Dynamics of an omnidirectional pendulum energy harvester: A comparative analysis between numerical and experimental results

The spherical pendulum is a mathematically interesting model that has been studied extensively in the past. In the field of energy harvesting however, the pendulum energy harvesters are generally confined to planar motions. This minimisation of the available degrees of freedom potentially limits the areas of application of the energy harvester, and certainly its overall capability. In this work an omnidirectional pendulum energy harvester is proposed in the form of a two degree of freedom system which has the potential to harvest energy from motions along the three axes of translation and from the three corresponding rotations about those axes. The dynamics of such an energy harvester are examined experimentally for different power take-off modes and are subsequently compared to numerical predictions from an analytical model. An optimal operational point is proposed for the harvester and it is shown how an up-sweep and down-sweep of the excitation frequency can significantly broaden the operational range of the energy harvester by up to 130%.