A 2DoFvibrational energy harvester exploiting velocity amplification: Modeling and testing

A two Degree of Freedom (2DOF) velocity-amplified electromagnetic vibrational energy harvester is presented. The device consists of two masses: a smaller mass which oscillates inside a larger one due to two sets of mechanical springs. The larger mass itself oscillates between two sets of springs. This configuration allows the larger mass to transfer momentum to the smaller mass during impact, which significantly amplifies the velocity of the smaller mass. The smaller mass is designed to disconnect from the larger mass, when input vibrations of sufficient magnitude are present. This leads to significant nonlinearities that increases the bandwidth over which the system can harvest energy. By coupling high strength magnets (placed on the larger mass) and a coil (embedded in the smaller mass), an electric current is induced in the coil through the relative motion of the two masses. This paper characterizes the nonlinear response of a 2DOF velocity-amplified electromagnetic energy harvester using a transfer function analysis. Optimization tools are then presented for designing efficient 2DOF vibration energy harvesters for use at various input frequencies and amplitudes. The first of these tools is a theoretical approach for optimizing the electromagnetic damping that is based on linear approximations. The second approach is a nonlinear model of the 2DOF system that takes into account collisions between the masses and the associated transfer of momentum. In all cases experimental results are used to validate the performance of the design tools. Finally, a performance evaluation using the volumetric Figure of Merit is presented and compared with recent literature, showing the favorable relative performance of the 2DOF system.