97% accuracy is achieved in continuous sentence recognition. In summary, the proposed high-performance sensor significantly improves the sensitivity and response range of the gesture recognition sensor. Meanwhile, the neural network technology is combined to further improve the way of daily communication by sign language users.

Comprehensive Study of Mechanical, Electrical and Biological Properties of Conductive Polymer Composites for Medical Applications through Additive Manufacturing.

Conductive polymer composites are commonly present in flexible electrodes for neural interfaces, implantable sensors, and aerospace applications. Fused filament fabrication (FFF) is a widely used additive manufacturing technology, where conductive filaments frequently contain carbon-based fillers. In this study, the static and dynamic mechanical properties and the electrical properties (resistance, signal transmission, resistance measurements during cyclic tensile, bending and temperature tests) were investigated for polylactic acid (PLA)-based, acrylonitrile butadiene styrene (ABS)-based, thermoplastic polyurethane (TPU)-based, and polyamide (PA)-based conductive filaments with carbon-based additives. Scanning electron microscopy (SEM) was implemented to evaluate the results. Cytotoxicity measurements were performed. The conductive ABS specimens have a high gauge factor between 0.2% and 1.0% strain. All tested materials, except the PA-based conductive composite, are suitable for low-voltage applications such as 3D-printed EEG and EMG sensors. ABS-based and TPU-based conductive composites are promising raw materials suitable for temperature measuring and medical applications.

Sodium alginate supramolecular nanofibers in synergy with surface crack engineering to prepare tough and highly sensitive hydrogels

Soft and wet hydrogels often struggle to achieve both toughness and high sensitivity simultaneously, limiting their usefulness in flexible devices. To tackle this challenge, we devised a strategy that combines supramolecular sodium alginate nanofibers, utilizing Zr4+ as physical crosslinkers, with surface crack engineering via the micro-phase separation of polyaniline, to create a physically and chemically dual crosslinked polyacrylamide (PAM)/sodium alginate (SA)/polyaniline (PANI) hydrogel with exceptional toughness and high sensitivity. Owing to the supramolecular sodium alginate nanofibers, the dual crosslinked hydrogel exhibited a tensile strength of 0.391 MPa, an elongation at break of 568.9 %, and a toughness of 1.020 MJ/m3. The in-situ polymerized polyaniline layer, confined within the dense network, introduced micro-cracks onto the hydrogel surface, resulting in a high gauge factor of 11.4 for the fabricated hydrogel. Furthermore, integrating this hydrogel into a triboelectric nanogenerator transformed it into self-powered sensors capable of detecting external forces and generating various signals without power supply. These findings suggest that the developed hydrogel held great potential in diverse fields, including human motion detection, human-machine interaction, and wearable electronic devices.

Hierarchical polypyrrole@MXene (Ti3C2TX) fiber strain sensors for wearable healthcare electronics

Flexible sensors are an important component of wearable medical electronics and hold considerable promise for research. Presently, stretchable strain sensors face two primary challenges: balancing the sensing range with sensitivity, and ensuring compatibility between conductivity and mechanical properties. Here, flexible sensing fibers with high gauge factor (GF) and wide monitoring range are reported based on a hierarchical structure composed of electrostatic adsorption principle and hydrogen bonding interactions. The hierarchical structure material consists of thermoplastic polyurethane (TPU), MXene, polypyrrole (PPy) and waterborne polyurethane (WPU). Among them, MXene (2D) and PPy (3D) are uniformly distributed on the surface of the MXene/TPU fiber (1D) to form a conductive and sensing pathway. This multi-dimensional combination approach enables the fiber sensor to have a high sensing range (0 ∼ 106 %) and high sensitivity (60 ∼ 3.23 × 106). In addition, the WPU acts as a protective layer, which not only reduces the damage to the sensing layer, but also improves the stretchability (>750 %) and modulus (∼12 MPa) of the sensor. Therefore, it can function as fiber sensor for monitoring not only human movement but also swelling in the legs of patients with varicose veins. The sensor also has a joule heating effect, as well as the potential to be integrated into fabrics, providing an important case for the construction of multifunctional flexible wearable medical electronics with practical applications.

Electromechanical response of multilayer graphene sheet/polypropylene nanocomposites and its relationship with the graphene sheet physicochemical properties

Abstract The mechanical, electrical, and piezoresistive responses of multilayer graphene sheet (GS)/polypropylene (PP) nanocomposites are investigated using four GSs of distinctive physicochemical properties. It is found that the morphology of the interconnected network of GS agglomerates at the mesoscale governs the mechanical, electrical, and electro-mechanical (piezoresistive) properties of the PP nanocomposites. The morphology of the mesoscale network of electroconductive fillers governs the effective properties of the nanocomposite. This network morphology strongly depends on the GS lateral size, dispersion, agglomeration, and, to a lesser extent, the specific surface area of the GSs. Within the range of lateral sizes investigated herein (1 - 21 m), larger GSs yields nanocomposites with higher electrical conductivity. On the other hand, GSs of moderate lateral size (~ 6.5 m) and specific surface area of ~ 141 m2/g render GS/PP nanocomposites with a more dispersed and more sparsely interconnected network. This better dispersed network with agglomerates of smaller dimensions is concomitant with improved stiffness and strength, and higher gauge factors (~ 18.2) for this GS/PP nanocomposites. Excellent capabilities for detection of human motion were proved for these nanocomposites.

Advancements in Ti3C2Tx MXene Stability: Synergistic Antioxidant Strategies and Their Impact on Long-Lasting Flexible Sensors.

Two-dimensional (2D) transition metal carbides (Ti3C2Tx MXene) have demonstrated substantial application potential across various fields, owing to their excellent metallic conductivity and solution processability. However, the rapid oxidation of Ti3C2Tx in aqueous environments, leading to a loss of stability within mere days, poses a significant obstacle for its practical applications. Herein, we introduce an antioxidant strategy that combines free radical scavenging with surface passivation, culminating in the design and synthesis of imidazolium-based ionic liquids (ILs) incorporating siloxane groups. By deploying a straightforward hydrolysis-addition reaction, we successfully fabricated IL-modified Ti3C2Tx materials (Ti3C2Tx-IL). The Ti3C2Tx -IL not only displayed exceptional conductivity exceeding 3.85 × 104 S/m and hydrophilic contact angles below 45° but also showcased its superior chemical stability and antioxidation mechanisms through various analyses, including visual color change experiments, spectroscopic and energy spectrum characterization, free radical scavenging tests, and density-functional-theory-based molecular simulations. Furthermore, when utilized as a conductive filler in the fabrication of a poly(vinyl alcohol)/nanocellulose fiber (PVA/CNF) composite hydrogel (PCMIL), the resultant sensors exhibited remarkable mechanical performance with up to 535% strain, 1.59 MPa strength, 4.35 MJ/m3 toughness, and a conductivity of 3.40 mS/cm, as well as a high sensitivity gauge factor of 3.3. Importantly, even after 45 days of storage, the PCMIL retained most of its functionalities, demonstrating superior performance in human-machine interaction applications compared to hydrogels made from unmodified Ti3C2Tx. This research establishes a robust antioxidant protection strategy for Ti3C2Tx, offering substantial technical reinforcement for its prospective applications in the realm of flexible electronics and sensing technologies.

Behavior of self-sensing masonry structures exposed to high temperatures and rehydration

High temperatures can compromise the structural integrity of structural masonry. Therefore, assessing the post-fire mechanical behavior is crucial for selecting suitable rehabilitation methods. Recent research has proposed the application of self-sensing cementitious composites for monitoring strains, stresses, and damage of structural masonry in room temperature. No previous research has been found on the self-sensing performance of fire-damaged masonry prisms exposed to elevated temperatures, with or without subsequent rehydration. Masonry prisms with integrated self-sensing joints and blocks were produced and exposed to different maximum temperature levels, followed or not by rehydration. Then, experimental tests for determination of compressive strength, modulus of elasticity, gauge factor (GF) and damage-detection performance were carried out. The exposure to 300 ºC caused a 7.4 % decrease in compressive strength and a 44.5 % reduction in elastic modulus. Rehydration methods had negligible effects in this case. After 600 ºC, substantial reductions of 42.2 % in compressive strength and 81.5 % in elastic modulus occurred. In this case, rehydration led to a 15.9 % increase in compressive strength and a 117.4 % increase in elastic modulus. Regardless of the exposure temperature, the predominant rupture mode initiated by vertical cracks originating at the block-mortar interfaces. After 300 ºC, slight GF increases occurred due to the thermal decomposition of hydrates of the cementitious matrix, while exposure to 600 ºC resulted in high GF increases due to partial oxidation of nanomaterials and substantial microcracking propagation. Post-fire curing improved the GF by sealing microcracks with nonconductive rehydration products and enhancing tunneling conduction mechanisms. The self-sensing prisms also demonstrated the ability for real-time damage detection and quantification, providing valuable predictive insights into the propagation of damage.

Polyvinyl alcohol/sodium alginate-based conductive hydrogels with in situ formed bimetallic zeolitic imidazolate frameworks towards soft electronics

Bimetallic zeolitic imidazolate frameworks (BZIFs) have received enormous attention due to their unique physi-chemical properties, but are rarely reported for electrically conductive hydrogel (ECH) applications arising from low intrinsic conductivity and poor dispersion. Herein, we propose an innovative strategy to prepare highly conductive and mechanically robust ECHs by in situ growing Ni/Co-BZIFs within the polyvinyl alcohol/sodium alginate dual network (PZPS). 2-methylimidazole (MeIM) ligands copolymerize with pyrrole monomers, enhancing the electrical conductivity; meanwhile, MeIM ligands act as anchor points for in-situ formation of BZIFs, effectively avoiding phase-to-phase interfacial resistance and ensuring a uniform distribution in the hydrogel network. Due to the synergism of Ni/Co-BZIFs, the PZPS hydrogel exhibits a high areal capacitance of 630.3 mF·cm−2 at a current density of 0.5 mA·cm−2, promising for flexible energy storage devices. In addition, PZPS shows excellent mechanical strength and toughness (with an ultimate tensile strength of 405.0 kPa and a toughness of 784.2 kJ·m−3 at an elongation at break of 474.0 %), a high gauge factor of up to 4.18 over an extremely wide stress range of 0–42 kPa when used as flexible wearable strain/pressure sensors. This study provides new insights to incorporating highly conductive and uniformly dispersed ZIFs into hydrogels for flexible wearable electronics.

Durable TPU/PDA/MXene Fiber‐Based Strain Sensors with High Strain Range and Sensitivity

AbstractWith the development of the ageing society, wearable strain sensors have great application prospects in the fields of health detection, artificial intelligence, and motion recognition. However, traditional forms of film‐like strain sensors suffer from low sensitivity, adhesion, and impermeability during use, which severely limit their practical applications. To overcome these problems, we propose a strategy to fabricate polyurethane/polydopamine/MXene (TPU/PDA/MXene) composite fibers by wet spinning. Furthermore, the outside is wrapped with (PDMS), giving mechanical strength and chemical resistance. Through a simple and low‐cost wet spinning process, TPU/PDA/MXene fibers are achieved in the preparation of flexible strain sensors, and they can be woven into various forms with good flexibility and comfort according to practical needs. The results indicated that the prepared flexible strain sensor exhibits a high gauge factor (GF) of 57.15 over a large strain range (300 %), which are superior to those of many fiber‐based sensors. Their application properties were also measured by attaching them to fingers, wrists and knees, showing high sensitivity, mechanical durability and chemical stability, and has great potential for wearable strain sensors and flexible strain sensors in complex environments.

Coaxially spinning spiral coils into concentric microtubes to synchronize motion and temperature sensing for stretchable and wearable device

Wearable electronical sensors with the combination of multi-mode sensing, stretchability and stability have long been in pursuit for various applications, such as the strain and temperature sensing for health assessment and disease diagnosis. To design endurable dual-mode sensor without signal interference, in this study, a coaxial wet spinning process were suggested to spin helical fibers into concentric double-layer microtubes to synchronize motion and temperature sensing with negligible signal interference. The inner helical fiber showed a high temperature-dependent ionic conductivity for the sensitivity of 5.76 % °C−1 and detection limit of 0.1 °C. Its helical geometry ensured large stretchability and minimal strain-induced interference. The outer coating shell could serve as the strain sensor with a high gauge factor of 11.36–1512 (up to 300 % strain) and response time of 120 ms. When filling the microtubes with polydimethylsiloxane, the multi-mode sensos could stay stable sensing abilities up to 104 stretching-release cycles. Thus, this study not only offers a coaxial spinning approach for production of stretchable multicomponent fibers, but also shows an unprecedented alternative of dual-mode sensor for healthcare, rehabilitation, and sleep monitoring.

Flexible high electrochemical active hydrogel for wearable sensors and supercapacitor electrolytes

With the rapid advancement of flexible, portable devices, hydrogel electrolytes have gained considerable attention as potential replacements for conventional liquid electrolytes. A hydrogel electrolyte was synthesised by cross-linking acrylic acid (AA), acrylamide (AM), carboxymethyl cellulose (CMC), and zinc sulphate (ZnSO4). The formation of hydrogen bonds and chelate interactions between the P(AA-co-AM) polymer, CMC, and ZnSO4 created a robust network, enhancing the mechanical properties of the hydrogel electrolytes. Notably, the hydrogel electrolyte containing 0.6 % CMC demonstrated superior mechanical strength (compression strength of 1.22 MPa, tensile stress of 230 kPa, tensile strain of 424 %, adhesion strength of 1.98 MPa on wood). Additionally, the CMC/P(AA-co-AM) hydrogels exhibited commendable electrical performance (38 mS/cm) and a high gauge factor (2.9), enabling the precise detection of physiological activity signals through resistance measurements. The unique network structure of the hydrogel electrolyte also ensured a stable bonding interface between the electrode and the electrolyte. After 2000 charge–discharge cycles, the supercapacitor maintained good capacitance characteristics, with a capacitance retention rate of 71.21 % and a stable Coulombic efficiency of 98.85 %, demonstrating excellent cyclic stability. This study introduces a novel methodology for fabricating multifunctional all-solid-state supercapacitors and suggests that the hydrogel can significantly advance the development of wearable energy storage devices.

Strong, tough, and freeze-tolerant all-natural cellulose-based ionic conductor enabled by multiscale cellulose networks

Soft ionic conductors are widely used in flexible electronics. However, the simultaneous enhancement of their mechanical properties and ionic conductivity remains challenging. This paper reports the successful development of a strong and tough cellulose-based ionic conductor with exceptional mechanical properties and high ionic conductivity by in situ dissolution and reorganization of the fiber matrix of filter paper to create a multiscale structure. The resulting ionic conductor exhibits a fracture strength of 14.13 MPa and a fracture energy of up to 2.84 MJ/m3, exceeding most reported ionic conductors. It also exhibits an impressive ionic conductivity of up to 76.3 mS/cm. Results of experiments on its use in a flexible quasi-solid-state zinc-hybrid supercapacitor show its remarkable features, such as a high capacity of 218 mAh/g, an energy density of 217 Wh/kg, and a power density of 17,520 W/kg. Furthermore, it exhibits excellent temperature resistance, working effectively even at −60 °C. In addition, by incorporating kirigami structures, we fabricated a strain sensor with the cellulose-based ionic conductor with a high gauge factor, as well as a piezoresistive sensor for handwriting recognition and a capacitance pressure sensor for force mapping with wide range and sensitivity. This study opens up new possibilities for fabricating flexible electronics with superior performance using sustainable and renewable resources.

Temperature-Tolerant Versatile Conductive Zwitterionic Nanocomposite Organohydrogel toward Multisensory Applications.

Conductive hydrogels (CHs) are emerging materials for next generation sensing systems in flexible electronics. However, the fabrication of competent CHs with excellent stretchability, adhesion, self-healing, photothermal conversion, multisensing, and environmental stability remains a huge challenge. Herein, a nanocomposite organohydrogel with the above features is constructed by in situ copolymerization of zwitterionic monomer and acrylamide in the existence of carboxylic cellulose nanofiber-carrying reduced graphene oxide (rGO) plus a solvent displacement strategy. The synergy of abundant dipole-dipole interactions and intermolecular hydrogen bonds enables the organohydrogel to exhibit high stretchability, strong adhesion, and good self-healing. The presence of glycerol weakens the formation of hydrogen bonds between water molecules, endowing the organohydrogel with excellent environmental stability (-40 to 60 °C) to adapt to different application scenarios. Importantly, the multimodal organohydrogel presents excellent sensing behavior, including a high gauge factor of 16.3 at strains of 400-1440% and a reliable thermal coefficient of resistance (-4.2 °C-1) over a wide temperature widow (-40 to 60 °C). Moreover, the organohydrogel displays a highly efficient and reliable photothermal conversion ability due to the favorable optical absorbing behavior of rGO. Notably, the organohydrogel can detect accurate human activities at ambient temperature, demonstrating potential applications in flexible intelligent electronics.