Novel Two-Stage Electrical Energy Generators for Highly-Variable and Low-Speed Linear or Rotary Input Motions

A novel class of two-stage, vibration-based electrical energy generators is presented for linear or rotary input motions in applications which the input speed is relatively low and varies significantly over time such as wind mills, turbo-machinery used to harvest tidal flows, devices for harnessing coastal wave energy, and the like. Current technologies use magnet-and-coil based electrical generators in such machinery. However, to make the generation cycle efficient, gearing or other similar mechanisms must be used to increase the input speed. Variable speed-control mechanisms are also usually needed to achieve high energy conversion efficiency. Additionally, in many applications, such as those where energy is to be harvested from very low frequency oscillations of a platform such as a buoy or a ship, the use of speed increasing mechanisms such as gearing or the like is impractical. In this paper, a novel class of two-stage electrical energy generators that could operate with very low speed and highly variable input rotations and/or oscillations is described. The first stage consists of simple linkage mechanisms, which are used to excite vibratory elements. These two-stage generators are designed to convert low-speed and highly variable input rotations and oscillations to relatively high and constant frequency vibratory motions, which are then used to generate electrical energy using mechanical to electrical energy conversion devices such as piezoelectric elements. The design of a number of such two-stage generators together with a discussion of their potential applications is presented.