Development of stretchable conductive hybrid yarn for e-textiles soft sensors applications

Abstract

Textiles have been the second necessity for humans to survive sense the beginning of mankind, just after nutrition of food and water that humans look for cloth and shelter to withstand the elements. As the technologies advance the roll of clothing surpassed the basic need for warmth, significant change for clothing performance aid has been the focal point of today's research, succeeding in breaking the world records for humans swimming speeds utilizing shark skin technologies and many others aids. Nowadays wearable textiles have a wide variety of applications in every aspect of human lives beginning from atmospheric pressurized astronaut's suits that withstand the vacuum of space to the deep diving suits that can endure the immense water pressure and everything in between including the extreme heat suits used on the edges of live volcanos, high velocity projectile protections, flame retardant clothing, antibacterial protections, etc. In recent years an increasing attention towards wearable electronics and electronic textiles have been the hot topic of research fields, recognizing their role towards more intelligent and comfortable world. Soft sensors have dominated the biggest share of this research owing to their designing flexibility to be utilized into wide range of applications, including human vitals that can be recorded by a specialized electrode, besides pressure and strain sensors that are affected by the joints and limps in motion where it the sensor's signal will be corresponded to the joint bending intensity. Corresponding with that research comes a huge demand on conductive substrates that can be integrated within the fabric design. This conductive substrates in their most basic form are cupper wires, although this cupper wires have excellent conductivity, they don't provide any of the human body comforting aspects such as stretchability, cycling flexibility, weight, air permanently and skin care values; Therefore these comforting aspects should be fulfilled as close as it can be to the bases of textile substrates i.e., fibers and filaments, so that if the building blocks of the textile substrates fulfil the above mentioned aspects it should by default meet the same demands in yarn manufacturing up to fabrics. There are many ongoing researches in pursuit of establishing an integrated soft sensor within a textile substrate by developing a conductive yarn that can be utilized during fabric manufacturing. In this study a stretchable conductive hybrid yarn (SCHY) is developed in order to satisfy the human comfort demands, utilizing the Direct-Twist technology to wrap a non-stretchable conductive yarn around a highly stretchable spandex core to create a hybrid yarn that combine both attributes. Finally, this hybrid yarn was successfully integrated within a knit fabric during production to fabricate an interdigital capacitive sensor that covers the working range of human joints. As of right now this SCHY integrated soft sensor is undergoing characterization tests to determine the suitable applications for the fabricated interdigital sensor.