A Study of Body Temperature and Sweat Measureable Functional Fiber

Abstract

We fabricated wearable flexible humidity sensor that can measure human sweat. Our sensor is based on Ionic-liquid-Gel-coated Fabrics and Cloths （IG-Fabric/Cloth）．We use EMIMBF4 as ionic liquid, which has a characteristic that it absorbs H2O and changes its impedance. For the humidity sensor substrate, we use “Bemcot TR-7F” （Asahi Kasei corp., Japan） and “Kimtowels” （NIPPON PAPER CRECIA Co., LTD, Japan） as fabric and Cotton and Polyester as cloth. Fabrication steps of ionic-liquid-gel-coated fabric and cloth are as follows. First, we prepare the mixture of ionic liquid and PolyVinylidene DiFluoride （PVDF） and Dimethylacetamide （DMAc） as ionic liquid gel solution. Then we dip the fabric and cloth into the ionic liquid gel solution for 5 minutes. After picking up, we baked the fabric on the 80ºC hotplate for 30 minutes. To evaluate IG-Fabric/Cloth humidity sensor, examined the relation between relative humidity and IG-fabric impedance change. There is linearity in humidity and resistance change. From the measurement data of sensor response speed test, the response speed τ63 estimated as around 0.7 seconds. This is 10 times faster than commercial CMOS humidity sensor. This is because IG-fabric has a large surface area and high gas permeability, compare to silicon wafers. We also evaluated the flexibility of our humidity sensor and showed high flexibility of our sensor. As a demonstration, we fabricated IG-Cloth based humidity sensor on the surface of polyester T-shirt and measured sweating of the human doing exercise and cooling down. From the experiment, we observed the impedance change of IG-Cloth according to the examinee’s activity. This sensor has many applications such as flu-mask-type human breath sensor that can monitor human breath, and wearable humidity sensor that can measure human sweat to decrease the risk of heat stroke.