High power electromagnetic vibration harvesting using a magnetic dumbbell structure

This paper considers an electromagnetic energy harvester consisting of a tube with two fixed magnets and two coils and containing a floating free-to-move dumbbell structure with two magnets. The dumbbell shape has a number of benefits, including an increased changing magnetic flux, a controllable resonance frequency and reduced friction. We experimentally characterize the power produced by the harvester between 4 Hz and 20 Hz in steps of 0.5 Hz for a fixed excitation amplitude of 3 mm. The frequency is swept in both ascending and descending order. The maximum power produced by the harvester is 1.04 mW which occurs at 8.5 Hz in descending frequency sweep where the maximum acceleration of the harvester is 0.87g. The power density of the harvester is 50 μW/cm³ and the power per unit mass is 32 μW/g. The dumbbell harvester shows a softening resonator response with hysteresis between ascending and descending frequency sweeps. Furthermore, the harvester has two resonance peaks in power as a function of the drive frequency, with the peaks being of almost equal magnitude. Finally, a Fourier analysis shows the two resonance peaks have different harmonics, with the first resonance peak being characterized by higher-order harmonics whereas the second resonance peak is characterized by a response at the excitation frequency.