Optimization of AA-Battery Sized Electromagnetic Energy Harvesters: Reducing the Resonance Frequency Using a Non-Magnetic Inertial Mass

Abstract

This paper presents an optimization study for a miniature electromagnetic energy harvester, by incorporating a non-magnetic inertial mass (tungsten) along with the axially oriented moving magnets. The aim is to decrease the operation frequency and increase the output power of the harvester with the usage of higher density material and larger magnetic flux density. Dimensions of the magnets are optimized according to the harvester dimensions and magnetic flux gradients. Additionally, coil length, width, resistance, and position have been optimized through finite element analysis and experimentally validated. Simulation results show that using a single-magnet structure is not efficient for increasing the output power of the system. Test results also reveal that multi-magnet structures with inertial mass yield to higher output voltages and smaller resonance frequencies. Effects of the improvements on the moving structure are analyzed in detail and experimentally validated. The operation frequency of the harvester decreases with the addition of inertial mass and axially oriented moving magnets, while the output power increases due to greater magnetic flux contributions provided by repulsive forces. Compared with the single-magnet structure, a modified design with a similar size yields to a decrease in the resonance frequency (from 10 to 7 Hz) and an increase in the output power. The optimized harvester has a volume of 7 cm3 and generates 0.5 $\text{V}_{\mathrm {RMS}}$ , 240 $\mu \text{W}_{\mathrm {RMS}}$ output power (@7 Hz and 0.5 g peak acceleration).