A piezoelectric energy harvester with inner beam adapting to low and high wind speeds: modeling, simulation and experiment

Traditional vortex-induced vibration energy harvesters could transform wind or water energy into electricity at low flowing speeds. However, it has the disadvantage of narrow working speed band, which limits wide application in velocity-changing environments. A piezoelectric harvester with an inner beam for harvesting wind energy at both low and high wind speed regions is presented. A comprehensive nonlinear distributed fluid–solid–electric governing equations for vortex-induced vibration piezoelectric energy harvesting are derived and the theoretical results show that dimensions of outer beam and diameter of attached cylinder can affect optimal wind speed and maximum power output at both low and high wind speeds. In contrast, the dimensions of the inner beam and mass block only have impacts at high wind speeds. The equivalent circuit modeling method is utilized to analyze energy harvesting output characteristics. Analogies between mechanical and electrical domains are built, and the governing equations are converted to circuit equations. Then the circuit equations are settled in electrical software for time-varying analysis. The electrical circuit simulation results show that the optimal load resistance is 400 kΩ at low wind speed and 500 kΩ at low wind speed, which is consistent with theoretical results. The prototypes were fabricated and experiments were carried out in a wind tunnel. Experimental results indicate that energy harvester could generate power at both low and high speeds. Mass block has great impact on optical speed and working wind speed band. The energy harvester with 7.06 g mass block could output 127.36 μW at 2.65 m s⁻¹ and 63.63 μW at 4.4 m s⁻¹. Numerical and circuit simulation results are consistent with experimental results on optical load resistances and optical wind speeds. This design provides a feasible method for broadening wind speed region for energy harvesting.