Broadband Piezoelectric Energy Harvesting and Vibration Suppression Using Nonlinear Mechanisms
Harvesting ambient vibration energy provides a promising solution to implement self-powered microwatts to milliwatts low-power electronic devices, as an alternative to batteries. Due to the high power density and simple construction, piezoelectric transducers have attracted the most attention in the field of vibration energy harvesting. Optimization of the performance of linear piezoelectric energy harvesters requires matching resonant frequencies with the dominant excitation frequency. Since ambient vibrations are usually distributed over a wide spectrum, nonlinear mechanisms have been widely explored to extend the bandwidths of energy harvesters with minimal reduction of power density. Moreover, nonlinear piezoelectric energy harvesters could also manifest broadband vibration suppression when attached to a primary structure. Internal resonance is a nonlinear mechanism which can achieve wide bandwidth due to extra resonant peaks. In this thesis, a two-degree-of-freedom energy harvester is designed and fabricated, whose first two natural frequencies can be tuned to a near 2:1 ratio. Double jumping, modal interaction, and saturation phenomena are revealed experimentally and numerically. A theoretical study based on two approximate methods is also conducted to gain insights into the key features of internal resonance and the benefits for energy harvesting. The optimal resistance to obtain the maximum power is determined. By and large, the operational bandwidth can be enlarged compared with conventional linear and nonlinear energy harvesters due to the two-to-one internal resonance. A nonlinear energy sink is another mechanism investigated in this thesis. This has been utilized for adaptive and broadband vibration absorption in previous studies. With the integration of a piezoelectric transducer, the nonlinear energy sink can serve as a vibration energy harvester as well as a vibration absorber. With alternative and direct current interface circuits, targeted energy transfer, an energy localized branch and their influence on the dynamic and electrical performance are revealed experimentally and numerically. Also, approximate methods are used to reveal the underlying mechanism of targeted energy transfer in the presence of electromechanical coupling. In summary, the piezoelectric energy harvester based on a nonlinear energy sink is able to absorb vibrational energy of the primary structure and effectively collect electric energy over a broad frequency range.
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