Rotational piezoelectric wind energy harvesting using impact-induced resonance

Abstract

To improve the output power of a rotational piezoelectric wind energy harvester, impact-induced resonance is proposed to enable effective excitation of the piezoelectric cantilevers' vibration modes and obtain optimum deformation, which enhances the mechanical/electrical energy transformation. The impact force is introduced by forming a piezoelectric bimorph cantilever polygon that is fixed at the circumference of the rotating fan's internal surface. Elastic balls are placed inside the polygon. When wind rotates the device, the balls strike the piezoelectric cantilevers, and thus electricity is generated by the piezoelectric effect. The impact point is carefully chosen to use the first bending mode as much as possible, and thus maximize the harvesting efficiency. The design enables each bimorph to be struck in a similar area and every bimorph is struck in that area at different moments. As a result, a relatively stable output frequency can be obtained. The output frequency can also be changed by choosing different bimorph dimensions, which will also make the device simpler and the costs lower. A prototype piezoelectric energy harvester consisting of twelve piezoelectric cantilevers was constructed. The piezoelectric cantilevers were made from phosphor bronze, the lead zirconium titanate (PZT)-based bimorph cantilever had dimensions of 47mm×20mm× 0.5mm, and the elastic balls were made from steel with a diameter of 10mm. The optimal DC output power was 613 μW across the 20kΩ resistor at a rotation speed of 200r/min with an inscribed circle diameter of 31mm. © 2014 AIP Publishing LLC.