Capacitance variation in electrostatic energy harvester with conductive droplet moving on electret film

This work addresses numerical finite element calculations on a droplet-based electrostatic energy harvester to reveal additional characteristics that supplement previous test results. Assumptions of 2D electrode and static droplet profile have been applied to make the simulation achievable based on the real prototype. We investigate the consequences of a uniform space charge distribution in the film. Capacitance variation and open-circuit voltage of the simulation model have been determined and display respectively maximum and minimum magnitudes when the droplet is in the middle of finger gap. The sharp variation of capacitance, during which the droplet moves from the gap centre to the finger centre, can explain the narrow peaks of output voltage seen in experiments. Additionally, the influence of droplet size on the capacitance variation is also investigated.