Nonlinear analysis of a two-degree-of-freedom energy harvester

In recent years the use of Wireless Sensor Networks (WSNs) has increased rapidly, enabled by the development of small and ultra-low power electronics. The majority of these sensors are battery powered, and this can lead to high maintenance costs when batteries have to be replaced. A practical solution to power sensor networks comes from kinetic energy harvesting, which is the conversion of the vibrations present in the ambient into electrical energy. To overcome the problems of narrow bandwidth and high resonant frequency at small scale for conventional harvesters, a nonlinear two-degree-of-Freedom (2DoF)velocity-amplified vibrational energy harvesting has been developed. Electromagnetic induction was chosen as the transduction mechanism because it can be readily implemented in a device that uses velocity amplification. The harvester consists of two masses relatively oscillating one inside the other, between four sets of magnetic springs. Collisions between the two masses can occur, and they transfer momentum from the heavier to the lighter mass, increasing the velocity of the latter. Bispectral analysis was carried out on the device, which revealed the presence of quadratic phase couplings between the Fourier modes and also period doubling. Both these phenomena are associated with the use of nonlinear magnetic springs, and an understanding of these effects can help to enlarge the bandwidth of the device.