Glossary and definition of terms
2 Literature review
2.4 Woven e-‐textiles via technical materials approach
This section of the literature review will discuss selected technical woven e-‐textiles, and draws on aspects that are related to this PhD research. Therefore, specifics of data collection, chemical and technical analysis are less relevant here. In particular, integration methods and techniques to develop woven e-‐textiles will be focused on.
Woven structures can be manipulated to build physical structures to accommodate for electronic properties, either as integrated components or by using the architecture of woven construction to support electronic behaviours. Securely embedding electronics into textile constructions allows for truer integration of e-‐textiles. Ultimately, an integrated e-‐textiles approach will lead to more useable e-‐textile interfaces for interactive smart textile products. A potential outcome of this approach could lead to the technology becoming less obtrusive and the textiles becoming more active and responsive materials.
2.4.1 Eriksson et al. ʹ 3D woven capacitive sensor
Woven fabric construction uses historical techniques that are applied to different forms of weaving. Some woven constructions are directly related to conventional two-‐ dimensional fabrics as used for fashion and textiles, whilst others are more sophisticated and have been adapted to fit with innovative weaving methods, such as three-‐ dimensional structures.
In an overview paper by Chen et al. they emphasise the significance of a range of woven three-‐dimensional structures (Chen, Taylor and Tsai, 2011). Woven three dimensional structures have led to the development of advanced three-‐dimensional weaving equipment (Gokarneshan and Alagirusamy, 2009). E-‐textiles have and will undoubtedly be inspired by these constructions. There have already been some examples of such outcomes, using adapted traditional weaving methods in technical products with the integration of electronics. For example, Eriksson et al. (2011) presented an interactive textile structure woven in three-‐dimensional form integrating electronic properties to fabricate a capacitive sensor (Figure 2.11). In this project, their objective was to integrate processes to make a three-‐dimensional multilayer woven interactive fabric, to establish a single process to ease manufacture of such materials. This was achieved by adapting a loom to demonstrate a handmade prototype of a capacitance sensor textile. A three dimensional structure consisting of conductive outer layers, layered between a non-‐conductive compressive spacer structure successfully demonstrated a functioning capacitive sensor. This outcome had only been possible in this way due to opportunities available to manipulate the woven structural form and weaving loom.
Figure 2.11 /ŵĂŐĞŽĨ ƌŝŬƐƐŽŶĞƚĂů͛͘ƐƚŚƌĞĞ-‐dimensional woven capcitive sensor structure with conductive layers and structure schematic; where A and D are conductive layers, B and E are stable insulating layers and C is the compressive spacer layer (Eriksson et al., 2011)
2.4.2 Georgia tech Wearable Motherboard (GTWM) woven e-‐textile
The GTWM, as shown in Figure 2.12, is another example of the innovative use of woven methods in e-‐textiles. The engineered vest was a working prototype and used weaving in a singular piece of textiles, facilitating an off the loom wearable technology with considered placement of body data sensors (Firoozbakhsh et al., 2000). The wearable vest was designed to integrate transmittable fibres to enable communication from body data sensors to external devices, directly passing ƚŚĞ ƵƐĞƌ͛Ɛ ƉŚLJƐŝŽůŽŐŝĐĂů ĚĂƚĂ͘ At present there are other products that are able to sense, detect and communicate in a similar manner. However, GTWM was one of the first projects to have been initiated with specifically woven e-‐textiles in the late 90s.
Figure 2.12 Image of GTWM (Smart Shirt GTWM, 2003)
The woven architecture has been mapped with electronic circuit matrices to function as a complete integrated circuit, created simultaneously on the loom. GTWM development was followed by a patent filed by Georgia Tech research Corp in 1998 by Jayaraman et
al. and patent approval in 2000 (Jayaraman, Park and Rajamanickam, 2000)͘dŚĞǀĞƐƚ͛Ɛ
aesthetics and comfort factors could potentially be improved upon; although on reflection, this was an early prototype and not developed by designers, but a team of engineers using a technical materials approach (Smart Shirt GTWM, 2003). The work was inspirational for the early advances of woven e-‐textiles, specifically where integrated woven methods were applied to achieve a specific application.
2.4.3 TITV ʹ galvanotextile yarn integrated into a woven e-‐textile RFID tag
The research centre at TITV Greiz, Germany had also conceptualised a similar woven RFID transponder and prototyped this idea into a physical sample. They demonstrated this in their application of galvanotextile yarn research and development (galvanic and electrochemical metal coated yarns on micro and millimetre scale). They used jacquard weaving, to weave three consecutive layers simultaneously, controlling interaction connection points between the conductive tracks in the warp and weft on each layer (Gimpel, 2004 p.184) (Figure 2.13). d/ds͛Ɛ paper did not disclose in-‐depth details of the making method; however, their research did follow a process of e-‐yarn (electronic yarn) development through to an example of woven material application and function with design consideration. However, parts of the woven design have opportunity to be simplified with other woven construction, such as extra warps (section 4.2.1).
Figure 2.13 d/ds͛ƐǁŽǀĞŶZ&/ƚĂŐƐĂŵƉůĞ͘dŚƌĞĞ layers are woven on jacquard loom to form interaction points making a coil configuration enabling the structure to work as a transponder (Gimpel, 2004 p.185)
2.4.4 TITV ʹ Conductive and electroluminescent woven e-‐textile display
TITV have also investigated woven displays using a technical materials approach. By applying woven double cloth structure with conductive weft yarns, these operated as electrodes and were coated with electroluminescent paste through screen printing processes. When a current was passed via the conductive path, the electroluminescent area became charged to activate light emission, highlighting an image or text (Figure 2.14) (Moehring et al., 2006). In this example, although the weaving was only utilised to support the conductive wefts, without electrically charging the entire track the exposed electroluminescent area would not be able to display an output. Therefore, the woven
construction allows the textiles to operate as a complete circuit. The project objective was an investigation of electroluminescent properties in textile structures, as TITV operates as a specialist research institution for flexible materials and works with industry based projects.
Figure 2.14 /ŵĂŐĞŽĨd/ds͛ƐĞůĞĐƚƌŽůƵŵŝŶĞƐĐĞŶƚǁŽǀĞŶĚŝƐƉůĂLJƐĂŵƉůĞ͕ǁŚĞƌĞƐĐĂůĞŝƐ depicted as 90 x 90 pixels per square inch (Gimpel, 2004 p.187)
2.4.5 Berzowska et al. ʹ ͚<ĂƌŵĂŚĂŵĞůĞŽŶ͛ũĂĐƋƵĂƌĚǁŽǀĞŶƉŚŽƚŽŶŝĐďĂŶĚŐĂƉ;W'Ϳ fibre e-‐textiles
Berzowska and her research team have investigated photonic textiles through jacquard weaving processes, where the end application of these textiles can be used for electronic visual displays. However, they felt at the time of investigating this project,
͞&Ğǁ ĨƵŶĐƚŝŽŶĂů LJĂƌŶƐ ;ŽƚŚĞƌ ƚŚĂŶ conductive or resistive yarns) are currently available commercially to enable functionality such as the display of information, sensing, or energy harnessing in a textile. The ability to integrate the desired functionality on the fundamental level of a fiber remains one of the greatest technological challenges in the development of smart textiles͟ (Sayed, Berzowska and Skorobogatiy, 2010 p.1). The
research team investigated photonic crystal fibres to fabricate PBG fibres, creating photonic textiles and adaptable aesthetic displays. Depending on the light source (whether natural ambient or artificial emitted light), and the angle of exposure, the PBG fibres refract this radiation to emit different coloured light. As a result, the project was ŶĂŵĞĚ ͚<ĂƌŵĂ ŚĂŵĞůĞŽŶ͛͘ Applying jacquard weaving with the PBG fibres enabled different patterns and shapes to be visibly exposed at varying levels depending on the woven structures, i.e. more weft facing or more warp facing (Figure 2.15), (woven structures further discussed in section 4.2.2).
Figure 2.15 Images of Karma Chameleon jacquard woven PBG fibres. Top: sample is exposed to ambient light. Bottom: sample is exposed to emitted light. The woven structure generates visual imagery (Berzowska and Skorobogatiy, 2010 p.298)
Photonic fibres were applied ĂƐƉĂƌƚŽĨƚŚĞĨĂďƌŝĐ͛ƐĐŽŶƐƚƌƵĐƚŝŽŶƚŽŵĂŬĞǀŝƐƵĂůĚŝƐƉůĂLJƐ. This resulted in an effective way to achieve photonic textiles, as they can operate with unpowered or powered light sources. Therefore, this enables photonic fibres to be effective under most lit conditions, although they were less effective under ambient light than emitted light. The fibres were able to operate successfully even after the rigorous process of being woven on an industrial jacquard loom. The applications of these types of photonic textiles are wide, particularly given the different coloured lights emitted depending on the angle at which the PGB fibres are exposed to a light source.
As Sayed et al. ƉŽŝŶƚĞĚ ŽƵƚ ŝŶ ƚŚĞ ͚<ĂƌŵĂ ŚĂŵĞůĞŽŶ͛ ƉƌŽũĞĐƚ͕ ĚĞǀĞůŽƉŵĞŶƚ ŽĨ compatible technology on fibre level is vital for the progression of integrated components for e-‐textiles. Perhaps with the eventual maturity of micro-‐components, this may see an evolution of e-‐ƚĞdžƚŝůĞƐ͛ form factor, making other fibre based electronics possible to be integrated directly into woven constructions. In turn, ͘͘͘͞ŝƚ ŝƐƉŽƐƐŝďůĞƚŽ
obtain a textile matrix that is particularly interesting for future developments in distributed sensor systems made on a textile platform͟(Locci et al., 2007 p.3972).
2.4.6 Eitan Bonderover and Sigurd Wagner ʹ woven inverter circuit
A project by Eitan Bonderover and Sigurd Wagner from Princeton University, sought to investigate the use of the woven construction to distribute different fibres and components in an integrated woven electronic inverter circuit. They proposed and prototyped a woven e-‐textile where e-‐fibres were only able to function due to their specific position and contact point within the woven structure (Bonderover and Wagner, 2004). The contacts were held in place solely by the pressure of the woven construction to maintain textile flexibility (Figure 2.16). Although this project had a large amount of technical and scientific knowledge applied in developing the e-‐fibres, in terms of the woven construction, the prototype only applied a plain weave structure that was sufficient to operate this complex circuit. In this case, much of the technical sophistication was incorporated into the e-‐fibres.
In describing the woven structure, the researchers called this Ă ͚ďĂƐŝĐ ƉĂƚƚĞƌŶ͛ ĂŶĚ ƌĞĨĞƌƌĞĚƚŽĂ͚ƐŝŵƉůĞƚŚƌĞĂĚ͛ƚŚĂƚǁĂƐƵƐĞĚŝŶƚŚĞĐŽŶƐƚƌuction. Clearly, the method of weaving was not fully explored here, or explained in-‐depth; potentially due to the researchers not being specialised in woven construction and the project only being an initial investigation of this concept. The final physical sample͛Ɛ ĂĞƐƚŚĞƚŝĐ ǁĂƐ partially that of plastic, as the e-‐fibres were based on Kapton (polyimide flexible film PCB). This was suitable for the integration of this prototype, however, use of a textile substrate base would realise this application as a complete soft e-‐textile. The final testing of the prototype proved successful.
Figure 2.16 ^ĐŚĞŵĂƚŝĐ ŝůůƵƐƚƌĂƚŝŽŶ ŽĨ ŽŶĞƌŽǀĞƌ ĂŶĚ tĂŐŶĞƌ͛Ɛ ǁŽǀĞŶ ŝŶǀĞƌƚĞƌ ĐŝƌĐƵŝƚ (Bonderover and Wagner, 2004 p.295)
2.4.7 ETH ʹ e-‐fibre strip temperature sensor integrated woven e-‐textile
As mentioned in the introduction, ETH Zurich has been researching e-‐fibres to specifically integrate into woven fabrics. They have investigated various sensors and LEDs on flexible thin e-‐yarns through their own fabrication methods, using technical material approaches (Figure 2.17).
Figure 2.17 d,͛ƐĞ-‐fibre fabrication process. In the above example, a temperature sensor is fabricated to be woven into a fabric construction (Cherenack et al., 2010 p.2)
They developed strip temperature sensors which were then integrated into a woven e-‐ textile, where the majority of the fibres were soft textile yarns (fibre compositions were not stated). However, the circuit contact point of the e-‐fibre was held in place by gluing into position using conductive glue (Figure 2.18), which also helped stabilise the connectivity. Although the woven sample was constructed on an industrial loom, the e-‐ fibres were inserted as weft picks manually by stopping the automatic loom process. The woven structure applied appears to be a basic twill structure, as this is not specifically documented in the research paper, but is visible in the image of the sample.
Figure 2.18 d,͛ƐǁŽǀĞŶĞ-‐fibre temperature sensor in a textile circuit with conductive yarn as buses. The e-‐fibre is illustrated where conductive glue is used to hold the contact in place (Cherenack et al., 2010 p.2)
As with Bonderover and tĂŐŶĞƌ͛s work, d,͛Ɛ ǁŽǀĞŶ Ğ-‐fibre temperature sensor͛Ɛ textile construction has only been used as a mesh scaffold to support the electronics. They have not fully utilised the woven structure as part of the e-‐textiles circuitry, as conductive yarns could have been integrated into the e-‐textile to help achieve interconnection with the circuit. In addition, other tighter woven structures and multilayer weaving would have stabilised the component integration.
d,͛ƐǁŽǀĞŶĞ-‐fibre temperature sensor project further progressed to test for electrical properties, mechanical analysis, washability and wearability (Zysset et al., 2012). ETH aimed to combine both electronics and textiles on a level that would result in feasible applications to monitor body motion, bio-‐physiological data and other e-‐textile product surfaces (e.g. furniture, automotive interiors, etc.), which could have sophisticated functions and operate successfully. ETH demonstrated that electronic and woven textiles can be combined for successful outcomes and that textiles ͘͘͘͞ƉƌŽǀŝĚĞĂƐƵŝƚĂďůĞ
platform for sensor integration to measure these parameters and signals close to the human body. To increase the acceptance of smart textiles and ultimately their wearability requires an unobtrusive integration of electronics into textiles͟ (Zysset et al.,
2012 p.1107)
2.4.8 Martin Ğƚ Ăů͛͘Ɛ e-‐textiles jumpsuit project with integrated fabric network and sensors
At Virginia Polytechnic Institute and State University, a group of researchers developed a jumpsuit for motion capture, specifically focusing on woven construction to design and make integrated fabric networks (Martin et al., 2009). The woven e-‐textiles for this project have already been mentioned in section 2.2.7 (Quirk, Martin and Jones, 2009). Woven integration of sensors (referred to as ͚Ğ-‐ƚĂŐƐ͛ͿǁŽƵůĚďĞĐŽŶŶĞĐƚĞĚǀŝĂĚŝĨĨĞƌĞŶƚ patterned pieces of the garment. Conductive threads were not used in this example, instead wires (insulated and bare) were applied for the electrical tracks. The concept was to make ͘͘͘͞ĂŶ ŽŶ-‐fabric digital network that allows [them] to quickly add new
ƐĞŶƐŽƌƐ ĂŶĚ ƌĞƉƌŽŐƌĂŵ ƚŚĞ ŐĂƌŵĞŶƚ ĨŽƌ Ă ŶĞǁ ĂƉƉůŝĐĂƚŝŽŶ͟ (ibid). Martin et al. used
woven construction to their advantage. For example, this can be seen in their use of a broken twill structure with elastic weft yarns, floating extra warp (wire) and floating wire wefts (Figure 2.19). The use of elastic yarn for a close-‐fitting garment and floating of
threads were effective ways to manipulate woven construction to suit the context of this e-‐ƚĞdžƚŝůĞ͛ƐĨĂďƌŝĐƵƐĞ͘/ŶƚŚŝƐĐĂƐĞ͕ƚŚĞĨůŽĂƚĞĚLJĂƌŶƐǁĞre used to attach the e-‐tags (sensors) at the same point for any size of garment, as this repeated effect could be controlled for consistency and repeatability. The floating wires also helped relieve strain as they were lifted out of the woven construction at this point.
Figure 2.19 Martin et al.͛Ɛ Ğ-‐textiles jumpsuit project. Left: close up of the e-‐textile construction where wire and elastic yarns have been integrated into the structure. Right: the jumpsuit final prototype (Martin
et al., 2009)
The loom used to construct the e-‐textiles for the jumpsuit was a 24 shaft AVL industrial loom, which was more elaborate than a standard handloom and enabled advantages in the weaving structures and styles. The e-‐textile jumpsuit research also addressed the digital network programming and hardware used in their project, combining a complete wearable system and designing for both attributes. The final jumpsuit was still far from perfect in regards to integration of all invisible electronics. Nevertheless, for a first prototype, and considering all of the technical aspects of this application, it was a successful attempt. It was reported to function effectively to enable recording physical movement when worn. The textiles for this project considered technical materials development from a design perspective that aimed to benefit the finished product utilising existing woven textile properties. However, the aesthetics and integration of softer yarns (e.g. conductive yarns) could improve the form and integration of electronic tracks.
2.4.9 Jones and Wise TWI ʹ welding LED component and conductive e-‐textile
Jones and Wise from The Welding Institute (TWI), Cambridge, UK, investigated the welding process to join conductive tracks in textiles. They specifically experimented with
laser welding, laser soldering, ultrasonic welding, hot bar welding, resistance welding, and applying conductive adhesives to joining woven e-‐textile conductive paths and components (Jones and Wise, 2005). They reported some successful outcomes with the positioning of connected components arranged in obvious ways, i.e. positioned directly on top of the fabric (Figure 2.20). However, the integration of components (LED in this example), could have been further investigated from an in-‐depth design approach to benefit both the form and function of the e-‐textile. (For example, integrated conductive paths and components could be constructed in a single woven e-‐textile). The research provided technical materials insights into methods of joining woven e-‐textiles. There appears to be potential for further investigation of complex woven structures designed to aid the joining processes. Selection of particular woven structures could expose more contact area of material for joining, (e.g. a weft faced structure would expose the maximum amount of conductive yarn onto the top side of the textile).
Figure 2.20 Image of :ŽŶĞƐ ĂŶĚ tŝƐĞ͛Ɛ ŚŽƚ ďĂƌ ǁĞůĚŝŶŐ ŽĨ > ĂŶĚ ǁŽǀĞŶ silver coated nylon/ cotton fabric