A self-powered three-dimensional lower-limb motion monitoring system with full-posture biomechanical energy harvesting capability

Lower limb motion monitoring is in high demand across various application scenarios, such as sports training and rehabilitation. However, existing monitoring systems face significant challenges, including limited power supply sustainability and the lack of mature technologies for three-dimensional motion sensing. To overcome these limitations, this study presents a self-powered three-dimensional lower limb motion monitoring system with full-posture biomechanical energy harvesting capability (TDLM-FPBEH). The system integrates a full-posture biomechanical energy harvester (FPBEH) and a three-dimensional sensing triboelectric nanogenerator (TDS-TENG). The main component of the FPBEH is mounted on the human back, which is more suitable for load-bearing, and it harvests energy from various motion postures without imposing any rigid constraints on body movement, thereby achieving high output power. Meanwhile, the TDS-TENG accurately detects both the direction and the displacement of lower limb movements, enabling comprehensive three-dimensional motion tracking. Experimental results show that under traction excitation at a frequency of 1 Hz and a displacement of 300 mm, a single FPBEH unit delivers an average output power of up to 3.99 W. Furthermore, wearability tests confirm the FPBEH's strong adaptability to various users and motion patterns. The TDS-TENG demonstrates sensitivity to different directions and amplitudes of movement, producing distinguishable electrical signals. Demonstrations involving representative football movements further validate the feasibility of this system for self-powered three-dimensional lower limb motion tracking. Overall, the proposed system offers an integrated solution for sustainable energy harvesting and precise 3D motion monitoring, supporting the requirements of diverse real-world applications.