Keypads
constructed from fabric materials are the ideal input devices
for smart clothing applications. However, multi-modal reaction problems
have to be addressed before they can be of practical use on apparels,
i.e., the fabric-based keypads need to distinguish between the legitimate
actions by the fingertips and the illegitimate deformations and stresses
caused by human movements. In this paper, we propose to use the humidity
sensor functionalized from graphene oxide (GO)-coated polyester fibers
to construct the e-textile keypads. As the moisture level in the proximity
of human fingertips is much higher (over 70%) than other parts of
the human body, humidity sensing has many advantages over other tactility
mechanisms. Experiments have demonstrated that the GO-functionalized
fabric keypad has a stable uni-modal tactility only to fingertip touches,
and it is not sensitive to deformation, pressure, temperature variation,
and other ambient interferences. With biasing and sensing circuits,
the keypad exhibits a quick response and recovery time (around 0.1
s), comparable to mechanical keyboards. To demonstrate its application
on smart clothing, the keypad was sewn on a sweater and embroidered
conductive yarns were used to control an MP3 player in the pocket.
Conductive yarns have emerged as a viable alternative to metallic wires in e-Textile devices, such as antennas, inductors, interconnects, and more, which are integral components of smart clothing applications. But the parasitic capacitance induced by their micro-structure has not been fully understood. This capacitance greatly affects device performance in high-frequency applications. We propose a lump-sum and turn-to-turn model of an air-core helical inductor constructed from conductive yarns, and systematically analyze and quantify the parasitic elements of conductive yarns. Using three commercial conductive yarns as examples, we compare the frequency response of copper-based and yarn-based inductors with identical structures to extract the parasitic capacitance. Our measurements show that the unit-length parasitic capacitance of commercial conductive yarns ranges from 1 fF/cm to 3 fF/cm, depending on the yarn’s microstructure. These measurements offer significant quantitative estimation of conductive yarn parasitic elements and provide valuable design and characterization guidelines for e-Textile devices.
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