Optimization of coil parameters for a nonlinear two degree-of-freedom (2DOF) velocity-amplified electromagnetic vibrational energy harvester

A 2DOF velocity amplified electromagnetic vibrational energy harvester is analyzed. The system consists of two masses, one larger than the other, oscillating relative to each other in response to external excitation. The large mass is designed with a centrally located cavity into 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), an electric current is induced in the coil 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. Between the two masses, and between the larger mass and the support, four springs are placed. The smaller mass is designed to disconnect from the larger mass, when input vibrations of sufficient magnitude are present, and this leads to significant nonlinearity in the system response, which is well described by its transfer function. The nonlinearity leads to an increased bandwidth over which the system can harvest energy. As a further improvement, the energy harvester is optimized by changing the properties of the coil. Four different coils are compared in terms of their voltage and power output. Finally, a theoretical model is proposed in order to predict the optimal configuration.