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 stim-ulating increasing research. Usually, they require external power, thus adding issues such as periodic mainte-nance 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 -mu 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 effi-ciently even from very low-frequency vibrations (<10 Hz, the range of human motion), and it is one of the most promising technologies for miniaturisation. 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 elec-trodes combined 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 mu W at 7 Hz with a power density of 9.1 nW/mu l.