Hybrid piezoelectric–electrostatic generators for wearable energy harvesting applications

Dielectric elastomer generators (DEGs) are promising soft electrostatic converters. Despite their several advantages, these generators are not well developed in the literature due to the need of an external polarization voltage to perform the energetic cycle. In order to overcome this drawback and to design a scavenger with a longer lifetime, we propose to substitute the external polarization source in DEGs by coupling them with piezoelectric materials. The charge produced by the piezoelectric material due to external mechanical excitation are employed as polarization source of the DEG. Two different prototypes have been designed, simulated and realized: the first one employs piezoelectric ceramic as polarization element of an acrylic-based DEG and the second one employing a piezoelectric polymer. A smart frame insures a perfect mechanical and electrical synchronization leading to interesting level of scavenged energy density (up to 14.3 μ J.g −1 and 0.39 μ J.g −1 respectively). These solutions, compared to the ones proposed in the literature, present the advantages to be compact, do not need additional electronic element and can guarantee a polarization source to the device at each deformation cycle. The devices structure, working principles and experimental performance will be presented and discussed, together with the possible improvements to enhance the performance of the devices.