High Performance KNN-Based Macro Fiber Composites for Human Motion Monitoring Applications

Piezoelectric materials are increasingly used in portable smart electronics and Internet of Things sensors. Among them, piezoelectric macro fiber composites (MFCs) have attracted much attention due to their architectural simplicity, scalability, and high-power density. However, most MFCs currently use toxic lead-based piezoelectric materials, hindering their applications for bio-friendly intelligent electronics. Here, a lightweight, thin, and high-performance lead-free MFC for human motion monitoring is developed using multilevel structure engineered (K,Na)NbO₃-based ceramics as eco-friendly piezoelectric matrix based on delicate simulation analysis. The variation of the effective electric field and piezo-potential inside the KNN-based MFC during polarization and under different stress distributions is analyzed by using the finite element analysis method. The electrical output signals of the KNN-based MFC are tested under different deformation modes, achieving high output voltage (≈25 V), as well as high output current (≈25 µA) and instantaneous output power density of 80.42 µW cm^-2. When the MFC is attached to the human body, it can sensitively convert even tiny body motion into a noticeable electrical response, with remarkable motion monitoring capabilities. This research provides a fundamental methodology for the development of lead-free MFCs, as well as an alternative material for next-generation smart sensing devices.