Dynamics of Wrist-Worn Eccentric-Rotor Energy Harvesters

This work concerns the steady-state dynamics of eccentric-rotor harvesters under the excitation of a forced pendulum, selected as a simplified representation of the swinging motion of the human arm during locomotion, to better understand their use for wrist-worn energy-harvesting applications. A linearized model predicts the behavior of nonresonant eccentric-rotor devices well and provides insight into the relationship between the rotor natural frequency and transducer-imposed electrical damping. Approximate analytical solutions are obtained via perturbation methods that show that the eccentric rotor shares many characteristics of a Duffing oscillator with softening spring nonlinearity. Finally, an interesting property of the eccentric rotor's dynamics, namely, invariance of power output to changes in forcing frequency and amplitude over certain ranges of design parameters, is observed, forming the basis for a proposed resonant eccentric-rotor harvester with a wideband power output response.