A WiFi Tracking Device Printed Directly on Textile for Wearable Electronics Applications

Abstract

Wearable technology is quickly becoming commonplace in our everyday life - fit-ness and health monitors, smart watches, and Google Glass, just to name a few. It is very clear that in near future the wearable technology will only grow. One of the biggest wearable fields is the E-textiles. E-textiles empower clothes with new functionality by enhancing fabrics with electronics and interconnects. The main obstacle to the development of E-textile field is the relative difficulty and large tolerance in its manufacturing as compared to the standard circuit production. Current methods such as the application of conductive foils, embroidering of conductive wires and treatment with conductive coatings do not possess efficient, fast and reliable mass production traits inherent to the electronic industry. On the other hand, the method of conductive printing on textile has the potential to unlock the efficiency similar to PCB production, due to its roll-to-roll and reel-to-reel printing capabilities. Further-more, printing on textiles is a common practice to realize graphics, artwork, etc. and thus adaptability to conductive ink printing will be relatively easier. Even though conductive printing is a fully additive process, the end circuit layout is very similar to the one produced via PCB manufacture. However, due to high surface roughness and porosity of textiles, efficient and reliable printing on textile has remained elusive. Direct conductive printing on textile is possible but only on specialized dense and tightly interwoven fabrics. Such fabrics are usually uncommon and expensive. Another option is to employ an interface layer that flattens the textile surface, thus allowing printing on it. The interface layer method can be used with a variety of textiles such as polyester/cotton that can be found in any store, making this method promising for wearable electronics. Very few examples and that too of simple structures such as a line, square patch or electrode have been reported which utilize an interface layer [1{13]. No sophisticated circuit or a system level design involving integration of components on textile has been demonstrated in this medium before. This work, for the first time, demonstrates a complete system printed on a polyester/cotton T-shirt, that helps in tracking the person who is wearing that T-shirt through a smart phone or any Internet enabled device. A low cost dielectric material (Creative Materials 116-20 Dielectric ink) is used to print the interface layer through manual screen printing method. The circuit layout and antenna have been ink-jet printed with silver nano-particles based conductive ink. Utilizing WiFi technology, this wearable tracking system can locate the position of lost children, senior citizens, patients or people in uniforms, lab coats, hospital gowns, etc. The device is small enough (55 mm x 45 mm) and light weight (10.5g w/o battery) for people to comfortably wear it and can be easily concealed in case discretion is required. Field tests have revealed that a person can be localized with up to 8 meters accuracy and the device can wirelessly communicate with a hand-held receiver placed 55 meters away. Future development of the method with techniques such as automated screen printing, pick and place components, and digital ink-jet printing can pave the way for mass production.