Optimizing multi-frequency excitations for piezoelectric vortex-induced vibration energy harvesting

Vortex-induced vibration (VIV) energy harvesting has emerged as a promising method for powering sensor nodes. Multi-frequency coupling mechanism involves complex nonlinear interactions among several key frequency components, including the vortex shedding frequency (f s ), the coupled natural frequency (f n ), the natural frequency of the bluff body (f sp ), the natural frequency of the piezoelectric cantilever (f p ), and the base excitation frequency (f b ). The dynamic characteristics arising from these interactions are difficult to accurately characterize. To elucidate the underlying mechanisms of multi-frequency coupling dynamics and to establish optimization criteria for key frequency matching, this study investigates the enhancement of VIV energy harvesting based on multifrequency coupling effects through base excitations. A theoretical model was established to examine the influence of base excitation on spherical VIV-based energy harvesting, and corresponding experimental studies were conducted. In particular, the effects of key frequency ratios, namely, f b /f n , f s /f n , and f sp /f p , on energy harvesting performance were systematically investigated, revealing their crucial roles in achieving maximum output efficiency. The results show that base excitation significantly broadens the effective operating flow velocity range-from 2.2~5.4 m/s to 2.2~7.2 m/s. Under optimal frequency matching conditions (wind speed of 4.47 m/s, f b =14.3Hz, and f sp /f p =1.03), the maximum output voltage reached 69.36 V, representing an increase of 41.45 V compared to VIV alone, and 61.75 V compared to base excitation alone. A distinct soft response behavior was observed when varying the frequency ratio fs /fn , whereas a linear response was observed when varying fb/fn . Furthermore, the system demonstrated adaptability to varying inflow angles, with base excitation significantly enhancing voltage output within the range of 150° to 210°.