Multi-frequency MEMS electromagnetic energy harvesting

We report multi-frequency MEMS electromagnetic energy harvesters employing two different topologies. The first is a single mass system, where different fundamental modes are obtained within a close frequency range through spring design innovation and by using a large magnetic proof mass. The second is a dual mass system, which inherently has two major vibration modes corresponding to the movement of each of the masses. In comparison to the reported MEMS scale electromagnetic generators, substantial improvement in the output power is achieved in our design primarily by using the bulk NdFeB magnet as proof mass. This enhanced performance is validated by benchmarking against a normalized power density parameter. The spring structures are fabricated on Silicon-on-Insulator (SOI) substrate while voltage is induced in electroplated double layer copper coils. The 3D finite element analysis on the devices shows that different modes are activated in the low frequency region. The out-of-plane and torsional modes of the single mass systems are obtained at 188, 255.1 and 287.9 Hz, respectively whereas the first two modes of dual mass device are at 241.4 Hz and 419.6 Hz respectively. At 0.5 g, the single mass device produces 0.37, 0.43 and 0.32 W respectively in mode I, II and III whereas the dual mass device generates 0.22 and 0.024 p.W in mode I and II respectively against matched load. The experimental results are qualitatively explained using the simulation results and indicate a good potential in the development of multi-frequency energy harvesters for a number of practical applications. (C) 2017 Elsevier B.V. All rights