Large stroke tri-stable vibration energy harvester: Modelling and experimental validation

An important issue in vibration energy harvesting is to increase the effective operation bandwidth. One solution is to develop multi-stable energy harvesters which can execute inter-well motion under certain conditions. However, almost all the n-stable harvesters are based on the cantilever-beam-magnets configuration if n > 2, namely, to arrange several fixed magnets near the free end of a piezoelectric cantilever beam with tip magnet, which usually has relatively small stroke due to the deformation limitation of the beam. In this paper, we propose a new tri-stable mechanism using four mechanical springs with well-designed configuration, which has large stroke due to the structural property. Thereafter a tri-stable electromagnetic energy harvester is constructed based on the proposed tri-stable mechanism. The dynamic response and electrical output characteristics are theoretically analyzed by numerical simulations using the dimensionless electromechanical coupled equations. It is shown that the inter-well oscillation can be activated in broadband low-frequency range, which generates considerable induced current. Experiments are also conducted to validate the theoretical model and to demonstrate the low-frequency broadband energy harvesting capability. The output power reaches the level of several hundred milliwatts, which is much larger than that of the previous tri-stable harvesters at milliwatt level.