Textile-based Strain Sensor Research Articles

Development of Textile-Based Strain Sensors for Compression Measurements in Sportswear (Sports Bra)

Women sports wearer’s comfort and health are greatly impacted by the breast movements and resultant sports bra compression to prevent excessive movement. However, as sports bras are only made in universal sizes, they do not offer the right kind of support that is required for a certain activity. To prevent this issue, textile-based strain sensors may be utilized to track compression throughout various activities to create activity-specific designed sports bras. Textile-based strain sensors are prepared in this study using various conductive yarns, including steel, Ag-coated polyamide, and polypropylene/steel-blended threads. Various embroidery designs, including straight, zigzag, and square-wave embroidery patterns, etc., were created on knitted fabric and characterized for strain sensing efficiencies. The experiments concluded that strain sensors prepared from polypropylene/steel thread using a 2-thread square-wave design were best performed in terms of linear conductivity, sensitivity of mechanical impact, and wide working range. This best-performed sample was also tested by integrating it into the sportswear for proposed compression measurements in different body movements.

Weft-Knitted Strain Sensors for Motion Capture

Motion capture, especially of the knee angle, is an important component for situational triggering of functional electrical stimulation (FES). One major disadvantage of commercial FES devices is their bulky design that prevents unobtrusive wearing in everyday life and limits the patient’s free choice of appearance. This paper presents an alternative approach of sensors for motion capture in form of textile-based strain sensors. These can be integrated in a FES system in form of functional leggings, which make the FES system suitable for an unobtrusive daily use. Textile sensors, especially knitted sensors have already proven to be very promising to detect tensile strain. In particular, weft-knitted strain sensors, which can be integrated directly into the clothing during the knitting process, have the potential to detect the knee angle and therefore derive the gait phase due to the bending of the limbs without disturbing the wearer unnecessarily. Different designs of the weft-knitted strain sensor and their influence on the measurement behaviour of the sensor have been investigated. The weft-knitted strain sensor can be directly integrated in the knee area of the functional leggings to be used as a soft trigger to initiate electrical impulses for FES.

Textile-based strain sensors for fiber-reinforced composites under tension, compression and bending

Abstract This research addresses the challenging task of monitoring the structural integrity of fiber-reinforced composite (FRC) components under complex loading conditions. Ensuring the safety and functionality of these components is critical but economically challenging. Therefore, this study presents an innovative approach using textile-based strain sensors that are cost-effective and structurally compatible with carbon fiber-reinforced plastic (CFRP) components. The investigation includes the systematic electromechanical characterization and comparison of four different sensor materials at the yarn and composite scale in various test scenarios. Cyclic tensile, compression, and bending tests of CFRP specimens are performed and show good reproducibility of sensor signals within the elastic range, with significant agreement observed with applied strain measurement methods, particularly in tensile tests. Although there are minor deviations in compression and bending evaluations, the signals are still meaningful for in-situ detection of complex loading patterns, crack initiation, and structural failure. The study demonstrates that the integration of textile-based sensor yarns allows for continuous structural health monitoring (SHM) of CFRP components under various loading scenarios, including tensile, bending, and especially compressive loads.

Assessing the Role of Yarn Placement in Plated Knit Strain Sensors: A Detailed Study of Their Electromechanical Properties and Applicability in Bending Cycle Monitoring.

In this study, we explore how the strategic positioning of conductive yarns influences the performance of plated knit strain sensors fabricated using commercial knitting machines with both conductive and non-conductive yarns. Our study reveals that sensors with conductive yarns located at the rear, referred to as 'purl plated sensors', exhibit superior performance in comparison to those with conductive yarns at the front, or 'knit plated sensors'. Specifically, purl plated sensors demonstrate a higher sensitivity, evidenced by a gauge factor ranging from 3 to 18, and a minimized strain delay, indicated by a 1% strain in their electromechanical response. To elucidate the mechanisms behind these observations, we developed an equivalent circuit model. This model examines the role of contact resistance within varying yarn configurations on the sensors' sensitivity, highlighting the critical influence of contact resistance in conductive yarns subjected to wale-wise stretching on sensor responsiveness. Furthermore, our findings illustrate that the purl plated sensors benefit from the vertical movement of non-conductive yarns, which promotes enhanced contact between adjacent conductive yarns, thereby improving both the stability and sensitivity of the sensors. The practicality of these sensors is confirmed through bending cycle tests with an in situ monitoring system, showcasing the purl plated sensors' exceptional reproducibility, with a standard deviation of 0.015 across 1000 cycles, and their superior sensitivity, making them ideal for wearable devices designed for real-time joint movement monitoring. This research highlights the critical importance of conductive yarn placement in sensor efficacy, providing valuable guidance for crafting advanced textile-based strain sensors.

Novel Weft-Knitted Strain Sensors for Motion Capture.

Functional electrical stimulation (FES) aims to improve the gait pattern in cases of weak foot dorsiflexion (foot lifter weakness) and, therefore, increase the liveability of people suffering from chronic diseases of the central nervous system, e.g., multiple sclerosis. One important component of FES is the detection of the knee angle in order to enable the situational triggering of dorsiflexion in the right gait phase by electrical impulses. This paper presents an alternative approach to sensors for motion capture in the form of weft-knitted strain sensors. The use of textile-based strain sensors instead of conventional strain gauges offers the major advantage of direct integration during the knitting process and therefore a very discreet integration into garments. This in turn contributes to the fact that the FES system can be implemented in the form of functional leggings that are suitable for inconspicuous daily use without disturbing the wearer unnecessarily. Different designs of the weft-knitted strain sensor and the influence on its measurement behavior were investigated. The designs differed in terms of the integration direction of the sensor (wale- or course-wise) and the width of the sensor (number of loops) in a weft-knitted textile structure.

Fabrication Techniques and Sensing Mechanisms of Textile-Based Strain Sensors: From Spatial 1D and 2D Perspectives

Fabrication Techniques and Sensing Mechanisms of Textile-Based Strain Sensors: From Spatial 1D and 2D Perspectives

Stretchable and sensitive sodium alginate ionic hydrogel fibers for flexible strain sensors

Ionic conductive hydrogel fibers based on natural polymers provide an immense focus for a new generation of electronics due to their flexibility and knittability. The feasibility of utilizing pure natural polymer-based hydrogel fibers could be drastically improved if their mechanical and transparent performances satisfy the requirements of actual practice. Herein, we report a facile fabrication strategy for significantly stretchable and sensitive sodium alginate ionic hydrogel fibers (SAIFs), by glycerol initiating physical crosslinking and by CaCl2 inducing ionic crosslinking. The obtained ionic hydrogel fibers not only show significant stretchability (tensile strength of 1.55 MPa and fracture strain of ∼161 %), but also exhibit wide-range sensing, satisfactorily stable, rapidly responsive, and multiply sensitive abilities to external stimulus. In addition, the ionic hydrogel fibers have excellent transparency (over 90 % in a wide wavelength range), and good anti-evaporation and anti-freezing properties. Furthermore, the SAIFs have been easily knitted into a textile, and successfully applied as wearable sensors to recognize human motions, by observing the output electrical signals. Our methodology for fabrication intelligent SAIFs will shed light on artificial flexible electronics and other textile-based strain sensors.

Two-dimensional carbon material incorporated and PDMS-coated conductive textile yarns for strain sensing

AbstractIn recent years, innovative technology based upon conductive textile yarns has undergone rapid growth. Nanocomposite-based wearable strain sensors hold great promise for a variety of applications, but specifically for human body motion detection. However, improving the sensitivity of these strain sensors while maintaining their durability remains a challenge in this arena. In the present investigation, polydopamine-treated and two-dimensional nanostructured material, e.g., reduced graphene oxide (rGO)-coated conductive cotton and polyester yarns, was encapsulated using polydimethylsiloxane (PDMS) to develop robustly wash durable and mechanically stable conductive textile yarns. Flexibility and extensibility of all textile yarns of every stage were analyzed using texture analysis. The chemical interactions essential for measuring coating performance among all components were confirmed by Fourier transform infrared and scanning electron microscopy. The rGO-coated cotton and polyester yarns exhibited an extensibility of 11.77 and 73.59%, respectively. PDMS-coated conductive cotton and polyester yarns also showed an electrical resistance of 12.22 and 20.33 kΩ, respectively, after 10 washing cycles. The PDMS coating layer acted as a physical barrier against impairment of conductivity during washing. Finally, the mechanically stable and flexible conductive textile yarns were integrated into a knitted cotton glove and armband to create a highly stretchable and flexible textile-based strain sensor for measuring finger and elbow movement. Truly wearable garments able to record proprioceptive maps are critical for further developing this field of application.

EFFECT OF TENSILE FATIGUE CYCLIC LOADING ONPERFORMANCE OF TEXTILE-BASED STRAIN SENSORS

Textile-based strain sensors are a potential platform used in wearable devices for sensing and. 8 sensors containing monitoring the human body. These sensors not only have all the conventional sensors benefits but also, they are low-cost, flexible, light-weight, and easily adopted with three-dimensional shape of the body. Moreover, recent research has shown they are the best candidates for monitoring human’s body motion. In this study, the effect of tensile fatigue cyclic loads on performance and sensitivity of textilebased strain sensors was investigated polyester/stainless steel staple fiber blend yarn as a conductive part with different structures were produced. The sensors varied in weft and warp density, percentage of stainless steel in conductive yarn, the number of conductive yarns, and weave pattern. The sensors were subjected to 500 cyclic loads operations and their tensile properties and sensitivity were investigated and compared before and after applying tensile fatigue cyclic loads. The results showed the textile-based strain sensors containing less percentage of stainless-steel fiber, lower number of conductive yarns, twill weave pattern and lower density in warp and weft direction have shown better performance after tensile fatigue cyclic loads.

Design and development of textile-based strain sensors via screen printing

Textile-based strain sensors have recently attracted attention due to not only their flexibility and adaptability but also stretchability. Therefore, the main focus of this work is to develop highly flexible, highly stretchable and novel sensors based on several types of knitted fabrics and electrospun membranes with different kinds of inks. Sensors were fabricated by screen printing of different inks of NovaCentrix Metalon HPS-FLX21 and Creative Materials 127–48 (both silver-based) on two fabrics with different fabric structures and membranes obtained by electrospinning of thermoplastic polyurethane (TPU) as substrate. Readymade knitted substrates supplied by SIM-ART TEXTILE and electrospinning of dissolved TPU pellets in Dimethylformamide (DMF) and Ethyl acetate (EA) mixture provided a fibrous substrate to be utilized in manufacturing of the sensors. The patterns predetermined were transferred onto these substrates by screen printing method using silver based conductive inks in order to ensure sufficient conductivity. For all of these sensors, optimum processing conditions have been determined within the scope of the experiments. As a result, the as-printed substrates have been oven-cured to finalize the fabrication process of the sensors. According to the findings of the study, Creative Materials ink was found to display quite good performance on both TPU membrane and knitted fabric-based strain sensors whereas NovaCentrix ink did not perform as well. Developed sensors in this study can be potentially used in wearable electronics for human motion monitoring applications.

The technology of wearable flexible textile-based strain sensors for monitoring multiple human motions: construction, patterning and performance

This paper discusses the development of wearable flexible textile-based strain sensors for monitoring multiple human motions.

Weft-Knitted Spacer Fabric for Highly Stretchable-Compressible Strain Sensor, Supercapacitor, and Joule Heater.

The development of wearable electronic devices has greatly stimulated the research interest of textile-based strain sensors, which can effectively combine functionality with wearability. In this work, the fabrication of highly stretchable and compressible strain sensors from weft-knitted spacer fabric was reported. Carbon nanotubes and polypyrrole were deposited on the surface of fabric via an in situ polymerization approach to reduce the electrical resistance. The as-fabricated WSP-CNT-PPy strain sensor exhibits high electrical conductivity and stable strain-sensing performance under different stretching deformations. The WSP-CNT-PPy strain sensor can be stretched up to 450% and compressed to 60% with a pressure of less than 50 KPa, which can be attributed to the unique loop and interval filament structures. The distinguishing response efficiency of WSP-CNT-PPy can effectively detect faint and strenuous body movements. In addition, the electrochemical behavior of WSP-CNT-PPy was also characterized to study the comprehensive properties. The electro-heating performance was also evaluated for feasible Joule heater applications. This work demonstrates the practicability of WSP-CNT-PPy strain sensor fabric for real-time monitoring in promising wearable garments.

Knitted structural design of MXene/Cu2O based strain sensor for smart wear

Electronic textiles present an enticing prospect for personal health assessment and physical monitoring, owing to their strong stretchability, high flexibility, mechanical robustness and high capacity in sensing small deformations in human motions. Herein, a multifunctional robust flexible knitting-shaped strain sensor based on the functional heterostructure composed of the conductive MXene (Ti3C2Tx) nanosheet and the antimicrobial Cu2O nanoparticles is prepared via a solution-processable dip-dry coating approach. The textile-based strain sensor exhibits a highly stable and immediate response over a wide range, which shows great advantages in detecting and monitoring human activities, such as smiling, swallowing, and wrist/finger/joint bending. Significantly, these prepared strain sensors present a promising application in smart wear, which was typically employed as the smart sensing gloves in barrier-free communication for hearing-impaired people. Interestingly, the different resistance evolutions of the knitted sensor under both low and high strain were carried out to study the sensing mechanism for the first time. Notably, the strain sensor displays a reliable antibacterial efficiency of ∼99.1% for Escherichia coli and outstanding breathability as high as 190 mm/s. This developed MXene/Cu2O hybrid materials supplies a new insight for the rational design and synthesis of multifunctional nanomaterials, as well as the achievement of the flexible wearable sensor with high performance.

Mechanically robust textile-based strain and pressure multimodal sensors using metal nanowire/polymer conducting fibers

SummaryRecently, multifunctional textile-based sensory systems have attracted a lot of attention because of the growing demand for wearable electronics performing real-time monitoring of various body signals and movements. In particular, textile-based physical sensors often require multimodal sensing capabilities to accurately detect and identify multiple mixed stimuli simultaneously. Here, we demonstrate a textile-based strain/pressure multimodal sensor using high-k poly(vinylidene fluoride)-co-hexafluoropropylene ion-gel film and silver nanowire/poly(3,4-ethylenedioxythiophene):polystyrene sulfonate-coated conducting fibers. The multimodal sensors exhibited reliable strain and pressure-sensing characteristics for strain ranges up to 25% and pressures up to 50 kPa, respectively, with a relatively high strain gauge factor (up to 2.74) and pressure sensitivity (0.32 kPa−1). More importantly, the textile-based multimodal sensor was able to detect the strain and pressure independently, allowing facile discrimination of strain and pressure. Using this approach, we demonstrated a textile-based multimodal sensor that incorporates one strain sensor and two pressure sensors detecting multiple weights simultaneously.

Highly Dispersed, Adhesive Carbon Nanotube Ink for Strain and Pressure Sensors.

Carbon nanotubes (CNT) with prominent electrical and mechanical properties are ideal candidates for flexible wearable devices. However, their poor dispersity in solvents greatly limits their applications as a conductive ink in the fabrication of wearable sensors. Herein, we demonstrate a kind of CNT-based conductive dispersion with high dispersity and adhesiveness using cellulose derivatives as the solvent, in which γ-aminopropyl triethoxy silane as a cross-linking agent reacts with cellulose to form copolymer networks, and simultaneously it also acts as an initiator to induce the self-polymerization of dopamine. Based on the conductive CNT ink, we also demonstrated textile-based strain sensors by stencil printing and sponge-based pressure sensors by the dipping method. The textile-based strain sensors could respond to external stimuli promptly. Then, the strain sensors were encapsulated via polydimethylsiloxane with the expansion of working ranges from less than 20 to nearly 70%. The encapsulated textile sensors exhibited excellent sensing performance as wearable strain sensors to monitor human motions including smile, throat vibration, finger folding, wrist bending, and elbow twisting. The sponge sensors hold high sensitivity and excellent durability as well. The conductive CNT-based ink provides an alternative idea in the development of flexible wearable devices.

The effect of washing on the electrical performance of knitted textile strain sensors for quantifying joint motion

Successful market penetration of textile-based strain sensors requires long-term reliability which in turn relies on the washability of the sensor. First, this paper presents an evaluation of the effect of 5 washing cycles on the electrical performance of a knitted conductive transducer, over 1500 cycles of repetitive elongation. The promising behaviour of the textile sensor in this study showed that it might be possible to make a smart garment, capable of quantifying elbow flexion-extension motion, by integrating it into an elbow sleeve. Second, a prototype sleeve, incorporating a knitted sensor (the so-called smart sleeve), was tested in a simulated training/clinical setting by performing 50 flexion-extension cycles after 1, 5, 15, 25, 50 and 75 washes. In both studies, the electrical resistance of the sensor increased with the number of washes in a predictable manner and exhibited a repeatable, reliable and prompt response to elongation. In particular, the electrical pattern representing flexion-extension motion measured using the sleeve was clear and distinguishable up to the 75th wash. Moreover, resistance measurements within the same trial were repeatable at maximum flexion (≤2% variation) and at maximum extension (≤3% variation) and predictable with increasing washes (R2 = 0.992 at maximum flexion and R2 = 0.989 at maximum extension). The good washability of the smart sleeve, evidenced by its ability to detect, distinguish and measure parameters of flexion-extension motion up to 75 washes, makes it a suitable and sustainable choice for applications, such as strength conditioning or rehabilitation, where repetition count and speed are useful.

Skin Strain Analysis of the Scapular Region and Wearables Design.

Monitoring scapular movements is of relevance in the contexts of rehabilitation and clinical research. Among many technologies, wearable systems instrumented by strain sensors are emerging in these applications. An open challenge for the design of these systems is the optimal positioning of the sensing elements, since their response is related to the strain of the underlying substrates. This study aimed to provide a method to analyze the human skin strain of the scapular region. Experiments were conducted on five healthy volunteers to assess the skin strain during upper limb movements in the frontal, sagittal, and scapular planes at different degrees of elevation. A 6 × 5 grid of passive markers was placed posteriorly to cover the entire anatomic region of interest. Results showed that the maximum strain values, in percentage, were 28.26%, and 52.95%, 60.12% and 60.87%, 40.89%, and 48.20%, for elevation up to 90° and maximum elevation in the frontal, sagittal, and scapular planes, respectively. In all cases, the maximum extension is referred to the pair of markers placed horizontally near the axillary fold. Accordingly, this study suggests interesting insights for designing and positioning textile-based strain sensors in wearable systems for scapular movements monitoring.

Wearable and self-healable textile-based strain sensors to monitor human muscular activities

In this study, a textile-based wearable strain sensor is fabricated to monitor human muscular activities with high sensitivity and large working range. To achieve electrical conductivity, a gum-like sticky polyvinyl acetate-co-vinyl laurate polymer (commercial name: VINNAPASS) is mixed with 50 wt % of carbon nanofiber (CNFs) using ethyl acetate as co-solvent. The VINNAPASS/CNFs-based ink is spray coated onto a stretchable polyethylene terephthalate fabric (commercial name: Lycra) and subsequently covered and stabilized with polydimethylsiloxane protective layer. Another reference sensor is also prepared using thermoplastic polyurethane (TPU) with equal concentration of CNFs. The strain sensor made with VINNAPASS demonstrated sheet resistance, maximum elongation at break, gauge factor (GF) and working range of 32.27 ± 1.60 Ω/□, 230 ± 6%, 67.12, >170% as compared to 48.44 ± 2.33 Ω/□, 122 ± 7%, 39.97 and ~100% for the sensor made with TPU, respectively. Moreover, the VINAPASS-based strain sensor displayed complete self-healing and >90% reversible electrical properties on damage, while the TPU-based sensor was not healable. Finally, the VINNAPASS-based sensor is used to monitor folding-unfolding of human finger and wrist as well as bicep muscle contraction and relaxation, and is envisioned for monitoring human muscular motions during physical activities and exercising.

Wearable Strain Sensors with Aligned Macro Carbon Cracks Using a Two-Dimensional Triaxial-Braided Fabric Structure for Monitoring Human Health.

Recently, wearable sensors, due to their ability to exhibit characteristics, have been appealing for health monitoring through detection of human motions and vital signals. The development of strain sensors with high sensing performance and wearability has been a great challenge to date. In this study, a textile-based strain sensor with good skin affinity was fabricated through a simple fabrication process of dip-coating 2D triaxial-braided fabrics using carbon ink and then drying. The macro crack aligned on the 2D triaxial-braided fabric with a high-density structure and good recovery force. The sensitivity of textile-based strain sensor can be enhanced due to aligned macro crack formed by prestrained fabricating process and characteristic of the 2D triaxial braided fabric with high dense structure. The optimized sensor exhibits high sensitivity (gauge factor: 128) in a strain range of 0-30%, durability (5000 cycles), washability, low hysteresis, and fast response time (90 ms). Therefore, it can be applied as a wearable sensor that can monitor human motions (large strain) and biosignals (subtle strain).

Ultrasensitive Strain Sensor Based on Pre-Generated Crack Networks Using Ag Nanoparticles/Single-Walled Carbon Nanotube (SWCNT) Hybrid Fillers and a Polyester Woven Elastic Band.

Flexible strain sensors are receiving a great deal of interest owing to their prospective applications in monitoring various human activities. Among various efforts to enhance the sensitivity of strain sensors, pre-crack generation has been well explored for elastic polymers but rarely on textile substrates. Herein, a highly sensitive textile-based strain sensor was fabricated via a dip-coat-stretch approach: a polyester woven elastic band was dipped into ink containing single-walled carbon nanotubes coated with silver paste and pre-stretched to generate prebuilt cracks on the surface. Our sensor demonstrated outstanding sensitivity (a gauge factor of up to 3550 within a strain range of 1.5–5%), high stability and durability, and low hysteresis. The high performance of this sensor is attributable to the excellent elasticity and woven structure of the fabric substrate, effectively generating and propagating the prebuilt cracks. The strain sensor integrated into firefighting gloves detected detailed finger angles and cyclic finger motions, demonstrating its capability for subtle human motion monitoring. It is also noteworthy that this novel strategy is a very quick, straightforward, and scalable method of fabricating strain sensors, which is extremely beneficial for practical applications.