Bio-inspired tridirectional energy harvesting system for efficient ultralow-frequency self-powered monitoring

Achieving high-performance, broadband, and multidirectional energy harvesting from ultralow-frequency vibrations presents significant challenges and remains a key research focus. This study introduces a bio-inspired 3D nonlinear limb-like mechanism that utilizes clamped bending-type piezoelectric beams to capture energy from vertical, horizontal, and in-plane rotational vibrations. Two configurations, the vertical-bender and horizontal-bender, were experimentally assessed. Notably, the designed harvesting system exhibited a robust and continuous band-pass-like harvesting bandwidth, effectively covering the ultralow-frequency spectrum. It was found that motion coupling, allowing the structure to vibrate in three dimensions under one-dimensional excitation, significantly enhances both output power density and harvesting bandwidth across all directions. A flattened post-resonant harvesting bandwidth with high power density was achieved in the vertical direction, outperforming many existing results in the literature. Additionally, a multi-modal resonance was realized in both the horizontal and in-plane rotational planes. Ultralow-frequency vibration tests revealed a continuous voltage output of 15 V across an effective harvesting frequency range (EHFR) of 11 Hz, spanning from 5 to 16 Hz, under vertical excitation. In the in-plane rotational and horizontal directions, the system achieved an EHFR of 11 Hz (from 2.6 to 13.7 Hz) with a 6 V output, and 12 Hz (from 3.6 to 15.6 Hz) with a 2 V output, respectively. The maximum power outputs achieved were 0.55 mW under vertical excitation, 0.113 mW during in-plane rotation, and 0.12 mW with horizontal excitation. The developed harvester effectively powered IoT-enabled self-powered monitoring applications under ultralow-frequency vibrations (2.5, 3, and 6 Hz). • A tridirectional X-structure is designed for broadband ultralow frequency energy harvesting . • Multidirectional motion coupling enables band-pass-like and multi modal properties. • A flattened post-resonant ultra-wide bandwidth is achieved in the vertical direction. • Self-powered IoT-enabled applications in all three directions are successfully demonstrated.