Nonlinearity of a 2 Degree of Freedom Velocity Amplified Electromagnetic Vibrational Energy Harvester and Optimization of Coil Parameters

A 2DOF velocity amplified electromagnetic vibrational energy harvester is analyzed. The system consists of two masses oscillating relative to each other in response to external excitation. The large mass is designed with a centrally located cavity in which a second smaller mass is placed. This configuration allows the larger mass to impart momentum to the smaller mass during impact, which significantly amplifies the velocity of the smaller mass. By coupling high strength magnets (placed on the larger mass) and a coil (embedded in the smaller mass) electric current is induced through the relative motion of the two masses. To intensify the magnetic field the magnets are arranged with alternating polarity within the soft-iron body of the larger mass. The smaller mass is designed to disconnect from the larger mass, when sufficient input vibrations are present, and this leads to significant nonlinearity in the system response, which is well described by its transfer function. The nonlinearity led to an increased bandwidth over which the system could harvest energy. As a further improvement, the energy harvester can be optimized by changing the properties of the coil: in this paper four different coils are taken into account and their voltage and power output are compared. A theoretical model is finally proposed in order to predict the optimal configuration.