Design and analysis of switchable magnetic polarity bistable energy harvester

Abstract

Multistable vibration harvesters that involve repelling magnet force result in improved efficiency over a wider bandwidth in comparison to the conventional resonant devices. However, the dynamic performance of the vibration harvester can be further improved by switching the magnetic force polarity to ensure pull force on the mass as it moves towards the mean position. In the presented work, the design and analysis of a switching polarity bistable harvester has been presented, which changes the magnetic interaction polarity in order to improve power output as well as efficient operational bandwidth. An innovative mechanism has been developed to operate the harvester with switching polarity for higher base acceleration amplitude. The proposed design has integrated switchable polarity magnetic interaction and rotary electric generator which is driven by a compound gear train in the conventional spring-mass harvester. Analytical and numerical simulations have been formulated to illustrate efficient operational characteristics over the operating frequency band and to determine the optimum electrical damping coefficient. Effects of magnetic interaction force, the inertia of the switching mechanism and gears have been considered in the numerical analysis. A prototype delivered the peak power of 1.49 W at the resonance frequency and exhibited 50% increase in power in comparison to fixed polarity design.