Electromagnetic energy harvester using coupled oscillating system with 2-degree of freedom

Abstract

This paper presents the design and fabrication of a 2-degree of freedom vibration energy harvesting device for converting kinetic energy into electrical energy using electromagnetic transduction. The relative motion between a magnet and a conductive coil induces an electromotive force. A non uniform magnetic field design is used where an oscillating magnet is suspended by a spring-damper system. In addition the coil is suspended to serve as the second oscillating mass to effectively harvest energy at two different frequencies. The design parameters are elucidated in this paper which describes the effects of voltage cancellation due to coil phase, coil placement for optimal performance and the benefits of separating magnets using material with high permeability. The investigation was performed using multi physics finite element analysis (COMSOL) with sinusoidal vibration input. A prototype was developed to demonstrate that practical amount of power can be generated from the design. The resonant frequencies of the prototype harvester were tuned to match the dominant frequencies of the host structure (i.e. heavy haul railcars). Peak output powers of 212 mW and 218 mW were generated from sinusoidal vibration with 0.4 g peak acceleration (where g = 9.8 m/s 2 ) at 6.5 Hz and 14.5 Hz respectively.