Broadband electromagnetic vibration energy harvesting system for powering wireless sensor nodes

This paper reports the design of an electromagnetic vibration energy harvesting system that provides high power density and broad bandwidth. The 'double cell' harvester was chosen as the generator for this system. In order to harvest power over a broad range of frequencies, four 'double cell' harvesters with varying resonances were incorporated in the system architecture. The average AC to regulated DC power conversion efficiency across the 4 Hz bandwidth was 78%, which is one of the highest reported magnitudes for an electromagnetic vibration harvesting system. The magnetic flux density variation within the double cell array was modeled using the finite element method and compared to a single cell with equivalent tip mass and magnet volume. The double cell array was found to generate a similar magnitude of power to a single cell but three times higher bandwidth. The average generator conversion efficiency for the double cell array was 45.3%, which approaches the maximum theoretical limit of 50%. (paper)