Fractal-inspired multifrequency piezoelectric energy harvesters

In this Letter, we propose fractal-based piezoelectric energy harvesters (PEHs) for broadband energy scavenging. The introduction of fractal topology into transducers significantly alleviates the inherent limitation of a narrow working bandwidth in commonly used cantilever PEHs. We conduct a finite element analysis and experiments to exploit the performance of fractal cantilever PEHs with different iteration times. Our findings reveal that the higher-order fractal structures generate an increased number of eigenfrequencies as well as modal patterns within a certain range of working bandwidth (i.e., <50 Hz). Experimental results indicate that the efficient energy harvesting bandwidth of the fractal PEHs of iterative levels 1 and 2 is 2.05 and 2.15 times, respectively, larger than the conventional PEHs (i.e., level 0). In addition, the harvested voltage and power of fractal PEHs can be enhanced by attaching a proof mass to compensate for the energy loss in producing iterations. This method exhibits superiority over capturing energy in low-frequency vibration environments, such as wave energy and human movement energy.