Advances to functional materials and flexible electronics have yielded new means of integrating electrical properties into textile materials, which invite researchers in various fields to apply woven-textile construction methods in eTextile development. However, common ground for woven eTextiles’ prototyping is still taking shape. This calls for greater understanding of how the knowledge now scattered across diverse research fields can benefit the textiles’ development for HCI. To investigate how eTextile research has employed weaving and extract insight for HCI purposes, the authors reviewed and categorised applications of woven structures and electrical functions, then identified specifically HCI-relevant qualities and means of creating them via weaving. The paper outlines those woven structures useful for HCI and advocates consistent weaving-related terminology, to improve knowledge transfer across disciplines. In addition, the results point to research opportunities involving haptic qualities, the ability to weave multiple layers, functionality integration, and tools and methods.

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Woven eTextiles in HCI — a Literature Review

On-body transmission represents a challenge due to human body shadowing. This paper proposes a Sommerfeld-Goubau single-wire transmission line (SWTL) implemented using electronic textiles for low-loss on-body links up to millimeter-wave frequencies, overcoming the spherical spreading loss and on-body absorption. The SWTL is fabricated using a conductive thread suitable for embroidery on textiles. A compact tapered launcher is implemented on a flexible polyimide substrate to excite the surface mode along the SWTL. In space, a 3 m-long line maintains a forward transmission over −10 dB between 1 and 3 GHz. The SWTL link is characterized for different body parts showing under 20 dB insertion loss with a 1 cm air gap. Across the torso, a forward transmission over −20 dB is maintained from 0.5 to 2.5 GHz, which represents at least 20 dB improvement over two antennas, of larger dimensions, over-the-air. Directly on-skin, the SWTL can be used around 1 GHz with an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S_{21}$ </tex-math></inline-formula> over −25 dB, over 50 dB improvement over two on-skin antennas. At 50 GHz, the shielded SWTL exhibits an ultra-low on-body attenuation around 0.11 dB/mm, a four-fold improvement over a microstrip line on the same substrate. It is concluded that SWTLs can enable ultra high-speed future body area networks. 

Broadband Low-Loss On-Body UHF to Millimeter-Wave Surface Wave Links Using Flexible Textile Single Wire Transmission Lines

On-body transmission represents a challenge due to human body shadowing. This paper proposes a Sommerfeld-Goubau single-wire transmission line (SWTL) implemented using electronic textiles for low-loss on-body links up to millimeter-wave frequencies, overcoming the spherical spreading loss and on-body absorption. The SWTL is fabricated using a conductive thread suitable for embroidery on textiles. A compact tapered launcher is implemented on a flexible polyimide substrate to excite the surface mode along the SWTL. In space, a 3 m-long line maintains a forward transmission over −10 dB between 1 and 3 GHz. The SWTL link is characterized for different body parts showing under 20 dB insertion loss with a 1 cm air gap. Across the torso, a forward transmission over −20 dB is maintained from 0.5 to 2.5 GHz, which represents at least 20 dB improvement over two antennas, of larger dimensions, over-the-air. Directly on-skin, the SWTL can be used around 1 GHz with an $S_{21}$ over −25 dB, over 50 dB improvement over two on-skin antennas. At 50 GHz, the shielded SWTL exhibits an ultra-low on-body attenuation around 0.11 dB/mm, a four-fold improvement over a microstrip line on the same substrate. It is concluded that SWTLs can enable ultra high-speed future body area networks.

https://ieeexplore.ieee.org/ielx7/8566058/8911222/09656565.pdf

This paper presents a holistic and authoritative review of the role of microwave technologies in enabling a new generation of wearable devices. A human-centric Internet of Things (IoT) covering remote healthcare, distributed sensing, and consumer electronics, calls for high-performance wearable devices integrated into clothing, which require interdisciplinary research efforts to emerge. Microwaves, the “interconnect” of wireless networks, can enable, rather than solely connect, the next generation of autonomous, sustainable, and wearable-friendly electronics. First, enabling technologies including wireless power transmission and RF energy harvesting, backscattering and passive communication, RFID, and electromagnetic sensing are reviewed. We then discuss the key integration platforms, covering smart fabrics and electronic textiles, additive manufacturing, printed electronics, natively-flexible and organic RF semiconductors, and fully-integrated CMOS systems, where opportunities for hybrid integration are highlighted. The emerging research trends, from mmWave 6G, RF sensing and imaging, to healthcare applications including neural implants, drug delivery, and safety upon exposure to microwaves are re-visited and discussed, presenting a future roadmap for interdisciplinary research towards sustainable and reliable next-generation wearables.

https://eprints.gla.ac.uk/285437/1/285437.pdf

Microwave-Enabled Wearables: Underpinning Technologies, Integration Platforms, and Next-Generation Roadmap

Abstract Printed electronics (PE) is one of the most dynamic technologies in the world. It proposes low-cost electronic network production in flexible substrates by numerous printing techniques, (screen printing, gravure, offset, flexographic, and inkjet printing), used in various industries. In PE, ink pigments are replaced by metallic particles or precursors that transmit electrical conductivity to the printed patterns such as carbon, polymers and conductive pigments. Conductive inks play an important role in printed electronics, and despite the number of conductive ink types available on the market, there are still issues to be addressed. Some of these restrictions include the use of toxic chemical reagents and solvents and complicated manufacturing protocols, which often make the industrialization of conductive inks an even more distant goal. In particular, conductive inks based on silver nanoparticles, Graphene and PEDOT:PSS are widely studied thanks to their high electrical conductivity. On the other hand, there is still work to be done to show the interest of inks based on phthalocyanine pigments, in particular copper phthalocyanine. Nevertheless, problems related to stability, dispersion and annealing temperature often limit the application of these four types of fillers. In this review, we present general information on available conductive fillers used for the formulation of conductive inks, focusing on metallic particles, carbon fillers, pigments and polymers. The influence and technical requirements of the regularly used printing techniques, as well as the post-processing treatments to achieve the targeted performance in the obtained inks have been discussed. In addition, the surface characteristics of the various types of extensible and flexible substrates used in portable electronics are described. Moreover, some types of printed flexible electronic components as well as notable applications of electronic textiles in various sectors are exhibited. Next, the major challenges for the manufacturing of printed flexible electronics and recommendations for future research are discussed in this review

Formulation of conductive inks printable on textiles for electronic applications: a review

Wearable devices are ideal for personalized electronic applications in several domains such as healthcare, entertainment, sports and military. Although wearable technology is a growing market, current wearable devices are predominantly battery powered accessory devices, whose form factors also preclude them from utilizing the large area of the human body for spatiotemporal sensing or energy harvesting from body movements. E-textiles provide an opportunity to expand on current wearables to enable such applications via the larger surface area offered by garments, but consumer devices have been few and far between because of the inherent challenges in replicating traditional manufacturing technologies (that have enabled these wearable accessories) on textiles. Also, the powering of e-textile devices with battery energy like in wearable accessories, has proven incompatible with textile requirements for flexibility and washing. Although current e-textile research has shown advances in materials, new processing techniques, and one-off e-textile prototype devices, the pathway to industry scale commercialization is still uncertain. This paper reports the progress on the current technologies enabling the fabrication of e-textile devices and their power supplies including textile-based energy harvesters, energy storage mechanisms, and wireless power transfer solutions. It identifies factors that limit the adoption of current reported fabrication processes and devices in the industry for mass-market commercialization.

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Guillaume Savelli

Papers

E-Textile Technology Review–From Materials to Application