Flexible sensors in smart textiles and their applications

Sensors are the core part of intelligent smart textiles, and flexible sensors play an important role in wearable smart textiles because of their softness, bend ability and stretch ability, and excellent electrical properties. Based on the working principle of sensors, the research progress of flexible sensors for smart textiles in recent years is reviewed, and the sensing mechanism, sensing materials and application status of different sensors are introduced respectively; the main research directions of flexible sensors for smart textiles are summarized: physiological parameter detection, pressure detection and motion detection, and the applications of the three research directions are reviewed. On this basis, the problems of intelligent flexible sensors and their development prospects are pointed out

The status of textile-based dry EEG electrodes

Electroencephalogram (EEG) is the biopotential recording of electrical signals generated by brain activity. It is useful for monitoring sleep quality and alertness, clinical applications, diagnosis, and treatment of patients with epilepsy, disease of Parkinson and other neurological disorders, as well as continuous monitoring of tiredness/ alertness in the field. We provide a review of textile-based EEG. Most of the developed textile-based EEGs remain on shelves only as published research results due to a limitation of flexibility, stickability, and washability, although the respective authors of the works reported that signals were obtained comparable to standard EEG. In addition, nearly all published works were not quantitatively compared and contrasted with conventional wet electrodes to prove feasibility for the actual application. This scenario would probably continue to give a publication credit, but does not add to the growth of the specific field, unless otherwise new integration approaches and new conductive polymer composites are evolved to make the application of textile-based EEG happen for bio-potential monitoring

Integration and embedding of vital signs sensors and other devices into textiles

The development of ubiquitous vital sign monitoring has become a very up-to-date research theme for many academics and industrial companies in the last years. With new materials and integration techniques, it is possible to implement vital sign monitoring in an economic manner, directly into textile products. This unobtrusive presence of sensors is especially important for the monitoring of children or elderly people. This paper focuses on two aspects of sensor integration: Integration of off-the-shelf electronic components, and the use of the textile material itself as sensor, or in general as an electrically active element presenting some exploratory work in the integration of electronic devices into textiles. The main objective was to reproduce and improve on previous work presented by other authors, and foster possibilities of developing garments for vital sign monitoring with immediate industrial and economic feasibility. The use of standard production techniques to produce textile-based sensors, easily integrated into garments and with mass-market potential, is one of the important motivations for this work

Wearable sensors for respiration monitoring: a review

This paper provides an overview of flexible and wearable respiration sensors with emphasis on their significance in healthcare applications. The paper classifies these sensors based on their operating frequency distinguishing between high-frequency sensors, which operate above 10 MHz, and low-frequency sensors, which operate below this level. The operating principles of breathing sensors as well as the materials and fabrication techniques employed in their design are addressed. The existing research highlights the need for robust and flexible materials to enable the development of reliable and comfortable sensors. Finally, the paper presents potential research directions and proposes research challenges in the field of flexible and wearable respiration sensors. By identifying emerging trends and gaps in knowledge, this review can encourage further advancements and innovation in the rapidly evolving domain of flexible and wearable sensors.This work was supported by the Spanish Government (MICINN) under Projects TED2021-131209B-I00 and PID2021-124288OB-I00.Peer ReviewedPostprint (published version

An investigation of textile sensors and their application in wearable electronics

Using a garment as a wearable sensing device has become a reality. New methods and techniques in the field of wearable sensors are being developed and can now be incorporated into the wearer’s everyday attire. This research focuses on two types of textile based sensors – a wearable textile electrode used for ECG continuous monitoring, and a stitch sensor for monitoring body movement. These sensors were designed into a purposely engineered Smart Sports Bra (SSB) which can be regarded as a sensor itself. After a thorough investigation, two optimum textile electrodes were created; a plain electrode using cut and sew method (CSM) and a net type knitted electrode using knitting method (KM). The CSM electrode was made with conductive fabric (MedTexTM P-130) and the KM electrode was made with conductive thread (silver-plated nylon 234/34 four-ply), these materials having the lowest tested contact impedance; 450Ω and 500Ω, respectively. Both electrodes demonstrated a level of noise and baseline drift comparable with standard commercial wet-gel electrodes, which was corrected by optimising their size to 20x40 mm, holding pressure of 4 kPa (30 mmHg) and the electrode position at the 6th intercostal space on the right and left mid-clavicular, with one placed at the scapular line in the rear side (i.e. back horizontal formation) which gives clear and reliable ECG signal. These optimum electrodes were integrated directly into SSBs, in which a novel high shear, net structure, acting as a shock absorber to body movement that shows more stable electrode to skin contact by reducing the body motion artefact. During the investigation of the stitch stretch sensor the single jersey nylon fabric (4.44 tex two-ply) with 25% spandex (7.78 tex) had the highest elastic recovery (93%). Using this fabric, the work went on to show that the stitch type 304 (Zig-zag lock stitch) using the 117/17 two-ply thread demonstrated the best results i.e., maximum working range 50%, gauge factor 1.61, hysteresis 6.25% ΔR, linearity (R2 ) is 0.98, and good repeatability (drift in R2 is -0.00). The stitch stretch sensor was also incorporated into a sports bra SSB and positioned across the chest for respiration monitoring. This thesis contributes to a growing body of research in wearable E -textile solutions to support health and well-being, with fully functional sensors and easy-to-use design, for continues health monitoring

Review on Smart Electro-Clothing Systems (SeCSs)

This review paper presents an overview of the smart electro-clothing systems (SeCSs) targeted at health monitoring, sports benefits, fitness tracking, and social activities. Technical features of the available SeCSs, covering both textile and electronic components, are thoroughly discussed and their applications in the industry and research purposes are highlighted. In addition, it also presents the developments in the associated areas of wearable sensor systems and textile-based dry sensors. As became evident during the literature research, such a review on SeCSs covering all relevant issues has not been presented before. This paper will be particularly helpful for new generation researchers who are and will be investigating the design, development, function, and comforts of the sensor integrated clothing materials

Decontamination of Wearable Textile Electrodes for Medical and Health Care Applications

In the medical and health care environment ‘intelligent’ clothing must endure all the same treatments and procedures as standard hospital textile; that is laundry, disinfection and sterilization. The decontamination level depends on the end-use of the product. The smart garment system for long term body monitoring must be like any other technical underwear; fit well, be comfortable, elastic, vapor permeable, and have easy-care properties capable of enduring multiple cycles of laundry washing. Thus the use of man-made fibers, instead of traditionally used natural fibers, in a body monitoring garment would be more reasonable.The research focuses on disinfected and sterilized textile electrodes which are applicable for long term body monitoring. As high elasticity, comfort and good vapor permeability are needed, the research concentrates on the electrical and mechanical properties of knitted sensors after sterilization, disinfection and water-repellent treatment. The most important mechanical features of elastic textile electrodes are elongation recovery and dimensional stability. Before sterilization the textile must be cleaned properly from body fluids like blood and sweat. Improving the easy-clean properties would consequently be desirable. By improving the stain repellent or easy cleaning properties, the need for washing can be decreased and a more protective, lower temperature program during laundry washing can be used. These factors not only save energy but also lengthen the lifetime of textile electronics.The textile surface electric resistance, abrasion resistance, dimensional change and elastic properties following decontamination processes were studied, including the evaluation of water repellent-treated electrode properties. In addition, the mechanical properties of conventional knits and elastic woven bands were observed after treatment in order to assess their use in smart wearable systems.In addition to electrodes, the research results can be applied to many other textile electronics components such as conductors, antennae, heat elements, switchers and detectors, because all these components can be achieved with same elements; conventional textile fibers combined with conductive fibers or coatings. The obvious application areas for body monitoring by using textile electrodes are hospitals, health care centers and medical research centers. The textile electrodes are more comfortable and invisible for long time body monitoring which is needed, for example, in rehabilitation after surgery or detection of chronic diseases, where they are more effective than conventional gel (Ag / AgCl) electrodes.In conclusion it can be stated that silver-plated PA fiber in a knitted or woven structure with added repellent treatment provides a highly conductive and durable solution for wearable electronics in medical and health care applications. The steel fiber and textile mixture cannot tolerate mechanical stress caused by disinfection, washing, or repellent treatment. The knitted textile with silver coating cannot tolerate sterilization, either electrically or mechanically. Based on the results of the study, the use of woven bands as an electrode would be recommended instead of knitted material because they are dimensionally more stable. The electrode dimensional changes might negatively affect the measurement quality. On the other hand, the knitted electrodes have additional useful properties like softness and flexibility, thus compromises must be made in using textile electrodes in wearable technology. All materials in the study, woven and knitted, elastic and inelastic, coated and non –coated showed clear shrinkage in the sterilization process. However, using only one heat treatment makes them much more stable. For this reason it can be assumed that man-made fibers are more useful for medical products as they are more resistant to being sterilized or disinfected than are natural fibers. The elastane fiber can be used for improving bi-directional textile material recovery, but the unrecovered elongation as a function of sterilization must be considered. The variation in unrecovered elongation (stretching) might be extremely high and success depends on raw materials and textile structures

Integration of conductive materials with textile structures : an overview

In the last three decades, the development of new kinds of textiles, so-called smart and interactive textiles, has continued unabated. Smart textile materials and their applications are set to drastically boom as the demand for these textiles has been increasing by the emergence of new fibers, new fabrics, and innovative processing technologies. Moreover, people are eagerly demanding washable, flexible, lightweight, and robust e-textiles. These features depend on the properties of the starting material, the post-treatment, and the integration techniques. In this work, a comprehensive review has been conducted on the integration techniques of conductive materials in and onto a textile structure. The review showed that an e-textile can be developed by applying a conductive component on the surface of a textile substrate via plating, printing, coating, and other surface techniques, or by producing a textile substrate from metals and inherently conductive polymers via the creation of fibers and construction of yarns and fabrics with these. In addition, conductive filament fibers or yarns can be also integrated into conventional textile substrates during the fabrication like braiding, weaving, and knitting or as a post-fabrication of the textile fabric via embroidering. Additionally, layer-by-layer 3D printing of the entire smart textile components is possible, and the concept of 4D could play a significant role in advancing the status of smart textiles to a new level

Innovative Wearable Sensors Based on Hybrid Materials for Real-Time Breath Monitoring

This chapter will present the importance of innovative hybrid materials for the development of a new generation of wearable sensors and the high impact on improving patient’s health care. Suitable conductive nanoparticles when embedded into a polymeric or glass host matrix enable the fabrication of flexible sensor capable to perform automatic monitoring of human vital signs. Breath is a key vital sign, and its continuous monitoring is very important including the detection of sleep apnea. Many research groups work to develop wearable devices capable to monitor continuously breathing activity in different conditions. The tendency of integrating wearable sensors into garment is becoming more popular. The main reason is because textile is surrounding us 7 days a week and 24 h a day, and it is easy to use by the wearer without interrupting their daily activities. Technologies based on contact/noncontact and textile sensors for breath detection are addressed in this chapter. New technology based on multi-material fiber antenna opens the door to future methods of noninvasive and flexible sensor network for real-time breath monitoring. This technology will be presented in all its aspects