The importance of coupling strength for maximizing the output power of electrodynamic vibrational energy harvesters

For electrodynamic (magnetic/inductive) vibrational energy harvesters, this paper introduces and explores the impact of a key design variable—“coupling strength”—that governs the energy harvesting effectiveness. First, the importance of magnetic coupling strength is explained analytically using a linear vibrational harvester model. Second, from Faraday’s law of induction it is shown that a radial magnetic field pattern is the most practical means for maximizing the coupling strength for oscillating rectilinear motions. Third, a harvester with tunable coupling strength is designed, built, and tested to demonstrate and validate the theory. By increasing the coupling strength, the harvester is shown to capture >90% of the theoretical available power, a significant improvement over most prior works (<<50%).