E-Textile-based sensing

Abstract

If textile can be instrumented with stretchable thin electronics, human motion could be monitored much more conveniently and comfortably than using IMU devices by wearing smart clothes made from such textile. With the advancement of stretchable electronics [131], researchers are indeed making inroad in this type of textile, which is often referred to as electronic-textile, or e-textile for short [132].The different types of e-textiles proposed so far all use some form of strain sensors to detect the strains caused by human motion. The predominant approach is to apply a small DC current and measure the resistance changes in the strain sensors attached to the clothing. Some work used AC current and measure the impedance changes in the strain sensor instead [133]. Due to the particular requirement of applying the strain sensors on clothing (or sometimes directly on the skin), the strain sensors must be thin (typically under a 1 mm) and highly stretchable. Hence, traditional strain sensors are not a good fit. For example, according to [131], the skin on the related body segments (feet, waist, knees) can stretch and contract by up to 55% while traditional strain sensors can only allow 5% stretch/contraction. While several different types of thin wearable strain sensors have been proposed, it appears that the conductive elastomer has been the dominating approach since the early days because they can be applied to the fabric either using a mask or attached to the fabric easily [134-141]. Newer proposed sensors relied on various materials, from commercial stretch sensors [142] and commercial sliver-coated yarn [143], to nanotube-based sensors [131], to copper wire stitched to the shirt [133].That said, compared with IMU, e-textile is still in its infancy. Although various e-textile-like sensors have been proposed, they need to add electrodes and wires connected to a processing unit with a microprocessor, storage, and wireless transmitter. The processing unit and the associated wiring would make the actual e-textile far less-convenient from the dream of monitoring human motion by only wearing clothes made from e-textile alone. Furthermore, e-textile sensors do not come in the form of textile that can be used to make clothing. They need to be attached to the clothes or directly to the human skin at particular locations. Nevertheless, this is an exciting new research area for human motion tracking.