Wideband fractal-inspired piezoelectric energy harvesters

Harvesting kinetic ambient energy from vibrations or impact loads to obtain electrical energy useful to supply electronic sensors is still a challenging issue, with a huge number of potential applications, from the industrial field to consumer goods. This work investigates four simple piezoelectric energy harvesters developed from fractal-inspired structures: these structures are square laminas with inner divisions that originate a fractal geometry, since it is obtained by the repetition of a base configuration. Starting from the description of the fractal-inspired structures, the work presents a computational modal analysis highlighting the peculiar wideband frequency response of these structures and thus their applicability as energy converters. Using commercial piezoelectric transducers, we built four energy harvesters and assessed their output voltage and output power performing dynamic tests on a vibrating table. The proposed structures exhibit a wideband frequency response and a good energy conversion, specifically at the fundamental eigenfrequency.