27.4 Multi-Beam Shared-Inductor Reconfigurable Voltage/SECE-Mode Piezoelectric Energy Harvesting of Multi-Axial Human Motion

The past few years have witnessed a growing demand for self-powered wearables that can enable vigilant health monitoring, with 24/7 operation. Energy harvesting from human-body motion is attractive for wearables; however, conventional unidirectional single-cantilever-beam piezoelectric energy harvesters (PEHs) [1]–[4] suffer from several body-motion harvesting challenges: such as multi-axial motion, irregular frequencies, and unpredictable amplitudes with frequent low-power levels [5]. To address these challenges, an eccentric rotor-based inertial PEH has been developed, which utilizes multiple magnetically plucked flexible thin-film $(60 \mu \mathrm {m})$ PZT-nickel-PZT beams to significantly increase the harvested energy within a small volume [5]; compared to bulk-PZT beams that are more feasible in direct-force-driven PEHs. The wrist-worn multi-beam PEH, shown in Fig. 27.4.1, converts multi-axial body motion into AC voltages with different phases and decaying amplitudes (up to several volts) within the frequency range of 90–160Hz for each beam.