Flexible piezoelectric transducers for energy harvesting and sensing from human kinematics

This study reports flexible nanocomposite-based piezoelectric nanogenerators (PENGs) fabricated by dispersing various piezoelectric nanoparticles (BaTiO₃, ZnO, and PZT) and graphene nanopowder in a silicone matrix. The results indicated that the PZT-based composites showed superior performance in comparison to other ceramics. Subsequently, practical application of PENGs was demonstrated by developing a fully functioning shoe-insole nanogenerator (SING). The SING generated high open-circuit voltage (∼27 V), short-circuit current (429.23 μA), and power density (402 mW/m²) under real-time human walking. Moreover, a facile and inexpensive fabrication method for efficient, skin-friendly, and highly stretchable biomechanical piezoelectric sensors is also proposed. In this regard, multiwall carbon nanotubes/silicone composite stretchable electrodes were prepared to be compatible with the sensors. The electrodes displayed stability even under high uniaxial elongation (100%), and the fabricated sensors responded effectively to almost every joint movement. The results suggested that the fabricated PENGs can be potentially used as self-powered biomechanical energy harvesters/sensors in wearable electronics, haptic sensing, or internet of human-related applications.