On magnetic plucking configurations for frequency up-converting mechanical energy harvesters

Abstract

Magnetic plucking applies the strategy of frequency up-conversion in inertial energy harvesting when the energy source, such as human motion, provides excitations with very low and irregular frequencies. In a typical implementation, a slower moving inertial mass magnetically plucks a piezoelectric cantilever beam which converts mechanical energy to electrical energy at a higher frequency. We categorize several feasible magnet configurations to achieve plucking. We classify these as either in-plane (the beam is deflected in the plane of proof mass motion) or out-of-plane (the beam is deflected orthogonal to the plane of proof mass motion). Whereas in-plane plucking induces a clean ring down due to its inherent jump phenomenon, out-of-plane plucking enables the capability of fabricating multiple piezoelectric beams on a single substrate. This paper presents an analysis of three different out-of-plane plucking configurations along with the in-plane repulsive configuration based on a three-dimensional analytical cube permanent magnet model. We derive a magnetically plucked piezoelectric beam model to investigate the dynamic characteristic for different plucking configurations. After validating the model with experimental results we extend the simulation into a larger driving frequency domain to compare two types of magnet configurations in terms of power generation.