Dual electromagnetic mechanisms with internal resonance for ultra-low frequency vibration energy harvesting

Ultra-low frequency vibration in ambient environment is an abundant renewable energy source. Corresponding energy harvesters have attracted increasing attention from both academic and industrial worlds. In this paper, a rotational electromagnetic energy harvester (EMEH) and a translational EMEH are combined into a spring pendulum system, thus forming a dual EMEH, in which internal resonance phenomenon is triggered to result in significantly enhanced energy harvesting efficiency. The spring pendulum system exhibits robustness and stability with the equivalent electromagnetic shunt damping constraints. Meanwhile, the tunable damping preserves the integrity of the system even the external excitation overloads. Experimental results demonstrate that the output power of the dual EMEHs can reach up to 0.9 W with a moving mass of 1.42 kg. Moreover, the swing angle of the pendulum can be reduced with the effect of internal resonance, which protects the main system and ensures its operation in harsh operating environment.