Smart textiles have been attracting considerable interest in imparting a wide range of functions to traditional clothing ranging from sensing, actuation, data processing, and energy storage. In the case of textile-based strain sensors, most of the studies proved that they can work in principle, however, producing strain sensors with desirable properties such as stable sensitivity, small hysteresis, large enough working range, and good repeatability still remains a challenge necessitating the developments of novel technologies for soft sensors. This paper conducts a systematic approach to investigate the electromechanical properties of the knitted strain sensors to find out the optimum process parameters. We found a repeatable and robust method to produce knitted strain sensors with low hysteresis at a working range of at least 40%.

In recent years, knitted strain sensors have been developed that aim to achieve reliable sensing and high wearability, but they are associated with difficulties due to high hysteresis and low gauge factor (GF) values. This study investigated the electromechanical performance of the weft-knitted strain sensors with a systematic approach to achieve reliable knitted sensors. For two elastic yarn types, six conductive yarns with different resistivities, the knitting density as well as the number of conductive courses were considered as variables in the study. We focused on the 1 × 1 rib structure and in the sensing areas co-knit the conductive and elastic yarns and observed that positioning the conductive yarns at the inside was crucial for obtaining sensors with low hysteresis values. We show that using this technique and varying the knitting density, linear sensors with a working range up to 40% with low hysteresis can be obtained. In addition, using this technique and varying the knitting density, linear sensors with a working range up to 40% strain, hysteresis values as low as 0.03, and GFs varying between 0 and 1.19 can be achieved.

Eleven phase change materials (PCMs) for cooling humans in heat-stressed conditions were evaluated for their cooling characteristics. Effects of packaging material and segmentation were also investigated. Sample packs with a different type PCM (water- and oil-based PCMs, cooling gels, inorganic salts) or different packaging (aluminum, TPU, TPU + neoprene) were investigated on a hotplate. Cooling capacity, duration, and power were determined. Secondly, a PCM pack with hexagon compartments was compared to an unsegmented version with similar content. Cooling power decreased whereas cooling duration increased with increasing melting temperature. The water-based PCMs showed a >2x higher cooling power than other PCMs, but were relatively short-lived. The flexible gels and salts did not demonstrate a phase change plateau in cooling power, compromising their cooling potential. Using a TPU or aluminum packaging was indifferent. Adding neoprene considerably extended cooling duration, while decreasing power. Segmentation has practical benefits, but substantially lowered contact area and therefore cooling power.

Prolonged exposure to solar radiation can cause considerable heat stress. The application of reflective materials in garments or sunscreens is generally considered as an appropriate protective strategy. In this study, we aimed to compare a range of reflective and control fabrics on their ability to reduce the thermal impact of solar radiation. We evaluated 16 reflective and 5 control fabrics, varying in applicability for garments and/or sunscreens. Transmission of ultraviolet, visible light and infrared radiation was studied using artificial solar light. Thermal impact reduction was first studied using artificial infrared light and secondly using natural sunlight, measuring temperature right at the back and 10 cm behind the fabric after a 10-minute exposure. Most samples showed comparably low radiation transmission (<10%). However, substantially higher transmission was observed in perforated and mesh-like reflective fabrics, as well as light-colored controls and coldblack® treated fabric. This resulted in larger temperature increases at 10 cm behind the fabric (+1-4°C in sunlight). Contact temperature at the back of the black fabrics ended up higher than at the back of the reflective and white control fabrics (T: 5-10°C in sunlight), the latter two showing minor mutual differences (T<3°C). In conclusion, the reflective fabrics (excluding perforated, mesh and coldblack®) showed minor mutual differences, lower heat absorption than the black control fabrics and lower heat transmission than the white ones. The results suggest that reflective or white fabrics are preferable for most garment applications, while reflective or possibly black fabrics are preferable for sunscreen applications.