Energy harvesting from wind by an axially retractable bracket-shaped piezoelectric vibrator excited by magnetic force

Highlights: • An axially retractable bracket-shaped piezoelectric vibrator excited by magnet. • Piezoelectric vibrators of the wind generator only undergo the compressive stress. • Higher reliability is obtained due to the unidirectionally deformed vibrators. • Wind speed bandwidth of generator can be easily adjusted by transducer parameters. • Effect of the bracket-shaped piezoelectric vibrator on generator property is characterized. Harvesting energy from the wind to replace the conventional electrochemical batteries has gained considerable interest. An axially retractable bracket-shaped piezoelectric vibrator excited by magnetic force is proposed to provide a practical solution to the low reliability and narrow bandwidth of the traditional turbine-based piezoelectric wind energy harvesters (PWEHs). To prove the feasibility and explore the influence of the structure parameters of the bracket-shaped vibrator on the power generation performance, the theoretical analysis, simulation, fabrication and experimental tests were performed for the turbine-based PWEH. The results showed that the bending angle, the excitation distance of magnets, the number ratio of exciting magnets and the stiffness ratio of springs brought significant effects on the performance in terms of electric output, cut-in wind speed, cut-out wind speed, and wind speed bandwidth. The maximal peak output voltage was significantly affected by the magnet spacing and the number of exciting magnets. The cut-in wind speed decreased with the increasing magnet spacing and meanwhile it was hardly influenced by both the number ratio of magnets and the stiffness ratio of springs. The cut-out wind speed was also decreased with the increase of magnet spacing and there was an optimal number ratio of magnets and an optimal stiffness ratio of spring to maximize the cut-out wind speed. Besides, there was an optimal excitation distance, number ratio of magnets and stiffness ratio of springs respectively, where the wind speed could reach the maximum value. A maximum power of 2.13 mW could be achieved with the magnet spacing of 7 mm, the magnet number ratio of 0.83 and stiffness ratio of 10.08, respectively. It was expected this study could provide a useful reference for improving the reliability and experimental adaptability of PWEHs.