Coolmax/graphene-oxide functionalized textile humidity sensor with ultrafast response for human activities monitoring

Among different fibrous e-textile sensors, humidity sensor has a particular significance in respiration monitoring, water presence alert, and skin contact/non-contact indication. These applications not only demand sensors to have fast response and recovery speed, robustness to attrition and friction, the sensors’ responses also need to be unimodal, i.e., only sensitive to humidity and insensitive to other impacts, such as temperature variation, folding and stretching of the fabric. Previously reported e-textile humidity sensors, when being used as a quick humidity indicator, suffered from slow response/recovery time, interference from multimodal sensitivities, or devices are non-fabric based and cannot be seamlessly integrated with apparels. In this paper, we have studied textile-based humidity sensors constructed from different natural and synthetic fibers (cotton, wool and Coolmax) and discovered that the graphene-oxide (GO) functionalized Coolmax humidity sensor (GO-Coolmax) exhibits ultrafast response/recovery time (less than 0.6 s). The senor is also insensitive to external pressure and temperature changes, i.e., the resistance variations caused by these impacts are within 10%, much smaller than that from humidity variations (above 80%). We have also demonstrated the use of the sensor as a humidity indicator/alert in various wearable applications through prototyping and experiments.