Strain Sensor Devices Research Articles

A garment-integrated textile stitch-based strain sensor device, IoT-Enabled for enhanced wearable sportswear applications

The field of wearable technology is undergoing a transformative shift with the integration of IoT-enabled, AI-assisted sensors into sportswear, bringing sophisticated performance analysis within reach for a broader audience. Despite advancements in stitch strain sensors, there is a significant research gap in developing high-performance, stable, and IoT-connected complete stitch strain wearable sensor systems. These advanced sensors are essential for enhancing wearable technology and meeting the growing demands for improved user experience and functionality. In this study by utilizing conductive sewing threads and innovative stitching techniques, we fabricated textile strain sensors that offer high sensitivity, flexibility, and durability. Extensive calibration tests revealed strong linear relationships between resistance and tensile strain, with highest sensor sensitivity (2.08 Ω/mm during loading and 2.72 Ω/mm during unloading). These sensors demonstrate reliable performance with minimal hysteresis, particularly in shorter lengths. The wearable sportswear device, tested in gym environments, demonstrated the sensor's capability to provide real-time feedback on knee flexing/bending and body movement during exercise. This functionality supports injury prevention and enhances workout efficiency. The sensor system is IoT-enabled, powered by an ESP8266 microcontroller, facilitating data transmission to the Thing Speak platform for advanced analysis and remote monitoring. This comprehensive approach not only advances wearable technology but also opens new avenues for remote health monitoring and smart e-textiles, contributing significantly to the fields of sports science and fitness technology.

Enhanced Performance of Epoxidized Natural Rubber Nanocomposites for Strain Sensor Application

In this study, the major objective was to investigate the mechanical and electrical properties, and strain sensibility of the carbon nanotube (CNT) filled epoxidized natural rubber (ENR) nanocomposite. The second filler, cellulose nanofibers (CNFs), at various proportions was incorporated into the CNT-filled ENR nanocomposites. The preparation of ENR nanocomposite was carried out using a latex mixing process. The CNT:CNF hybrid filler was pre-dispersed in deionized water before being added to the ENR latex. The ratios of CNTs to CNFs varied from 1:0 to 1:0.05, 1:0.5, 1:1, 1:1.25, and 1:1.5. Although the presence of CNFs enhanced the stiffness of the substance, its negative effect on the tensile strength was noted. From the evaluated electrical properties, the outcomes demonstrated that the presence of CNFs with suitable proportions can have a positive effect on the performance of the substance when used as a stain-sensitive substance. The electrical conductivity of the hybrid ENR nanocomposite initially increased with the increase of CNF proportion up to 0.5. Beyond this proportion, the conductivity declined gradually. Moreover, the CNT:CNF1:0.5 filled ENR nanocomposite had the highest recoverable piezoresistive property. From this finding, it can be inferred that the CNT:CNF1:0.5 filled ENR nanocomposite is suitable to be used as a strain sensor device.

Strain sensor based on polyurethane/carbon nanotube elastic conductive spiral yarn with high strain range and sensitivity

AbstractWearable flexible electronic strain sensor devices have gained significant attention in recent years due to their potential for detecting human motion in various scenarios. However, the development of strain sensors with high sensitivity across a wide range of strains remains a major challenge. We present herein a novel strain sensor based on a graded structure thermoplastic polyurethane (TPU)/carbon nanotube (CNT) composite yarn with significantly enhanced mechanical performance imparted by the designed structure. The twisted CNTs/TPU spiral yarn demonstrated a fracture elongation of up to 1066% while maintaining charge conductivity under high‐strain conditions. Moreover, it exhibited sensitive changes in resistance versus tensile strain, excellent repeatability, and stability. As a strain sensor, it achieved a gauge factor (GF) of 67.2 within a strain range below 50%, reaching 51.7 in a strain range exceeding 150%. With a fast response time of 0.12 s, it enabled accurate identification of movements in different body parts. These findings highlight the broad application potential of the designed spiral yarn strain sensor in areas such as human motion monitoring and human–computer interaction.Highlights Prepares a flexible strain sensor with graded‐structure (CNT‐fiber‐yarn). Shows high sensitivity and a wide strain response range Reveals the conductive model of strain sensor.

Thermally stable metallic glass strain sensors with extended sensing range and sensitivity

This research thoroughly analyzes strain sensing performance and thermal stability of metallic glass (MG) electrodes. The amorphous characteristic of MG film endows a high gauge factor and bending motion detection of the strain sensor device.

Layer-sliding-mediated controllable synthetic strategy for the preparation of multifunctional materials

Strategies capable of inducing multifunctionality in materials in a controllable manner are highly desirable. In this work, we have brought multifunctionality to a two-dimensional (2D) van der Waals heterostructure (vdW-HS) consisting of a layer of puckered silicene and indium selenide (InSe) through layer-sliding. Electronic, optical and interfacial properties of silicene/InSe vdW-HS have been varied dynamically by sliding silicene over InSe. The aforementioned layer-sliding is carried out in a gradual manner without and with Mg-intercalation. The buckling parameter relating to the corrugation of silicene drops from 0.438 Å to 0.351 Å on Mg-intercalation, whereas in the case of InSe buckling remains unaffected. The calculated band structure for un-intercalated vdW-HS shows a small band gap opening 205/210 meV with LDA/GGA functional) along high symmetry K direction in the first Brillion zone. The widening of the bandgap makes it suitable for optoelectronics and strain sensor devices, where a small band gap (0.1–1 eV) is required. To look inside into the interface of the vdW-HS, various interfacial electronic parameters such as planar average charge density difference (Δρ), dipole charge transfer (ΔQ) and dipole moment (Δµ) have been determined. It is found that the charge accumulation peaks have appeared near the silicene layer and the charge is transferred from silicene to the InSe layer in both un-intercalated and Mg-intercalated vdW-HSs. Further, we investigated the different optical parameters including real [ε1(ω)] and imaginary [ε2(ω)] parts of dielectric function (DF), energy loss function [L(ω)] and diagonal components of dielectric tensor [ε (iω)] for un-intercalated and Mg-intercalated vdW-HSs. The anisotropic analysis shows that the computed in-plane components significantly dominate the out-of-plane component of the DF, which show minor change as the sliding proceeds. The study endorses that multifunctional electronic 2D materials can be achievable by employing the layer-sliding dynamical strategy.

Highly stretchable, adhesive, and biocompatible hydrogel platforms of tannic acid functionalized spherical nanocellulose for strain sensors

The development of multifunctional wearable electronic devices has received considerable attention because of their attractive applications. However, integrating multifunctional abilities into one component remains a challenge. To address this, we have developed a tannic acid-functionalized spherical nanocellulose/polyvinyl alcohol composite hydrogel using borax as a crosslinking agent for strain-sensing applications. The hydrogel demonstrates improved mechanical and recovery strengths and maintains its mechanical strength under freezing conditions. The hydrogels show ultra-stretching, adhesive, self-healing, and conductive properties, making them ideal candidates for developing strain-based wearable devices. The hydrogel exhibits good sensitivity with a 4.75 gauge factor. The cytotoxicity of the developed hydrogels was monitored with human dermal fibroblast cells by WST-8 assay in vitro. The antibacterial potential of the hydrogels was evaluated using Escherichia coli. The hydrogels demonstrate enhanced antibacterial ability than the control. Therefore, the developed multifunctional hydrogels with desirable properties are promising platforms for strain sensor devices.

Liquid metal/CNTs hydrogel-based transparent strain sensor for wireless health monitoring of aquatic animals

Strain sensors are intriguing in advanced electronics and are typically composed of active sensing materials. Good elastic recovery, self-healing, good adhesion, high transparency, and great mechano-response are essential but can be rarely met in one material. Here, we report a wireless strain sensor that exhibits tissue-like mechanical properties (softness), is conformable to soft tissues (heart and tail) and has the lowest limit of detection (0.25 % stretch). After introducing multiwalled carbon nanotubes (CNTs) bridged liquid metal (LM) composites (LM/CNTs), the strain sensor simultaneously achieves excellent transparency and conductivity. This LM/CNTs hydrogel overcomes the limitations of the traditional hydrogel and achieves high conductivity (up to 94 S/m), good stretchability (2,200 %), and a high degree of transparency (93 %), in addition to enough adhesion (20 kPa) and rapid self-healing (20 min). The strain sensor device is composed of intrinsically soft LM/CNTs hydrogel as sensing material, a microcontroller, signal-processing circuits, and Bluetooth transceiver. This device is applied to recording high-quality heartbeat signals and clear in-site observation of cardiac bleeding, which has helped a Chinese sturgeon survive after Caesarean. This approach provides an ideal strategy for protecting and saving endangered animals and broadens the applications of strain sensors.

Highly Stretchable and Sensitive Flexible Strain Sensor Based on Fe NWs/Graphene/PEDOT:PSS with a Porous Structure.

With the rapid development of wearable smart electronic products, high-performance wearable flexible strain sensors are urgently needed. In this paper, a flexible strain sensor device with Fe NWs/Graphene/PEDOT:PSS material added under a porous structure was designed and prepared. The effects of adding different sensing materials and a different number of dips with PEDOT:PSS on the device performance were investigated. The experiments show that the flexible strain sensor obtained by using Fe NWs, graphene, and PEDOT:PSS composite is dipped in polyurethane foam once and vacuum dried in turn with a local linearity of 98.8%, and the device was stable up to 3500 times at 80% strain. The high linearity and good stability are based on the three-dimensional network structure of polyurethane foam, combined with the excellent electrical conductivity of Fe NWs, the bridging and passivation effects of graphene, and the stabilization effect of PEDOT:PSS, which force the graphene-coated Fe NWs to adhere to the porous skeleton under the action of PEDOT:PSS to form a stable three-dimensional conductive network. Flexible strain sensor devices can be applied to smart robots and other fields and show broad application prospects in intelligent wearable devices.

Flexible Strain Sensors for Wearable Hand Gesture Recognition: From Devices to Systems

Hand gesture recognition has attracted extensive research interest, as an essential approach for human−machine interaction. The development of flexible strain sensors offers the possibility of directly measuring the finger motion behaviors for accurate and cost‐effective hand gesture recognition, by placing the sensors on the fingers or integrating them on data gloves. Herein, the operation mechanisms of various flexible strain sensor designs are introduced first. Progresses on related materials and device structures to achieve the demanded figure of merits for flexible strain sensors are then reviewed. In addition to continuous performance optimization of the flexible strain sensor devices, the development of system‐level algorithms is shown to be important for not only recognition functions but also for suppression of nonidealities of the sensor devices, which are difficult to be addressed at device and material level.

A Highly Stretchable and Sensitive Strain Sensor Based on Dopamine Modified Electrospun SEBS Fibers and MWCNTs with Carboxylation

AbstractWearable flexible electronic strain sensor devices have developed rapidly in recent years due to their potential capacity to detect human motion in various situations. However, it still remains still a big challenge to fabricate strain sensors with high sensitivity over a wide workable strain range. In order to meet this challenge, a new type of strain sensor based on elastomer/carbon nanotube composite fiber is reported in this work. Elastomer fibers are initially prepared via the electrospinning of styrene ethylene butene styrene block copolymer (SEBS). The resultant SEBS fibers are then functionalized by sequentially coating with dopamine (DA) coating and carboxyl group (‐COOH) grafted multi‐walled carbon nanotubes (MWCNTs) under vacuum filtration and ultrasonication. Scanning electron microscopy (SEM) and thermogravimetric analysis reveals that a large amount of MWCNTs is firmly bonded onto the SEBS fibers and evenly distributed. SEBS@PDA/MWCNTs composite fibers based strain sensors exhibit excellent performance, including a high gauge factor of 3717 and large workable strain range up to 530%. Furthermore, the developed sensors demonstrate excellent washing fastness and superior sensitivity in monitoring both small strains (e.g., pulse beats and vocal cord vibrations) and large strains (e.g., finger, elbow, and knee bending).

Self‐Healing Polyurethane Elastomer Based on Crosslinked‐Linear Interpenetrating Structure: Preparation, Properties, and Applications

AbstractDespite tremendous advances in the preparation of self‐healing flexible strain sensor devices, it remains a great challenge to large‐area synthesis, relatively high mechanical strength, and sensitive sensing properties into one self‐healing materials system, which have received increasing interests because of their many potential applications. Herein, the design and synthesis of a crosslinked‐linear interpenetrating structure polymer containing disulfide and hydrogen bonds is reported to address this conundrum. The resulting self‐healable polymer is highly stretchable (up to 551.7%) with a high tensile strength (4.14 MPa) and excellent healing efficiency of similar to 90% at mild temperature without using any external reagents. Furthermore, a novel method for fabricating flexible sensor is also proposed to endow the resulted sensor with large‐area (20 cm × 12 cm), low cost, and outstanding sensitivity to strain, which makes it very suitable for human motion monitoring applications. This work will provide afflatus on future design, fabrication, and application of self‐healing flexible strain sensor devices.

Ferroelectric polymer-based fully printed flexible strain rate sensors and their application for human motion capture

Flexible strain sensors are essential to realizing novel wearable electronics applications that include dynamic human-motion capture sensing devices. Various technologies have been proposed to fabricate flexible strain sensors for motion capture using low-cost printing methods. A new approach utilizing piezoelectric polymers has recently been proposed whereby ferroelectric polymer layers are formed on plastic substrates and employed in wearable sensor devices. However, in printed strain sensor devices using ferroelectric polymers, the influence of layer formulation on sensor properties has not been clear. We have developed fully-printed flexible strain sensors by optimizing the concentration and viscosity of a ferroelectric polymer solution. It was found that the ferroelectric layers using screen printing can be formed with flat morphologies and good crystallinity using solutions with viscosities of over 3.0 Pa s. Moreover, these printed ferroelectric strain sensors achieved practical performance levels, exhibiting ferroelectric characteristics of 6.0 μC cm-2 and 50 MV m−1. The sensors were employed in wearable bending sensors for human fingers to demonstrate their feasibility in motion capture applications. Despite a wide range of operating speeds, the fabricated sensors effectively measured bending rates.

Response characteristics of strain sensors based on closely spaced nanocluster films with controlled coverage

Flexible strain sensor devices were fabricated by depositing Pd nanoclusters on PET membranes patterned with interdigital electrodes. The sensors responded to the deformation of the PET membranes with the conductance changes of the nanocluster films and were characterized by both high gauge factor and wide detection range. The response characteristics of the strain sensors were found to depend strongly on the nanocluster coverage, which was attributed to the percolative nature of the electron transport in the closely spaced nanocluster arrays. By controlling the nanocluster deposition process, a strain sensor composed of nanocluster arrays with a coverage close to the effective percolation threshold was fabricated. The sensor device showed a linear response with a stable gauge factor of 55 for the applied strains from the lower detection limit up to 0.3%. At higher applied strains, a gauge factor as high as 200 was shown. The nanocluster films also demonstrated the ability to response to large deformations up to 8% applied strain, with an extremely high gauge factor of 3500.

Fabrication of 3D graphene foam for a highly conducting electrode

A large number of pitting pits were formed on the surface of Ni foam by immersion corrosion in NaCl solution. The graphene was deposited on Ni foam templates, then 3D graphene foams were obtained by removing Ni foam in the mixed solution of ferric chloride and hydrochloric acid. It was found that pitting pits on Ni foam facilitated to form fewer-layers graphene, however, pitting pits on Ni foam induced more defects on 3D graphene foam. The graphene with fewer-layers exhibited better electrical and mechanical properties for strain sensor devices. Moreover, fewer-layers graphene effectively inhibited degradation of resistance during cycling stability tests.

3D printable composite dough for stretchable, ultrasensitive and body-patchable strain sensors.

The recent development of strain sensor devices which can actively monitor human body motion has attracted tremendous attention, for application in various wearable electronics and human-machine interfaces. In this study, as materials for strain sensor devices, we exploit the low-cost, carbon-based, 3-dimensional (3D) printable composite dough. The dough is prepared via a chemical method based on the formation of electrostatic assemblies between 1-dimensional, amine-functionalized, multi-walled carbon nanotubes and 2-dimensional graphene oxides. The resulting composite dough has an extremely high storage modulus, which allows a vertically-stackable, 3D printing process for fabricating strain sensor devices on various dense, porous and structured substrates. The device performance parameters, including gauge factor, hysteresis, linearity, and overshooting behavior are found to be adjustable by controlling the printing process parameters. The fabricated strain sensor devices demonstrate the ability to distinguish actual human body motions. A high gauge factor of over 70 as well as other excellent device performance parameters are achievable for the printed sensor devices, and even small strains, below 1%, are also detectable by the fabricated sensor devices.

Self-Powered energy harvester strain sensing device for structural health monitoring

This paper presents an envisaged autonomous strain sensor device, which is dedicated to structural health monitoring applications. The paper introduces the ASIC approach that replaces the discrete approach of some of the main modules.

Remarkable piezoresistance effect on the flexible strain sensor based on a single ultralong tellurium micrometre wire

Flexible strain sensors based on a single ultralong tellurium micrometre wire have been prepared. The strain sensor device consists of a flexible polystyrene substrate with a single tellurium micrometre wire placed on its surface and bonded by silver paste. Two types of strain sensor were fabricated. One sensor uses back to back Schottky barrier contacts. This sensor has different shape I–V behaviours due to the change of the Schottky barrier height when there are no strain, stretch, and compressive strains. The current increases as the compressive strain increases. The second sensor uses a single Schottky barrier contact. The current increases more significantly under compression strain at a negative voltage. By contrast, the latter is more suitable for detecting strains.

Strain-induced switching of magnetoresistance and perfect spin-valley filtering in graphene

We study spin-dependent valley currents and magnetoresistance (TMR) in double magnetic layer graphene-based N/ F 1/St/ F 2/ N junction where N, F 1,2 and St are normal, ferromagnetic and strain-engineered graphene, respectively. Local strain in the St region causes a pseudo-vector potential with the same magnitude for the K- and K′-valleys but different sign, leading to valley polarization when applying real vector potential into the junction. The F layers cause the Zeeman field for controlling spin current and can be orientated either parallel ( P) or anti parallel ( AP). As an effect of the interplay of the Zeeman field and the strain field, the current in the junction is split into four current groups, I k↑ , I k↓ , I k′↑ and I k′↓ , called spin-valley currents. We find that, the interplay of the Zeeman and strain field causes a perfect spin-valley filtering in the angular space only for the P configuration. Large TMR and switching of TMR triggered by a very small strain are also predicted. Our work reveals the potential of the interplay of the Zeeman and the strain field for application of spin-valley-based nanoelectronics and the switching effect induced by a very small strain should be applicable for strain sensor device.

Fiber laser strain sensor device

We present a fiber laser strain sensor (FLSS) with noise-equivalent sensitivity equal to or better than 80?p?rms?(Hz)?1/2 at very low frequencies, from 100?mHz to several hundreds of hertz. The strain affects the fiber laser emission wavelength, and an imbalanced Mach?Zender interferometer (MZI) converts wavelength variations into phase-amplitude variations. The sensor has been also tested in the time domain by applying sinusoidal strain bursts: the device also shows a good signal-to-noise ratio at the lowest burst frequencies.