Harvesting Energy From Low-Frequency Excitations Using a Rolling Ball With Frequency Up-Conversion

Abstract This paper presents the design and testing of an electromagnetic device that harvests energy from low-frequency, low-amplitude excitations. The concept is based on a steel ball that acts as an inertial mass that rolls along two parallel guides. Tilting the guides cyclically causes the ball to roll back and forth, magnetically plucking a cantilever beam that is fixed underneath it and carrying a tip magnet. Frequency up-conversion is achieved as the beam vibrates at its natural frequency, which is higher than the excitation frequency, and this is employed to harvest energy by electromagnetic induction as the tip magnet moves relative to a stationary coil. Experimental testing at frequencies ranging from 0.075 Hz – 1.125 Hz with tilt angles ranging from 1.8° – 5.7° demonstrate the effectiveness of the device in harvesting energy from low-frequency, low-amplitude tilting excitations. The experiments are used to gain insight into the frequency up-conversion mechanism and its characteristics. The direction of the ball’s rolling was observed to affect the output voltage magnitude, and the experiments were used to determine the most favorable frequencies, drive conditions as well as limitations of the proposed concept, as plucking the cantilever beam essentially draws from the kinetic energy of the ball. The device was also used to charge a capacitor through a rectifying circuit to validate the concept. Potential applications include utilizing the concept in low-frequency environments, such as human motion or the vibration of tree branches.