Experiment-driven electromechanical coupling optimization of a pendulum-based electromagnetic energy harvester with a compact variable transmission ratio mechanism

Pendulum-based electromagnetic energy harvesters (PEEHs) often employ gear trains for frequency-up conversion to enhance output power, where mechanical and electrical energies are inherently coupled. However, systematic multiparameter optimization of electromechanical coupling factors—such as transmission ratio and load resistance—has not been fully addressed. To bridge this gap, we propose an experiment-driven optimization approach using a compact variable transmission ratio mechanical frame, in which the transmission ratio is adjusted by altering the degrees of freedom and positions of components within a compound non-circular and circular gear train. A forward design methodology for non-circular gears, coupled with parameter optimization of the power unit and dynamics modelling, is developed, followed by a series of experiments aimed at optimization. Results reveal that PEEHs exhibit distinct optimal transmission ratios and load resistance under different energy input levels. After transmission ratio and impedance optimization, the prototype achieves up to a 626 % performance enhancement and a maximum output power of 3.67 mW at 1.2 Hz and 30°. This study demonstrates an effective multiparameter optimization strategy for designing high-performance PEEHs.