Fractal-inspired multi-frequency structures for piezoelectric harvesting of ambient kinetic energy

The investigation of energy harvesting devices, able to convert freely-available ambient energy into electrical energy, has significantly improved. To this aim, the most suitable form of ambient energy is the kinetic one, being almost ubiquitous and easily accessible. Among the available conversion technologies, piezoelectric energy harvesting devices are one of the most promising, due to their simple configuration and high conversion efficiency. The most demanding task is to identify simple and efficient multi-frequency structures in the ambient vibration range. To this aim, this work proposes four fractal-inspired structures for piezoelectric energy harvesting. Through computational analysis, their frequency response is calculated up to 100Hz. The structures are examined both in the micro and macro scale and the effect of the iteration level of the fractal geometry is also assessed. By considering the bending strain associated to each mode shape, a quantitative criterion to assess the harvesting efficiency of the proposed structures is introduced.