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Abstract
Ocean, as a natural system containing a tremendous amount of energy, can be used for either the large-scale power grid network or small-scale distributed off-grid electronic devices via the energy harvesting technology. As one low-cost and effective way to capture flow energy, the vortex induced vibration (VIV) energy harvesting is attracting more and more attention. However, the direction of water flow in a natural water environment is changeable while most existing VIV harvesters are limited by their directional sensitivity. These harvesters only respond to flow excitations from one fixed direction and become insufficient once the flow direction varies. In this paper, we take the lead to address the unidirectional sensitivity issue and propose a novel direction-adaptive energy harvester. We establish theoretical models to analyze the Kármán vortex street, the torque excitation, and the vortex-induced pressure oscillations. Prototypes are fabricated and tested to characterize the direction-adaptive capability of the proposed design under different flow conditions. The experiments demonstrate that the energy harvesting angle span is extended by the guide wing from 40° to 360° under a wide flow velocity range. The guide-wing method endows harvesters with an all-around multidirectional sensitivity, and thus will accelerate energy harvesters’ applications in oceans.

Keywords
Energy harvester; Piezoelectric; Vortex shedding; Directional sensitivity; Vibration

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