Secondary Impact bandwidth effects using Embedded Vertical Moving Mass Energy Harvester

Narrow bandwidths is considered a major limitation of MEMS piezoelectric energy harvesters. Recent research has demonstrated that vertical moving masses embedded within a stationary mass is a viable option to increasing bandwidth. The concept operates by altering the effective mass during oscillation of the cantilever. Secondary impact forces caused from bouncing of the movable mass results in non-linear dynamics. This paper investigates the effect of the impact force and secondary impact forces due to the bouncing movable mass. The phenomenon was investigated using multiple movable mass balls which either enable or eliminate bouncing to determine the role that secondary impacts have on bandwidth. The results demonstrate that masses with secondary bouncing impacts have significantly larger bandwidth (26 Hz) compared to non-bouncing masses (4.32 Hz). However, the non-bouncing masses still provide higher bandwidth than a non-moving mass (1.3 Hz), due to the change in effective mass. The secondary impact of the mass generates complex output waveforms with multiple frequencies compared to a stationary mass and non-bouncing masses which demonstrate linear sinusoidal output waveforms.