  We describe and demonstrate a new energy harvesting technology based on a
microfluidic realization of a Wimshurst influence machine. The prototype device
converts the mechanical energy of a pressure-driven flow into electrical
energy, using a multiphase system composed of droplets of liquid mercury
surrounded by insulating oil. Electrostatic induction between adjacent metal
droplets drives charge through external electrode paths, resulting in
continuous charge amplification and collection. We demonstrate a power output
of 4 nW from the initial prototype and present calculations suggesting that
straightforward device optimization could increase the power output by more
than 3 orders of magnitude. At that level the power efficiency of this energy
harvesting mechanism, limited by viscous dissipation, could exceed 90%. The
microfluidic context enables straightforward scaling and parallelization, as
well as hydraulic matching to a variety of ambient mechanical energy sources
such as human locomotion.
