Bioinspired omnidirectional piezoelectric energy harvester with autonomous direction regulation by hovering vibrational stabilization

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Multidirectional approaches are essential for harnessing mechanical energy of random varying directions. Traditional multidirectional technologies are difficult to effectively harvesting vibration energy in complex physical environments due to their complex and auxiliary designs. Inspired by the vibrational stabilization of hummingbirds to maintain stable in hovering flight for any desired direction, we propose an omnidirectional piezoelectric energy harvester with the compact coaxial design and autonomous direction regulation capability. Our design scheme is to endow all-around directional sensitivity in a single oscillator rather than multiple installation directions of the oscillators. The dynamics of this omnidirectional vibration energy harvesting device are described for explaining the autonomous direction regulation mechanism realized by vibrational stabilization. Compared to its unidirectional counterpart, this omnidirectional energy harvester with the autonomous direction-regulating ability shows a 696% increase in maximum open-circuit voltage and 49.0 times higher maximum power density when the external excitation direction is perpendicular to the initial vibration direction. Practical applications of powering an electronic clock demonstrate the feasibility of the proposed omnidirectional energy harvester for the engineering community. Field experiments of harvesting energy from bicycle riding or human movement to charge a capacitor also validate the significant improvement of the direction-regulating design strategy in endowing an all-around uniform directional sensitivity. The vibrational stabilization mechanism provides a new design philosophy for omnidirectional energy harvesters. With its high flexibility and desirable enhancement, this direction-regulating design strategy has the potential to be applied in vibration energy harvesters with different mechanisms (electrostatic, electromagnetic or triboelectric ones) to extend their multidirectional capabilities.