Comparisons of bioinspired piezoelectric wind energy harvesters with different layout of stiffeners based on leaf venation prototypes

In this paper, we analyze the energy harvesting capacity of different piezoelectric elements with bionic stiffeners derived from venation growth algorithm (VGA) that have the prototypes of dicotyledonous plant leaf venations. Three types of polyvinylidene fluoride (PVDF) leaves are designed and fabricated. The contours of these models are isosceles triangle, isosceles trapezoid and 60 degrees sector that correspond to the palmate leaf, pinnate leaf and ginkgo leaf, respectively. In wind tunnel tests, the PVDF leaves are connected with a cylinder bluff body by a double-layer beam and driven by the vortex-induced vibration in the wind flow after crossing the cylinder. The performances of energy harvester are evaluated by the open circuit voltage and output power. Through some control group test, the influence of the contours of leaves was proved to be negligible. Experiment results show that the maximum output power can reach 0.855 mu W for the model with pinnate venation at the wind speed of 11 m/s with a power density of 3.29 mu W/cm(3). In this condition, the open circuit RMS (root mean square) voltage is 1.695 V and also the best performance of our models. Furthermore, the experimental results indicate that the energy harvesting capacity of PVDF models with bionic veins is 2-3 times higher than the traditional reinforced structure with orthogonal stiffeners. From these studies, it is confirmed that the bionic reinforced structure can significantly improve the efficiency of piezoelectric energy harvesters operating on wind-induced vibration principle. At present, the dicotyledonous vein configuration has proved to be the best prototype, which can be obtained by venation growth algorithm (VGA). (C) 2019 Elsevier B.V. All rights reserved.