Dielectric Properties of Textile Materials: Analytical Approximations and Experimental Measurements—A Review

Deciphering how the dielectric properties of textile materials are orchestrated by their internal components has far-reaching implications. For the development of textile-based electronics, which have gained ever-increasing attention for their uniquely combined features of electronics and traditional fabrics, both performance and form factor are critically dependent on the dielectric properties. The knowledge of the dielectric properties of textile materials is thus crucial in successful design and operation of textile-based electronics. While the dielectric properties of textile materials could be estimated to some extent from the compositional profiles, recent studies have identified various additional factors that have also substantial influence. From the viewpoint of materials characterization, such dependence of the dielectric properties of textile materials have given rise to a new possibility—information on various internal components could be, upon successful correlation, extracted by measuring the dielectric properties. In view of these considerable implications, this invited review paper summarizes various fundamental theories and principles related to the dielectric properties of textile materials. In order to provide an imperative basis for uncovering various factors that intricately influence the dielectric properties of textile materials, the foundations of the dielectrics and polarization mechanisms are first recapitulated, followed by an overview on the concept of homogenization and the dielectric mixture theory. The principal advantages, challenges and opportunities in the analytical approximations of the dielectric properties of textile materials are then discussed based on the findings from the recent literature, and finally a variety of characterization methods suitable for measuring the dielectric properties of textile materials are described. It is among the objectives of this paper to build a practical signpost for scientists and engineers in this rapidly evolving, cross-disciplinary field.

Aromatherapy in Textiles: A Systematic Review of Studies Examining Textiles as a Potential Carrier for the Therapeutic Effects of Essential Oils

Integrative medicine is a rapidly growing specialty field of medical care that emphasizes the amalgamation of complementary therapies and conventional medicine. Aromatherapy, one of the complementary therapies, is a centuries-old tradition, used in many cultures and societies as an alternative to, or in conjunction with, conventional medicine. However, there is very little understanding of its therapeutic benefits in the scientific realm related to the correct dosage of essential oils, their delivery mechanism and their efficacy on human physiology in general. We reviewed studies published between 2011–2021 focused on aromatherapy and textiles, and explore “textile” materials as a possible carrier for essential oils in this paper. Due to their proximity to the biggest organ of the human body, textiles can potentially serve as a good delivery system for the therapeutic benefit of essential oils. After this rigorous review, we found gaps in the field. Therefore, we propose cross-disciplinary synergies for future research to fully understand the therapeutic efficacy of essential oils.

Characterizing Steam Penetration through Thermal Protective Fabric Materials

This study performs an analysis of steam penetration through thermal protective fabric materials. Different, multilayered thermal protective fabrics were selected and tested in a laboratory-simulated steam exposure, and their steam protective performance (SPP) was measured in terms of the time required to generate second-degree burns on the bodies of wearers. Additionally, the total transmitted thermal energy (TTTE) through the fabrics during testing was measured. Through statistical analysis, it was established that fabric properties, namely air permeability and thickness, are the key factors that affect the SPP and TTTE; the relationship among the fabric properties, SPP, and TTTE is also summarized. Theoretically, it has been found that heat and mass (steam) transfer occur through fabrics in the course of steam exposure, which mainly affect the SPP and TTTE. This study could help textile/materials engineers to develop high performance thermal protective fabrics for the increased occupational health and safety of firefighters and industrial workers.

Modelling of Auxetic Woven Structures for Composite Reinforcement

The current research is focused on the design and development of auxetic woven structures. Finite element analysis based on computational modeling and prediction of axial strain as well as Poisson’s ratio was carried out. Further, an analytical model was used to calculate the same parameters by a foldable zig-zag geometry. In the analytical model, Poisson’s ratio is based on the crimp percentage, bending modulus, yarn spacing, and coefficient of friction. In this yarn, properties and fabric parameters were also considered. Experimental samples were evaluated for the actual performance of the defined auxetic material. Auxetic fabric was developed with foldable strips created in a zig-zag way in the vertical (warp) direction. It is based on the principle that when the fabric is stretched, the unfolding of the folds takes place, leading to an increase in transverse dimensions. Both the analytical and computational models gave close predictions to the experimental results. The fabric with foldable strips created in a zig-zag way in the vertical (warp) direction produced negative Poisson’s ratio (NPR), up to 8.7% of axial strain, and a maximum Poisson’s ratio of −0.41 produced at an axial strain of around 1%. The error percentage in the analytical model was 37.14% for the experimental results. The computational results also predict the Poisson’s ratio with an error percentage of 22.26%. Such predictions are useful for estimating the performance of auxetic woven structures in composite reinforcement. The auxetic structure exhibits remarkable stress-strain behavior in the longitudinal as well as transverse directions. This performance is useful for energy absorption in composite reinforcement.

A Comparison of Two Different Light Booths for Measuring Color Difference of Metameric Pairs

A standardized source of light is essential for visual color assessments, which is why lighting booths were developed. For the best results in visual assessment, it is important to consider the right choice of light source, the right viewing conditions, and the variability of the viewer. To date, many light booth technologies have been introduced to meet user demands. Since most of the light sources on the market are characterized by the designer or manufacturer, the resulting variations from booth-to-booth remain. In this study, we compared the performance of two standard light booths to assess the color difference of eleven metameric pairs. In this study, we checked an earlier technology-based light booth that is still used in the textile industry and contains illuminant A (Tungsten lamp) with CCT 2700 K, TL84 (tri-band fluorescent tube) with CCT 4000 K, and simulator D65 (CCT 6500 K) with a different light booth whose original light sources have been replaced by currently available LED retro kits from equivalent CCTs. As an inexperienced customer or industrial user, our question was, how important is this replacement? The results revealed that two different standard lighting technologies with similar CCTs cannot reproduce the same estimates because the light sources produced different SPDs. It is illustrating that caution is necessary when comparing results obtained from two different light booths containing light sources with similar CCTs but different SPDs. This comparative study suggested that the variability of the light sources’ SPDs or the observer or the sample should be modeled considering light booth’s technology to estimate its contribution to the overall variability. The close relationship between perceived and CAM02-UCS suggests that if both booths are used after the light sources have been calibrated, a formula based on color appearance models must be used to predict color appearance. To obtain better agreement between perceived and calculated color difference, one must need to avoid light booths with nominally white light sources.

Stretchable Textile Yarn Based on UHF RFID Helical Tag

In the context of wearable technology, several techniques have been used for the fabrication of radio frequency identification (RFID) tags such as 3D printing, inkjet printing, and even embroidery. In contrast to these methods where the tag is attached to the object by using sewing or simple sticking, the E-Thread® technology is a novel assembling method allowing for the integration of the RFID tag into a textile yarn and thus makes it embeddable into the object at the fabrication stage. The current E-Thread® yarn uses a RFID tag in which the antenna is a straight half-wave dipole that makes the solution vulnerable to mechanical strains (i.e., elongation). In this paper, we propose an alternative to the current RFID yarn solution with the use of an antenna having a helical geometry that answers to the mechanical issues and keeps quite similar electrical and radiative properties with respect to the present solution. The RFID helical tag was designed and simulated taking into consideration the constraints of the manufacturing process. The helical RFID tag was then fabricated using the E-Thread® technology and experimental characterization showed that the obtained structure exhibited good performance with 10.6 m of read range in the ultra high frequency (UHF) RFID band and 10% of tolerance in terms of elongation.

Manufacturing and Characterization of Customizable Flexible Carbon Nanotube Fabrics for Smart Wearable Applications

The integration of carbon nanotube fabric into textiles is paving its way into smart materials and wearable applications. Potential novel applications of carbon nanotube hybrid (CNTH) materials and fabric composites span across a range of market levels from high-level PPE appropriate for military and industrial applications down to consumer products that can be used in everyday scenarios. The high-level performance properties of CNTH materials and their ability to be customized provide new possibilities for constructing fabrics with properties that are made to order. Furthermore, CNTH in combination with advanced textile compositing and construction methods allows the CNTH material to further leverage material customization aspects to meet specific requirements. The unique synthesis process for nanotube fabric allows for modification of the physical properties of the CNTH itself. The CNTH fabric combined with the customizability of standard textile composite materials and with the use of apparel design features allows for the design of materials with new combinations of physical properties. These unique properties offer high potential for developing families of smart wearable garments that can be scaled for industrial production. This article discusses the synthesis of carbon nanotube hybrid fabric, the process of hybrid fabric and textile integration, properties of the hybrid textile, and potential applications. The paper also provides an outlook towards large scale production of the hybrid textile material.

A Review on Tough Soft Composites at Different Length Scales

Soft composites are widely employed in industrial and biomedical fields, which often serve as load-bearing structural materials by virtue of a special combination of high strength, high toughness, and low flexural stiffness. Understanding the toughening mechanism of such composites is crucial for designing the next-generation soft materials. In this review, we give an overview of recent progress in soft composites, focusing on the design strategy, mechanical properties, toughening mechanisms, and relevant applications. Fundamental design strategies for soft composites that dissipate energy at different length scales are firstly described. By subsequently elucidating the synergistic effects of combining soft and hard phases, we show how a resulting composite can achieve unprecedented mechanical performance by optimizing the energy dissipation. Relevant toughening models are discussed to interpret the superior strength and fracture toughness of such soft composites. We also highlight relevant applications of these soft composites by taking advantage of their special mechanical responses.

An Alternative Method to Develop Embroidery Textile Strain Sensors

In this paper, a method to develop embroidered textile strain resistive sensors is presented. The method is based on two overlapped zigzag conductive yarn patterns embroidered in an elastic textile. To demonstrate the functionality of the proposed configuration, a textile sensor embroidered with a conductor yarn composed of 99% pure silver-plated nylon yarn 140/17 dtex has been experimentally characterised for an elongation range from 0% to 65%. In order to show the sensor applicability, a second test with the sensor embroidered in a knee-pad has been done to evaluate the flexion knee angle from 180° to 300°. The experimental results show the usefulness of the proposed method to develop fabric strain sensors that can help to manufacture commercial applications on the healthcare sector.

Development of a Consumer-Based Quality Scale for Artisan Textiles: A Study with Scarves/Shawls

Modern textile consumers are increasingly becoming more watchful of the quality of the textiles that they purchase. This has increased the need for textile producers, especially artisan textile makers (e.g., knitters, tailors, dressmakers, seamstresses, and quilters), to improve the quality of their textile products. Information on several analytical tools that are commonly used for assessing the quality of textiles is abundant, but consumer-based tools for evaluating the quality of textiles remain limited. A consumer-based artisan textile-quality scale was developed using data collected from two focus groups (Phase 1) and a consumer quantitative study, n = 196 (Phase 2). Ten scarves and shawls were evaluated in the quantitative study and analysis of variance (ANOVA) was used to determine the differences between the mean textile ratings for all the statements. Coefficient alpha (final raw alpha = 0.87) was also used to assess if the statements were consistent in the way they measured the quality of the textiles. Pearson correlation tests were used to validate the six-statement quality scale that included statements such as overall attention to detail, the fabric is durable, and stitching is even and consistent. Artisan textile makers in the USA can use this scale to better meet the functional needs of their customers. Additionally, the process that was employed in the development of the six-statement quality scale can be used by researchers in other countries to understand better the key quality characteristics of artisan as well other textile products.