Advances in Science and Technology Vol. 80

Abstract: Polymer/carbon nanotube (CNT) composite monofilaments were produced and tested for sensing activity. Polylactide (PLA) was the polymer selected for humidity sensing, while a mixture of polypropylene (PP) and poly(ε-caprolactone) (PCL) was used for temperature sensing. The PP/PCL/CNT composite filaments developed a co-continuous structure with CNT localized in the PCL phase. The filaments were characterized in terms of tensile properties and electrical resistivity. Textile fabrics were produced with both types of filaments. The electrical resistance of the fabrics subjected to humidity or temperature variations was measured in a climatic chamber.

Abstract: Recently there has been growing interest in developing smart photovoltaic fabric devices. These devices could be used as a sustainable and ubiquitous power source for wearable and other electronic devices. Three woven photovoltaic fabric structures were constructed with fiber-shaped organic photovoltaic wire from Konarka Technologies, Inc. (Lowell, MA, USA). The organic photovoltaic wire is a flexible, lightweight and wire shaped organic photovoltaic fiber based on bulk hetero-junction nanocomposites. The power conversion characteristics of photovoltaic fabrics developed were thoroughly investigated. It was found that the power conversion efficiency of the photovoltaic fabric depends on the incident light quality; fabric cover factor, swatch size, and fabric weave structure. This study also includes photovoltaic fabric model for understanding the effects of different fabric geometry on power conversion efficiency of photovoltaic fabrics. The model predicts the performance of the photovoltaic fabrics with different shape, size and structures, and it provides design criteria for more efficient photovoltaic fabric device.

Abstract: We demonstrate a woven textile with an integrated humidity and temperature sensor on flexible PI substrates. We discuss the fabrication process of the smart textile and compare two methods of sensor fabrication, first conventional photo lithography and second printing using ink jet. The humidity sensor is based on a capacitive interdigitated transducer covered with a sensing layer while the temperature sensor is made of a resistive metallic meander. An encapsulation method protecting the sensors during dicing, weaving and operation has been successfully implemented. The fabricated structures are tested to bending strain, a main source of failure during the fabrication of textiles. We were able to bend bare electrodes and complete sensors down to a minimal bending radius of 100 μm without loss of functionality. The woven temperature sensor has a temperature coefficient of 0.0027 /° C for lithography made and 0.0029 /°C for printed sensors. The humidity sensor shows a repeatable behaviour in the tested humidity range between 20 to 70 %RH. The weaving process does not damage or change the behaviour of the fabricated sensors. This contribution will highlight the challenges and promises of printing and laminating processes for the large scale fabrication of smart polymeric stripes to be woven into textiles.

Abstract: Abstract. During the last decade, research on intelligent textile systems progressed steadily. Today, science is focusing on full integration of electronics into textiles. E-textiles function like their rigid electronic companions but keep their textile properties. To interconnect components within the system, textile structures need to be equipped with electro-conductive properties. For flexible solar cells or fibrous transistors, electro-conductive coatings are applied. Transistors, acting as electrical switches, are essential for realizing fully integrated intelligent textile systems. By electroless deposition of pyrrole and copper on polyester fibres, conductivity is achieved. A DC conductive gate electrode is designed. In this paper, the development of the gate layer within the fibrous transistor is described. Ideal pH and optimal reaction time are determined as well as the effect of variation in fibre diameter is investigated. A reproducible polypyrrole layer has been obtained. Ideal reaction time was 180 minutes at a temperature of 278K. The electroless copper coating process on the polypyrrole layer showed optimal results when the substrate was immersed into the plating bath coated for 6 minutes at a pH of 13. Analysis through resistance measurements has been completed.

Abstract: In order to improve comfort of smart garment, rigid electronic boards can be replaced with textile circuits, which use conductive yarns. When one tries to improve wearing comfort, often the most problematic items turn to be connection points of the electronic circuitry. The aim of this research is to determine behaviour of conductive yarns after they have been sewn into textile material, as well as to determine their suitability for the intended applications. In order to determine the quality of a conductive connective seams resistance has been measured (in Ω) under the influence of various variable factors: type of yarn, length of stitch, number of layers, type of seam. Besides that seam durability tests were carried, which show resistance changes over time and after washing.

Abstract: This work presents a polymer based force-fit interconnection module (Click-Bond) that can be used to establish reliable electrical and mechanical interconnections between electronic components and textile circuit boards at room temperature. It is an extremely fast and cost-efficient process that is able to bring smart textile applications into the mass market. The semi-crystalline polymer POM-C is selected as material. It has good physical properties and can be used in injection molding. After the design is made mechanical experiments are performed to analyze the maximum forces and stress relaxation of the modules. Additionally, the compressibility of fabrics is analyzed to be able to design the module to apply a certain pressure. Finally, a multi-terminal board is presented that allows to easily integrate more complex electronics boards into smart textiles.

Abstract: The premise of this research is to integrate sensing and actuation functions into a fibre composite material system. Fibre composites, which are anisotropic and heterogeneous, offer the possibility for local variations in their material properties. Embedded fibre optics are herein used to sense, while shape memory alloys provide actuation capabilities to the resulting composite. The definition of the geometry, inspired by the organization strategies found in biological composites, complements the functioning of the adaptive material system at both local and global levels, allowing it to display integrated functionality.

Abstract: Research through design allows creating a dialogue with the material. It uses making and reflection on action as a generator of knowledge. Our aim is to explore the opportunities and challenges of smart textiles. The Fablab is our set up, a place that allows us to combine the hacking- scientific-, and design community. It stimulates collaboration and the knowledge exchange needed for the development of smart textile systems. A collaborative prototyping workshop for medical products combined two worlds. The textile world in Saxion aims at incorporating conductive materials into textile structures and functional- / 3D printing to create systems for applications such as flexible heating systems and wearable technology. We combined this with the world of Industrial Design at TU/e, focused on the design of intelligent products, systems and services by the research through design approach. The collaboration between these different disciplines speeded up the process by reducing the resistance to the new and skipped the frustration on failure.

Abstract: The wireless communication systems are applied in different applications such as computers, mobile phones, satellites and antennas for off-body communication. A lot of efforts were made to have the antennas in a smaller size, flat and with better performance. In the last decade the rigid antennas are replaced with textile in order to be flexible and to be integrated into garments in order to have wearable textile systems. The textile antennas can find use in medical, military and first responders monitoring. The conductivity of the antennas can be achieved by using coated textile materials which are available in the market, conductive threads for embroidery or conductive inks. When using the conductive coated textile it is necessary to cut the patch in the desired pattern but using a simple cutting tool sometimes is not very precise and accurate. Thus in our study we decide to screen print with silver conductive inks on Polyester and Cotton/Polyester substrates. The screen printed antennas are than washed in order to conform that antennas for off-body communication integrated in garments can be easily washed five times.

Abstract: Silver or copper coatings printed in fabric have shown good electrical conductivity, an essential property in wearable electronics, however they have problems when stretched due to their fragility. On the other hand, carbon nanofiber or nanofiber-silver nanocomposites dispersed in polymeric matrices can combine high electrical conductivity with exceptional stretching properties. The use of carbon nanofiber based ink as smart textile electrodes is demonstrated in this paper by using two novel sensing methods. The first method achieves wide range pressure measurements, being able to measure the pressure on the printed sensor from soft caress to hard press. This feature allows the implementation of an artificial skin that could be used in robots or in toys for children or disabled people. The second detection method has been designed for user distinction, allowing permission control. Technical prototypes have been developed to prove the above concepts.