Enhanced stochastic, subharmonic, and ultraharmonic energy harvesting

Abstract

Nonlinear bistable systems have been shown to provide improved efficiency for harvesting energy from random and broadband vibration sources. This article explores the distinct frequency response in the broadened spectrum of a particular nonlinear energy harvester, a piezoelectric cantilever with magnetic coupling. The cantilever response evolves dynamically with frequency around the main cantilever resonance. Both stochastic and multifrequency vibration responses are observed and account for some of the improved efficiency. In addition, subharmonics and ultraharmonics of the main resonance, along with various combinations of these, appear. An analytical model of the bistable dynamics produces results consistent with those observed experimentally. Overall, four distinct types of efficiency improvements appear, in which the signal is amplified above the noncoupled cantilever response: (a) ultraharmonic amplification below resonance frequency, (b) stochastic amplifications in multifrequency and multiamplitude oscillations, (c) ultrasubharmonic amplification, and (d) subharmonic amplification. Taken together, the stochastic, subharmonic, and ultraharmonic responses produce an average of threefold to fivefold increase in voltage production.