An indirectly excited piezoelectric rotational energy harvester exploiting a flexible diaphragm for magnetic coupling

Harvesting energy from rotational motion using piezoelectric mechanism has attracted significant attention for powering wireless sensors over the past decade. To improve structural robustness and environmental adaptability of existing piezoelectric rotational energy harvesters (PREHs), an indirectly excited piezoelectric rotational energy harvester utilizing a flexible diaphragm to facilitate magnetic coupling (FD-PREH) was proposed. Unlike the traditional PREHs, the proposed FD-PREH introduces a flexible diaphragm to convert the excitation force into gas pressure acting uniformly on the surface of the piezoelectric transducer for electric output. This method reduced significantly the damage possibility of piezoelectric transducer under unexpected high-intensity impacts and torsions. The feasibility of the structure and principle of the FD-PREH was demonstrated through theoretical analysis, fabrication and experimentation. The results indicated the structural parameters of excitation ratio, radius ratio, and thickness ratio all had a remarkable influence on the peak voltage and effective rotational speed of the FD-PREH. With the increase in load resistance, there was an optimal load resistance of 18 kΩ at which the RMS power reach a maximum of 0.94 mW. Meanwhile, the energy harvester charged the 100, 220, 470, and 1000 μF capacitors to the voltages of 6.92, 6.9, 6.35, and 6.01 V in about 10, 15, 20, and 25 s, respectively. More importantly, the FD-PREH could simultaneously and continuously power at least 250 LEDs and it also provides real-time power for calculators and thermometer, showing its potential for sustainable energy generation.