An All-Fabric Tactile-Sensing Keypad with Uni-Modal and Ultrafast Response/Recovery Time for Smart Clothing Applications

Abstract

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.

Recent Advances in 2D Wearable Flexible Sensors

“…The sweater has no solid-state or metallic components because the (a-e) Reproduced with permission. [50] Copyright 2020, American Chemical Society.…”

“…According to Chen et al., polyester fibers functionalized with a Gr oxide coating could be used to create e‐textile keypads. [ 50 ] Due to the fact that human fingertips have a significantly higher moisture content (over 70%) than other body parts. There are several advantages to using humidity sensing in comparison to using other tactile systems.…”

“…The presence of the water layer speeds up the conversionof H 2 O to H 3 O + ( Figure a). [ 50 ] As the relative humidity rises, more ions will be able to pass through the water layer on top, which will result in a decrease in the sensor's resistance. They recommend using polyester fibers as the base material for the Gr oxide nanoparticle coating process in order to get a quick response to humidity changes and a quick recovery.…”

“…Under various keypad operations c) levels of the corresponding keys' voltage, d) intermittently played audio, e) levels of the LED indicator's logic are shown. (a-e) Reproduced with permission [50]. Copyright 2020, American Chemical Society.…”

High-Performance Flexible Humidity Sensor Based on MoOx Nanoparticle Films for Monitoring Human Respiration and Non-Contact Sensing

“…To meet the requirement of humidity sensing in the field of flexible wearable electronics, many efforts have been focused on developing humidity-sensitive materials with good performance that can be combined with flexible substrates. Various humidity-sensing materials, such as polymers, , carbon materials, , two-dimensional materials, ,, fiber, , composites, − graphene-related materials, − paper-based materials, , and metal oxides, − have been investigated extensively.…”