Meshed, Flexible, and Self-Supported Humidity Sensors by Direct-Writing with Multifunctional Applications.

Flexibility endows humidity sensors with new applications in human health monitoring except for traditionally known environmental humidity detection in recent years. In this study, a flexible, mesh-structured, and self-supported humidity sensor was designed and manufactured by direct writing in a homemade two-dimensional stepping numerical control workstation. Bacterial cellulose with humidity sensitivity and good film-forming properties was applied as the self-supporting substrate, in which conductive activated carbon and water-absorptive magnesium chloride (MgCl) were incorporated. The humidity sensing performance of the printed sensor was measured and optimized. Besides, the fundamental insight into the sensing mechanism of the printed humidity sensor was analyzed by a complex impedance spectrum. The multifunctional applications of the self-supported humidity sensor were demonstrated by human breathing detection, noncontact distance sensing, and speaking recognition. The simple self-supported structure combined with the meshed attribute of the flexible sensor showed large use potential in real-time monitoring of human respiration, voice detection, environmental humidity monitoring, and noncontact switches.