Experimental investigation of a novel hybrid piezoelectric energy harvester for enhanced frequency tuning and wideband performance

Piezoelectric vibration energy harvesters (PVEHs) efficiently harvest the small vibrations and provide a reliable, clean, and continuous energy. However, most PVEHs are limited to operating at only one resonant frequency, limiting their ability to respond to the time-varying vibrational frequencies present in environments. To overcome this limitation, the study presents a novel PVEH design that incorporates a cavity within a cantilever beam and an internally movable magnet mass, combined with an externally placed magnet. The mass in the cavity was allowed to move along the length of the beam, thereby altering the system's center of gravity and effective mass. In addition, the separation distance between the internal and external magnets creates controllable magnetic forces. This dual mechanism enables simultaneous mass and stiffness-based frequency tuning. The experimental investigation results indicate that mass tuning effectively alters the harvester's natural frequency, whereas magnetic tuning effectively increases the harvester's bandwidth. The proposed hybrid tuning mechanism in the PVEH system generated an average output voltage of approximately 2.25 V near resonance at optimum load resistance, with a usable voltage bandwidth of nearly 3.5 Hz. The average output power of about 260 µW was achieved, while the overall usable power bandwidth was 3.1 Hz, indicating enhanced broadband energy harvesting performance.