C.2. Tectonic Elelments
PIEZOELECTRIC EFFECT DUE TO WIND
lexible piezoelectric material Polyvinylidene Fluoride (PVDF) is used as the basic component, as it could withstand unpredictable wind strength. Together, these flexible plate and film are driven to oscillate like a leaf flap in wind. The flapping motion is attributed to instability of the aero-elastic system. The basic design is to clamp one edge of PVDF element to the secondary structure and leave the other edge free. Thus, when wind blows across, it will lead to a vortex shedding and the periodic pressure difference will drive the piezo-leaf to bend in the downstream of the air wake, synchronously. AC signal is collected from the flapping piezo-panel and the electrical energy is stored in a capacitor. The wiring and capacitor components would be kept inside of the secondary structure to maintain the aesthetical value of the sculpture. Later, all these green energy would be stored at the electrical storage device, which locates underground of the sculpture. At the original state without the wind impact, the positive and negative charges in the piezo patch are mixing around. However, when wind blows onto it and caused deflection, this force would cause the polarisation of the charges that move the positive and negative charges to opposite ends as shown. The poled patch will hence produce electrical energy through the movement between negative and positive charges. At our case, the use of simply PVDF is not enough to meet the high electricity requirement, since the power generated level would just about 100pW(with the use of 2cm diameter circular cylinder as bluff boday in 5 m/s wind). Thus, by referring to a research done, we decided to attach a piece of plastic film to the end of the panel along the direction of air flow, which resulted about 100 times increase in efficiency.