An Ammonite-Inspired Wrist-Worn Spiral Piezoelectric Energy Harvester for Multidirectional and Multifrequency Energy Scavenging

Energy harvesting technology provides a prom- ising alternative to powering wearable devices by extracting kinetic energy from human motions and converting it into electricity. However, previously reported studies suffer from unidirectional energy collection, narrow working bandwidth, and large volume. Inspired by the ammonite morphology, this study proposes a compact and lightweight bionic spiral piezoelectric energy harvester (S-PEH) for scavenging multidirectional and multifrequency ambient vibrations. Benefiting from the unique characteristics of the spiral structure, the proposed bionic harvester works efficiently in low-frequency and directionally random environments compared to the conventional straight-beam-based Piezoelectric energy harvesters (PEHs). We use finite element analysis and experiments to systematically investigate the multidirectional and multifrequency characteristics of the bionic device. We also analyze the effect of the thickness of the spiral substrate, the length, and the location of the piezoelectric element on the mechanical and electrical responses of the S-PEH. To further validate the feasibility of the S-PEH, we install it inside a watch body and conduct wrist motion tests. Experimental results show that the device achieves 18.37 V of output voltage and $35.43~\mu $ W of output power when a tester walks at a normal pace. This study delivers a fresh solution to broadband and multidirectional energy scavenging for wrist-worn electronics.