Flexible and self-powered blinking and eyeball movements sensing based on electrospun lead-free piezoelectric nanofibers

Abstract

Potassium sodium niobate (KNN)-based nanofibers could combine piezoelectric properties with exceptional flexibility and biocompatibility, making them highly promising for flexible sensors in electronic skin and wearable applications. However, the suboptimal piezoelectric performance limits their sensitivity in detecting minute human body motions, such as blinking and eye movements. Herein, Li and Ta-doped KNN nanofibers were fabricated via an electro-spinning process. Co-doping with 6% Li at the A-site and 30% Ta at the B-site induces lattice distortion and an orthorhombic (O) to tetragonal (T) phase transition in the electrospun nanofibers, resulting in a significantly enhanced piezoelectric response, with an average d₃₃* value reaching 110.7 pm/V. The outstanding piezoelectric response gives rise to a remarkable sensitivity (0.3365 V/(N cm²)) in a self-powered flexible pressure sensor based on the doped KNN nanofibers, encapsulated in a polydimethylsiloxane matrix. The sensors, when attached to the temple regions, can detect tiny facial motions induced by blinking, enabling the distinction of abnormal blinking patterns associated with mental fatigue and excessive eye use. Additionally, they support real-time, continuous, and unobtrusive eyeball tracking, highlighting their potential as critical components in human-computer interaction and artificial intelligence applications.