Customizing Three-Dimensional Elastic Barium Titanate Sponge for Intelligent Piezoelectric Sensing
Jingfeng Liu, Jintao Liu, Xuan Zhang, Xingang Liu, Chuhong Zhang
Abstract
Piezoelectric energy harvesters (PEHs) with porous structures, such as piezoelectric elastic sponges, exhibit high force-to-electricity conversion efficiencies owing to their excellent compression recovery properties. However, conventional preparation methods are limited to producing bulk-form sponge-like PEHs and fail to create more elaborate three-dimensional (3D) structures that could enhance conversion efficiency. Herein, we invent a composite ink consisting of waterborne polyurethane (WPU), barium titanate (BTO), and cellulose nanofibers (CNFs) that is suitable for direct ink writing (DIW) 3D printing. This ink, when coupled with freeze-drying, allows the customization of piezoelectric sponges with functional 3D structures. The printed lattice sponge exhibits remarkable compression recovery of 70% and a notably high relative sensitivity of 9.83 mV/kPa*wt % (where *wt % denotes the BTO content) across a wide pressure range of 2.98-37 kPa, which is approximately three times broader than those of other composite piezoelectric pressure sensors based on BTO or piezoceramic (PZT) materials. Furthermore, a customized 3D piezoelectric sponge with a "boomerang" configuration is utilized as an anisotropic bending sensor on the wrist for intelligently monitoring the stroke posture and programming scientific training for table tennis players. This study highlights a versatile strategy for constructing elastic sponges with high piezoelectricity and designing 3D PEH functional structures that can be applied to flexible self-powered intelligent sensing systems.