Wind generated electricity using flexible piezoelectric materials.

Abstract

Wind generated electricity using thin, flexible sheets of piezoelectric materials attached to flag like membranes termed bimorphs is presented. Piezoelectric wind generated electricity presents a simple, yet effective means to extract energy from the environment. The harvested energy would most likely be used to power wireless sensor networks and other low power applications where batteries would normally be used. Replacing batteries is inconvenient for the users of wireless sensor networks and consumers of other low power electronics. Recharging batteries with power extracted directly from the ambient eliminates the need for frequent battery replacement. Bimorphs are constructed with piezoelectric materials such as poled Polyvinylidene Fluoride (PVDF) and Lead Zirconate Titanate (PZT). Various thin, flexible polymers such as overhead projector film or ink jet transparency film make up the substrate. Several adhesives are researched to determine which can withstand the high strain levels over long periods of time. Bluff bodies were used to create vortex shedding; to increase the undulation amplitude of the bimorph and overall efficiency of the piezoelectric energy harvesting system. Due to the low source capacitance of piezoelectric materials and the low oscillation frequency of the bimorph, the source impedance is very high. In order to reduce the source impedance of the bimorph (increase output current), an inductor must resonate out some or all of the reactance of the piezoelectric. However, thousands of henries of inductance would be necessary to have a vast impact on piezoelectric source impedance. Hence, a quasi-resonant rectifier switching circuit is employed to reduce the source impedance of the bimorph. An energy harvesting circuit termed ‘Series Synchronized Switch Harvesting on Inductor’ (SSSHI) is implemented in order to maximize AC to DC power flow from a piezoelement bimorph to a storage capacitor. The circuit comprises of a peak-triggering circuit, inductor, switch, and regulated micro-power step-down converter powered directly from the piezoelement.