Double-mass pendulum energy harvester with tunable ultra-low frequency: An experimental study

Nonlinear widening and frequency tuning strategies are two typical approaches to enhance the energy harvesting performance of a vibration-based energy harvester. Double-mass pendulum energy harvester (DMPEH) is a recently emerging oscillator with tunable ultra-low frequencies for wave energy harvesting. This study systematically investigates the nonlinear dynamics and energy harvesting capacity of the DMPEH through numerical simulations and experimental tests. First, the DMPEH mathematical model is established. Subsequently, the numerical studies on the dynamics and power performance of the DMPEH are performed, followed by the shake table tests on a scaled prototype. Several observations are made: (1) the load resistance influences both the nonlinear dynamics and the output power; (2) by using frequency tuning strategy, the output power was dramatically improved, high to hundreds of percentages improvement compared with the un-tuned counterpart. Moreover, the power generation performance of a medium-scale broadband DMPEH for a navigation buoy is discussed. Sufficient power levels are demonstrated, supporting the development of self-powered navigation buoys. The results demonstrate the promising energy harvesting performance of the DMPEH and its potential to serve as a frequency-tunable broadband energy harvester. This study makes a step toward practical applications of DMPEH for ocean wave energy harvesting.