Nonlinear analysis of a two-degree-of-freedom vibration energy harvester using high order spectral analysis techniques

Abstract

Conventional vibration energy harvesters are generally based on linear massspring oscillator models. Major limitations with common designs are their narrow bandwidths and the increase of resonant frequency as the device is scaled down. To overcome these problems, a two-degree-of-freedom nonlinear velocity-amplified energy harvester has been developed. The device comprises two masses, oscillating one inside the other, between four sets of nonlinear magnetic springs. Impacts between the masses allow momentum transfer from the heavier mass to the lighter, providing velocity amplification. This paper studies the nonlinear effects introduced by the presence of magnetic springs, using high order spectral analysis techniques on experimental and simulated data obtained for a range of excitation levels and magnetic spring configurations, which enabled the effective spring constant to be varied. Standard power spectrum analysis only provide limited information on the response of nonlinear systems. Instead, bispectral analysis is used here to provide deeper insight of the complex dynamics of the nonlinear velocity-amplified energy harvester. The analysis allows identification of period-doubling and couplings between modes that could be used to choose geometrical parameters to enhance the bandwidth of the device.

The Identification of Period Doubling in a Nonlinear Two-Degree-of-Freedom Electromagnetic Vibrational Energy Harvester

“…The nonlinear 2-DoF velocity-amplified VEH analysed in this paper is based on an improved design of the harvester previously reported by the authors [15], [16]; an overview is shown in figure 1. The overall volume of the VEH is 13.68 cm 3 (59.6 mm height, 17.10 mm diameter), smaller than the prototype that was previously reported (V = 30 cm 3 ) [15], [16].…”

A Vibration Energy Harvester and Power Management Solution for Battery-Free Operation of Wireless Sensor Nodes

“…This usually limits the energy transfer in realistic applications, since ambient vibrations generally have a broad spectrum with several peaks [9]. An alternative to overcome the problem of narrow bandwidth is the two-degree-of-freedom (2DoF) velocity-amplified EM-VEH device introduced in [12,13,14].…”

“…To overcome the problem of narrow bandwidth, a two-degree-of-freedom (2DoF) EM-VEH device that exploits multiple masses and a patented velocity-amplification principle has been developed by the authors’ group [10,11,12,13]. In this harvester, harmonic and random excitations can be used as vibration sources for producing higher voltage and power than in prior art.…”

Two-degree-of-freedom velocity-amplified vibrational energy harvester for human motion applications

“…The nonlinear 2-Dof velocity-amplified VEH presented in this paper is based on a design similar to the one presented in [12,13]; and it is shown in overview in figure 1. The VEH consists of two masses, a large primary mass (m 1 ) and a smaller secondary one (m 2 ), that oscillate vertically one inside the other, in a Teflon tube between four sets of magnetic springs, as illustrated in figure 1a.…”

“…Moreover, most of wearable devices (such as fitness trackers) are worn on the arm and not on legs as in most of the devices reported in the literature. To overcome these problems, a nonlinear electromagnetic two degree-of-freedom (2-Dof) velocityamplified VEH [12,13], that could be worn on an arm, has been developed in this paper. Velocity amplification is used to enhance the output power of the device while a nonlinear potential is used to broaden the bandwidth of the device so that the harvester could still generate energy even in presence of such a time-varying excitation as human motion.…”