Called the “Piezo-tree”, the system is able to convert the wind energy into electricity whilst remaining light, easily scaled and low-cost. Researchers said that in the prototype, the flexible plate and film are driven to oscillate just as a leaf or flag might flap in the wind. The flapping motion of the leaves is attributed to instability of the aero-elastic system.
The “Piezo-tree” has been made using flexible piezoelectric material Polyvinylidene Fluoride (PVDF), and could withstand unpredictable wind speeds. The basic design is to fix one edge of Polyvinylidene Fluoride element to a cylinder bluff body and leave the other edge free. A vortex shedding will be created when the wind crosses this bluff body and the periodic pressure difference will drive the piezo-leaf to bend in the downstream of the air wake. After rectifying the electricity with a full-wave bridge it is stored in a capacitor and the AC signal is collected from the flapping piezo-leaf, which is working on a periodic bending model.
Due to the weak piezoelectric strain coefficient of Polyvinylidene Fluoride the power level of the preliminary Piezo-Leaf Generator just about 100 pW, being unable to light even a normal LED. Then, scientists tried to put a piece of plastic film to the end of the leaf along the direction of air flow. This change showed about 100 times increase of power in the same condition. However, a series of experiments were conducted using attachments of various flexibility, area, shape and density of polymer and plastic film producing different results in the level of power.
A recent study made by the researchers shows that a particular vertical stalk, horizontal leaf arrangement could increase power output by an order of magnitudes, being a great improvement over current leaf-stalk arrangements. In the future, researchers plan to build plant-like devices with hundreds or thousands of piezo-leaves for practical application. Being a robust and simple scaled device, the “piezo-tree” could be used in a variety of environments, serving as an unique and affective power generator.
[Source: Energy Harvesting Journal]
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