Nonlinear dynamic characteristics of dual-coupling beams energy harvester

Abstract Environment vibrations are usually in a low and broadband frequency range. In order to harvest such vibration sources, nonlinear energy harvesting techniques, especially bistable energy harvesters (BEH), have been extensively investigated as a promising way to power microelectronic devices such as autonomous wireless sensors. For such BEH, large-amplitude interwell oscillations between two potential wells can significantly enhance energy harvesting capability over the broadband vibration. However, under low excitation levels, the BEH is unable to overcome the potential barriers and will exhibit small-amplitude intrawell motion, resulting in low energy harvesting performance. This paper proposes to solve this problem by investigating the nonlinear dynamic characteristics of dual-coupling beams energy harvester (DEH) at a low excitation level. The proposed device is comprised of a linear oscillator, a bistable oscillator, and a linear spring elastically connected above two oscillators. A lumped-parameter nonlinear equation is derived to describe the response of the harvester with various coupling spring stiffness values. The dynamic behavior of the proposed DEH is numerically investigated under harmonic base excitation with bifurcation diagrams, Poincaré maps, basins of attraction. The numerical results indicate that introduced linear oscillator and linear spring can not only reduce the barrier height, but also provide the bistable oscillator additional external excitation in the beginning or during the oscillation. Thus, the potential well barrier of the DEH could be significantly reduced. Compared with conventional BEH, the threshold for activating large-amplitude interwell oscillation is reduced by 55.4% (from 5.6 m/s2 to 2.5 m/s2). In addition, the numerical results reveal that the DEH could optimize the potential width and depth of the energy harvester simultaneously under geometric constraints. The dynamic potential width is only decreased by 30%, but the potential depth is reduced by 86% (Ks = 15 N/m), which is also validated by experiment.