The vibrating piezoelectric cantilevered generator under vortex shedding excitation and voltage tests

A renewable electricity harvesting system consisting of a bluff body, a thin piezoelectric cantilever beam and a fixing base plate has been developed and attachable with running cars. The polymer cantilever beam with an optimum piezoelectric layer vibrates in a vortex street whose frequency is tuned to the natural frequency of the beam structure for maximum outputs. Computational fluid dynamic analyses were done to obtain the vortex shedding frequency of 15.7 Hz and to determine the efficient cross-sectional shape of bluff bodies in an air stream. The optimum shape of a piezoelectric material layer that is a small rectangle near a beam wall was obtained by the topology optimization method with frequency constraints. In addition, finite element analyses were applied for combined substrate and piezoelectric materials of harvesting beams in order to calculate their natural frequencies and voltage outputs generated from bending vibrations in an air flow. The PMN-PT harvesting polymer beams were fabricated and tested by a shaker and a wind tunnel (1.89 V) with a bluff body to validate the analytic results (2.11 V). Analytic and experimental results showed reasonably good agreement with approximately 10% error.