Photodiodes embedded within electronic textiles

Abstract

A novel photodiode-embedded yarn has been presented and characterized for the first time, offering new possibilities for applications including monitoring body vital signs (including heart rate, blood oxygen and skin temperature) and environmental conditions (light, humidity and ultraviolet radiation). To create an E-Textile integrated with electronic devices that is comfortable, conformal, aesthetically pleasing and washable, electronic components are best integrated within the structure of a textile fabric in yarn form. The device is first encapsulated within a protective clear resin micro-pod before being covered in a fibrous sheath. The resin micro-pod and covering fibres have a significant effect on the nature of light received by the photoactive region of the device. This work characterised the effects of both encapsulating photodiodes within resin micro-pods and covering the micro-pod with a fibrous sheath on the opto-electronic parameters. A theoretical model is presented to provide an estimate for these effects and validated experimentally using two photodiode types and a range of different resin micro-pods. This knowledge may have wider applications to other devices with small-scale opto-electronic components. Wash tests confirmed that the yarns could survive multiple machine wash and drying cycles without deterioration in performance.

Wash Testing of Electronic Yarn

“…The data only shows results where the E-yarns were attached to T-shirts. For completeness literature values for photodiode embedded E-yarns have been included (from [17]). The test results indicated that the properties of the copper wire in the E-yarns were key to wash durability.…”

“…The wash durability of E-yarns containing LEDs [16] has been reported, stating that LED E-yarns survived 7 to 25 machine washing and tumble drying cycles, however full details were not provided. Complete wash trails were conducted for both E-yarns containing photodiodes [17] and E-yarns containing solar cells [18]. For wash testing with photodiode embedded E-yarns two sets of five E-yarns were tested; five embroidered onto the surface of a cotton T-shirt, which were machine washed and tumble-dried and five woven into a textile structure, which were machine washed and line dried.…”

“…The washing procedure was based on Procedure 4N of ISO 6330:2012. It was observed that 20% of the embroidered E-yarns survived 25 washing/drying cycles and that 60% of the woven E-yarns survived 25 washing/drying cycles, with the first failures not observed until after wash 15 [17]. Solar cells embedded within E-yarns were also wash tested.…”

Flexible Sensors—From Materials to Applications

“…This must be taken into account when integrating sensors with textiles since otherwise this leads to detachment of the sensor from the textile structure. Sensors were generally incorporated into textile structures either by using glue [100], or by using the textile manufacturing techniques discussed in Section 2.5 such as knitting [443,444,446], weaving [388,630], or sewing [631]. In most cases the flexible sensors were directly attached onto the surface of the textile [100,323,404,455].…”

“…A more integrative approach looked into incorporating functional sensor strips as yarns in textile structures [388,[437][438][439]447]. Furthermore, Dias and coworkers [443,444,446,630,632,633] have pioneered a different method where surface mount sensor chips were seamlessly integrated within the core of a textile yarn and this yarn was used to fabricate textile garments. In general, the connections between the sensors and external circuits were made using conductive wires/threads [323,443,444,446,630,632,633], Bluetooth [555,634], NFC [635].…”