REWoD-based vibrational energy harvesting exploiting saline-solutions loaded PAAm hydrogels on micro-structured aluminium oxides electrodes

Nowadays, sensors are among the most exploited systems in everyday life, with widespread applications stimulating increasing research. Usually, they require external power, thus adding issues such as periodic maintenance and size constraints. Energy harvesting (EH) from mechanical vibrations (VEH) can overcome such limitations: in particular, Reverse Electrowetting on Dielectric (REWoD) can provide a high-power density of ~?W/cm2 by exploiting the mechanical modulation of the capacitance at the liquid/dielectric interface without additional external bias. Compared with other vibrational EH (VEH) techniques, REWoD harvests energy efficiently even from very low-frequency vibrations (<10 Hz, the range of human motion), and it is one of the most promising technologies for iniaturisation. Here we present a feasibility study and proof of concept for a portable VEH device, exploiting low-cost materials such as highly hydrophobic micro-structured Al oxide electrodescombined with off-the-shelf polyacrylamide (PAAm) hydrogels loaded with saline solutions. The PAAm hydrogels, thanks to heat treatment in LiCl solution, exhibit a negligible degradation compared to the typical hydrogel drying time. A laboratory prototype using 3 hydrogel hemispheres simultaneously generated an average power of ~1.55 ?W at 7 Hz with a power density of 9.1 nW/?l.