Ultra-flexible nanofiber-based multifunctional motion sensor

Recently, human motion and respiration monitoring sensors have attracted significant research attention in the field of wearable electronics and healthcare applications. Fiber-based electronic sensors demonstrate significant potential for such applications due to their flexibility. However, the superior flexibility of fiber-based sensors is generally limited due to the partial use of rigid elements such as metal electrode layers. In this paper, a simple method is presented for the fabrication of all-nanofiber multifunctional sensors, which consist of triboelectric (TE), piezoresistive (PR), and thermoresistive (TR) sensing elements and demonstrate superior flexibility, excellent wearability, and multifunctionality. The TE sensing unit was fabricated by integrating two triboelectrically dissimilar nanofiber surfaces using a polymer mesh separator, for the formation of internal macroscale air gaps; followed by the electrical polarization of nanofibers. The TR and PR sensing elements were realized using vapor-phase polymerized fiber electrode layers. Using the sensor developed in this study, different motions and breathing frequencies can be individually or simultaneously detected using the TE, PR, and TR sensing elements. This work therefore presents a novel scheme for human motion sensors and breathing sensors, which are widely applicable to wearable electronics, healthcare monitoring, and human-machine interfaces.