Vibration Energy Harvesting From Impulsive Excitations Via Bistable Nonlinear Attachment

A vibration-based electromagnetic bistable energy harvesting system coupled to a directly excited primary system is numerically and experimentally examined. The system consists of a grounded weakly damped linear oscillator (LO) coupled to a light-weight, weakly damped nonlinear oscillator by means of an element which provides both essential cubic nonlinear and negative linear stiffness components and electromechanical coupling elements. The transverse deflection of a beam that supports the harvester mass in its midspan provides the desired geometric nonlinearity, while the negative stiffness term arises from its buckled configuration. The electromechanical coupling is achieved via a permanent magnet and an induction coil. The primary goal of the present work is to investigate the potential benefit of the bistability for low input energy, for which the essential cubic nonlinear attachment loses its effectiveness. This is due to the existence of an impulse magnitude threshold, below which no significant energy absorption occurs for the latter device. Due to the double-well potential of the bistable system, several dynamic regimes arise. Depending on the energy level, the inertial mass can exhibit in-well oscillations (the mass oscillates around one of the two stable equilibra) or aperiodic or chaotic vibrations between wells or, as the energy level increases, it may exhibit periodic cross-well oscillations (it snaps from one stable state to the other). Moreover, these main dynamic regimes may coexist with super- and subharmonic resonances. The first excitation scenario of a single impulse (applied to the primary mass of the described two-dof system) reveals that the bistable system outperforms the monostable counterpart for all of the impulse levels examined. The mechanisms that allow the most intense energy transfer between the two oscillators are shown to be the in-well and both periodic as well as aperiodic cross-well oscillations. The role of key design parameters, such as the mass ratio and the damping in the coupling, on the coupled system response and the ensuing harvesting performance is analyzed, revealing the existence of threshold values of these parameters above which the desired aforementioned regimes cannot occur. Under periodically repeated impulses on the LO, the bistable configuration leads the system to surpass its monostable counterpart in terms of energy harvesting efficiency (defined as the energy harvested normalized by the total energy in the system at the time of arrival of each impulse); however, it harvests a greater amount of energy only for certain conditions, depending on the inter-arrival time of the system.