Experimental study of a piezoelectric cantilever beam under droplet impact

The dynamic response of a piezoelectric cantilever beam under droplet impact is investigated by conducting impact tests. Both droplet dynamic behaviours and voltage output can be acquired simultaneously by means of high-speed camera capturing technique. The surface wettability and the macrotextures affect the voltage generation in different ways. For all droplet sizes, both the super-hydrophobic-treated and untreated surfaces of the cantilever beam can generate the same magnitude of peak voltage. However, at lower impact velocity, the voltage generated from the untreated surface is slightly higher than the treated surface due to different impact mechanisms upon droplet-substrate interactions. For higher impact velocity, large-scaled droplets can experience splash and water spilling phenomena on the treated and untreated surface respectively, leading to mechanical energy loss of the system. But the treated surface shows a better performance. With the presence of a single macrotexture on the treated surface, there is a critical impact velocity which determines the transition of voltage output. For small-scaled droplets, the surface with the presence of a single macrotexture outperforms only with velocities over the critical value. For larger droplet size, the same trend can be obtained but the effect of the macrotexture is less significant. These outcomes from impact experiments may lay a foundation for future study of exploring new surfaces for piezoelectric energy harvesting devices in the aim of improving the raindrop energy recovery efficiency.